Amino Acid Metabolism in MBBS 1
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Questions and Answers

What is the primary reason why there is no 'storage' form of protein in the body?

  • The body has a limited capacity to store protein
  • Protein is rapidly catabolized and excreted as urea
  • Protein is not essential for human health
  • Protein is needed to replace lost amino acids and allow for tissue repair (correct)

    • What is the recommended daily intake of protein?

  • 50 – 70 g per day (correct)
  • 100 – 150 g per day
  • 70 – 100 g per day
  • 30 – 50 g per day

    • What happens to surplus amino acids in a well-fed individual?

  • They are converted into energy
  • They are used to synthesize other nutrients
  • They are stored in the body for later use
  • They are rapidly catabolized and the nitrogen is excreted as urea (correct)

    • Which of the following amino acids can be synthesized by humans?

    <p>One of the 10 amino acids that can be synthesized from other intermediates</p> Signup and view all the answers

    What is the state of nitrogen balance when the amount of nitrogen taken in equals the amount of nitrogen excreted?

    <p>Nitrogen equilibrium</p> Signup and view all the answers

    What is the consequence of prolonged negative nitrogen balance?

    <p>Irreversible loss of essential body tissue</p> Signup and view all the answers

    In which of the following conditions is positive nitrogen balance commonly seen?

    <p>Normal growth in children</p> Signup and view all the answers

    What is the consequence of high protein intake in a well-fed individual?

    <p>Rapid catabolism of surplus amino acids and excretion of nitrogen as urea</p> Signup and view all the answers

    What is the primary role of the ubiquitin breakdown system in cellular protein regulation?

    <p>To remove damaged or old proteins</p> Signup and view all the answers

    What is the fate of most amino acids after losing their amino groups during transamination and deamination?

    <p>They are metabolized by the TCA pathway to CO2 and H2O</p> Signup and view all the answers

    Which of the following amino acids can only be degraded to acetyl CoA?

    <p>Leucine and lysine</p> Signup and view all the answers

    What is the role of cortisol in protein degradation?

    <p>It stimulates protein breakdown in muscle</p> Signup and view all the answers

    What is the process by which cells take in foreign proteins or damaged organelles?

    <p>All of the above</p> Signup and view all the answers

    What is the primary fate of the carbon skeletons of 13 amino acids during starvation?

    <p>They are converted back to glucose by the liver</p> Signup and view all the answers

    What happens to the amino groups of amino acids in the liver?

    <p>They are converted into urea for excretion.</p> Signup and view all the answers

    Which amino acid is a safe carrier of ammonia in the blood stream?

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

    What is the result of impaired conversion of NH3 to urea?

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

    Which of the following is NOT a product of nitrogen metabolism?

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

    What is the primary function of the liver in nitrogen metabolism?

    <p>To degrade excess amino acids and convert them into urea</p> Signup and view all the answers

    Which amino acid can be converted into glucose?

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

    What is the consequence of ammonia toxicity in the brain?

    <p>Cerebral oedema, coma, and death</p> Signup and view all the answers

    What is the name of the cycle that converts ammonia into urea?

    <p>Urea cycle</p> Signup and view all the answers

    What is the average daily protein turnover in an adult?

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

    What is the primary role of amino acids in the body?

    <p>Building blocks for proteins and other molecules</p> Signup and view all the answers

    What is the term for the process of converting an amino acid into a keto acid, releasing ammonia in the process?

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

    What is the significance of the classification of amino acids as essential or non-essential?

    <p>It determines the body's ability to synthesise them</p> Signup and view all the answers

    What is the term for the process of transferring an amino group from one amino acid to a keto acid, resulting in the formation of a new amino acid and a keto acid?

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

    What is the term for the balance between the amount of nitrogen ingested and the amount of nitrogen excreted in the body?

    <p>Nitrogen balance</p> Signup and view all the answers

    What is the term for the process of degrading proteins into amino acids?

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

    What is the significance of glutamate, glutamine, aspartate, and alanine in amino acid metabolism?

    <p>They are involved in the metabolism of amino acids</p> Signup and view all the answers

    Study Notes

    Protein Turnover and Amino Acid Pools

    • Body proteins are continuously degraded to amino acids and re-synthesized, with an average turnover of 300-400g per day in an adult
    • Most proteins have half-lives of several days, while structural proteins like collagen may have half-lives of years
    • Hormones and digestive enzymes are degraded very rapidly, with half-lives of minutes
    • The amino acid pool consists of free amino acids in very low concentrations inside cells or in the bloodstream
    • Amino acids in the pool mix and exchange with other free amino acids distributed throughout the body

    Nitrogen Balance

    • Nitrogen balance is a state where the total amount of nitrogen taken in the diet as protein is equal to the amount of nitrogen excreted from the body
    • Positive nitrogen balance occurs when protein synthesis exceeds the rate of breakdown, and is seen in normal growth in children, convalescence after serious illness, and pregnancy
    • Negative nitrogen balance occurs when protein breakdown exceeds synthesis, and is seen in starvation, serious illness, and injury

    Classification of Amino Acids

    • There are 20 amino acids commonly found as building blocks of proteins
    • Humans can synthesize only 10 amino acids from other intermediates, and rely on dietary sources for the remaining essential amino acids
    • Essential amino acids include valine, methionine, histidine, lysine, phenylalanine, leucine, isoleucine, and threonine

    Pathways of Protein Degradation

    • Most cellular proteins are removed by the ubiquitin breakdown system
    • Foreign proteins and old or damaged subcellular organelles are taken into vesicles by endocytosis or autophagocytosis, and then degraded by proteolytic enzymes in lysosomes

    Transamination and Deamination

    • Transamination involves the transfer of the amino group of an amino acid to an acceptor molecule, such as 2-oxoglutarate, resulting in an oxo acid and glutamate
    • Deamination involves the release of the ammonia group as ammonia (NH3) or ammonium ions (NH4+)

    Amino Acid Metabolism

    • The liver plays a central role in nitrogen metabolism, removing amino acids, glucose, and fats from the portal blood supply
    • The liver is responsible for the synthesis of cellular proteins, plasma proteins, haem, purines, and pyrimidines
    • The liver also degrades excess amino acids by trans-deamination and converts NH3 to urea for excretion
    • Glutamine is an important amino acid in the inter-organ transport of nitrogen, carrying amino groups to the liver for urea formation

    The Urea Cycle

    • The urea cycle (ornithine cycle) is responsible for the excretion of excess nitrogen in the form of urea
    • The end products of nitrogen metabolism include urea, creatinine, uric acid, and ammonia
    • Impaired conversion of NH3 to urea can lead to hyperammonaemia, which can cause cerebral oedema, coma, and death

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    Description

    This quiz covers the concepts of protein turnover, nitrogen balance, and amino acid classification in the context of MBBS 1. It also outlines the pathways of protein degradation.

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