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PROTEIN METABOLISM
BC_PROTEIN METAB
| Question | Answer |
|---|---|
| Where does protein digestion start? | In the stomach. |
| What is released due to the presence of dietary protein in the stomach? | Gastrin |
| What is secreted due to the gastrin released? | Pepsinogen and hydrochloric acid |
| 3 characteristics of HCl. | Antiseptic, Denaturing action and acidic |
| What function does HCl have due to its antiseptic property? | It can kill most bacteria. |
| What function does HCl have due to its denaturing action? | It unwinds globular proteins, making peptide bonds more accessible to digestive enzymes. |
| What function does HCl have due to its acidic property? | Activation of pepsinogen into pepsin. |
| What is the pH of gastric juice? | 1.5-2.0 |
| Pepsin affects the hydrolysis of __% peptide bonds, producing a variety of polypeptides. | 10 |
| When is pepsin most effective? | At pH 2. |
| What do passage of small amounts of acidic protein content into the small intestine stimulate? | Production of secretin. |
| What does secretin stimulate? | Production of bicarbonate. (HCO3) |
| What is the function of bicarbonate (HCO3)? | neutralize acidified gastric content and increase pH to 7-8 (slightly basic). |
| What attacks peptide bonds? | Aminopeptidase |
| What secretes aminopeptidase? | Intestinal mucosal cells |
| Enzymes that attack peptide bonds and help break down and digest protein. | Proteolytic enzymes |
| 3 proteolytic enzymes | Pepsin, trypsin, and chymotrypsin |
| What are inactive forms of proteolytic enzymes that are activated in the digestive tract. | Zymogens |
| What is the net result of protein digestion? | Release of protein's constituent amino acids. |
| How and where are liberated amino acids transported? | Into the bloodstream via active transport process. |
| It is where amino acids formed through the digestion process enter. | Amino acid pool in the body |
| The total supply of free amino acids available for use in the body. | Amino acid pool |
| Sources of the amino acid pool. | Dietary protein, protein turnover and biosynthesis of nonessential amino acids in the liver |
| Most abundant amino acid in the amino acid pool. | Glutamine |
| It is the repetitive process in which proteins are degraded and resynthesized. | Protein turnover |
| State where the amount of nitrogen taken into the human body as protein is equal to the amount of nitrogen excreted from the body in waste materials. | Nitrogen balance |
| It happens when protein degradation exceeds protein synthesis. | Negative nitrogen imbalance |
| It happens when the rate of protein synthesis is more than protein degradation. | Positive nitrogen imbalance |
| What is an example of negative nitrogen imbalance? | Amount of nitrogen in urine exceeds consumed amount. |
| What is an example of positive nitrogen imbalance? | Synthesis of large amounts of tissues. |
| 4 uses of amino acid in the human body. | Protein synthesis, synthesis of non-protein nitrogen containing compounds, synthesis of nonessential amino acids, and production of energy. |
| This uses 75% of free amino acids. | Protein synthesis |
| Where are proteins continually needed? | Protein turnover and growth |
| Amino acid precursor of dopamine and norepinephrine. | Tyrosine |
| Amino acid precursor of serotonin. | Tryptophan |
| Why is the body unable to synthesize essential amino acids? | Lack of an appropriate carbon chain |
| What happens to excess amino acids? | Used as energy sources, degraded to substances that can be processed through the common metabolic pathways. |
| In what form is the amino nitrogen atom removed from the body? | As urea. |
| What happens to the remaining carbon skeleton of an amino acid after nitrogen is removed? | It is converted to pyruvate, acetyl CoA, or a citric acid cycle intermediate. |
| Why can the human body not oxidize the nitrogen in amino acids? | Because amino acids contain nitrogen, which cannot be oxidized by the body. |
| What are the two main stages of amino acid degradation? | Removal of the α-amino group and degradation of the remaining carbon skeleton. |
| What does a removal of an amino group require? | Transamination and oxidative deamination |
| It is the interchange of an amino group in an α-amino acid with the keto group in an α-keto acid, using aminotransferases. | Transamination |
| It is when an α-amino acid is converted to an α-keto acid with the release of an ammonium ion. | Oxidative deamination |
| What is the net effect of transamination and oxidative deamination? | The production of ammonium ions and aspartate molecules. |
| What are the products of a transamination reaction? | A new amino acid and a new keto acid. |
| How many keto acids are commonly involved in transamination, and what are they? | Two; α-ketoglutarate and oxaloacetate. |
| Why are only two keto acids typically used in transamination? | To limit the amino acid products to only two. |
| What is transferred between molecules in a transamination reaction? | The -NH₃ (amino) group. |
| What enzyme and coenzyme are required for transamination? | Aminotransferase and pyridoxal phosphate. |
| Where is pyridoxal phosphate derived from? | Vitamin B6 (pyridoxine) |
| What is the most common and important transamination reaction in protein metabolism? | The one in which α-ketoglutarate acts as the amino group acceptor. |
| It is the enzyme that facilitates the transfer of the amino group from one carbon skeleton to another during transamination. | Aminotransferase |
| How many aminotransferases are associated with transamination? | At least 50. |
| How specific are aminotransferases to their substrates? | They are highly specific to the amino acid substrates they accept. |
| Why are aminotransferase levels measured in blood tests? | To help diagnose liver and heart disorders. |
| Which aminotransferase is released in cases of liver damage? | Alanine aminotransferase (ALT). |
| Which aminotransferase is released in cases of heart muscle damage? | Aspartate aminotransferase (AST). |
| How are different aminotransferases named? | By including the amino group donor as part of their name. |
| What happens in the oxidative deamination reaction? | An α-amino acid is converted into an α-keto acid, with the release of an ammonium ion. |
| Where does oxidative deamination primarily occur? | In the mitochondria of the liver and kidneys. |
| What molecule serves as the amino group acceptor in glutamate production via transamination? | α-Ketoglutarate. |
| Which amino acid and keto acid react to produce aspartate via transamination? | Glutamate (amino acid) and oxaloacetate (keto acid). |
| What is the enzyme responsible for ammonium ion production in oxidative deamination? | Glutamate dehydrogenase. |
| What is unique about the enzyme glutamate dehydrogenase? | It can function with either NADP+ or NAD+ as a coenzyme. |
| What new amino acid is produced when glutamate reacts with oxaloacetate? | Aspartate. |
| Cyclic biochemical pathway in which urea is produced from ammonium ions and aspartate as nitrogen sources. | Urea cycle |
| What is the primary purpose of the urea cycle? | To produce urea from ammonium ions and aspartate as nitrogen sources. |
| Where is urea produced in the body? | In the liver. |
| How is urea excreted from the body? | It is transported via the blood to the kidneys and eliminated in urine. |
| Describe the physical properties of urea. | Oorless, white, solid with a salty taste, has a melting point of 133°C, and is water-soluble. |
| How do ammonium ions enter the urea cycle? | Indirectly, by first being incorporated into carbamoyl phosphate. |
| At what stage do aspartate molecules enter the urea cycle? | Directly in the second step of the cycle. |
| Approximately how much urea is excreted daily in human urine? | About 30 grams. |
| Where in the cell does the urea cycle primarily take place? | Primarily in the mitochondria, with some steps occurring in the cytosol. |
| Name the three amino acids used as intermediates in the urea cycle. | Arginine, ornithine, and citrulline. |
| Which amino acid in the urea cycle is the most nitrogen-rich? (4 nitrogen) | Arginine. |
| Which amino acids in the urea cycle are not found in proteins? | Ornithine and citrulline. |
| It serves as one of the sources of fuel for the urea cycle. | Carbamoyl phosphate |
| What are the reactants needed to form carbamoyl phosphate? | Ammonium ion, carbon dioxide, water, and 2 ATP molecules. |
| Where is carbamoyl phosphate formed in the cell? | In the mitochondrial matrix. |
| What type of bond does carbamoyl phosphate contain? | A high-energy phosphate bond. |
| What are the stages of the urea cycle? | Stage 1: Carbamoyl group transfer Stage 2: Citrulline-aspartate condensation Stage 3: Argininosuccinate cleavage Stage 4: Urea from arginine hydrolysis |
| In stage 1, where is the carbamoyl group transferred to? | To ornithine. |
| What enzyme catalyzes the transfer of the carbamoyl group to ornithine? | Ornithine transcarbamoylase. |
| Where does the first stage of the urea cycle occur? | Inner mitochondrial membrane. |
| What three components are introduced in Stage 1 of the urea cycle? | 1 nitrogen atom, 1 carbon atom, and citrulline. |
| What happens to citrulline in the second stage of the urea cycle? | It is transported into the cytosol, where it reacts with aspartate to form argininosuccinate. |
| Which enzyme is involved in the condensation of citrulline and aspartate? | Argininosuccinate synthase. |
| Where does the second stage of the urea cycle take place? | In the cytosol. |
| What are introduced in Stage 2 of the urea cycle? | Argininosuccinate and 1 nitrogen atom. |
| Where is argininosuccinate cleaved into in the 2nd stage of the urea cycle? | Arginine and fumarate. |
| What enzyme is responsible for the argininosuccinate cleavage? | Argininosuccinate lyase. |
| What does the hydrolysis of arginine produce in the fourth stage of the urea cycle? | It produces urea and regenerates ornithine. |
| Which enzyme catalyzes the production of urea from arginine? | Arginase. |
| Where does the oxygen atom in urea come from? | From water. |
| What happens to ornithine after it is regenerated in Stage 4? | Ornithine is transported back to the mitochondria to be reused in the first stage of the urea cycle. |
| How many ATP molecules are required to produce 1 molecule of urea? | 4 ATP molecules |
| How is ATP used in the urea cycle? | 2 ATP = production of carbamoyl phosphate 2 ATP = production of AMP and PPi (stage 2) |
| What is the connection between the urea and citric acid cycles? | Fumarate produced in the citric acid cycle can be converted into intermediates that enter the urea cycle. |
| What happens to fumarate produced in the citric acid cycle? | It is converted to malate, then oxaloacetate, and finally aspartate (through transamination). |
| At which stage does aspartate re-enter the urea cycle? | Stage 2 |
| What are the three potential fates of oxaloacetate in cellular metabolism? | Oxaloacetate can be converted to glucose via gluconeogenesis, condensed with acetyl CoA to form citrate, or converted to pyruvate. |
| What process removes the amino group from an amino acid? | Transamination and oxidative deamination. |
| What is produced after the amino group is removed from an amino acid? | An α-keto acid with the carbon skeleton of the amino acid. |
| Why do different amino acids have different degradation pathways? | Because each amino acid has a unique carbon skeleton. |
| How many products do the degradation pathways of the 20 standard amino acids converge to produce? | 7 products. |
| Name the seven products formed from amino acid degradation pathways. | α-ketoglutarate, succinyl CoA, fumarate, oxaloacetate, pyruvate, acetyl CoA, and acetoacetyl CoA. |
| An amino acid whose degradation product can be used to produce glucose via gluconeogenesis. | Glucogenic amino acid. |
| An amino acid whose degradation product can contribute to ketone body formation. | Ketogenic amino acid. |
| What are the primary source of essential amino acids for humans and animals? | Plants |
| What is the main function of red blood cells (RBCs)? | Deliver oxygen to cells and remove carbon dioxide from body tissues. |
| What is absent in RBCs? | Nucleus and DNA. |
| What is the primary component that fills red blood cells? | Hemoglobin |
| Where are red blood cells formed in the body? | In the bone marrow. |
| How many red blood cells are produced daily? | Approximately 200 billion. |
| What is the average lifespan of a red blood cell? | About 4 months. |
| What are the two main components of hemoglobin? | Heme (the prosthetic group) and globin (the protein portion) and . |
| What is the role of the iron atom in the heme group? | It interacts with oxygen to form a reversible complex. |
| Where do old red blood cells get broken down? | In the spleen and liver. |
| What happens to the globin part of hemoglobin during its degradation? | It is converted to amino acids, contributing to the amino acid pool. |
| What occurs to the iron atom during hemoglobin degradation? | It is stored in ferritin, an iron-storage protein. |
| What is produced from the degradation of the tetrapyrrole structure of heme? | Bile pigments. |
| How are bile pigments eliminated? | Through the feces or urine. |
| What are the key characteristics of the degradation process of heme? | Requires O2, ring opening releases iron for ferritin, and produces carbon monoxide. |
| What are the types of bile pigments? | Biliverdin, Bilirubin, Stercobilin, and Urobilin. |
| What are the colors of Biliverdin, Bilirubin, Stercobilin, and Urobilin. | Green, reddish orange, brown, and yellow |
| What is the normal daily excretion of bilirubin in urine and feces? | Urine: 1-2 mg; Feces: 250-350 mg. |
| What condition is caused by an imbalance in bilirubin formation and removal? | Jaundice. |
| What is the visible effect of jaundice on the body? | A yellow tint to the skin and the whites of the eyes. |
| What byproduct is generated when the heme ring opens? | Carbon monoxide. |
| Which two of the 20 standard amino acids contain a sulfur atom in their side chain? | Cysteine and methionine. |
| What are the two main steps in the biodegradation of cysteine? | Transamination reaction and release of -SH. |
| What is the end product of cysteine biodegradation? | Pyruvate. |
| What is the precursor for the biosynthesis of cysteine? | Serine. |
| What are the two steps involved in converting serine to cysteine? | Activation of serine by acetyl CoA and sulfhydration with hydrogen sulfide. |
| How is hydrogen sulfide produced in the body? | Through sulfate assimilation. |
| What role does hydrogen sulfide play as a biochemical signaling agent? | It regulates vascular blood flow and blood pressure and also influences brain function and insulin levels in type I diabetes. |
| How does hydrogen sulfide influence brain function? | Brain levels of H2S are lower than normal in cases of Alzheimer’s disease. |
| What effect does hydrogen sulfide have on insulin levels in type I diabetes? | An excess of H2S leads to reduced insulin production. |
| How does hydrogen sulfide regulate vascular blood flow and blood pressure? | It acts as a smooth muscle relaxant and vasodilator. |
| How are the metabolic pathways of carbohydrates, lipids, and proteins related? | They are integrally linked; a change in one pathway can affect many others. |
| It is when the body stores a limited amount of energy as glycogen and the rest as fat. | Feasting (over-eating) |
| What does the body use for energy during fasting (when food is not ingested)? | Stored glycogen and fat. |
| What occurs in the body during starvation (prolonged fasting)? | Body protein is broken down to amino acids to synthesize glucose. |
| How many B vitamins participate in various pathways of metabolism? | All 8 B vitamins. |
| What role does niacin play in protein metabolism? | It is involved in oxidative deamination. |
| What is the function of PLP (pyridoxal phosphate) in protein metabolism? | It is involved in transamination. |
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