Amino Acids Metabolism
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Questions and Answers

Which disease is characterized by protein deficiency with adequate energy intake in children?

  • Marasmus
  • Fatty liver
  • Kwashiorkor (correct)
  • Oedema
  • At what age does Marasmus commonly occur?

  • Between 3 and 6 months
  • Under 1 year
  • Above 3 years (correct)
  • Between 6 months and 3 years
  • Which disease is associated with the preservation of subcutaneous fat?

  • Fatty liver
  • Marasmus
  • Kwashiorkor (correct)
  • Oedema
  • In which disease is fatty liver enlarged?

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

    Which classification of amino acids is based on the polarity of side chains?

    <p>Chemical Classification</p> Signup and view all the answers

    What is a common feature of both Kwashiorkor and Marasmus diseases?

    <p>Presence of oedema</p> Signup and view all the answers

    What is the primary pathway where extracellular, membrane-associated, and long-lived intracellular proteins are degraded?

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

    What percentage of total body protein do humans turn over daily?

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

    Which organelle contains proteases for proteins, lipases for lipids, and many other hydrolases involved in non-specific protein degradation?

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

    What is the term used to express the relative susceptibility of a protein to degradation?

    <p>Half-life (t1/2)</p> Signup and view all the answers

    In which processes do increased lysosomal activity play a significant role?

    <p>Disuse atrophy of muscles and regression of the uterus after childbirth</p> Signup and view all the answers

    What percentage of amino acids liberated by protein degradation are reutilized?

    <p>75%</p> Signup and view all the answers

    What is the primary enzyme involved in proteolytic digestion in the stomach?

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

    During which situations must protein synthesis exceed protein degradation?

    <p>Growth, pregnancy, and illness recovery</p> Signup and view all the answers

    Which enzyme cleaves peptide chains mainly at the carboxyl side of lysine or arginine?

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

    What is the function of elastase in protein digestion?

    <p>Hydrolysis of large hydrophobic residues</p> Signup and view all the answers

    What is the optimal pH for pepsin, the primary enzyme in stomach digestion?

    <p>2 (highly acidic)</p> Signup and view all the answers

    Which type of bonds does chymotrypsin preferentially hydrolyze in protein digestion?

    <p>Involving tyrosine, phenylalanine, and tryptophan</p> Signup and view all the answers

    What is the main cellular mechanism responsible for the degradation of regulatory proteins with short half-lives and abnormal proteins?

    <p>Ubiquitin-Proteasome System</p> Signup and view all the answers

    Which molecule is required for the attachment of Ub molecules to the target protein during ubiquitination?

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

    How does the number of Ub molecules attached to a protein affect its degradation rate?

    <p>Increases degradation rate</p> Signup and view all the answers

    What type of bond is formed between the carboxyl terminal of Ub and lysyl residues in the target protein during ubiquitination?

    <p>Isopeptide bond</p> Signup and view all the answers

    Which amino acid residues at the amino terminus of a protein affect its rate of ubiquitination?

    <p>Methionine (Met) or Serine (Ser)</p> Signup and view all the answers

    Where does the subsequent degradation of Ub-tagged proteins take place?

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

    Which amino acid is primarily extracted by the liver in the postabsorptive state?

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

    Which amino acid serves as a source of ammonia for excretion by the kidney?

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

    Which amino acid is predominantly taken up by the brain from muscle in the postabsorptive state?

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

    In the fed state after a protein-rich meal, which tissues release amino acids?

    <p>Splanchnic tissues</p> Signup and view all the answers

    Which organ provides a major source of serine for uptake by peripheral tissues in humans?

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

    What is the function of ubiquitin in eukaryotic cells?

    <p>It differentiates between functional and intracellular proteins for degradation</p> Signup and view all the answers

    Which amino acid residues at the amino terminus accelerate the ubiquitination of a protein?

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

    What macromolecule is responsible for the degradation of Ub-tagged proteins in eukaryotic cells?

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

    What is the energy requirement for the addition of Ub molecules to proteins during ubiquitination?

    <p>ATP hydrolysis</p> Signup and view all the answers

    Which type of residues at the amino terminus of a protein retard its ubiquitination?

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

    Which cellular organelle is responsible for the degradation of regulatory proteins with short half-lives?

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

    What determines the rate of degradation of a protein with Ub molecules attached to it?

    <p>Number of Ub molecules attached</p> Signup and view all the answers

    In which cellular compartment does the degradation of Ub-tagged proteins mainly occur?

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

    Which enzyme is responsible for adding Ub molecules to proteins during ubiquitination?

    <p>Ubiquitin ligase</p> Signup and view all the answers

    What is the role of lysosomal enzymes in chronic inflammatory diseases such as rheumatoid arthritis?

    <p>Attack surrounding tissues</p> Signup and view all the answers

    What determines the rate of degradation of normal proteins with comparable functions?

    <p>N-terminal residue</p> Signup and view all the answers

    Which amino acid residues at the amino terminus of a protein accelerate its ubiquitination?

    <p>Arginine (Arg) and Aspartate (Asp)</p> Signup and view all the answers

    What is the function of PEST sequences in proteins?

    <p>Accelerate ubiquitination</p> Signup and view all the answers

    Where does the degradation of polyubiquitinated proteins occur?

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

    Which type of protein degradation occurs for abnormal proteins?

    <p>Rapid degradation</p> Signup and view all the answers

    What role do enzymes at important metabolic control points play in protein degradation?

    <p>Accelerate protein degradation</p> Signup and view all the answers

    What is the primary reason for the net balance of circulating plasma amino acids between meals?

    <p>Utilization by various tissues</p> Signup and view all the answers

    Which residues in the N-terminal region of a protein retard its ubiquitination?

    <p>(M)ethionine and (S)erine residues</p> Signup and view all the answers

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