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APHY 201 Exam 1e
Ch. 6 Interactions Between Cells and the Extracellular Environment
| Question | Answer |
|---|---|
| what does GLUT stand for? | glucose transporter |
| what type of diffusion does glucose use to get into cells, and what are its carriers named? | glucose goes through facilitated diffusion proteins, designated GLUT (carrier) proteins |
| where are GLUT1 proteins found? | found at CNS to let glucose in |
| where are GLUT2 proteins found? | found at pancreatic beta cells & hepatocytes at the liver to let glucose in |
| where are GLUT3 proteins found? | found at neurons to let glucose in |
| where are GLUT4 proteins found? | found at adipose tissue & skeletal muscles to let glucose in; can be inserted into the plasma memrane of skeletal muscle when stimulated to increase glucose uptake in muscle |
| which GLUT protein has clinical significance for insulin-stimulated glucose uptake in muscle and fat? this centers on blood sugar regulation; its dysfunction is cause of insulin resistance and type 2 diabetes | GLUT4 |
| what percent of a body's water is within cells in the intracellular compartment? | 67% |
| 33% of a body's water is in the extracellular compartment. of this, what percent is in blood plasma and what makes up tissue fluid (interstitial fluid)? | 20% and 80% |
| what is extracellular matrix (ECM) made of? | protein fibers such as collagen and elastin, gel-like ground substance composed of glycoproteins, and proteoglycans of polysaccharides, plus water, and specific glycoproteins called integrins that extend from the cytoskeleton and bind to the ECM |
| what are the 3 functions of integrins (glycoproteins that extend from the cytoskeleton and bind to the ECM)? | 1. impart a polarity to cells (differentiate one end to the other), 2. affect adhesion and motility, 3. affect proliferation of the cells in tissues (cancer cells lose polarity and wreak havoc on healthy proliferation) |
| (recognize for multiple choice) what molecules is the selectively-permeable plasma membrane NOT permeable to? | generally it's not permeable to proteins, nucleic acids, or other large molecules |
| (recognize for multiple choice) what molecules IS the plasma membrane permeable to? | generally it is permeable to ions, nutrients including oxygen, and wastes including CO2 |
| are processes for bringing molecules in/out of the cell generally passive processes or active? (hint, passive processes often contain letter F except osmosis!) | active |
| diffusion obeys what law? | 2nd law of thermodynamics - entropy increases as diffusion goes on |
| is net diffusion more organized or is no net diffusion more organized? | net diffusion is more organized (concentration gradient exist(ed)). less entropy when more organized |
| what is the term for the average time it takes for a solute to diffuse? | mean diffusion time, which increases with the square of the distance the solute must travel |
| beyond what distance is too long for diffusion to be effective in regards to traveling from cell to cell, or cell to capillary? | distances beyond 100 micrometers (cells are generally closer than this to the nearest capillary) |
| what are some examples of small, nonpolar (or uncharged) lipid-soluble molecules that pass easily through the lipid portion of the membrane? | O2, CO2, and steroid hormones |
| what is the name of the special channel-like structure through which water can pass through the plasma membrane via osmosis? | aquaporins |
| what type of structure may CHARGED IONS pass through at the plasma membrane? | ion channels that cross the plasma membrane. they may be either always open or gated (voltage-, ligand-...) |
| what type of structure may LARGER POLAR MOLECULES pass through at the plasma membrane? (hint: not by simple diffusion...) | these need special carrier proteins |
| true or false, potassium (K+) and sodium (Na+) have leakage channels to maintain the sodium-potassium gradient | false, trick question, there are only leakage channels for K+, not Na+ |
| what 4 factors does the rate of diffusion depend on? | magnitude of concentration difference (the driving force for diffusion), permeability of the membrane to the molecules, temperature of the solution (higher temp increases rate up to a point), and surface area of the membrane--increased by microvilli |
| why can water molecules pass through the plasma membrane slowly? | they don't carry a charge. this prevents cell rupturing in general... cells also regulate water intake via aquaporins |
| where in the body are many aquaporins found? (5 options) | collecting duct of the kidneys; eyes; lungs; salivary glands; brain |
| what are the 2 requirements of osmosis? | there must be a solute concentration difference on either side of a membrane permeable to water; the membrane must be impermeable to the solute, or the concentration difference will not be maintained |
| solutes that cannot cross a membrane and do permit osmosis are called _____ (2 words) | osmotically active |
| what is the term for the force surrounding a cell required to stop osmosis (containing box analogy) | osmotic pressure |
| osmotic pressure can be used to describe the osmotic pull of a solution. how? | a higher solute concentration would require a higher osmotic pressure in a cell |
| pure water has an osmotic pressure of how many units? | 0 |
| how do molarity and molality differ? | molarity: based on total volume of the final solution; molality: based strictly on the mass of the solvent. so, molarity changes when the temperature of a solution shifts, whereas molality remains completely constant regardless of temperature or pressure |
| what is the term for the TOTAL MOLALITY of a solution when one combines all of the molecules within it? | osmolality |
| electrolytes that dissociate in water must be assessed differently. a 1M NaCl solution would actully be how many Osm? | 2 |
| how can osmolality be measured by freezing point depression? | it's based on the principle that adding solute particles to a solvent lowers its freezing point: the depression is directly proportional to the total number of dissolved particles |
| what is the tonicity of blood plasma? | plasma has the same osmolality as a 0.3 glucose or 0.15m NaCl solution, which are isosmotic to plasma. however, if you place RBCs into a 0.3 solution of urea, the tonicity will not be isotonic |
| what is the term for a solution when there is no net movement of water? | isotonic |
| true or false, isosmotic is another word for isotonic | false |
| where are the osmoreceptors that detect increases in osmolality due to dehydration? | hypothalamus |
| true or false, constant osmolality must be maintained, or neurons will be damaged | true |
| the hypothalamus triggers thirst, decreased excretion of water in urine through release of ADH, also called what? | vasopressin |
| does a lower osmolality mean your blood is diluted or has a relatively high concentration of solutes? | diluted, so more water is excreted as urine because ADH is not present in the bloodstream |
| what are some examples of molecules that cannot diffuse across the membrane? why can't they? what moves them? | molecules that are large or polar such as amino acids, glucose, and other organic molecules are moved by carrier proteins |
| what are characteristics of carrier proteins for large/polar molecules? | may be specific to a given molecule; there may be competition for similar carriers or molecules; number of carriers may be limited at saturation as is the speed with which they work (the transport maximum) |
| facilitated diffusion uses specific carrier-mediated proteins. do these always exist in the plasma membrane? why or why not | some may always exist in the mbmrane but others are inserted when needed |
| what is the mechanism for ADH being on or off at the kidneys? | insertion of carrier membranes into the membrane; the process can reverse when the plasma membrane folds inward, taking the carrier proteins with it back into the cell |
| what are the active transport carrier-mediated proteins often called? | pumps |
| what is the difference between ATPase and ATP synthase? | ATPase is a type of transport protein everywhere in the body that will hydrolyze ATP to release energy (ex. sodium-potassium pump); ATP synthase builds ATP to make energy |
| how does breaking down an ATP make a protein move? | when the pump cleaves the ATP, it takes that leftover Pi group and covalently attaches it to itself (phosphorylates itself!). that acts like a molecular switch, forcing a protein shape-change and the cargo can go through |
| what are 4 details you should know for the Ca2+ pump? | on all cells and in ER of striated muscle; removes Ca2+ from cytoplasm by pumping it into extracellular fluid or cisternae of ER; creates strong concentration gradient for Ca2+ mvt back into the cell; aids in release of NTs in neurons/muscle contraction |
| the Na+/K+ pump is found in all body cells. what 3 functions does it serve? | fuels coupled transport: makes steep concentration gradient that provides energy for coupled transport; charges cellular battery: produces electrochemical impulses in neuron and muscles; prevents bursting: maintains osmolality so cells don't swell |
| what is the common transport method to transport glucose? | symport/cotransport (moved with sodium together in the same direction across the membrane)--TYPE OF SECONDARY ACTIVE TRANSPORT |
| is there any energy cost to expel Ca2+ from a cell? | yes, it's an antiport type of secondary active transport. the NCX (sodium-calcium exchanger) hooks gears to incoming sodium to power its calcium ejections. if Ca2+ remained inside heart cell after a heartbeat, could lead to over-contraction or arrhythmia |
| what 5 terms are important to be associated with active transport across epithelial membranes? | absorption, reaborption, transcellular transport, paracellular transport, carrier-mediated proteins (ex. Na+/K+ pump or Na+/H+ pump) |
| what kind of junctions allow ions to pass from cell to cell? | gap junctions |
| what three junctional complexes limit paracellular transport? | tight junctions, belt desmosomes, desmosomes |
| what mechanisms are involved in bulk transport? | exo- and endocytosis, which require ATP for large molecules such as proteins, hormones, and NTs |
| what is another name for pinocytosis? | fluid-phase endocytosis |
| what 3 factors influence the difference in charge on each side of the plasma membrane? | membrane permeability, Na+/K+ pump action, and fixed anions that are negatively charged (incl. proteins) |
| the difference in charge on each side of the plasma membrane is termed what? | potential difference, which makes the inside of the cell negative compared to the outside |
| what are the reasons K+ accumulates at high concentrations in the cell? it is even limited by its own strong concentration gradient | 1. the sodium-potassium pumps actively bring in K+. 2. the membrane is very permeable to K+. 3. negative anions inside the cell attract cations from outside the cell |
| with all the K+ inside the cell, the negative molecules inside and all the sodium outside, how does that affect equilibrium potentials? | the cell is more negative inside compared to outside, and this potential difference can be measured as voltage, greatly being affected by the K+ concentration gradient (at rest, it has the most leakage channels) |
| the measurement associated with K+ is measured at -90mV. this potential difference is a result of what termed potential? | equilibrium potential, meaning this is the voltage needed to maintain the normal 150mM K+ inside and 5mM K+ outside |
| what is the equilibrium potential for sodium, and then what is the actual membrane potential? | the equilibrium potential for sodium is +66mV, but the membrane is less permeable to Na+, so the actual membrane potential is closer to that of the more permeable K+ |
| why is the amount of calcium so low in a cell? | proteins have a lot of phosphates. if calcium were allowed in the cell at high levels, the protein phosphates and calcium would bind to each other, forming a fatal amount of hard precipitate |
| what four ions contribute to the resting potential? | K+, Na+, Ca2+, and Cl- |
| a change in the permeability of the membrane for any ion will change the resting potential. this is key to how neurons work. which ions are associated with depolarization and hyperpolarization, respectively? | opening Na+ channels is associated with depolarization (voltage goes up to maybe +30mV) for a nerve impulse; opening Cl- channels is associated with hyperpolarization (voltage goes down) and makes it harder for the neuron to fire |
| what is a/the electrogenic effect? | the electrogenic effect refers to the ability of certain membrane transport proteins to directly generate an electrical voltage across a cell membrane; without the electrogenic pump, passive leaks would destroy the chemistry and electricity of the cell |
| what are the 4 types of cell signaling? 2 are short distance and 2 are longer distance (text message vs radio broadcast) | gap junctions (ions and regulatory molecules), paracrine signaling (local signaling), synaptic signaling (neurons and their transmitters across a synapse), endocrine signaling (glands secrete hormones into bloodstream) |
| what are some nonpolar signal molecules that can penetrate the plasma membrane and interact with receptor proteins inside the cell? | nonpolar: steroid hormones, thyroid hormone, and nitric oxide gas |
| what are some polar signal molecules that can penetrate the plasma membrane and interact with receptor proteins on the plasma cell membrane? | polar: epinephrine, acetylcholine, insulin bond to receptors on the plasma membrane |
| what are some specific types of second messengers? | ions such as Ca2+; molecules... |
| cAMP (cyclic AMP) is a common second messenger. what are the steps to activate it? | 1) signaling molecule (ligand, polar) binds to a receptor, which 2) activates effector enzyme such as adenylate cyclase that produces cAMP from ATP (2 dephosphorylations of ATP), and then 3) cAMP activates other enzymes like kinases (add phosphate groups) |
| true or false, receptor proteins that bind to a signal and enzyme proteins that produce a second messenger occur one after the other | false, they usually require something to shuttle between them such as G-proteins |
| G-proteins are hetertrimeric. they are made of 3 subunits--alpha, beta, gamma. which is the "anchor" of the group? | alpha, it holds on to the low-energy GDP molecule and the ligand binds to the receptor, nudging the alpha subunit to replace GDP with GTP--this changes the G-protein shape and all the subsequent pieces do their jobs |
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