Protein Metabolism

Describe the physiology and biochemistry of fat, carbohydrate and protein metabolism

Essential amino acids cannot be produced by transamination - they must be supplied in the diet.


Protein catabolism involves the deamination of amino acids. Deamination can occur in one of two ways:

  • Oxidative deamination
    Hepatic deamination, removing the amino group to create a ketoacid and ammonia. Ammonia produced in the liver enters the urea cycle and becomes urea, which requires 3 ATP.
  • Transamination
    Amino group is transferred by aminotransferases to another amino acid or a ketoacid to produce:
    • Keto acids, which:
      • Enter the citric acid cycle and produce ATP
      • Get converted to glucose or fatty acids
    • Amino groups
      • Enter the urea cycle and become urea


Ammonia can also be produced in the kidney by the deamination of glutamate in the kidney. In this instance:

  • It is eliminated directly in urine as ammonium
  • Does not enter the urea cycle



  1. Chambers D, Huang C, Matthews G. Basic Physiology for Anaesthetists. Cambridge University Press. 2015.
Last updated 2019-07-18

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