Lecture 3.2b - Protein and amino acid metabolism
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Questions and Answers

What is the primary function of the urea cycle?

  • To detoxify ammonia by converting it to urea (correct)
  • To generate energy for the cell
  • To store energy in the form of glycogen
  • To synthesize proteins from amino acids

    • What is the reactant that combines with ornithine to form citrulline in the urea cycle?

  • Urea
  • Carbamoyl phosphate (correct)
  • Arginine
  • Aspartate

    • What is the clinical consequence of rapid re-feeding in malnourished patients?

  • Hypoglycemia
  • Ketoacidosis
  • Lactic acidosis
  • Hyperammonemia (correct)

    • What is the product of the reaction catalyzed by the enzyme arginase in the urea cycle?

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

    In which cellular compartment does the first step of the urea cycle take place?

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

    What is the recommended caloric intake per day for re-feeding malnourished patients?

    <p>5-10 kcal/kg/day</p> Signup and view all the answers

    What is the probability of inheriting defects of amino acid metabolism?

    <p>1 in 250,000</p> Signup and view all the answers

    What is the primary cause of phenylketonuria (PKU)?

    <p>Decreased activity of phenylalanine hydroxylase</p> Signup and view all the answers

    What is the reference range for phenylalanine in serum?

    <p>0.05-0.1 mM</p> Signup and view all the answers

    What is the gene associated with homocystinuria (HCU)?

    <p>CBS gene on chromosome 21</p> Signup and view all the answers

    What is the treatment for homocystinuria (HCU)?

    <p>Vitamin B6, folic acid, betaine, and dietary restrictions</p> Signup and view all the answers

    What is the diagnosis method for phenylketonuria (PKU)?

    <p>Heel stick on new-born babies within 48 hours of birth</p> Signup and view all the answers

    What is the consequence of untreated phenylketonuria (PKU)?

    <p>Intellectual impairment</p> Signup and view all the answers

    What is the normal range of homocysteine levels in plasma?

    <p>5-15 uM</p> Signup and view all the answers

    Study Notes

    Urea Cycle

    • Urea is produced from ammonium ions to prevent toxicity
    • Urea is soluble and excreted in urine
    • The first reaction in the urea cycle involves the conjugation of ammonia and CO2 to generate carbamoyl phosphate
    • The cycle consists of four steps:
      • Carbamoyl phosphate combines with ornithine to form citrulline (inside the mitochondria)
      • Citrulline combines with aspartate to generate argininosuccinate (in the cytoplasm, part of the Krebs cycle)
      • Argininosuccinate is cleaved to generate arginine
      • Arginine is converted to urea by the enzyme arginase, producing ornithine

    Urea Cycle in Clinical Context

    • Gradually reintroducing nutritional intake in malnourished patients is important to prevent re-feeding syndrome
    • Re-feeding syndrome causes:
      • No feedback inhibition for enzymes involved in the urea cycle
      • Increased levels of ammonia
      • Inducible enzymes
      • Hyperammonaemia
    • Treatment for re-feeding syndrome involves:
      • Re-feeding at 5-10 kcal/kg/day
      • Gradually increasing to full needs within a week

    Defects of Amino Acid Metabolism

    • Defects include:
      • Phenylketonuria
      • Tyrosinemia
      • Homocystinuria
      • Non-ketotic hyperglycinemia
      • Maple syrup urine disease
    • Over 50 inherited diseases are autosomal recessive
    • These disorders are rare (1< 250,000)
    • Treatment involves restricting amino acid in diet
    • If untreated, may lead to intellectual impairments

    Phenylketonuria (PKU)

    • Caused by decreased activity of phenylalanine hydroxylase (PAH)
    • Symptoms include:
      • Progressive developmental delay
      • Small head circumference
      • Behaviour disturbances
      • Seizures
    • Autosomal recessive - chromosome 12
    • Treatment involves:
      • Foods low in phenylalanine and protein
    • Reference range for phenylalanine in serum: 0.05-0.1 mM
    • Phenylketones accumulate in tissue, plasma, and urine
    • Diagnosis: heel stick on new-born babies within 48 hours of birth
    • Lifelong treatment allows most people with PKU to lead healthy lives

    Homocystinuria (HCU)

    • Caused by defect in cystathionine beta-synthase
    • Symptoms include:
      • Flush of the cheeks
      • Tall, thin frame
      • Lens dislocation
      • Vascular disease
      • Osteoporosis
      • Intellectual disability
      • Psychiatric disorders
    • Autosomal recessive - chromosome 21
    • Treatment involves:
      • Vitamin B6
      • Folic acid
      • Betaine
      • Dietary restrictions
    • Diagnosis: heel stick on new-born babies within 48 hours of birth
    • Levels: 5-15 uM
    • Symptoms similar to Marfan's syndrome
    • Elevated plasma homocysteine is associated with cardiovascular disease
    • CBS involved in gasotransmitter hydrogen sulphide synthesis

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    Related Documents

    Protein and Amino Acid Metabolism Lecture 3.2b PDF

    Description

    This quiz covers the process of urea cycle, where ammonium ions are converted into urea, preventing toxicity and excreted in urine. Learn about the steps involved in the urea cycle.

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