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CHAPTER 2
| Question | Answer |
|---|---|
| A chemical element is the simplest form of matter to have unique chemical properties. | Water, for example, is not an element; it has unique properties, but it can be broken down into two elements, hydrogen and oxygen, that have unique chemical properties of their own. |
| If we carry this process any further, however, we find that hydrogen and oxygen are made of protons, neutrons, and electrons | —and none of these are unique. |
| A proton of ----- is identical to a proton of oxygen. | gold |
| are the simplest chemically unique components of water and are thus elements. | Hydrogen and oxygen |
| Each element is identified by an -----, the number of protons in its nucleus. | atomic number |
| atomic number for carbon | 6 |
| atomic number for oxygen | 8 |
| The periodic table of the elements arranges the elements in order by their | atomic numbers |
| C | Carbon |
| Mg | Magnesium |
| Cl | Chlorine |
| A few symbols represent their original Latin names | K for potassium (kalium), Na for sodium (natrium), and Fe for iron (ferrum) |
| Latin for Potassium | K (Kalium) |
| Latin for Sodium | Na (natrium) |
| Latin for Iron | Fe (Ferrum) |
| There are 91 naturally occurring elements on earth | 24 of which play normal physiological roles in humans. |
| Six of them account for 98.5% of the body's weight | oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. |
| The next 0.8% (of body weight) consists of another 6 elements: | sulfur, potassium, sodium, chlorine, magnesium, and iron. |
| The remaining 12 elements total only 0.7% of body weight; | thus, they are known as trace elements. |
| Despite their minute quantities, ------ play vital roles in physiology. | trace elements |
| Other elements without natural physiological roles can contaminate the body and severely disrupt its functions | as in heavy-metal poisoning with lead or mercury. |
| Oxygen (O) | 65.0 Percentage of Body Weight |
| Carbon (C) | 18.0 Percentage of Body Weight |
| Hydrogen (H) | 10.0 Percentage of Body Weight |
| Major Elements (98.5%) | Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N), Calcium (Ca), Phosphorus (P) |
| Nitrogen (N) | 3.0 Percentage of Body Weight |
| Calcium (Ca) | 1.5 Percentage of Body Weight |
| Phosphorus (P) | 1.0 Percentage of Body Weight |
| Lesser Elements (0.8%) | Sulfur (S), Potassium (K), Sodium (Na), Chlorine (Cl), Magnesium (Mg), Iron (Fe) |
| Sulfur (S) | 0.25 Percentage of Body Weight |
| Potassium (K) | 0.20 Percentage of Body Weight |
| Sodium (Na) | 0.15 Percentage of Body Weight |
| Chlorine (Cl) | 0.15 Percentage of Body Weight |
| Magnesium (Mg) | 0.05 Percentage of Body Weight |
| Iron (Fe) | 0.006 Percentage of Body Weight |
| Trace Element (Total 0.7%) (Names and Symbols only) | Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn) |
| Chromium (Cr) | Trace Element (Total 0.7%) (Names and Symbols only): ----, Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn) |
| Cobalt (Co) | Trace Element (Total 0.7%) (Names and Symbols only): Chromium (Cr), -----, Copper (Cu), Fluorine (F), Iodine (I), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn) |
| Copper (Cu) | Trace Element (Total 0.7%) (Names and Symbols only): Chromium (Cr), Cobalt (Co), -----, Fluorine (F), Iodine (I), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn) |
| Fluorine (F) | Trace Element (Total 0.7%) (Names and Symbols only): Chromium (Cr), Cobalt (Co), Copper (Cu), -----, Iodine (I), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn) |
| Iodine (I) | Trace Element (Total 0.7%) (Names and Symbols only): Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), -----, Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn) |
| Manganese (Mn) | Trace Element (Total 0.7%) (Names and Symbols only): Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), ----, Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn) |
| Molybdenum (Mo) | Trace Element (Total 0.7%) (Names and Symbols only): Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), Manganese (Mn), ------, Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn) |
| Selenium (Se) | Trace Element (Total 0.7%) (Names and Symbols only): Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), Manganese (Mn),Molybdenum (Mo), ------, Silicon (Si), Tin (Sn), Vanadium (V), Zinc (Zn) |
| Silicon (Si) | Trace Element (Total 0.7%) (Names and Symbols only): Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), Manganese (Mn), Molybdenum (Mo), Selenium (Se), -----, Tin (Sn), Vanadium (V), Zinc (Zn) |
| Tin (Sn) | Trace Element (Total 0.7%) (Names and Symbols only): Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), -----, Vanadium (V), Zinc (Zn) |
| Vanadium (V) | Trace Element (Total 0.7%) (Names and Symbols only): Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), -----, Zinc (Zn) |
| Zinc (Zn) | Trace Element (Total 0.7%) (Names and Symbols only): Chromium (Cr), Cobalt (Co), Copper (Cu), Fluorine (F), Iodine (I), Manganese (Mn), Molybdenum (Mo), Selenium (Se), Silicon (Si), Tin (Sn), Vanadium (V), ----- |
| Several of these elements are classified as ---inorganic elements extracted from the soil by plants and passed up the food chain to humans and other organisms. | minerals |
| Minerals | constitute about 4% of the human body by weight. |
| Nearly three-quarters of this is Ca and P; the rest is mainly Cl, Mg, K, Na, and S. | Human Bone |
| Minerals | contribute significantly to body structure. |
| The bones and teeth consist partly of crystals of | calcium, phosphate, magnesium, fluoride, and sulfate ions. |
| The bones and teeth consist partly of crystals of: ----, phosphate, magnesium, fluoride, and sulfate ions. | calcium |
| The bones and teeth consist partly of crystals of: calcium, -----, magnesium, fluoride, and sulfate ions. | phosphate |
| The bones and teeth consist partly of crystals of: calcium, phosphate, ----, fluoride, and sulfate ions. | magnesium |
| The bones and teeth consist partly of crystals of: calcium, phosphate, magnesium, ----, and sulfate ions. | fluoride |
| The bones and teeth consist partly of crystals of: calcium, phosphate, magnesium, fluoride, and -----. | sulfate ions |
| Many proteins (for bones) include sulfur, and phosphorus is a major component of | nucleic acids, ATP, and cell membranes. |
| Minerals also enable enzymes and other organic | molecules to function |
| Iodine is a component of | thyroid hormone |
| Iron is a component of | hemoglobin |
| Some enzymes function only when | manganese, zinc, copper, or other minerals bound to them. |
| Some enzymes function only when: ----, zinc, copper, or other minerals bound to them. | manganese |
| Some enzymes function only when: manganese, -----, copper, or other minerals bound to them. | zinc |
| Some enzymes function only when: manganese, zinc, ----, or other minerals bound to them. | copper |
| Some enzymes function only when: manganese, zinc, copper, or | other minerals bound to them. |
| The ---- need for nerve and muscle function are mineral salts | electrolytes |
| In the fifth century BCE, the Greek philosopher Democritus reasoned that we can cut matter such as a gold nugget into smaller and smaller pieces | but there must ultimately be particles so small that nothing could cut them. He called these imaginary particles atoms (“indivisible”). |
| Atoms were only a philosophical concept until 1803, when English chemist ----- began to develop an atomic theory based on experimental evidence. | John Dalton |
| In 1913, Danish physicist ----- proposed a model of atomic structure similar to planets orbiting the sun | Niels Bohr |
| Bohr's model | is a useful schematic for visualizing the constituents of an atom and chemical reactions between them, but it doesn't represent real atomic structure any more than a student's ball-and-stick model kit resembles real molecules. |
| According to -----, atoms are not spherical; they have no solid surface or boundary; and their subatomic particles have only certain probabilities of being in any given place at any given time | quantum mechanics |
| The ----- model of carbon, with electrons in two concentric energy levels (shells), the higher-energy electrons farther from the nucleus. | Bohr planetary |
| The Bohr model of sodium, with a ---- | third electron shell |
| The more realistic quantum mechanical model of carbon, in which electrons are depicted only by their probability of being in a given place at a given time, in shells separated by ---- of low to zero probability. | clear zones (nodes) |
| At the center of an atom is the ----, composed of protons and neutrons. | nucleus |
| Protons (p*) | have a single positive charge |
| neutrons (no) | have no charge |
| Each ---- weighs approximately 1 atomic mass unit (amu). | proton or neutron |
| The atomic mass of an element is approximately equal to its total number of | proton and neutron |
| Around the nucleus are one or more clouds of -----, tiny particles with a single negative charge and very low mass. | electrons (e ̄) |
| It takes ----- to equal the mass of one proton, so for most purposes we can disregard their mass. | 1,836 electrons |
| A person who weighs 64 kg (140 lb) | contains less than 24 g (1 oz) of electrons. |
| This hardly means that we can ignore electrons, however. | They determine the chemical properties of an atom, governing what molecules can exist and what chemical reactions can occur. |
| The number of electrons equals the number of protons | so their charges cancel each other and an atom is electrically neutral. |
| Electrons swarm about the nucleus in concentric regions called | electron shells (energy levels) |
| The more energy an electron has, the farther away from the ---- its orbit lies. | nucleus |
| Each shell holds a limited number of -----. | electrons |
| The elements known to date have up to seven electron shells | but those ordinarily involved in human physiology don't exceed four. |
| Electrons of the outermost shell, called -----, determine the chemical bonding properties of an atom. | valence electrons |
| Illustrations of ---- greatly understate the distances between their nuclei and electrons in order to fit the page. | atoms |
| If you imagine the nucleus of an atom to be the size of a basketball, its nearest electron would be about | 48 km (30 mi.) away |
| Dalton believed that every atom of an element was identical. | We now know, however, that all elements have varieties called isotopes, which differ from one another only in number of neutrons and therefore in atomic mass |
| Hydrogen atoms, for example, have only one proton. In the most common isotope, symbolized 1H | that's all there is to the nucleus. |
| Hydrogen has two other isotopes, however: | deuterium (2H) with one proton and one neutron, and tritium (3H) with one proton and two neutrons |
| Over 99% of carbon atoms have an atomic mass of 12 (6p*, 6n°) and are called carbon-12 (12C) | but a small percentage of carbon atoms are 13C, with seven neutrons, and 14C, with eight. |
| Despite their differences in neutrons, however, all isotopes of a given element behave the same chemically. | Deuterium (2H), for example, reacts with oxygen the same way 1H does to produce water. |
| In 1896, French scientist ---- discovered that uranium darkened photographic plates through several thick layers of paper. | Henri Becquerel (1852-1908) |
| Marie Curie (1867-1934) and her husband Pierre Curie (1859–1906) | discovered that polonium and radium did likewise. |
| Marie | coined the term radioactivity for the emission of energy by these elements. |
| Becquerel and the Curies | shared a Nobel Prize in 1903 for this discovery |
| Marie Curie | was not only the first woman in the world to receive a Nobel Prize, but also the first woman in France to receive a Ph.D. |
| She received a second Nobel Prize in 1911 for further work in radiation. | Marie Curie |
| Curie crusaded to train women for careers in science, and in World War I, she and her daughter, Irène Joliot-Curie (1897-1956) | trained physicians in the use of X-ray machines. |
| Marie pioneered ----- for breast and uterine cancer. | radiation therapy |
| In the wake of such discoveries, radium was regarded as a | wonder drug |
| Unaware of its danger, people drank ---- tonics and flocked to health spas to bathe in radium-enriched waters. | radium |
| Marie herself suffered extensive damage to her hands from handling radioactive minerals and died of radiation poisoning at age 67. | The following year, Irène and her husband, Frédéric Joliot (1900-1958), were awarded a Nobel Prize for work in artificial radioactivity and synthetic radioisotopes. |
| Apparently also a martyr to her science, ---- died of leukemia, possibly induced by radiation exposure. | Irène |
| Isotopes of Hydrogen | Hydrogen, Deuterium, Tritium |
| Isotopes of Hydrogen | The three isotopes differ only in the number of neutrons present |
| The atomic weight (relative atomic mass) of an element accounts for the fact that an element is a | mixture of isotopes. |
| If all --- were 12C, the atomic weight of ---- would be the same as its atomic mass, 12.000. | carbon |
| But since a sample of ---- also contains small amounts of the heavier isotopes 13C and 14C, the atomic weight is slightly higher, 12.011. | carbon |
| Although different isotopes of an element exhibit identical chemical behavior, they differ in | physical behavior |
| Many of them are unstable and decay (break down) to more stable --- by giving off radiation | isotopes |
| Unstable isotopes are therefore called radioisotopes, and the process of decay is called | radioactivity |
| Every element has at least one | radioisotope |
| Oxygen | for example, has three stable isotopes and five radioisotopes |
| All of us contain radioisotopes such as | 14C and 40K-that is, we are all mildly radioactive! |
| High-energy radiation | such as that emitted by radioisotopes, ejects electrons from other atoms, converting atoms to ions; thus, it is called |
| ionizing radiation | It destroys molecules and produces dangerous free radicals and ions in human tissues. |
| ionizing radiation | In high doses ---- is quickly fatal. In lower doses, it can be mutagenic (causing mutations in DNA) and carcinogenic (triggering cancer as a result of mutation). |
| Examples of ionizing radiation include ultraviolet rays, X-rays, and three kinds of radiation produced by nuclear decay: | alpha (a) particles, beta (B) particles, and gamma (y) rays. |
| An ---- consists of two protons and two neutrons (equivalent to a helium nucleus), and a beta particle is a free electron. | alpha particle |
| Alpha particles | are too large to penetrate the skin, and beta particles penetrate only a few millimeters. |
| Alpha particles | They're relatively harmless when emitted by sources outside the body, but very dangerous when emitted by radioisotopes that have gotten into the body. |
| Strontium-90 (9oSr), for example, has been released by nuclear accidents and the atmospheric testing of nuclear weapons in the 1950s and 1960s. | It settles onto pastures and contaminates cow's milk. |
| Strontium-90 (9oSr) | In the body, it behaves chemically like calcium, becoming incorporated into the bones, where it emits beta particles for years. |
| Uranium and plutonium emit gamma rays | Because of their high penetrating power, these rays are very dangerous even when emitted by sources outside the body. |
| Each ---- has a characteristic physical half-life, the time required for 50% of its atoms to decay to a more stable isotope. | radioisotope |
| One gram of 90Sr, for example, would be half gone in | 28 years |
| In 56 years, there would still be 0.25 g left, in 84 years 0.125 g, and so forth. | Many radioisotopes are much longer-lived. |
| The half- life of 40K, for example, is 1.3 billion years. | Nuclear power plants produce hundreds of radioisotopes that will be intensely radioactive for at least 10,000 years- longer than the life of any disposal container yet conceived. |
| The ---- of a radioisotope is the time required for half of it to disappear from the body. | biological half-life |
| biological half-life | Some is lost by radioactive decay and even more by excretion from the body. |
| Cesium-137, for example, has a physical half-life of 30 years but a biological half-life of only 17 days. | Chemically, it behaves like potassium; it is quite mobile and rapidly excreted by the kidneys. |
| There are several ways to measure the intensity of ------, the amount absorbed by the body, and its biological effects | ionizing radiation |
| To understand the units of measurement requires a grounding in physics beyond the scope of this book | but the standard international (SI) unit of radiation dosage is the sievert (Sv), which takes into account the type and intensity of radiation and its biological effect. Doses of 5 Sv or more are usually fatal. |
| The average person worldwide receives about 2.4 millisieverts (mSv) per year in background radiation from natural sources and another 0.6 mSv from artificial sources. | Sievert (Sv) |
| The most significant natural source is ----, a gas produced by the decay of uranium in the earth; it can accumulate in buildings to unhealthy levels. | radon |
| Artificial sources | of radiation exposure include medical X-rays, CT and PET scans, radiation therapy, and consumer products such as televisions, smoke detectors, and luminous watch dials. |
| A CT scan averages about 10 to 30 mSv for a full-body scan and 10 mSv for an | abdominopelvic scan only |
| a typical mammogram is 0.4 to 0.6 mSv | a chest X-ray is about 0.1 mSv; |
| and a hand or foot X-ray is about | 0.001 mSv |
| Such ----- must be considered from the standpoint of its risk-to-benefit ratio. | voluntary exposure |
| The benefits of a ----- far outweigh the risk from the low levels of radiation involved. | smoke detector or mammogram |
| Radiation therapists and radiologists | face a greater risk than their patients, however, and astronauts and airline flight crews receive more than average exposure. |
| U.S. federal standards set a limit of 50 mSv/year as acceptable occupational exposure to | ionizing radiation |
| Ions | are charged particles with unequal numbers of protons and electrons. |
| An ion can consist of a single atom with a positive or negative charge (such as Na* or CI ̄); a group of atoms such as phosphate (PO3 ̄) and bicarbonate (HCO3 ̄) ions | or a molecule as large as a protein with many charges on it. |
| Ions | form because elements with one to three valence electrons tend to give them up, and those with four to seven electrons tend to gain more. |
| If an atom of the first kind is exposed to an atom of the second, electrons may transfer from one to the other and turn both of them into ions. | This process is called ionization. |
| The particle that gains electrons acquires a negative charge and is called an anion (AN-eye-on) | The one that loses electrons acquires a positive charge (because it then has a surplus of protons) and is called a cation (CAT-eye-on) |
| This happens, for example, when sodium and chlorine meet | Cation |
| One electron transfers from sodium to chlorine, producing a sodium ion with a unit positive charge (Na1) and a ---- with a unit negative charge (CI ̄). | chloride ion |
| 11 Protons, 12 Neutrons, 11 Electrons | Sodium Atom |
| 17 Protons, 18 Neutrons, 17 Electrons | Chlorine Atom |
| Transfer of an electron from a sodium atom to a chlorine atom (1) | The charged sodium ion (Na+) and the chloride ion (Cl-) that result |
| Some elements exist in two or more ionized forms. | Iron, for example, has ferrous (Fe2+) and ferric (Fe3+) ions. |
| Note that some ions have a single positive or negative charge, whereas others have charges of ±2 or ±3 because they gain or lose more than one electron. | The charge on an ion is called its valence. |
| Ions with opposite charges are attracted to each other and tend to follow each other through the body. | Thus, when Na+ is excreted in the urine, Cl ̄ tends to follow it. |
| The attraction of cations and anions to each other is especially important in the excitation of muscle and nerve cells, as we shall see in later chapters. | Salts such as sodium chloride (NaCl) and calcium chloride (CaCl2) are electrically neutral compounds of cations and anions |
| Salts | In most cases relevant to human physiology, they readily dissociate in water into their respective ions, and thus act as electrolytes. |
| Electrolytes | are substances that ionize in water (acids, bases, or salts) and form solutions capable of conducting electricity. |
| Electrolytes | We can detect electrical activity of the muscles, heart, and brain with electrodes on the skin because electrolytes in the body fluids conduct electrical currents from these organs to the skin surface |
| Electrolytes | are important for their chemical reactivity (as when calcium phosphate becomes incorporated into bone), osmotic effects (influence on water content and distribution in the body), and electrical effects (which are essential to nerve and muscle function). |
| Electrolyte balance is one of the most important considerations in patient care. | Electrolyte imbalances have effects ranging from muscle cramps and brittle bones to coma and cardiac arrest. |
| To understand hydration, we start here with a sodium chloride crystal in a beaker. | As water is added, the salt dissolves into positive sodium ions and negative chloride ions. |
| Hydration refers to the final state of this process such that the water molecules tend to orient around the ions with the oxygen atom of the water pointing toward the positive sodium ions | and the hydrogen atoms point toward the negative chloride ions." |
| A sodium chloride crystal is placed inside a beaker. | The beaker is zoomed in showing sodium chloride as a space-filled lattice structure made of spheres. |
| Water is added to the beaker | . The beaker is further zoomed in showing an animation of a small purple sodium ion and a large green chloride ion each surrounded by a ring of water molecules. |
| Each water molecule has a central red sphere attached to a small yellow sphere on its lower left and to a small yellow sphere on its lower right. | The water molecules are shown orienting around the ions such that the red sphere of each water molecule is toward the sodium ion and the yellow spheres of each water molecule are toward the chloride ion. |
| Water molecules | around these rings are also shown but oriented in random directions. |
| Electrolyte (salt): Calcium chloride (CaCl2) | Cations & Anions: Ca^2+ + 2Cl - |
| Electrolyte (salt): Disodium phosphate (Na2HPO4) | Cations & Anions: 2Na^+ + HPO4^2- |
| Electrolyte (salt): Magnesium chloride (MgCl2) | Cations & Anions: Mg^2+ + 2Cl- |
| Electrolyte (salt): Potassium Chloride (KCl) | Cations & Anions: K^+ +Cl^- |
| Electrolyte (salt): Sodium bicarbonate (NaHCO3) | Cations & Anions: Na^+ HCO3- |
| Electrolyte (salt): Sodium chloride (NaCl) | Cations & Anions: Na^+ + Cl^- |
| Free radicals | are unstable, highly reactive chemical particles with an odd number of electrons. |
| For example, ----- normally exists as a stable molecule composed of two ---- atoms, O2-, but if an additional electron is added, it becomes a free radical called the superoxide anion, O2- | oxygen |
| Free radicals | are represented with a dot to symbolize the odd electron. |
| Free radicals are unstable, highly reactive chemical particles with an odd number of electrons. | For example, oxygen normally exists as a stable molecule composed of two oxygen atoms, O2; but if an additional electron is added, it becomes a free radical called the superoxide anion, O2 - |
| Free radicals are represented with a dot to symbolize the | odd electron |
| Free radicals are produced by some normal metabolic reactions of the body (such as the ATP-producing oxidation reactions in mitochondria, and a reaction that some white blood cells use to kill bacteria) | by radiation (such as ultraviolet radiation and X-rays); and by chemicals (such as nitrites, used as preservatives in some wine, meat, and other foods). |
| They're short-lived and combine quickly with molecules such as fats, proteins, and DNA, converting them into free radicals and triggering chain reactions that destroy still more molecules. | Free-Radicals |
| One theory of aging is that it results in part from lifelong cellular damage by | Free-Radicals |
| Because ----- are so common and destructive, the body has natural mechanisms for neutralizing them. | Free-Radicals |
| An antioxidant is a chemical that neutralizes free radicals. | For example, the body produces an enzyme called superoxide dismutase (SOD) that converts superoxide into oxygen and hydrogen peroxide. |
| Selenium, vitamin E (a-tocopherol), vitamin C (ascorbic acid), and carotenoids (such as ẞ-carotene) | are some antioxidants obtained from the diet |
| ----- have been associated with increased risk of heart attacks, sterility, muscular dystrophy, and other disorders. | Dietary deficiencies of antioxidants |
| Molecules are chemical particles composed of two or more atoms united by a chemical bond. | The atoms may be identical, as in nitrogen (N1⁄2), or different, as in glucose (C6H12O6). |
| Molecules | composed of two or more elements are called compounds. |
| Oxygen (O2) and carbon dioxide (CO2) are both molecules, because they consist of at least two atoms | but only CO2 is a compound, because it has atoms of two different elements. |
| Molecules | are represented by molecular formulae that identify their elements and show how many atoms of each are present. |
| Molecules with identical molecular formulae but different arrangements of their atoms are called isomers of each other. | For example, both ethanol and ethyl ether have the molecular formula CHO, but they are certainly not interchangeable! |
| To show the difference between them, we use ----- that show the location of each atom | structural formulae |
| H H I I H ---- C ------- C ------ OH I I H H | Ethanol (Structural) |
| CH3CH2OH | Ethanol (Condensed structural formuluae) |
| C2H6O | Molecular formulae |
| H H I I H---- C----O ------C -------H I I H H | Ethyl Ether (Structural) |
| CH3OCH3 | Ethyl Ether (Condensed) |
| C2H6O | Ethyl Ether (Molecular Formulae) |
| Two structural Isomers - Ethanol and Ethyl Ether | The molecular formulae are identical, but their structures, chemical properties, and psychological effects are different |
| The ---- of a compound is the sum of the atomic weights of its atoms. | molecular weight (MW) |
| 6 C atoms x 12 amu each = | 72 amu |
| 12 H atoms x 1 amu each = | 12 amu |
| 6 O atoms x 16 amu each = | 96 amu |
| 72 amu + 12 amu + 96 amu | 180 amu |
| Molecular weight | is needed to compute some measures of concentration discussed later |
| A molecule is held together, and molecules are attracted to one another, by forces called | chemical bonds |
| The bonds of greatest physiological interest are | ionic bonds, covalent bonds, hydrogen bonds, and van der Waals forces |
| The bonds of greatest physiological interest are: -----, covalent bonds, hydrogen bonds, and van der Waals forces | ionic bonds |
| The bonds of greatest physiological interest are: ionic bonds, ----- hydrogen bonds, and van der Waals forces | covalent bonds, |
| The bonds of greatest physiological interest are: ionic bonds, covalent bonds, ------ and van der Waals forces | hydrogen bonds, |
| The bonds of greatest physiological interest are: ionic bonds, covalent bonds, hydrogen bonds, and | van der Waals forces |
| Ionic Bond | Relatively weak attraction between an anion and a cation. Easily disrupted in water, as when salt dissolves. |
| Covalent Bond | Sharing of one or more pairs of electrons between nuclei. |
| Single covalent | Sharing of one electron pair. |
| Double covalent | Sharing of two electron pairs. Often occurs between carbon atoms, between carbon and oxygen, and between carbon and nitrogen. |
| Nonpolar covalent | Covalent bond in which electrons are equally attracted to both nuclei. May be single or double. Strongest type of chemical bond. |
| Polar covalent | Covalent bond in which electrons are more attracted to one nucleus than to the other, resulting in slightly positive and negative regions in one molecule. May be single or double. |
| Hydrogen Bond | Weak attraction between polarized molecules or between polarized regions of the same molecule. Important in the three-dimensional folding and coiling of large molecules such as DNA and proteins. Easily disrupted by temperature and pH changes. |
| Van der Waals Force | Weak, brief attraction due to random disturbances in the electron clouds of adjacent atoms. Weakest of all bonds individually, but can have strong effects collectively. |
| An ionic bond is the attraction of a cation to an anion. | Sodium (Na1) and chloride (CI) ions, for example, are attracted to each other and form the compound sodium chloride (NaCl), common table salt. |
| Ionic compounds can be composed of more than two ions, such as calcium chloride, CaCl1⁄2. | Ionic bonds easily dissociate (break up) in the presence of something more attractive, such as water. |
| The ionic bonds of NaCl break down easily as salt dissolves in water | because both Na and CI= are more attracted to water molecules than they are to each other. |
| Do you think ionic bonds are common in human body fluids? | Ionic bonds are common in human body fluids, as they form between charged ions like sodium (Na+) and chloride (Cl−). |
| Covalent bonds form by the sharing of electrons. | For example, two hydrogen atoms share valence electrons to form a hydrogen molecule, H2 |
| The two electrons, one donated by each atom | swarm around both nuclei in a dumbbell-shaped cloud. |
| A single covalent bond is the sharing of a single pair of electrons. It is symbolized by a single line between atomic symbols, for example, H—H. | A double covalent bond is the sharing of two pairs of electrons. |
| In carbon dioxide, for example, a central carbon atom shares two electron pairs with each oxygen atom. | Such bonds are symbolized by double lines—for example, 0=C=0 |
| Hydrogen atom + Hydrogen atom | H -- H Hydrogen molecule (H2) |
| O ==== C ===== O | Carbon dioxide (CO2) |
| Two hydrogen atoms share a single pair of electrons to form a hydrogen molecule | A carbon dioxide molecule, in which a carbon atom shares two pairs of electrons with each oxygen atom, forming double covalent bonds |
| When shared electrons spend approximately equal time around each nucleus, they form a -----, the strongest of all chemical bonds. | nonpolar covalent bond |
| Carbon atoms bond to each other with | nonpolar covalent bonds |
| If shared electrons spend significantly more time orbiting one nucleus than they do the other, they lend their negative charge to the region where they spend the most time, and they form a | polar covalent bond |
| When ----- with oxygen, for example, the electrons are more attracted to the oxygen nucleus and orbit it more than they do the hydrogen. | hydrogen bonds |
| This makes the ---- region of the molecule slightly negative and the hydrogen region slightly positive. | oxygen |
| The ------ is used to symbolize a charge less than that of one electron or proton. | Greek delta (8) |
| A slightly negative region of a molecule is represented d- | and a slightly positive region is represented 8+ |
| A nonpolar covalent | bond between two carbon atoms, formed by electrons that spend an equal amount of time around each nucleus, as represented by the symmetric blue cloud. |
| A polar covalent bond | , in which electrons orbit one nucleus significantly more than the other, as represented by the asymmetric cloud. |
| Nonpolar Bond | This results in a slight negative charge (8-) in the region where the electrons spend most of their time, and a slight positive charge (8+) at the other pole. |
| A ---- is a weak attraction between a slightly positive hydrogen atom in one molecule and a slightly negative oxygen or nitrogen atom in another | hydrogen bond |
| Water molecules | , for example, are weakly attracted to each other by hydrogen bonds |
| Hydrogen bonds | also form between different regions of the same molecule, especially in very large molecules such as proteins and DNA. |
| Hydrogen bonds | They cause such molecules to fold or coil into precise three-dimensional shapes. |
| Hydrogen bonds are represented by dotted or broken lines between atoms | —C=O...H—N—. |
| ----- are relatively weak individually, but they have a strong collective effect and are enormously important to physiology. | Hydrogen bonds |
| Hydrogen Bonding of Water | The polar covalent bonds of water molecules enable each oxygen to form a hydrogen bond with a hydrogen of a neighboring molecule. Thus, the water molecules are weakly attracted to each other. |
| Why would this behavior raise the boiling point of water above that of a nonpolar liquid? | Because water molecules are attracted to each other, it requires more thermal energy for any of them to break free and evaporate. |
| Van der Waals forces are important in protein folding, the binding of proteins to each other and to other molecules such as hormones, and the association of lipid molecules with each other in cell membranes. | They're weak, brief attractions between neutral atoms. |
| When electrons orbit a nucleus, they don't maintain a uniform distribution but show random fluctuations in density. | If the electrons briefly crowd toward one side of an atom, they render that side slightly negative and the other side slightly positive for a moment. |
| If another atom is close enough to this one, the second atom responds with disturbances in its own electron cloud. | Oppositely charged regions of the two atoms then very briefly attract each other. |
| A single van der Waals force is only about 1% as strong as a covalent bond, but when two surfaces or large molecules meet, the van der Waals forces between large numbers of atoms can create a very strong attraction. | This is how plastic wrap clings to food and dishes and even a heavy lizard, such as a gecko, can walk up a windowpane. |
| Iron (Fe) | is an atom, as it consists of a single type of element. |
| Hydrogen gas (H2) | is a molecule, formed by two hydrogen atoms bonded together. |
| Ammonia (NH3) | is both a molecule and compound, composed of nitrogen and hydrogen atoms |
| Why is the biological half-life of a radioisotope shorter than its physical half-life? | The biological half-life of a radioisotope is shorter than its physical half-life because the body actively processes and eliminates the isotope. |
| Where do free radicals come from? | Free radicals originate from metabolic reactions, radiation, and chemicals. |
| What harm does free radicals do? | They damage cells by converting fats, proteins, and DNA into more free radicals, potentially causing cancer and heart tissue death. |
| How is the body protected from free radicals? | The body protects itself using antioxidants, which neutralize free radicals, preventing chain reactions that lead to cellular damage. |
| How does an ionic bond differ from a covalent bond? | An ionic bond forms when electrons are transferred between atoms, creating charged ions that attract each other, like magnets. |
| How does an ionic bond differ from a covalent bond? | . Covalent bonds can be single, double, nonpolar, or polar, with nonpolar covalent bonds being the strongest due to equal electron sharing. |
| What is a hydrogen bond? | A hydrogen bond is an attraction between a hydrogen atom, bonded to a highly electronegative atom like oxygen or nitrogen, and another electronegative atom |
| Why do hydrogen bonds depend on the existence of polar covalent bonds? | These bonds rely on polar covalent bonds because they create the slight positive and negative charges necessary for the attraction. |
| Our body fluids are complex mixtures of chemicals. | A mixture consists of substances that are physically blended but not chemically combined; each substance retains its own chemical properties. |
| To contrast a mixture with a compound, consider --- again. | sodium chloride |
| Sodium | is a lightweight metal that bursts into flame upon contact with water, and chlorine is a yellow-green poisonous gas that was once used in chemical warfare. |
| When these elements chemically react, they form common table salt. | Clearly, the compound has properties much different from the properties of its elements. |
| But if you were to put a little salt on your melon, the melon would taste salty and sweet because the sugar of the melon and the salt you added would merely form a mixture in which each compound retained its | individual properties. |
| Most mixtures in the body consist of ----- or suspended in water. | chemicals dissolved |
| Water constitutes ---- of one's body weight, depending on age, sex, fat content, and other factors. Its structure, simple as it is, has profound biological effects. | 50% to 75% |
| Two aspects of its structure are particularly important | (1) Its atoms are joined by polar covalent bonds, and (2) the molecule is V-shaped, with a 105° bond angle (fig. 2.9a). |
| This makes the molecule as a whole polar, because there is a slight negative charge (8–) on the oxygen at the apex of the V and a slight positive charge (8+) on each hydrogen. | Like little magnets, water molecules are attracted to one another by hydrogen bonds (fig. 2.8). |
| This gives water a set of properties that account for its ability to support life: (slight negative and positive) | solvency, cohesion, adhesion, chemical reactivity, and thermal stability. |
| Water and Hydration Spheres | (a) A water molecule showing its bond angle and polarity poles facing the CI. |
| Water and Hydration Spheres | . (b) Water molecules aggregate around a sodium ion with their negatively charged oxygen poles facing the Nat and aggregate around a chloride ion with their positively charged hydrogen |
| Solvency is the ability to dissolve other chemicals. | Water is called the universal solvent because it dissolves a broader range of substances than any other liquid. |
| Substances that dissolve in water, such as sugar, are said to be hydrophilic (HY-dro-FILL-ic); | the relatively few substances that do not, such as fats, are hydrophobic (HY-dro-FOE-bic). |
| Virtually all metabolic reactions depend on the solvency of water. | Biological molecules must be dissolved in water to move freely, come together, and react. |
| The solvency of water also makes it the body's primary means of transporting substances from place to place | To be soluble in water, a molecule usually must be polarized or charged so that its charges can interact with those of water. |
| When NaCl is dropped into water, for example, the ionic bonds between Na1 and CI= are overpowered by the attraction of each ion to water molecules. | Water molecules form a cluster, or hydration sphere, around each sodium ion with the O- pole of each water molecule facing the sodium ion. |
| They also form a hydration sphere around each chloride ion, with the Ho+ poles facing it. | Water molecules |
| hydration process | This isolates the sodium ions from the chloride ions and keeps them dissolved |
| Adhesion | is the tendency of one substance to cling to another, whereas cohesion is the tendency of molecules of the same substance to cling to each other. |
| Water adheres to the body's tissues and forms a lubricating film on membranes such as the ---- | pleura and pericardium. |
| This reduces friction as the lungs and heart contract and expand and rub against these membranes. | Lubricating film |
| Water | also is a very cohesive liquid because of its hydrogen bonds. |
| This is why, when you spill water, it forms a puddle and evaporates slowly. | hydrogen bond |
| By contrast, if you spill a nonpolar substance such as liquid nitrogen, it dances about and evaporates in seconds, like a drop of water in a hot dry skillet. | This is because nitrogen molecules have no attraction for each other, so the little bit of heat is enough to disperse them into the air. |
| The cohesion of water is especially evident at its surface, where it forms an elastic layer called the surface film held together by a force called surface tension. | This force causes water to hang in drops from a leaky faucet and travel in sweaty rivulets down one's perspiring skin. |
| Cohesion plays an important role in breathing. | When you inhale, the muscles between your ribs pull the chest wall outward, including the parietal pleura lining the rib cage (see atlas A). |
| The ----- on the lung surface goes with it because of the cohesion between the water layers of both membranes, and this movement expands the lungs. | wet visceral pleura |
| The chemical reactivity of water is its ability to participate in chemical reactions. | Not only does water ionize many other chemicals such as acids and salts, but water itself ionizes into H+ and OH. |
| These ---- can be incorporated into other molecules, or released from them, in the course of chemical reactions such as hydrolysis and dehydration synthesis, described later in this chapter. | ions |
| The thermal stability of water helps to stabilize the internal temperature of the body. | It results from the high heat capacity of water-the amount of heat required to raise the temperature of 1 g of a substance by 1°C. |
| The base unit of heat is the calorie (cal)—1 cal is the amount of heat that raises the temperature of 1 g of water 1°C. The same amount of heat would raise the temperature of a nonpolar substance such as nitrogen about four times as much. | The difference stems from the presence or absence of hydrogen bonding. |
| To increase in temperature, the molecules of a substance must move around more actively. | The hydrogen bonds of water molecules inhibit their movement, so water can absorb a given amount of heat without changing temperature (molecular motion) as much. |
| The high heat capacity of water also makes it a very effective coolant. | When it changes from a liquid to a vapor, water carries a large amount of heat with it. |
| One milliliter of perspiration evaporating from the skin removes about 500 cal of heat from the body. | This effect is very apparent when you're sweaty and stand in front of a fan or in a cooling breeze. |
| Why are heat and temperature not the same thing? | Heat is the total energy of molecular motion in a substance, measured in calories. Temperature, however, is the average energy of molecular motion, measured in degrees |
| Mixtures of other substances in water can be classified as | solutions, colloids, and suspensions |
| A solution consists of particles of matter called the solute mixed with a more abundant substance (usually water) called the ----. | solvent |
| The solute can be a gas, solid, or liquid— | as in a solution of oxygen, sodium chloride, or alcohol in water, respectively. |
| Solutions are defined by the following properties: | The solute particles are under 1 nanometer (nm) in size. The solute and solvent therefore cannot be visually distinguished from each other, even with a microscope. |
| Solutions are defined by the following properties: | Such small particles don't scatter light noticeably, so solutions are usually transparent |
| Solutions are defined by the following properties: | The solute particles can pass through most selectively permeable membranes, such as dialysis tubing and cell membranes. |
| Solutions are defined by the following properties: | The solute doesn't separate from the solvent when the solution is allowed to stand. |
| Solution | Is blue |
| Colloid | Is white |
| Suspension | Half blood full |
| Suspension | Pushed down |
| In a -----, the solute particles are so small they remain permanently mixed and the solution is transparent. | copper sulfate solution |
| In ----, the protein molecules are small enough to remain permanently mixed, but large enough to scatter light, so the mixture is opaque. | milk |
| In ----, the red blood cells scatter light and make the mixture opaque. | blood |
| Red blood cells | are too large to remain evenly mixed, so they settle to the bottom as in this blood specimen that stood overnight. |
| The most common ----- in the body are mixtures of protein and water, such as the albumin in blood plasma. | colloids |
| Many --- can change from liquid to gel states-gelatin desserts, agar culture media, and the fluids within and between our cells, for example. | colloids |
| The colloidal particles range from | 1 to 100 nm in size. |
| Particles this large scatter light, so ---- are usually cloudy | Colloids |
| The particles are too large to pass through most selectively permeable membranes | Colloids |
| The particles are still small enough, however, to remain permanently mixed with the solvent when the mixture stands. | Colloids |
| The blood cells in our blood plasma exemplify a -----. | suspension |
| The suspended particles exceed 100 nm in size. | blood cells |
| Such large particles render suspensions cloudy or opaque. | blood cells |
| The particles are too large to penetrate selectively permeable membranes. | blood cells |
| The particles are too heavy to remain permanently suspended, so suspensions separate on standing. | blood cells |
| Blood cells | for example, form a suspension in the blood plasma and settle to the bottom of a tube when blood is allowed to stand without mixing |
| An ---- is a suspension of one liquid in another, such as oil-and-vinegar salad dressing. | emulsion |
| The fat in breast milk is an ----, as are medications such as Kaopectate and milk of magnesia. | emulsion |
| A single mixture can fit into more than one of these categories. ---- is a perfect example-it is a solution of sodium chloride, a colloid of protein, and a suspension of cells. | Blood |
| Milk | is a solution of calcium. a colloid of protein. and an emulsion of fat. |
| Particle Size for Solution | <1nm |
| Particle Size for Colloid | 1-100nm |
| Particle Size for Suspension | >100nm |
| Appearance for Solution | Clear |
| Appearance for Colloid | Often Cloudy |
| Appearance for Suspension | Cloudy-opaque |
| Does Solution Particles settle out? | No |
| Does Colloid Particles settle out? | No |
| Does Suspension Particles settle out? | Yes |
| Will particles pass through a selectively permeable membrane? Solution | Yes |
| Will particles pass through a selectively permeable membrane? Colloid | No |
| Will particles pass through a selectively permeable membrane? Suspension | No |
| Glucose in blood | Solution Examples: -----, O2 in Water, Saline Solutions, Sugar in Coffee |
| O2 in Water | Solution Examples: Glucose in blood, ------, Saline Solutions, Sugar in Coffee |
| Saline Solutions | Solution Examples: Glucose in blood, O2 in Water, ------, Sugar in Coffee |
| Sugar in Coffee | Solution Examples: Glucose in blood, O2 in Water, Saline Solutions, ------- |
| Proteins In Blood | Colloid Examples: ----, Intracellular fluid, milk protein, gelatin |
| Intracellular fluid | Colloid Examples: Proteins In Blood, ------, milk protein, gelatin |
| milk protein | Colloid Examples: Proteins In Blood, Intracellular fluid, -----, gelatin |
| gelatin | Colloid Examples: Proteins In Blood, Intracellular fluid, milk protein, ----- |
| Blood cells | Suspension Examples: ------, Cornstarch in water, fats in blood, kaopectate |
| Cornstarch in water | Suspension Examples: Blood cells, -----, fats in blood, kaopectate |
| fats in blood | Suspension Examples: Blood cells, Cornstarch in water, -----, kaopectate |
| kaopectate | Suspension Examples: Blood cells, Cornstarch in water, fats in blood, ----- |
| Most people have some sense of what acids and bases are. | Advertisements are full of references to excess stomach acid and pH-balanced shampoo. |
| We know that drain cleaner (a strong base) and battery acid can cause serious ------ | chemical burns |
| An acid is any proton donor, a molecule that releases a proton (H+) in water. | A base is a proton acceptor. |
| Since ----- accept H±, many bases are substances that release hydroxide ions—sodium hydroxide (NaOH), for example | hydroxide ions (OH-) |
| . A base doesn't have to be a hydroxide donor, however. | Ammonia (NH3) is also a base. |
| Ammonia (NH3) | It doesn't release a hydroxide ion, but it readily accepts a hydrogen ion to become an ammonium ion (NH4+). |
| Acidity | is expressed in terms of pH, a measure derived from the molarity of H+. |
| Molarity | (explained in the next section) is represented by square brackets, so H+ molarity is symbolized [H+]. |
| pH | is the negative logarithm of hydrogen ion molarity—that is, pH = -log [H*]. |
| In -----, 1 in 10 million molecules ionizes into hydrogen and hydroxide ions: H2O = H+ + OH ̄. (The symbol denotes a reversible chemical reaction.) | pure water |
| Pure water has a neutral pH because it contains equal amounts of H* and OH ̄. | Since 1 in 10 million molecules ionize, the molarity of H* and the pH of water are |
| [H+] = 0.0000001 molar | = 10-7M |
| log[H+] | -7 |
| pH = | -log[H+] = 7. |
| The pH scale (fig. 2.11) was invented in 1909 by Danish biochemist | and brewer Sören Sörensen to measure the acidity of beer. |
| pH Scale | The scale extends from 0.0 to 14.0. |
| A solution with a pH of 7.0 is neutral | solutions with pH below 7 are acidic; and solutions with pH above 7 are basic (alkaline). |
| The lower the -----, the more hydrogen ions a solution has and the more acidic it is. | pH value |
| Since the pH scale is logarithmic, a change of one whole number on the scale represents a 10-fold change in H+ concentration. | In other words, a solution with pH 4 is 10 times as acidic as one with pH 5 and 100 times as acidic as one with pH 6. |
| 1 M hydrochloric acid | 0 - Increasingly acid |
| Gastric juice | 0.9-3.0 - Increasingly acid |
| Lemon juice | 2.3 - Increasingly acid |
| Wine, vinegar | 2.4-3.5 - Increasingly acid |
| Bananas, tomatoes | 4.7 - Increasingly acid |
| Bread, black coffee | 5.0 - Increasingly acidic |
| Milk | 6.3–6.6 - Increasingly acidic |
| Pure water | 7.0 - Neutral |
| Egg white | 8.0 - Increasingly basic |
| Household bleach | 9.5 - Increasingly basic |
| Household ammonia | 10.5–11.0 - Increasingly basic |
| Oven cleaner, lye | 13.4- Increasingly basic |
| 1 M sodium hydroxide | 14-Increasingly basic |
| Slight disturbances of pH can seriously disrupt physiological functions and alter drug actions, | so it is important that the body carefully control its pH |
| Blood, for example, normally has a pH ranging from 7.35 to 7.45. | Deviations from this range cause tremors, fainting, paralysis, or even death. |
| Chemical solutions that resist changes in pH are called ----. | buffers |
| A buffer is an ----- containing both a weak acid and weak base that are a conjugate acid based pair. | aqueous solution |
| The ---- shown contains the weak acid acetic acid and its conjugate base, acetate; these species are dissolved in water. | buffer |
| Water molecules | are not shown in this animation to draw focus to the buffer components. |
| A --- has the ability to resist changes in pH upon the addition of small amounts of either acid or base | buffer solution |
| Only ----- from the hydrochloric acid are shown entering the solution. | hydrogen ions H+ |
| Chloride | is not shown because it is a spectator ion; it does not participate in the reaction. |
| The ----- reacts with a base component of the buffer acetate CH3COO- producing the acid component of the buffer acetic acid CH3COOH. | strong acid H+ |
| The buffer has resisted a change in pH by removing ----, H+ from the solution. | strong acid |
| Only hydroxide ions OH- from the strong base ----- are shown entering the solution. | sodium hydroxide |
| ----- are not shown because they are spectator ions; they do not participate in the reaction. | Sodium ions |
| The strong base, ---- reacts with the acid component of the buffer acetic acid, CH3COOH producing the base component of the buffer acetate, CH3COO- and water. | hydroxide OH- |
| This buffer has resisted a change in ---- by removing the strong base hydroxide from the solution. | pH |
| A pH of 7.20 is slightly alkaline, yet a blood pH of 7.20 is called acidosis. Why do you think it is called this? | Though a pH of 7.20 is slightly alkaline, blood is normally between 7.35 and 7.45. Thus, 7.20 is below the body's typical range, indicating acidosis. |
| The pH of the body fluids has a direct bearing on how one reacts to drugs. | Depending on pH, drugs such as aspirin, phenobarbital, and penicillin can exist in charged (ionized) or uncharged forms. |
| Whether a drug is charged or not can determine whether it will pass through cell membranes. | When aspirin is in the acidic environment of the stomach, for example, it is uncharged and passes easily through the stomach lining into the bloodstream. |
| Here it encounters a basic pH, whereupon it ionizes. In this state, it is unable to pass back through the membrane, so it accumulates in the blood. | This effect, called ion trapping (pH partitioning), can be controlled to help clear poisons from the body. |
| This effect, called ion trapping (pH partitioning), can be controlled to help clear poisons from the body. | The pH of the urine, for example, can be manipulated so that poisons become trapped there and are more rapidly excreted from the body. |
| Solutions are often described in terms of their concentration- | how much solute is present in a given volume of solution. |
| Weight per volume. | This is the weight of solute (such as grams, g, or milligrams, mg) in a given volume of solution (such as liters, L, or deciliters, dL). For example, a typical serum cholesterol concentration is 200 mg/dL. |
| This is the weight of solute as a percentage of solution volume (weight per volume, w/v) or volume of a liquid as a percentage of total solution volume (volume per volume, v/v). | Percentage |
| For example, a common intravenous fluid is D5W, which means 5% w/v dextrose in distilled water. Ethanol is often used as a 70% v/v solution. | Percentage |
| One mole of a chemical is the number of grams equal to its molecular weight, and molarity (M) is a measure of the number of moles of solute per liter of solution. | Molarity. |
| This reflects not merely the weight of solute in the solution, but the number of molecules per volume | Molarity. |
| . It is the number of molecules, not their total weight, that determines the physiological effect of a solution, so molarity is often the most meaningful measure of concentration. Body fluids are usually quantified in millimolar (mM) concentrations, | since they are one less molar. Molarity. |
| Milliequivalents per liter. | This unit of measure (expressed mEq/L) is used to denote electrolyte concentration; it takes into account not only the millimolar concentration of a solute but the electrical charge on its particles. |
| intravenous fluids. | This is important to processes such as nerve firing, the heartbeat, and muscle contractions, which are driven by electrical phenomena. The mEq/L concentration of electrolytes is critically important in giving |
| What is the difference between a mixture and a compound? | A mixture consists of substances physically blended without chemical bonding, so each retains its properties—like a fruit salad where each piece keeps its flavor |
| What is the difference between a mixture and a compound? | . In contrast, a compound results from a chemical reaction between elements, forming a new substance with different properties—like table salt, where sodium and chlorine combine to form a stable compound. |
| What are hydrophilic and hydrophobic substances? | Hydrophilic substances are those that dissolve easily in water, like sugar, due to their affinity for water molecules. Conversely, hydrophobic substances, such as fats, repel water and do not dissolve. |
| Why would the cohesion and thermal stability of water be less if water did not have polar covalent bonds? | Without these bonds, water would behave more like a nonpolar liquid, reducing its ability to stabilize temperature and maintain surface tension. |
| ----, like blood, have even larger particles that settle over time, causing separation | Suspensions |
| Solutions, colloids, and suspensions differ mainly in | particle size and behavior |
| . In ----, like glucose in blood, tiny particles stay mixed and transparent. | solutions |
| ----, such as milk, have larger particles that scatter light, making them cloudy but stable. | Colloids |
| -----, like blood, have even larger particles that settle over time, causing separation | Suspensions |
| If solution A had a H+ concentration of 10-8 M, what would be its pH? If solution B had 1,000 times this H+ concentration, what would be its pH? Would solution A be acidic or basic? What about solution B? | To determine the pH of solution A with an H⁺ concentration of 10⁻⁸ M, use the formula pH = -log[H⁺], giving a pH of 8, indicating a basic solution. |
| 10-8 M, what would be its pH? If solution B had 1,000 times this H+ concentration, what would be its pH? Would solution A be acidic or basic? What about solution B? | For solution B, which has 1,000 times the H⁺ concentration, the concentration becomes 10⁻⁵ M, resulting in a pH of 5, indicating an acidic solution. |
| What information can we get from the molarity of a solution that we cannot know from its percentage concentration? What do we know from a concentration in mEq/L that we cannot know from molarity alone? | Molarity gives the number of moles of solute per liter of solution, revealing the actual quantity of substance present. |
| What information can we get from the molarity of a solution that we cannot know from its percentage concentration? What do we know from a concentration in mEq/L that we cannot know from molarity alone? | Percentage concentration only indicates the proportion of solute in a solution, not the specific amount. |
| What information can we get from the molarity of a solution that we cannot know from its percentage concentration? What do we know from a concentration in mEq/L that we cannot know from molarity alone? | mEq/L, or milliequivalents per liter, accounts for the charge of ions, offering insight into the solution's ionic balance, which molarity alone cannot provide. |
| Energy is the capacity to do work. To do work means to move something, whether a muscle or a molecule | . Some examples of physiological work are breaking chemical bonds, building molecules, pumping blood, and contracting skeletal muscles. All of the body's activities are forms of work. |
| Potential energy is energy contained in an object because of its position or internal state but that is not doing work at the time. | Energy is broadly classified as potential or kinetic energy. |
| Kinetic energy is energy of motion, energy that is doing work. | It is observed in musculoskeletal movements, the flow of ions into a cell, and vibration of the eardrum, for example |
| The water behind a dam has potential energy because of its position. | Let the water flow through, and it exhibits kinetic energy that can be tapped for generating electricity. |
| Like water behind a dam, ions concentrated on one side of a cell membrane have potential energy that can be released by opening gates in the membrane. | As the ions flow through the gates, their kinetic energy can be tapped to create a nerve signal or make the heart beat. |
| Within the two broad categories of -----, several forms of energy are relevant to human physiology. | potential and kinetic energy |
| Chemical energy | is potential energy stored in the bonds of molecules. |
| Heat | is the kinetic energy of molecular motion. |
| The temperature of a substance is a measure of rate of this motion, and adding heat to a substance increases | molecular motion |
| Electromagnetic energy | is the kinetic energy of moving quanta (“packets") of radiation called photons |
| The most familiar form of electromagnetic energy is light. | Electrical energy has both potential and kinetic forms. |
| It is potential energy when charged particles have accumulated at a point such as a battery terminal or on one side of a cell membrane; it becomes kinetic energy when these particles begin to move and create an electrical current | for example, when electrons move through your household wiring or sodium ions move through a cell membrane. |
| Free energy is the potential energy available in a system to do useful work. | In human physiology, the most relevant free energy is the energy stored in the chemical bonds of organic molecules. |
| A ----- is a process in which a covalent or ionic bond is formed or broken. | chemical reaction |
| The course of a chemical reaction is symbolized by a chemical equation that typically shows the reactants on the left, the products on the right, and an arrow pointing from the reactants to the products. | For example, consider this common occurrence: If you open a bottle of wine and let it stand for several days, it turns sour. |
| Wine “turns to vinegar” because oxygen gets into the bottle and reacts with ethanol to produce acetic acid and water. | Acetic acid gives the tart flavor to vinegar and spoiled wine. The equation for this reaction is |
| CH3CH2OH Ethanol + O2 Oxygen -> | CH3COOH Acetic acid + H2O Water |
| Ethanol and oxygen are the reactants, and acetic acid and water are the products of this reaction. | Not all reactions are shown with the arrow pointing from left to right. |
| In complex biochemical equations, reaction chains are often written | vertically, diagonally, or even in circles |
| Chemical reactions can be classified as | decomposition, synthesis, or exchange reactions. |
| In decomposition reactions, a large molecule breaks down into two or more smaller ones (fig. 2.12a); symbolically, | AB → A + B |
| When you eat a potato, for example, digestive enzymes decompose its starch into thousands of glucose molecules, and most cells further decompose glucose to water and carbon dioxide. | Starch, a very large molecule, ultimately yields about 36,000 molecules of H2O and CO2. |
| Starch molecule -> Glucose molecules | Decomposition Reaction |
| Amino Acids -> Protein Molecules | Synthesis Reaction |
| AB + CD -> AC + BD | Exchange Reaction |
| In a ----- reaction, large molecules are broken down into simpler ones. | decomposition |
| In a ----- reaction, smaller molecules are joined to form larger ones. | synthesis |
| In an ----- reaction, two molecules ----- atoms. | exchange |
| To which of these categories does the digestion of food belong? | Decomposition |
| Synthesis reactions are just the opposite-two or more small molecules combine to form a larger one; symbolically, | A + B → AB |
| When the body ------, for example, it combines 50 or more amino acids into one protein molecule. | synthesizes proteins |
| In exchange reactions, two molecules exchange atoms or groups of atoms; | AB + CD → AC + BD |
| For example, when stomach acid (HCl) enters the small intestine, the pancreas secretes sodium bicarbonate (NaHCO3) to neutralize it. | Exchange Reaction |
| The reaction between the two is | NaHCO3 + HCl →NaCl + H2CO3. |
| We could say the sodium atom has exchanged its bicarbonate group (—HCO3) for a | chlorine atom |
| Reversible reactions can go in either direction under different circumstances. For example, carbon dioxide combines with water to produce carbonic acid, which in turn decomposes into bicarbonate ions and hydrogen ions: | CO₂ + H₂O ⇌ H₂CO₃ ⇌ HCO₃⁻ + H⁺ |
| The direction in which a ----- goes is determined by the relative abundance of substances on each side of the equation. | reversible reaction |
| If there is a surplus of CO2, the foregoing reaction proceeds left to right and produces bicarbonate and hydrogen ions. | If bicarbonate and hydrogen ions are present in excess, the reaction proceeds right to left and generates CO2 and H2O. |
| Reversible reactions follow the law of mass action: They proceed from the reactants in greater quantity to the substances with the lesser quantity. | This law will help to explain processes discussed in later chapters, such as why hemoglobin binds oxygen in the lungs yet |
| In the absence of upsetting influences, reversible reactions exist in a state of -----, in which the ratio of products to reactants is stable. | equilibrium |
| The carbonic acid reaction, for example, normally maintains a 20:1 ratio of | bicarbonate ions to carbonic acid molecules. |
| This ------ can be upset, however, by a surplus of hydrogen ions, which drives the reaction to the left, or adding carbon dioxide and driving it to the right. | equilibrium |
| In the absence of upsetting influences, reversible reactions exist in a state of ----- , in which the ratio of products to reactants is stable. | equilibrium |
| The carbonic acid reaction, for example, normally maintains a 20:1 ratio of bicarbonate ions to ------- | carbonic acid molecules |
| This ----- can be upset, however, by a surplus of hydrogen ions, which drives the reaction to the left, or adding carbon dioxide and driving it to the right. | equilibrium |
| Chemical reactions are based on molecular motion and collisions. | All molecules are in constant motion, and reactions occur when mutually reactive molecules collide with sufficient force and the right orientation. |
| The rate of a reaction depends on the nature of the reactants and on the frequency and force of these collisions. | Some factors that affect reaction rates are |
| Concentration. | Reaction rate increases when the reactants are more concentrated. This is because the molecules are more crowded and collide more frequently. |
| Temperature. | Reaction rate increases as the temperature rises. This is because heat causes molecules to move more rapidly and collide with greater force and frequency. |
| Catalysts (CAT-uh-lists) | These are substances that temporarily bind to reactants, hold them in a favorable position to react with each other, and may change the shapes of reactants in ways that make them more likely to react. |
| Catalysts (CAT-uh-lists) | By reducing the element of chance in molecular collisions, a catalyst speeds up a reaction |
| Catalysts (CAT-uh-lists) | It then releases the products and is available to repeat the process with more reactants. |
| Catalysts (CAT-uh-lists) | The catalyst itself is not consumed or changed by the reaction. The most important biological catalysts are enzymes, discussed later in this chapter. |
| All the chemical reactions in the body are collectively called | metabolism |
| Metabolism has two divisions | catabolism and anabolism |
| Catabolism | consists of energy-releasing decomposition reactions. |
| Such reactions break covalent bonds, produce smaller molecules from larger ones, and release energy that can be used for other physiological work. | Metabolism, Oxidation, and Reduction |
| Energy-releasing reactions are called exergonic reactions. If you hold a beaker of water in your hand and pour sulfuric acid into it, for example, the beaker will get so hot you may have to put it down. | If you break down energy-storage molecules to run a race, you too will get hot. In both cases, the heat signifies that exergonic reactions are occurring. |
| Anabolism (ah-NAB-oh-lizm) consists of energy-storing synthesis reactions, such as the production of protein or fat. Reactions that require an energy input, such as these, are called endergonic reactions. | Anabolism is driven by the energy that catabolism releases, so endergonic and exergonic processes, anabolism and catabolism, are inseparably linked. |
| Oxidation is any chemical reaction in which a molecule gives up electrons and releases energy. | A molecule is oxidized by this process, and whatever molecule takes the electrons from it is an oxidizing agent (electron acceptor). |
| The term ---- stems from the fact that oxygen is often involved as the electron acceptor. Thus, we can sometimes recognize an oxidation reaction from the fact that oxygen has been added to a molecule. | oxidation |
| The rusting of iron, for example, is a slow oxidation process in which oxygen is added to iron to form iron oxide (FeO3). | Many oxidation reactions, however, don't involve oxygen at all. |
| For example, when yeast ferments glucose to ethanol, no oxygen is required | indeed, the ethanol contains less oxygen than the glucose originally did, but it is more oxidized than the glucose |
| indeed, the ethanol contains less oxygen than the glucose originally did, but it is more oxidized than the glucose: | C6H12O6 Glucose -> 2 CH3CH2OH Ethanol + 2 CO2 Carbon dioxide |
| Reduction is a chemical reaction in which a molecule gains electrons and energy. | When a molecule accepts electrons, it is said to be reduced; a molecule that donates electrons to another is therefore called a reducing agent (electron donor). |
| The oxidation of one molecule is always accompanied by the reduction of another, so these electron transfers are known as | oxidation-reduction (redox) reactions |
| Displacement reactions are among the most common redox reactions. | For example, a metal in a compound can be displaced by another metal in the uncombined state." |
| "When metallic zinc is added to a solution containing copper 2 sulfate, it displaces copper 2 plus ions from the solution. Zinc reduces copper 2 plus ions by donating 2 electrons to it, producing copper metal and zinc 2 plus ions in solution. | Note that copper metal is depositing on the zinc bar. Also, during the reaction, the solution loses the blue color that characterizes the presence of hydrated copper 2 plus ions." |
| It isn't necessary that only electrons be transferred in a redox reaction. | Often, the electrons are transferred in the form of hydrogen atoms. The fact that a proton (the hydrogen nucleus) is also transferred is immaterial to whether we consider a reaction oxidation or reduction. |
| Ae⁻ High-energy reduced state + B Low-energy oxidized state → | A Low-energy oxidized state + Be⁻ High-energy reduced state |
| Ae- is a reducing agent because it reduces B, | and B is an oxidizing agent because it oxidizes Ae- |
| Exergonic Reactions | Reactions in which there is a net release of energy. The products have less total free energy than the reactants did. |
| Oxidation | An exergonic reaction in which electrons are removed from a reactant. Electrons may be removed one or two at a time and may be removed in the form of hydrogen atoms (H or H₂). The product is then said to be oxidized. |
| Decomposition | A reaction such as digestion and cell respiration, in which larger molecules are broken down into smaller ones. |
| Catabolism | The sum of all decomposition reactions in the body. |
| Endergonic Reactions | Reactions in which there is a net input of energy. The products have more total free energy than the reactants did. |
| Reduction | An endergonic reaction in which electrons are donated to a reactant. The product is then said to be reduced. |
| Synthesis | A reaction such as protein and glycogen synthesis, in which two or more smaller molecules are combined into a larger one. |
| Anabolism | The sum of all synthesis reactions in the body. |
| Define energy | Energy is the capacity to do work, whether it's moving a muscle or a molecule. |
| Distinguish potential energy from kinetic energy | Potential energy is like a book on a shelf—it has stored energy due to its position. If the book falls, it transforms into kinetic energy, which is the energy of motion. |
| Define metabolism | Metabolism is the sum of all chemical reactions in the body that convert food into energy. |
| Define catabolism | Catabolism involves breaking down larger molecules into smaller ones, releasing energy in the process. |
| Define anabolism | Anabolism is when the body uses energy to build things like proteins and fats. It gets energy from breaking down other substances. |
| Oxidation | Oxidation is a chemical reaction where a molecule loses electrons and releases energy. |
| Reduction | Reduction in chemistry refers to a reaction where a molecule gains electrons and energy. |
| Which of them is endergonic and which is exergonic? | In chemical reactions, oxidation is exergonic, meaning it releases energy as electrons are removed from a reactant. |
| When sodium chloride forms, which element - is oxidized ?Which one is reduced? | When sodium chloride forms, sodium is oxidized, and chlorine is reduced. |
| Organic chemistry is the study of compounds of carbon. | By 1900, biochemists had classified the large organic molecules of life into four primary categories: carbohydrates, lipids, proteins, and nucleic acids. |
| Carbon is an especially versatile atom that serves as the basis of a wide variety of structures | . It has four valence electrons, so it bonds covalently with other atoms that share four more to complete its valence shell |
| Carbon atoms readily bond with each other and can form long chains, branched molecules, and rings-an enormous variety of carbon backbones for organic molecules. | Carbon also commonly forms covalent bonds with hydrogen, oxygen, nitrogen, and sulfur. |
| Carbon backbones carry a variety of functional groups-small clusters of atoms that determine many of the properties of an organic molecule. | For example, organic acids bear a carboxyl group (car-BOC-sil), and ATP is named for its three phosphate groups. Other common functional groups include hydroxyl, methyl, and amino groups |
| Hydroxyl (-OH) | Structure: O-H Occurs in: Sugars, alcohols |
| Methyl (—CH₃) | Structure: H I C—H (with the bond extending from C) I H Occurs in: Fats, oils, steroids, amino acids |
| Carboxyl (—COOH) | O // C Occurs in: Amino acids, sugars, proteins \ O \ H |
| Amino (—NH₂) | Amino Acids, Proteins H // N \\ H |
| Phosphate (H₂PO4) | H / O I -O-P ==== O I O \ H |
| Since carbon can form long chains, some organic molecules are gigantic ------ with molecular weights that range from the thousands (as in starch and proteins) to the millions (as in DNA). | macromolecules |
| Most macromolecules are ---- -molecules made of a repetitive series of identical or similar subunits called monomers. | polymers |
| -----, for example, is a polymer of about 3,000 glucose monomers. | Starch |
| In -----, the monomers are identical, whereas in other polymers, the monomers have a basic structural similarity but differ in detail. | starch |
| ----, for example, is made of 4 kinds of monomers (nucleotides), and proteins are made of 20 kinds (amino acids). | DNA |
| The joining of ---- to form a polymer is called polymerization. | monomers |
| Living cells achieve this by means of a reaction called | dehydration synthesis (condensation) |
| An ------ removes a hydroxyl group (—OH) from one monomer and a hydrogen (—H) from another, producing water as a by-product. | enzyme |
| The two monomers become joined by a covalent bond, forming a -----. | dimer |
| This is repeated for each monomer added to the chain, potentially leading to a chain long enough to be considered a ------. | polymer |
| Dehydration synthesis | , creating a new covalent bond between two monomers and producing water as a by-product |
| ----- consuming a water molecule to | Hydrolysis |
| The opposite of dehydration synthesis is | hydrolysis |
| In -----, a water molecule ionizes into OH and H+. | hydrolysis |
| An ---- breaks the covalent bond linking one monomer to another, and adds OH to one monomer and H* to the other one. | enzyme |
| All chemical digestion consists of | hydrolysis reactions |
| A carbohydrate is a hydrophilic organic molecule with the general formula (CH2O)n, where n represents the number of carbon atoms. In glucose, for example, n = 6 and the formula is C6H12O6. | As the generic formula shows, carbohydrates have a 2:1 ratio of hydrogen to oxygen. |
| Why is carbohydrate an appropriate name for this class of compounds? | Carbohydrates are aptly named because they are composed of carbon (carbo-) and water (-hydrate), as reflected in their general formula (CH₂O)ₙ. |
| The names of individual carbohydrates are often built on the word root sacchar- or the suffix -ose, both of which mean “sugar” or “sweet.” | The most familiar carbohydrates are sugars and starches. |
| The simplest carbohydrates are monomers called | monosaccharides |
| The three of primary importance are glucose, galactose, and fructose, all with the molecular formula ----; they are isomers of each other | CH1206 |
| We obtain these sugars mainly by the digestion of more complex carbohydrates. ----- is the "blood sugar" that provides energy to most of our cells. | Glucose |
| Two other -----, ribose and deoxyribose, are important components of RNA and DNA, respectively. | monosaccharides |
| The Three Major Monosaccharides | Glucose, galactose, and fructose all have the molecular formula C6H12O6, but with the atoms arranged differently as shown. |
| Each angle in the rings represents a carbon atom except the one where ----- is shown. | oxygen |
| This is a conventional way of representing carbon in the structural formulae of -----. | organic compounds |
| Disaccharides are sugars composed of two monosaccharides. The three disaccharides of greatest importance are sucrose (made of glucose + fructose) | lactose (glucose + galactose), and maltose (glucose + glucose) |
| Sucrose is produced by sugarcane and sugar beets and used as common table sugar | . Lactose is milk sugar. Maltose is a product of starch digestion and is present in a few foods such as malt beverages and germinating grains. |
| . Sucrose, lactose, and maltose all consist of two monosaccharides joined through an oxygen atom. | The Three Major Disaccharides |
| Short chains of three or more monosaccharides are called oligosaccharides | and long chains (up to thousands of monosaccharides long) are called polysaccharides |
| There is no exact criterion for when a chain is long enough to be called a -----, but a chain of 10 or 20 monosaccharides is generally considered an oligosaccharide, whereas a chain of 50 or more is generally considered a ---- | polysaccharide |
| Polysaccharides | can be thousands of sugars long and may have molecular weights of 500,000 or more (compared with 180 for a single glucose). |
| Three ----- of interest to human physiology are glycogen, starch, and cellulose-all composed solely of glucose. Animals, including ourselves, make glycogen, whereas starch and cellulose are plant products. | polysaccharides |
| Animals | including ourselves, make glycogen, whereas starch and cellulose are plant products. |
| Glycogen | is an energy-storage polysaccharide made by cells of the liver, muscles, brain, uterus, and vagina |
| It is a long, branched, glucose polymer | Glycogen |
| The ---- produces glycogen after a meal, when the blood glucose level is high, and then breaks it down between meals to maintain blood glucose levels when there is no food intake. | liver |
| stores glycogen for its own energy needs, and the uterus uses it in early pregnancy to nourish the embryo. | Muscle |
| Glycogen. | This is the only polysaccharide found in human tissues. (a) Part of a glycogen molecule showing the chain of glucose monomers and branching pattern. (b) Detail of the molecule at a branch point. |
| Starch | is the correspondino enerov-storage nolysaccharide of plants |
| Starch | They store it when sunlight and nutrients are available and draw from it when photosynthesis is not possible (for example, at night and in winter, when a plant has shed its leaves) |
| Starch | is the only significant digestible polysaccharide in the human diet. |
| Cellulose is a structural polysaccharide that gives strength to the cell walls of plants. It is the principal component of wood, cotton, and paper. | It is composed of a chain of a few thousand glucose monomers. |
| Cellulose is the most abundant organic compound on earth and it is a common component of the diets of humans and other animals—yet we have no enzymes to digest it. | Nevertheless, it is important as dietary fiber (“bulk” or “roughage”). |
| It swells with water in the digestive tract and helps move other materials through the intestine. | Cellulose |
| We get some ------ from the breakdown products of bacterial action on cellulose in the large intestine. | nutritional benefit |
| Carbohydrates are, above all, a source of energy that can be quickly mobilized. | All digested carbohydrate is ultimately converted to glucose, and glucose is oxidized to make ATP, a high-energy compound discussed later |
| But carbohydrates have other functions as well (table 2.6). | They are often conjugated 20 with (covalently bound to) proteins and lipids. |
| Many lipid and protein molecules at the external surface of the cell membrane have chains of up to 12 sugars attached to them, thus forming glycolipids and glycoproteins, respectively. | Among other functions, glycoproteins are a major component of mucus, which traps particles in the respiratory system, resists infection, and protects the digestive tract from its own acid and enzymes. |
| Glucose | Blood sugar—energy source for most cells |
| Galactose | Converted to glucose and metabolized |
| Fructose | Converted to glucose and metabolized |
| Monosaccharides | Glucose, Galactose, Fructose |
| Disaccharides | Sucrose, Lactose, Maltose |
| Sucrose | Cane sugar—digested to glucose and fructose |
| Lactose | Milk sugar—digested to glucose and galactose; important in infant nutrition |
| Maltose | Malt sugar—product of starch digestion, further digested to glucose |
| Polysaccharides | Cellulose, Starch, Glycogen |
| Cellulose | Structural polysaccharide of plants; dietary fiber |
| Starch | Energy storage in plant cells; energy source in human diet |
| Glycogen | Energy storage in animal cells (liver, muscle, brain, uterus, vagina) |
| Conjugated Carbohydrates | Glycoprotein, Glycolipid, Proteoglycan |
| Glycoprotein | Component of the cell surface coat and mucus, among other roles |
| Glycolipid | Component of the cell surface coat |
| Proteoglycan | Cell adhesion; lubrication; supportive filler of some tissues and organs |
| Proteoglycans | are macromolecules in which the carbohydrate component is dominant and a peptide or protein forms a smaller component. |
| Proteoglycans form | gels that hold cells and tissues together, form a gelatinous filler in the umbilical cord and eye, lubricate the joints of the skeletal system, and account for the tough rubbery texture of cartilage. |
| When discussing conjugated macromolecules, it is convenient to refer to each chemically different component as a moiety. | Proteoglycans have a protein moiety and a carbohydrate moiety, for example. |
| A ---- is a hydrophobic organic molecule, usually composed only of carbon, hydrogen, and oxygen, with a high ratio of hydrogen to oxygen. | lipid |
| A fat called -----, for example, has the molecular formula C57H11006-more than 18 hydrogens for every oxygen. | tristearin (tri-STEE-uh-rin) |
| Lipids | are less oxidized than carbohydrates, and thus have more calories per gram. |
| Beyond these criteria, it is difficult to generalize about lipids; | they are much more variable in structure than the other macromolecules we are considering. |
| We consider here the five primary types of lipids in | humans-fatty acids, triglycerides, phospholipids, eicosanoids, and steroids |
| Bile acids | Steroids that aid in fat digestion and nutrient absorption |
| Cholesterol | Component of cell membranes; precursor of other steroids |
| Eicosanoids | Chemical messengers between cells |
| Fat-soluble vitamins (A, D, E, and K) | Involved in a variety of functions including blood clotting, wound healing, vision, and calcium absorption |
| Fatty acids | Precursor of triglycerides; source of energy |
| Phospholipids | Major component of cell membranes; aid in fat digestion |
| Steroid hormones | Chemical messengers between cells |
| Triglycerides | Energy storage; thermal insulation; filling space; binding organs together; cushioning organs |
| A fatty acid is a chain of usually 4 to 24 carbon atoms with a carboxyl group at one end and a methyl group at the other. | Fatty acids and the fats made from them are classified as saturated or unsaturated. |
| A saturated fatty acid such as palmitic acid has as much hydrogen as it can carry. | No more could be added without exceeding four covalent bonds per carbon; thus, it is “saturated" with hydrogen. |
| In unsaturated fatty acids such as linoleic acid, however, some carbon atoms are joined by double covalent bonds (fig. 2.18a). | Each of these could potentially share one pair of electrons with another hydrogen atom instead of the adjacent carbon, so hydrogen could be added to this molecule. |
| Polyunsaturated fatty acids are those with multiple C=C bonds. | Most fatty acids can be synthesized by the human body, but a few, called essential fatty acids, must be obtained from the diet because we cannot synthesize them. |
| Triglyceride (Fat) Synthesis. The three fatty acids above the arrow (a) combine with glycerol (left) to produce the triglyceride (fat) below the arrow (b). | Note the difference between saturated and unsaturated fatty acids and the production of 3 H2O as a by-product of this dehydration synthesis reaction. |
| A triglyceride (try-GLISS-ur-ide) is a molecule consisting of a three-carbon alcohol called glycerol linked to three fatty acids; | triglycerides are more correctly, although less widely, also known as triacylglycerols. |
| Each bond between a fatty acid and glycerol is formed by dehydration synthesis (fig. 2.18b). | Once joined to glycerol, a fatty acid can no longer donate a proton to solution and is therefore no longer an acid. |
| For this reason, triglycerides are also called neutral fats. | Triglycerides are broken down by hydrolysis reactions, which split each of these bonds apart by the addition of water. |
| Triglycerides that are liquid at room temperature are also called oils, but the difference between a fat and an oil is fairly arbitrary. | Coconut oil, for example, is solid at room temperature. |
| Animal fats are usually made of saturated fatty acids, so they are called saturated fats. | They are solid at room or body temperature. |
| Most plant triglycerides are polyunsaturated fats, which generally remain liquid at room temperature. | Examples include peanut, olive, corn, and linseed oils. |
| Saturated fats contribute more to cardiovascular disease than unsaturated fats | and for this reason it's healthier to cook with vegetable oils than with lard, bacon fat, or butter |
| Trans fats have been a significant part of the American diet for more than a century | Yet in 2015, the U.S. Food and Drug Administration (FDA) ordered food manufacturers to stop using them. |
| A---- is a triglyceride containing one or more trans-fatty acids | trans fat |
| In such fatty acids, there is at least one unsaturated C=C double bond. | On each side of that bond, the single covalent C-C bonds angle in opposite directions (trans means "across from") like a pair of bicycle pedals (see arrows in fig. 2.19a). |
| This is in contrast to cis-fatty acids, in which the two C-C bonds adjacent to the C=C bond angle in the same direction (cis means "on the same side”). | As you can see, the cis configuration creates a kink in the chain, whereas the trans configuration results in a relatively straight chain. The kink prevents triglycerides with cis bonds from packing closely together; hence they are oils. |
| Trans fats | however, are more densely packed and therefore solid at room temperature. |
| Trans- and Cis-Fatty Acids. | Each example is unsaturated at the C-C double bond in red |
| In a trans-fatty acid, the bonds on opposite sides of the C-C bond angle in opposite directions (arrows). | In a cis-fatty acid, the bonds on opposite sides of the C-C bond angle in the same direction. |
| The straight-chain trans-fatty acids pack more tightly together, thus remain solid (greasy) at room temperature. | Oleic acid melts at 13.5°C (56.3°F), whereas elaidic acid melts at 46.5°C (115.7°F) and therefore doesn't liquify in the human body. |
| Small amounts of trans fat occur naturally in meat and dairy products, but in 1911, a food manufacturer invented a method for forcing hydrogen through liquid vegetable oils and converting liquid cis-fatty acids to | solid trans-fatty acids |
| The resulting partially hydrogenated oil (PHO), sold as vegetable shortening, had several advantages and was heavily marketed for household and industrial use. | It was easier to use in making such baked goods as pie crusts and biscuits, and it gave products a desirable texture and longer shelf life. |
| To those who avoid pork products, such as vegans, Jews, and Muslims, it was more acceptable than animal fat such as lard. | Trans fats came to be abundantly used not only by home cooks but also in snack foods, baked goods, frosting, coffee creamer, margarine, and fast foods such as french fries and take-out fried chicken. |
| But trans fats resist enzymatic breakdown in the human body, remain in circulation longer, and have more tendency to deposit in the arteries than saturated and cis fats do. | Therefore, they raise the risk of coronary artery disease (CAD). |
| A study of more than 80,000 nurses who tracked their diets from 1980 to 1994 showed, among other things, that for every 2% increase in calories from trans fats as compared to carbohydrates, the women had a 93% elevated incidence of CAD. | As the dangers of trans fats became widely known, their consumption in the US declined after 2003 and they were banned in cities and states, until the FDA concluded in 2015 that they are “not safe for human consumption" and must be eliminated from foods. |
| The ----- of fat is energy storage, but when concentrated in adipose tissue, it also provides thermal insulation and acts as a shock-absorbing cushion for vital organs. | primary function |
| Phospholipids | are similar to neutral fats except that in place of one fatty acid, they have a phosphate group which, in turn, is linked to other functional groups. |
| Lecithin | is a common phospholipid in which the phosphate is bonded to a nitrogenous group called choline (CO-leen) (fig. 2.20). Phospholipids have a dual nature |
| The two fatty acid “tails" of the molecule are hydrophobic, but the phosphate “head” is hydrophilic. Thus, phospholipids are said to be amphipathic. Together, the head and the two tails of a phospholipid give it a shape like a clothespin. | The most important function of phospholipids is to serve as the structural foundation of cell membranes. |
| Eicosanoids | are 20-carbon compounds derived from a fatty acid called arachidonic acid. |
| Eicosanoids | They function primarily as hormonelike chemical signals between cells. |
| The most functionally diverse eicosanoids are prostaglandins, in which five of the carbon atoms are arranged in a ring (fig. 2.21). | These were originally found in the secretions of bovine prostate glands—hence their name-but they are now known to be produced in almost all tissues. |
| The most functionally diverse eicosanoids are prostaglandins, in which five of the carbon atoms are arranged in a ring (fig. 2.21). | They play a variety of signaling roles in inflammation, blood clotting, hormone action, labor contractions, control of blood vessel diameter, and other processes. |
| Prostaglandin | This is a modified fatty acid with five of its carbon atoms arranged in a ring. |
| A steroid is a lipid with 17 of its carbon atoms arranged in four rings (fig. 2.22). | Cholesterol is the "parent" steroid from which the other steroids are synthesized. |
| A steroid is a lipid with 17 of its carbon atoms arranged in four rings (fig. 2.22). | The others include cortisol, progesterone, estrogens, testosterone, and bile acids. These differ from each other in the location of C=C bonds within the rings and in the functional groups attached to the rings. |
| Cholesterol | All steroids have this basic four-ringed structure, with variations in the functional groups and locations of double bonds within the rings. |
| We obtain dietary cholesterol only from foods of animal origin; plants make only trace amounts of no dietary importance. | The average adult contains over 200 g (half a pound) of cholesterol. |
| Cholesterol has a bad reputation as a factor in cardiovascular disease (see Deeper Insight 2.4), and it is true that hereditary and dietary factors can elevate blood cholesterol to dangerously high levels. | Nevertheless, cholesterol is a natural product of the body and is necessary for human health. |
| cholesterol | In addition to being the precursor of other steroids, it is an important component of cell membranes and is required for proper nervous system function. |
| Only about 15% of our ----- comes from the diet; the other 85% is internally synthesized, primarily by the liver. | cholesterol |
| There is only one kind of cholesterol, and it does far more good than harm. | When the popular media refer to "good" and "bad" cholesterol, they are actually referring to droplets in the blood called lipoproteins, which are a complex of cholesterol, fat, phospholipids, and protein |
| So-called bad cholesterol refers to low-density lipoprotein (LDL), which has a high ratio of lipid to protein and contributes to cardiovascular disease. | So-called good cholesterol refers to high-density lipoprotein (HDL), which has a lower ratio of lipid to protein and may help to prevent cardiovascular disease. |
| Even when food products are advertised as cholesterol-free, they may be high in saturated fat, which stimulates the body to produce more cholesterol. | Palmitic acid seems to be the greatest culprit in stimulating elevated cholesterol levels, while linoleic acid has a cholesterol-lowering effect. |
| The word protein is derived from the Greek word proteios, meaning "of first importance." | Proteins are the most versatile molecules in the body, and many discussions in this book will draw on your understanding of protein structure and behavior. |
| A protein is a polymer of amino acids. | An amino acid has a central carbon atom with an amino (—NH2) and a carboxyl (—COOH) group bound to it (fig. 2.23a). |
| The 20 amino acids used to make proteins are identical except for a third functional group called the R (radical) group attached to the central carbon. | In the simplest amino acid, glycine, R is merely a hydrogen atom, whereas in the largest amino acids it includes rings of carbon. |
| Some R groups are hydrophilic and some are hydrophobic. | Being composed of many amino acids, proteins as a whole are therefore often amphipathic. |
| The ----- involved in proteins are shown in appendix D along with their standard abbreviations. | 20 amino acids |
| A ---- is a polymer of amino acids. | protein |
| An ----- has a central carbon atom with an amino (―NH2) and a carboxyl (-COOH) group bound to it | amino acid |
| The 20 amino acids used to make proteins are identical except for a third functional group called the R (radical) group attached to the central carbon. | In the simplest amino acid, glycine, R is merely a hydrogen atom, whereas in the largest amino acids it includes rings of carbon. |
| Some R groups are hydrophilic and some are hydrophobic. | Being composed of many amino acids, proteins as a whole are therefore often amphipathic. |
| A peptide is any molecule composed of two or more amino acids joined by peptide bonds. | A peptide bond, formed by dehydration synthesis, joins the amino group of one amino acid to the carboxyl group of the next |
| Peptides are named for the number of amino acids they have-for example, dipeptides have two and tripeptides have three. | Chains of fewer than 10 or 15 amino acids are called oligopeptides, and chains larger than that are called polypeptides. |
| An example of an oligopeptide is the childbirth-inducing hormone oxytocin, composed of 9 amino acids. | A representative polypeptide is adrenocorticotropic hormone (ACTH), which is 39 amino acids long. |
| A ----- is a polypeptide of 50 amino acids or more. A typical amino acid has a molecular weight of about 80 amu, and the molecular weights of the smallest proteins are around 4,000 to 8,000 amu. | protein |
| The average ----- weighs in at about 30,000 amu, and some of them have molecular weights in the hundreds of thousands. | protein |
| Proteins have complex coiled and folded structures that are critically important to the roles they play. | Even slight changes in their conformation (three- dimensional shape) can destroy protein function. |
| Protein structure | is now visible even to the level of individual atoms by the newly invented technique of cryo- electron microscopy (cryo-EM), pairing a transmission electron microscope with a supercomputer to image supercooled protein molecules |
| transmission electron microscope | This invention won the 2017 Nobel Prize in Chemistry for its inventors Joachim Frank, Richard Henderson, and Jacques Dubochet. Protein molecules have three to four levels of complexity, from primary through quaternary structure |
| Protein molecules | have three to four levels of complexity, from primary through quaternary structure |
| Primary structure | Sequence of amino acids joined by peptide bonds |
| Secondary structure | Alpha helix or beta sheet formed by hydrogen bonding |
| Tertiary structure | A single polypeptide chain folded and coiled by interactions among R groups and between R groups and surrounding water |
| Quaternary structure | Association of two or more polypeptide chains with each other |
| Primary structure | the amino acid sequence. |
| Secondary structure | , the alpha helix or beta sheet. |
| Tertiary structure | folding and coiling of the chain. |
| Quaternary structure, the association of two or more chains with each other. | This example of quaternary structure is hemoglobin, composed of four polypeptide chains. The heme groups are iron-containing nonprotein moieties. |
| Primary structure | is the protein's sequence of amino acids, which is encoded in the genes |
| Primary Structure of Insulin | Insulin is composed of two polypeptide chains joined by three disulfide bridges (heavy bars) with 51 amino acids in total. |
| Secondary structure | is a coiled or folded shape held together by hydrogen bonds between the slightly negative —C=O group of one peptide bond and the slightly positive -NH group of another one some distance away. |
| The most common secondary structures are a springlike shape called the alpha (a) helix and a pleated, ribbonlike shape, the beta (ß) sheet (ß-pleated sheet). | Many proteins have multiple a-helical and ẞ-pleated regions joined by short segments with less orderly geometry. |
| A single protein molecule may fold back on itself and have two or more ẞ-pleated regions linked to one another by hydrogen bonds. | Separate, parallel protein chains also may be hydrogen-bonded to each other through their ẞ-pleated regions. |
| Tertiary structure | is formed by the further bending and folding of proteins into various globular and fibrous shapes. |
| It results from hydrophobic R groups associating with each other and avoiding water while hydrophilic ones are attracted to the surrounding water. | Tertiary structure |
| Van der Waals | forces play a significant role in stabilizing tertiary structure. |
| Globular proteins | somewhat resembling a wadded ball of yarn, have a compact tertiary structure well suited for proteins embedded in cell membranes and proteins that must move around freely in the body fluids, such as enzymes and antibodies. |
| Fibrous proteins | such as myosin, keratin, and collagen are slender filaments better suited for such roles as muscle contraction and providing strength to skin, hair, and tendons. |
| The amino acid cysteine (Cys), whose R group is —CH2—SH (see fig. 2.23a) | often stabilizes a protein's tertiary structure by forming covalent disulfide bridges. |
| When two cysteines align with each other, each can release a hydrogen atom, leaving the sulfur atoms to form a disulfide bridge (—S—S—). | Disulfide bridges hold separate polypeptide chains together in such molecules as antibodies and insulin |
| Quaternary structure is the association of two or more polypeptide chains by noncovalent forces such as ionic bonds and hydrophilic- hydrophobic interactions. | It occurs in only some proteins. Hemoglobin, for example, consists of four polypeptides: two identical alpha chains and two identical, slightly longer beta chains (fig. 2.24d). |
| One of the most important properties of proteins is their ability to change shape, especially tertiary structure. | This can be triggered by such influences as voltage changes on a cell membrane during the action of nerve cells, the binding of a hormone to a protein, or the dissociation of a molecule from a protein. |
| Subtle, reversible changes in conformation are important to processes such as enzyme function, muscle contraction, and the opening and closing of pores in . | cell membranes |
| Denaturation | is a more drastic conformational change in response to conditions such as extreme heat or pH. It is seen, for example, when you cook an egg and the egg white (albumen) turns from clear and runny to opaque and stiff |
| Denaturation | makes a protein unable to perform its normal function. It is sometimes reversible, but usually it permanently destroys protein function. |
| Conjugated proteins have a non-amino acid moiety called a ----- covalently bound to them. | prosthetic group |
| , for example, not only has the four polypeptide chains described earlier, but each chain also has a complex iron-containing ring called a heme moiety attached to it | Hemoglobin |
| Hemoglobin | cannot transport oxygen unless this group is present. |
| In glycoproteins | , as described earlier, the carbohydrate moiety is a prosthetic group. |
| Proteins have more diverse functions than other macromolecules. These include | Structure, Communication, Membrane transport, Catalysis, Recognition and protection, Movement, Cell adhesion |
| Proteins have more diverse functions than other macromolecules. These include: -----, Communication, Membrane transport, Catalysis, Recognition and protection, Movement, Cell adhesion | Structure |
| Proteins have more diverse functions than other macromolecules. These include: Structure, -----, Membrane transport, Catalysis, Recognition and protection, Movement, Cell adhesion | Communication |
| Proteins have more diverse functions than other macromolecules. These include: Structure, Communication, -----, Catalysis, Recognition and protection, Movement, Cell adhesion | Membrane transport |
| Proteins have more diverse functions than other macromolecules. These include: Structure, Communication, Membrane transport, ----, Recognition and protection, Movement, Cell adhesion | Catalysis |
| Proteins have more diverse functions than other macromolecules. These include: Structure, Communication, Membrane transport, Catalysis, ------, Movement, Cell adhesion | Recognition and protection |
| Proteins have more diverse functions than other macromolecules. These include: Structure, Communication, Membrane transport, Catalysis, Recognition and protection, -----, Cell adhesion | Movement |
| Proteins have more diverse functions than other macromolecules. These include: Structure, Communication, Membrane transport, Catalysis, Recognition and protection, Movement, ----- | Cell adhesion |
| Structure | Keratin, a tough structural protein, gives strength to the nails, hair, and skin surface. Deeper layers of the skin, as well as bones, cartilage, and teeth, contain an abundance of the durable protein collagen. |
| Communication | . Some hormones and other cell-to-cell signals are proteins, as are the receptors to which the signal molecules bind in the receiving cell. |
| Insulin, for example, is a protein hormone that binds to another protein, its receptor, on the cell surface. | Any hormone or other molecule that reversibly binds to a protein is called a ligand |
| Membrane transport | Some proteins form channels in cell membranes that govern what passes through the membranes and when. Others act as carriers that briefly bind to solute particles and transport them to the other side of the membrane. |
| Membrane transport | One such protein, for example, is the sodium-potassium pump, which continually pumps sodium ions out of a cell and potassium ions in, maintaining the excitability of nerve and muscle cells. |
| Catalysis | Most metabolic pathways of the body are controlled by enzymes, which are globular proteins that function as catalysts. Other examples are the digestive enzymes that break food down into absorbable nutrients. |
| Recognition and protection | The role of glycoproteins in immune recognition was mentioned earlier. Antibodies and other proteins attack and neutralize organisms that invade the body. Clotting proteins protect the body against blood loss. |
| Movement | Movement is fundamental to all life, from the intracellular transport of molecules to the galloping of a racehorse. Proteins, with their special ability to change shape repeatedly, are the basis for all such movement. |
| Movement | Some proteins are called molecular motors (motor proteins) for this reason. One prominent example is the myosin that drives all muscle contraction. |
| Cell adhesion | Proteins bind cells to each other, which enables sperm to fertilize eggs, enables immune cells to bind to enemy cancer cells, and keeps tissues from falling apart. |
| Enzymes are macromolecules that function as biological catalysts. | Some of them are ribonucleic acid (RNA) molecules called ribozymes, found in the ribosomes (see chapter 4). |
| Most enzymes, however, are proteins. | They enable biochemical reactions to occur rapidly at normal body temperatures. |
| Enzymes were initially given somewhat arbitrary names, some of which are still with us, such as pepsin and trypsin. | The modern system of naming enzymes, however, is more uniform and informative. |
| It identifies the substance the enzyme acts upon, called its substrate; sometimes refers to the enzyme's action; and adds the suffix -ase. | Thus, amylase digests starch (amyl- = starch) and carbonic anhydrase removes water (anhydr-) from carbonic acid |
| . Enzyme | names may be further modified to distinguish different forms of the same enzyme found in different tissues |
| A given enzyme may exist in slightly different forms, called -----, in different cells. | isoenzymes |
| Isoenzymes catalyze the same chemical reactions but have enough structural differences that they can be distinguished by standard laboratory techniques. | This is useful in the diagnosis of disease. |
| When organs are diseased, some cells break down and release specific isoenzymes that can be detected in the blood. | Normally, these isoenzymes would not be present in the blood or would have very low concentrations. |
| An --- in blood levels can help pinpoint what cells in the body have been damaged. | elevation |
| For example, creatine kinase (CK) occurs in different forms in different cells. | An elevated serum level of CK-1 indicates a breakdown of skeletal muscle and is one of the signs of muscular dystrophy. |
| An elevated CK-2 level indicates heart disease, because this isoenzyme comes only from cardiac muscle. | There are five isoenzymes of lactate dehydrogenase (LDH). |
| High serum levels of LDH-1 may indicate a tumor of the ovaries or testes, whereas LDH-5 may indicate liver disease or muscular dystrophy. | Different isoenzymes of phosphatase in the blood may indicate bone or prostate disease. |
| To appreciate the effect of an enzyme, think of what happens when paper burns. | Paper is composed mainly of glucose (in the form of cellulose). |
| The burning of glucose (paper) can be represented by the equation | C6H12O6 +6 02 → 6 CO2 + 6 H2O |
| Paper doesn't spontaneously burst into flame because few of its molecules have enough kinetic energy to react. | Lighting the paper with a match, however, raises the kinetic energy enough to initiate combustion (rapid oxidation). The energy needed to get the reaction started, supplied by the match, is called the activation energy |
| . (a) Without catalysts, some chemical reactions proceed slowly because of the high activation energy needed to get molecules to react. | (b) A catalyst facilitates molecular interaction, thus lowering the activation energy and making the reaction proceed more rapidly. Notice that the catalyzed reaction reaches completion in a shorter time. |
| Does an enzyme release more energy from its substrate than an uncatalyzed reaction would release? | No, the amount of energy released is the same with or without an enzyme |
| In the body, we carry out the same reaction and oxidize glucose to water and carbon dioxide to extract its energy. | We can't tolerate the heat of combustion in our bodies, however, so we must oxidize glucose in a more controlled way at a biologically feasible and safe temperature |
| . Enzymes make this happen by lowering the activation energy—that is, by reducing the barrier to glucose oxidation (fig. 2.26b)—and by releasing the energy in small steps rather than a single burst of | heat |
| A substrate molecule (such as sucrose) approaches a pocket on the enzyme surface called the active site. | Amino acid side groups in this region of the enzyme are arranged so as to bind functional groups on the substrate molecule. |
| Many ----- have two active sites, enabling them to bind two different substrates and bring them together in a way that makes them react more readily with each other. | enzymes |
| The substrate binds to the enzyme, forming an enzyme-substrate complex. The fit between a particular enzyme and its substrate is often compared to a lock and key. | Just as only one key fits a particular lock, sucrose is the only substrate that fits the active site of sucrase. |
| Sucrase cannot digest other disaccharides such as maltose or lactose. | This selectivity is called enzyme-substrate specificity. |
| Unlike a simple ------, however, the substrate slightly changes the shape of the enzyme to create a better fit between the two, as shown by the arrows in the figure. | lock and key |
| Sucrase breaks the bond between the two sugars of sucrose, adding — H* and — OH groups from water. This hydrolyzes sucrose to two monosaccharides, glucose and fructose, which are then released by the enzyme as its reaction products. | The enzyme remains unchanged and is ready to repeat the process if another sucrose is available. |
| Since an enzyme is not consumed by the reaction it catalyzes, one enzyme molecule can consume millions of substrate molecules, and at astonishing speed. | A single molecule of carbonic anhydrase, for example, breaks carbonic acid (H2CO3) down to H2O and CO2 at a rate of 36 million molecules per minute. |
| Factors that change the shape of an enzyme-notably temperature and pH-tend to alter or destroy the ability of the enzyme to bind its substrate. | They disrupt the hydrogen bonds and other weak forces that hold the enzyme in its proper conformation, essentially changing the shape of the "lock" so that the "key" no longer fits. |
| Enzymes vary in optimum pH according to where in the body they normally function. Thus, salivary amylase, which digests starch in the mouth, functions best at pH 7 and is inactivated when it is exposed to stomach acid; | pepsin, which works in the acidic environment of the stomach, functions best around pH 2; and trypsin, a digestive enzyme that works in the alkaline environment of the small intestine, has an optimum pH of 9.5. |
| Our internal body temperature is nearly the same everywhere, however, and all human ---- have a temperature optimum near 37°C at which they produce their fastest reaction | enzymes |
| Why does enzyme function depend on homeostasis? | Enzyme function depends on homeostasis because enzymes require specific conditions, like temperature and pH, to maintain their shape and function. |
| This animation demonstrates how B vitamin coenzymes must be present in order to enable some enzymes to carry out their functions. | Many of the B vitamins assist in the complex biochemical processes that produce energy from food. |
| "Enzymes | are large protein molecules that catalyze biochemical reactions by lowering activation energies. Enzymes accomplish catalysis by configuring chemical reactants in the best possible spatial arrangement for reactivity." |
| An enzyme molecule with wide, U-shaped active site on one side is shown. | The enzyme is called out as an inactive enzyme. |
| This enzyme catalyzes the release of carbon dioxide when producing energy from carbohydrates. Combining with the coenzyme helps the inactive enzyme achieve the appropriate three dimensional configuration. | "For this reaction thiamine must be present as the coenzyme. The green coenzyme molecule above is thiamine pyrophosphate, the cofactor needed to permit the enzyme and the substrate pyruvate to combine in the correct orientation to catalyze the reaction." |
| a small, green, oblong-shaped molecule moves into view and is called out as a coenzyme. The coenzyme attaches inside the upper end of the enzyme’s active site | and is called out as thiamine pyrophosphate. |
| The attachment of the coenzyme changes the shape of the active site to an L shape, converting the inactive enzyme to an active enzyme. | Next, an L-shaped molecule identified as Substrate (pyruvate) moves into view and binds to the enzyme-coenzyme complex to form an active enzyme substrate complex. |
| Now all three molecules are nested together and the substrate pyruvate combines chemically with the coenzyme thiamine | The biochemical reaction can take place and energy as ATP and CO2 are produced as products of the reaction. |
| "Once this happens the remaining complex containing the two-carbon fragment thiamine and the apoenzyme rearranges and releases the two-carbon fragment, acetaldehyde and the ATP. | The departure of the acetaldehyde opens the thiamine pyrophosphate to combine with another molecule of pyruvate and the cycle continues. Meanwhile the energy is now in the molecule ATP and is available to do work or to be stored." |
| Pyruvate is broken down, producing one molecule of carbon dioxide, one two-carbon fragment, and one molecule of ATP. These molecules are then released from the thiamine-apoenzyme complex | . A new molecule of pyruvate approaches and binds to the active enzyme complex to continue the cycle. |
| Another way that a coenzyme can influence the reaction between substrate and enzyme is to cause a change in configuration of the enzyme without interacting with the substrate. | Here you see the conformational change in the enzyme needed to configure the enzyme to accept the substrate in a lock and key complex. This is called an allosteric control." |
| A new inactive enzyme molecule is shown. | This molecule has a large, curved active site on one side, and a narrow v-shaped active site on the side opposite the larger active site. |
| The cofactor approaches the inactive enzyme and bonds to it in an enzyme coenzyme complex. | The new configuration is a good fit for the substrate. |
| "Once this enzyme cofactor substrate complex is formed, energy can be released as ATP and the other reaction products can be released from the complex. | Now the correctly configured active site on the enzyme is free to engage another substrate." |
| a narrow oblong coenzyme molecule approaches the large curved binding site of the apoenzyme causing the apoenzyme to fold around the coenzyme molecule, enclosing the coenzyme on both long sides. | This action widens the smaller v-shaped binding site on the opposite side from the bound coenzyme. |
| Next, a molecule of substrate approaches the active enzyme complex and binds to the substrate binding site. | The substrate is broken down, releasing a molecule of ATP. |
| The products of the reaction are released from the binding site and a new molecule of substrate binds to the active enzyme complex. As before, the substrate is broken down and a molecule of ATP and the reaction products are released. | The process of substrate binding, reaction, and ATP and product release repeats once more. |
| The amount of B vitamins that are needed to serve as coenzymes is quite small. | There is enough thiamine activity in 1.2 milligrams to meet the average person's needs all day. |
| "Extra B vitamins will not produce more energy | . Excess B vitamins in the body will pass out of the kidneys into the urine. |
| Thiamine (Vitamin B1) | Source: Meat, leafy vegetables, grains, legumes Coenzyme: Thiamine pyrophosphate, coenzyme for enzymes involved in decarboxylation reactions |
| Riboflavin (Vitamin B2) | Source: Milk, meat, grains Coenzyme: Serves as hydrogen carrier in important oxidation-reduction (respiration) reactions |
| Niacin (Nicotinamide) | Source: Meat, peanuts Coenzyme: Hydrogen carrier in Krebs cycle, oxidative phosphorylation |
| Pyridoxine (Vitamin B6) | Source: Meat, fish, poultry Coenzyme: Reactions of protein metabolism |
| Pantothenic Acid | Source: Meat, grain, legumes, egg yolk Coenzyme: Part of Coenzyme A |
| Biotin | Source: Egg yolk, legumes, nuts, liver Coenzyme: Carboxylation, decarboxylation, deamination reactions |
| About two-thirds of human enzymes require a nonprotein partner called a cofactor. | Inorganic cofactors include iron, copper, zinc, magnesium, and calcium ions. Some of these work by binding to the enzyme and inducing it to fold into a shape that activates its active site. |
| Coenzymes are organic cofactors usually derived from niacin, riboflavin, and other water-soluble vitamins. They accept electrons from an enzyme in one metabolic pathway and transfer them to an enzyme in another. | For example, cells partially oxidize glucose through a pathway called glycolysis |
| A coenzyme called NAD+,28 derived from niacin, shuttles electrons from this pathway to another one called aerobic respiration, which uses energy from the electrons to make ATP. | If NAD+ is unavailable, the glycolysis pathway shuts down. |
| The Action of a Coenzyme. | A coenzyme such as NAD acts as a shuttle that picks up electrons from one metabolic pathway (in this case, glycolysis) and delivers them to another (in this case, aerobic respiration). |
| A row of four different molecules is shown. Labels appear identifying the molecules in order as "Enzyme 1", "Enzyme 2", "Enzyme 3", and "Enzyme 4." | Each enzyme has a single active site, and each active site has a different shape. |
| "Organisms contain many different kinds of enzymes that catalyze a variety of different reactions. | "Many of these reactions, such as those involved in the biosynthesis of an amino acid are carried out in a specific sequence called a . |
| biochemical pathway | In such pathways, a substrate is converted into a product by the first enzyme in the pathway, and the product of the first reaction then becomes the substrate for the next reaction. |
| biochemical pathway | The product of the first reaction then becomes the substrate for the second enzyme. |
| The ----- continues until the final product is made | sequence of reactions |
| Step 1 | Substrate 1 is converted to Product 1 and released from Enzyme 1. |
| Step 2 | Product 1 and binds to the active site of Enzyme 2 as Substrate 2. |
| Step 3 | Enzyme 2 catalyzes the conversion of Substrate 2 into Product 2. |
| Step 4 | Product 2 is released from Enzyme 2 and binds to the active site of Enzyme 3 as Substrate 3. |
| Step 5 | Substrate 3 undergoes reaction and is released from the enzyme as Product 3 |
| Step 6 | Product 3 becomes Substrate 4 and binds to the active site of Enzyme 4. |
| Step 7 | Substrate 4 is converted into the Final Product, which is then released from Enzyme 4. |
| When a biochemical pathway is functioning | the initial substrate is continually converted to the final product through a series of steps in the pathway." |
| As before, Substrate 1 enters the pathway by binding to Enzyme 1, is converted to Product 1 and released. Product 1 becomes Substrate 2 and moves to Enzyme 2. | Meanwhile, a new molecule of Substrate 1 binds to Enzyme 1. |
| These substrates are converted to products, becoming substrates for the next enzymes in the pathway. | Each time a product is released from an enzyme, a new substrate molecule attaches to that enzyme’s binding site. The process continues, resulting in an accumulation of final product in the cell. |
| A metabolic pathway is a chain of reactions with each step usually catalyzed by a different enzyme. A simple metabolic pathway can be symbolized | alpha Beta Upsilon A -----> B ------> C ------> D |
| alpha Beta Upsilon A -----> B ------> C ------> D | where A is the initial reactant, B and C are intermediates, and D is the end product. |
| alpha Beta Upsilon A -----> B ------> C ------> D | The Greek letters above the reaction arrows represent enzymes that catalyze each step of the reaction. |
| A is the substrate for enzyme a, B is the substrate for enzyme ẞ, and C for enzyme y. | Such a pathway can be turned on or off by altering the conformation of any of these enzymes, thereby activating or deactivating them. |
| A is the substrate for enzyme a, B is the substrate for enzyme ẞ, and C for enzyme y. | This can be done by such means as the binding or dissociation of a cofactor, or by an end product of the pathway |
| A is the substrate for enzyme a, B is the substrate for enzyme ẞ, and C for enzyme y. | In these and other ways, cells are able to turn on metabolic pathways when their end products are needed and shut them down when the end products are not needed. |
| Nucleotides are organic compounds with three principal components: a single or double carbon-nitrogen ring called a nitrogenous base, a monosaccharide, and one or more phosphate groups. | One of the best-known nucleotides is ATP (fig. 2.29a), in which the nitrogenous base is a double ring called adenine, the sugar is ribose, and there are three phosphate groups. |
| Two Major Nucleotides. | (a) Adenosine triphosphate (ATP). (b) Cyclic adenosine monophosphate (CAMP). The last two P~O bonds in ATP, indicated by wavy lines, are high-energy bonds. |
| Adenosine triphosphate (ATP) is the body's most important energy-transfer molecule. | It briefly gains energy from exergonic reactions such as glucose oxidation and releases it within seconds for physiological work such as polymerization reactions, muscle contraction, and pumping ions through cell membranes. |
| The ----- of ATP are attached to the rest of the molecule by high-energy covalent bonds traditionally indicated by a wavy line (~) in the structural formula. | second and third phosphate groups |
| Since phosphate groups are negatively charged, they repel each other. | It requires a high-energy bond to overcome that repellent force and hold them together-especially to add the third phosphate group to a chain that already has two negatively charged phosphates. |
| Most energy transfers to and from ---- involve adding or removing that third phosphate. | ATP |
| Enzymes called adenosine triphosphatases (ATPases) are specialized to hydrolyze the third phosphate bond, producing adenosine diphosphate (ADP) and an inorganic phosphate group (P;). | This reaction releases 7.3 kilocalories (kcal) of energy for every mole (505 g) of ATP. Most of this energy escapes as heat, but we live on the portion of it that does useful work. |
| This reaction releases 7.3 kilocalories (kcal) of energy for every mole (505 g) of ATP. Most of this energy escapes as heat, but we live on the portion of it that does useful work. We can summarize this as follows: | ATPase ATP + H2O →→ ADP+ Pi + Energy |
| The free phosphate groups released by ATP hydrolysis are often added to enzymes or other molecules to activate them. | This addition of P¡, called phosphorylation, is carried out by enzymes called kinases. |
| The ----- of an enzyme is sometimes the "switch" that turns a metabolic pathway on or off | phosphorylation |
| ATP is a short-lived molecule, usually consumed within 60 seconds of its formation. | The entire amount in the body would support life for less than 1 minute if it weren't continually replenished. |
| At a moderate rate of physical activity, a full day's supply of ATP would weigh twice as much as you do. | Even if you never got out of bed, you would need about 45 kg (99 lb) of ATP to stay alive for a day. |
| The reason cyanide is so lethal is that it halts ATP synthesis. | but you will find it necessary to become familiar with the general idea of it before you reach that chapter— especially in understanding muscle physiology (chapter 11). |
| Much of the energy for ATP synthesis comes from glucose oxidation. The first stage in glucose oxidation is the reaction pathway known as glycolysis | This literally means "sugar splitting," and indeed its major effect is to split the six-carbon glucose molecule into two three-carbon molecules of pyruvate. A little ATP is produced in this stage |
| ATP Production. | Glycolysis produces pyruvate and a net gain of two ATPs |
| Anaerobic fermentation converts pyruvate to lactate and permits glycolysis to continue producing ATP in the absence of oxygen. | Aerobic respiration produces a much greater ATP yield but requires oxygen. |
| What happens to pyruvate depends on how much oxygen is available relative to ATP demand. When the demand for ATP outpaces the oxygen supply, excess pyruvate is converted to lactate by a pathway called anaerobic fermentation | This pathway has two noteworthy disadvantages: First, it doesn't extract any more energy from pyruvate; second, the lactate it produces is toxic, so most cells can use anaerobic fermentation only as a temporary measure. |
| fermentation | The only advantage to this pathway is that it enables glycolysis to continue (for reasons explained in chapter 26) and thus enables a cell to continue producing a small amount of ATP. |
| If enough oxygen is available, a more efficient pathway called aerobic respiration occurs. This breaks pyruvate down to carbon dioxide and water and generates up to 30 more molecules of ATP for each of the original glucose molecules. | The reactions of aerobic respiration are carried out in the cell's mitochondria, described in the next chapter, so mitochondria are regarded as a cell's principal "ATP factories." |
| Guanosine triphosphate (GTP) is another nucleotide involved in energy transfers. In some reactions, it donates phosphate groups to other molecules. | For example, it can donate its third phosphate group to ADP to regenerate ATP. |
| Cyclic adenosine monophosphate (cAMP) (fig. 2.29b) is a nucleotide formed by the removal of both the second and third phosphate groups from ATP. | In many cases, when a hormone or other chemical signal (“first messenger") binds to a cell surface, it triggers an internal reaction that converts ATP to cAMP. |
| The ----- then acts as a "second messenger" to activate metabolic effects within the cell. | CAMP |
| When a signal molecule such as epinephrine binds to a cell surface receptor protein it activates a G protein on the inside of the cell. | The G protein then stimulates adenylyl cyclase to produce large amounts of cyclic AMP from ATP within the cell |
| A cell is shown with a cell surface receptor protein and an adenylyl cyclase enzyme in its upper membrane. The cell surface protein has a notch in its extracellular end and a G protein attached to its intracellular end. | The adenylyl cyclase has a notch in its intracellular end. |
| A signal molecule travels toward the cell and binds to the notch in the cell surface receptor protein. | This activates the G protein inside the cell and causes it to travel away from the cell surface receptor protein and bind to the notch in the adenylyl cyclase, where it remains. |
| ATP molecules appear in the cell. | The adenylyl cyclase converts the ATP molecules one at a time into cyclic AMP, or cAMP, molecules. |
| The cyclic AMP then binds to and activates a target protein such as alpha kinase which adds phosphates to specific proteins in the cell. The effect of this phosphorylation depends on the identity of the cell and the proteins that are | phosphorylated. |
| A rod-shaped target protein, -----, appears in the cell. A cAMP molecule binds to a notch in the target protein and remains there. | alpha kinase |
| Nucleic acids (new-CLAY-ic) are polymers of nucleotides. The largest of them, deoxyribonucleic acid (DNA), is typically 100 million to 1 billion nucleotides long. | It constitutes our genes, gives instructions for synthesizing all of the body's proteins, and transfers hereditary information from cell to cell when cells divide and from generation to generation when organisms reproduce |
| Three forms of -----, which range from 70 to 10,000 nucleotides long, carry out those instructions and synthesize the proteins, assembling amino acids in the right order to produce each protein “described” by the DNA. | ribonucleic acid (RNA) |
| Nucleic acids (new-CLAY-ic) are polymers of nucleotides. | The largest of them, deoxyribonucleic acid (DNA), is typically 100 million to 1 billion nucleotides long. |
| Nucleic acids | It constitutes our genes, gives instructions for synthesizing all of the body's proteins, and transfers hereditary information from cell to cell when cells divide and from generation to generation when organisms reproduce |
| Three forms of ribonucleic acid (RNA), which range from 70 to 10,000 nucleotides long, carry out those instructions and synthesize the proteins, assembling amino acids in the right order to produce each protein “described” by the DNA. | The detailed structure of DNA and RNA and the mechanisms of protein synthesis and heredity |
| It is routine news to hear of sports celebrities suspended or stripped of their honors for the use of anabolic steroids. | Magazines of physical culture carry many tragic reports of the deaths of amateur athletes, or violent crimes committed by them, attributed to steroid abuse. |
| Anabolic steroids, as they are known on the street, are more properly called anabolic-androgenic steroids. | They are hormones derived from testosterone that stimulate muscle growth (the anabolic effect) and masculinize the body (the androgenic effect). |
| Perhaps the earliest notion to put them to use arose in Nazi Germany, where testosterone was given to SS troops in an effort to make them more aggressive-but with no proven success. | Anabolic steroids |
| In the 1950s, however, when Soviet weight-lifting teams were routinely defeating American teams, it came to light that the Soviets were using testosterone as a performance enhancer. | Anabolic steroids |
| American team physician John Ziegler began experimenting with this back in the United States. | He disliked the androgenic side effects and approached the Ciba Pharmaceutical Company to develop a testosterone analog (a molecule of slightly altered structure) that would enhance the anabolic effect and weaken the androgenic effect. |
| Ciba soon developed Dianabol. It produced spectacular effects in weight lifters and by the 1960s, | several testosterone analogs were freely and legally available, designed to enhance anabolic potency, reduce androgenic effects, and prolong the half-life of the drug in the body. Some are taken orally and others by intramuscular (I.M.) injection. |
| In limited doses, these steroids have legitimate medical uses such as the treatment of anemia, breast cancer, osteoporosis, and some muscle diseases and to prevent the atrophy of muscles in immobilized patients. | Some amateur and professional athletes, however, use them in doses 10 to 1,000 times stronger than therapeutic doses. |
| Steroids. While such doses bulk up the ----, they have hidden, devastating effects on the body | muscles |
| They raise cholesterol levels, which promotes fatty degeneration of the arteries (atherosclerosis). This can lead to coronary artery disease, heart and kidney failure, and stroke. | steroids |
| Deteriorating circulation also sometimes results in gangrene, and many users have suffered amputation of the lower limbs as a result. | As the liver attempts to dispose of the high concentration of steroids, liver cancer and other liver diseases may ensue. |
| They cause a premature end to bone elongation, so people who use ------ in adolescence may never attain normal adult height. | anabolic steroids |
| Paradoxically, anabolic-androgenic steroids can have masculinizing effects on women and feminizing effects on men. | In women, who are especially sensitive to the androgenic effect, the steroids commonly produce growth of facial hair, enlargement of the clitoris, atrophy of the breasts and uterus, and irregularities of ovulation and menstruation. |
| The body converts excess testosterone to estrogens. | In men, these can have a feminizing effect such as breast enlargement (gynecomastia), as well as cause atrophy of the testes, impotence (inability to achieve or maintain an erection), low sperm count, and infertility. |
| Especially in men, steroid abuse can be linked to severe emotional disorders. Individuals vary in susceptibility, but the androgenic effects include heightened aggressiveness | and unpredictable mood swings, so some abusers vacillate between depression and violence ("roid rage”), including physical abuse of family members and crimes as serious as homicide. |
| As the recreational use of anabolic-androgenic steroids became widespread, so did the tragic side effects of such heavy use-an outcome that ---- deeply regretted as the low point of his career. | Dr. Ziegler |
| The U.S. Congress classified anabolic-androgenic steroids as a controlled substance in 1991. Their use in sports has been condemned by the | Just think about every sports organization |
| Yet in spite of such warnings and bans, many continue to use steroids and related performance-enhancing drugs, which remain available through unscrupulous coaches, physicians, Internet sources, and foreign mail-order suppliers | under a cloud of confusing trade names (Durabolin, Anadrol, Oxandrin, Dianabol, Winstrol, Primobolan, and others). |
| By some estimates, as many as 80% of competitive weight lifters, 30% of college and professional athletes, and 20% of male high-school athletes now use anabolic-androgenic steroids. | The National Institutes of Health finds increasing use among high-school students and increasing denial that the steroids present a significant health hazard. |
| Which reaction-dehydration synthesis or hydrolysis-converts a polymer to its monomers? Which one converts monomers to a polymer? | Dehydration synthesis builds complexity, while hydrolysis simplifies structures, facilitating digestion and cellular processes. |
| What is the chemical name of blood sugar? | The chemical name of blood sugar is glucose. |
| What carbohydrate is polymerized to form starch and glycogen? | The carbohydrate polymerized to form both starch and glycogen is glucose. |
| What is the main chemical similarity between carbohydrates and lipids? What are the main differences between them | Carbohydrates are like a quick-release energy snack, providing rapid energy through simple sugars. In contrast, lipids act as long-term energy reserves, akin to a slow-burning candle, offering sustained energy through fats and oils. |
| , All proteins are polypeptides but not all polypeptides are proteins. | The statement "All proteins are polypeptides but not all polypeptides are proteins" highlights the complexity of proteins. Polypeptides are chains of amino acids. |
| Which is more likely to be changed by heating a protein, its primary structure or its tertiary structure? | Heating a protein is more likely to alter its tertiary structure than its primary structure. |
| Use the lock-and-key analogy to explain why excessively acidic body fluids (acidosis) could destroy enzyme function. | Acidosis alters the enzyme's shape, similar to changing the lock, making it incompatible with the key (substrate). This prevents the enzyme from functioning properly, disrupting essential biochemical reactions. |
| How does ATP change structure in the process of releasing energy? | ATP, or adenosine triphosphate, releases energy by breaking its third phosphate bond. |
| What advantage and disadvantage does anaerobic fermentation have compared with aerobic respiration? | Anaerobic fermentation allows ATP production without oxygen, useful during intense, short bursts of activity. |
| How is DNA related to nucleotides? | DNA is composed of nucleotides, which are the basic building blocks. |
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