Protein Metabolism Quiz
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Questions and Answers

Which pancreatic enzyme hydrolyzes peptide bonds of aromatic amino acids?

  • Chymotrypsin (correct)
  • Elastase
  • Trypsin
  • Carboxypeptidase

    • What is the process by which di- and tri-peptides are taken up into intestinal mucosa?

  • Passive transport
  • H+-linked transport system (correct)
  • Sodium-dependent active transport
  • Facilitated diffusion

    • What is the role of α-ketoglutarate in amino acid metabolism?

  • Donating amino groups to other amino acids
  • Accepting amino groups from most amino acids to become glutamate (correct)
  • Accepting amino groups from most amino acids to become α-ketoglutarate
  • Donating amino groups to α-ketoglutarate

    • Which two amino acids do not participate in transamination?

    <p>Lysine and threonine</p> Signup and view all the answers

    What is the fate of absorbed amino acids in the anabolic pathway?

    <p>Synthesis of proteins, enzymes, and hormones</p> Signup and view all the answers

    What is the primary function of carboxypeptidase?

    <p>Hydrolyzing peptide bonds adjacent to free COOH group</p> Signup and view all the answers

    What is the coenzyme required for all transamination reactions?

    <p>Pyridoxal phosphate (PLP)</p> Signup and view all the answers

    What is the outcome of the removal of amino group from amino acids?

    <p>Production of ammonia, urea, and α-keto acids</p> Signup and view all the answers

    What is the enzyme responsible for oxidative deamination?

    <p>Glutamate dehydrogenase</p> Signup and view all the answers

    What is the byproduct of oxidative deamination?

    <p>Free ammonia (NH3)</p> Signup and view all the answers

    Which enzyme has autocatalytic activity and activates the remaining amount of trypsinogen and other pancreatic zymogens?

    <p>Trypsin</p> Signup and view all the answers

    What is the primary function of elastase?

    <p>Hydrolyzing peptide bonds of small amino acids</p> Signup and view all the answers

    What is the purpose of glutamine synthetase?

    <p>To combine ammonia with glutamate to form glutamine</p> Signup and view all the answers

    What is the result of the complete oxidation of α-keto acids?

    <p>Production of CO2 and H2O</p> Signup and view all the answers

    Which enzyme cleaves glutamine into glutamate and free ammonia?

    <p>Glutaminase</p> Signup and view all the answers

    What is the significance of elevated plasma AST and ALT levels?

    <p>Indication of liver disease</p> Signup and view all the answers

    What is the primary function of enteropeptidase in the digestion of dietary proteins?

    <p>To activate trypsinogen into active trypsin</p> Signup and view all the answers

    What is the pH range at which pepsin is most active?

    <p>1-2</p> Signup and view all the answers

    What is the term used to describe the process of constant synthesis and degradation of proteins in the body?

    <p>Protein turnover</p> Signup and view all the answers

    What is the primary characteristic of High Biological Value (HBV) proteins?

    <p>They provide all the essential amino acids</p> Signup and view all the answers

    Which of the following is an example of a Low Biological Value (LBV) protein?

    <p>Rice</p> Signup and view all the answers

    What is the estimated amount of body protein that is hydrolyzed and re-synthesized daily?

    <p>300-400 gm</p> Signup and view all the answers

    What is the function of bicarbonate in the pancreatic juice?

    <p>To neutralize gastric secretion</p> Signup and view all the answers

    What is the term used to describe proteins that are found in animal sources such as meat, poultry, and seafood?

    <p>High Biological Value (HBV) proteins</p> Signup and view all the answers

    Study Notes

    Protein Metabolism

    • Proteins are large, complex molecules that play critical roles in the body.
    • There are 20 amino acids that occur in mammalian proteins.
    • Amino acids are the fundamental units of proteins.

    Types of Proteins

    • High Biological Value (HBV) proteins:
      • Provide all essential amino acids.
      • Also known as complete proteins.
      • Found in animal sources (meat, poultry, seafood, milk, and cheese) and plant sources (soya beans).
    • Low Biological Value (LBV) proteins:
      • Lack one or more essential amino acids.
      • Also known as incomplete proteins.
      • Found in plant sources (cereals, legumes, and nuts), except for soya beans.

    Protein Turnover

    • Proteins in the body are constantly synthesized and degraded.
    • This process, called protein turnover, leads to the hydrolysis and re-synthesis of 300-400 gm of body protein each day.
    • In healthy adults, the total amount of protein in the body remains constant.

    Digestion of Dietary Proteins

    • In the stomach:
      • HCl initiates the activation of pepsinogen into active pepsin.
      • Pepsin is an endopeptidase with an optimum pH of 1-2.
    • In the intestine:
      • Pancreatic juice rich in bicarbonate neutralizes gastric secretion.
      • Pancreatic zymogens are released, including trypsinogen, chymotrypsinogen, pro-carboxypeptidase, and pro-elastase.
      • Enteropeptidase initiates activation of trypsinogen into active trypsin.
      • Active trypsin has autocatalytic activity, activating the remaining pancreatic zymogens.

    Pancreatic Enzymes

    • Trypsin: an endopeptidase that hydrolyzes peptide bonds of basic amino acids (e.g., lysine and arginine).
    • Chymotrypsin: an endopeptidase that hydrolyzes peptide bonds of aromatic amino acids.
    • Carboxypeptidase: an exopeptidase that hydrolyzes peptide bonds adjacent to the free COOH group of the polypeptide chain.
    • Elastase: an endopeptidase that hydrolyzes peptide bonds of small amino acids (e.g., glycine, alanine, and serine).

    Absorption of Proteins

    • Free amino acids are taken into intestinal mucosa by sodium-dependent active transport through Na+-dependent co-transporters.
    • Di- and tri-peptides are taken up by a H+-linked transport system and hydrolyzed in the cytosol to amino acids.

    Fate of Absorbed Amino Acids

    Anabolic Pathways

    • Synthesis of proteins: tissue proteins, enzymes, and hormones.
    • Synthesis of specialized products (e.g., creatine, choline, nitrogen bases of nucleic acids).
    • Synthesis of small peptides (e.g., glutathione).

    Catabolic Pathways

    • Removal of amino group (NH2) from amino acids by transamination and deamination processes.
    • The resulting products are ammonia, urea, and α-keto acids.
    • α-Keto acids are further metabolized to be completely oxidized into CO2, H2O, or converted into glucose or ketones.

    Removal of Nitrogen from Amino Acids

    • Removing the amino group is essential to produce energy from amino acids.
    • The nitrogen can be incorporated into other compounds or excreted, with the carbon skeletons being metabolized.

    Transamination

    • α-Ketoglutarate plays an essential role in amino acid metabolism by accepting the amino groups from most amino acids, thus becoming glutamate.
    • Glutamate produced by transamination can be oxidatively deaminated or used as an amino group donor in the synthesis of nonessential amino acids.
    • All amino acids, except lysine and threonine, participate in transamination.
    • All transamination reactions are reversible.
    • Pyridoxal phosphate (PLP) is a coenzyme in all transamination reactions.

    Oxidative Deamination

    • Oxidative deamination is catalyzed by Glutamate dehydrogenase.
    • It results in the liberation of the amino group as free ammonia (NH3).
    • These reactions occur primarily in the liver and kidney.

    Diagnostic Importance of Plasma Aminotransferases

    • Elevated plasma levels of ALT and AST indicate damage to cells rich in these enzymes.
    • Liver disease: Plasma AST and ALT are elevated, with ALT being more specific than AST for liver disease.
    • Myocardial infarction and muscle disorders: Elevated AST only, with normal ALT plasma levels.

    Transport of NH3 to the Liver

    • Glutamine synthetase combines ammonia (NH3) with glutamate to form glutamine (a nontoxic transport form of ammonia).
    • Glutamine is transported in the blood to the liver, where it is cleaved by glutaminase to produce glutamate and free ammonia.

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    Description

    This quiz covers the basics of protein metabolism, including the structure and function of proteins, amino acids, and types of proteins.

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