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Protein Metabolism

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Protein Metabolism Starvation Amino acids released by proteolysis Channeled to the liver for gluconeogenesis Although not all amino acids can be made into glucose ... – PowerPoint PPT presentation

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Title: Protein Metabolism


1
Protein Metabolism
2
Starvation
  • Amino acids released by proteolysis
  • Channeled to the liver for gluconeogenesis
  • Although not all amino acids can be made into
    glucose
  • Some must be made into ketone bodies
  • Removal of amine group
  • Achieved by transaminases
  • Put amino group onto a 2-oxo acid
  • Creating a new amino acid
  • But limited to a select few
  • Amino acid becomes a 2-oxo acid
  • A carbon-skeleton
  • Destined for gluoconeogensis or ketogenesis

3
Transamination
4
Transamination
  • If R2
  • -CH3
  • a keto acid pyruvate
  • amino acid alanine
  • -CH2-COO-
  • a keto acid oxaloacetate
  • amino acid aspartate
  • -CH2-CH2-COO-
  • a keto acid a-ketoglutarate
  • amino acid glutamate

5
Fate of NH2
  • Amine groups are channeled into urea
  • Synthesised from aspartate and glutamates amine
    groups in the urea cycle
  • Urea is non-toxic
  • The alternative would be conversion to ammonia,
    which is toxic
  • Urea cycle only occurs in the liver

6
Protein Metabolism - Fed State
  • Protein intake 1g/kg/day
  • Mixture of amino acids
  • Essential cannot be made by us
  • Non-essential can be made from amination of
    carbon skeletons

7
Protein Quality
  • Some food (especially vegetables) are deficient
    in some essential amino acids
  • Rice thr lys are low
  • Maize lysine is low
  • Protein quality is
  • Low if some essential amino acids are missing
  • High if full mixture of essential amino acids are
    present
  • If one amino acid is missing, then proteins
    contain that amino acid cannot be made
  • cannot make ½ a protein! Its all or nothing.
  • Compromises pool of the other amino acids

8
No Protein Store
  • Amino acids from diet are used to make new
    proteins
  • very expensive to make a new protein, ? new
    proteins are made only when they are needed
  • Excess amino acids have to be degraded
  • There is no amino acid storage in our body
  • Transamination is the key smashing up reaction
  • Slightly different emphasis in fed state than in
    starvation
  • C-skeletons burnt in the tissues of origin
    rather than being sent, as amino acids, to liver
  • Amine groups put onto pyruvate (forming alanine)
    for transport from peripheral tissues to liver
  • Amine groups still made into urea by liver

9
Transamination in Muscle Liver
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