Amino acid catabolism - During times of starvation, amino acids are used to replenish TCA cycle intermediates and as precursors for gluconeogenesis - Organisms with a diet rich in proteins can oxidize excess amino acids as fuels - Amino acids are not stored - In animals, amino acids (in the form of polypeptides) are the major source of nitrogen. - What is the key difference between amino acids and the other 2 types of oxidizable molecules?
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Amino acid catabolism
- During times of starvation, amino acids are used to replenish TCA cycle intermediates and as precursors for gluconeogenesis
- Organisms with a diet rich in proteins can oxidize excess amino acids as fuels
- Amino acids are not stored
- In animals, amino acids (in the form of polypeptides) are the major source of nitrogen.
- What is the key difference between amino acids and the other 2 types of oxidizable molecules?
Transamination (in liver):
Universal amino group acceptor
PLP : pyridoxal phosphate
Deamination (oxidative deamination) - in liver:
Dehydrogenation (oxidation)
deamination
Transamination + Deamination = Transdeamination
urea
Glutamate Dehydrogenase
How do non-hepatic tissues remove ammonia?
Amino group
Amide group
Transport of glutamine to liver:
Removal of excess ammonia from muscle
The Urea Cycle In liver cells:
Formation of carbomoyl phosphate
Argininosuccinate synthase reaction:
Transamination
Lyase
Arginase
Links between the urea cycle and the TCA cycle
Cytosolic fumarase
transamination
fumarase
OAA
“Kreb Bicycle”
Oxidation of the carbon skeletons in amino acids
Amino acids giving rise to -ketoglutarate: Glutamate, Glutamine, Histidine
Histidine ammonia lyase
Methyl group transfer
(oxidative deamination)
Amino acids giving rise to -ketoglutarate: Arginine and Proline
α-Ketoglutarate
Aspartate and Asparagine
(Asp)
(Asn)
aspartate aminotransferase
Amino acids giving rise to oxaloacetate:
asparaginase
Amino acids giving rise to pyruvate: Cysteine, tryptophan, threonine, serine, glycine and alanine
pyruvate
glutamate α-ketoglutarate
5, 10-Methylene THF
THF
H2O
Amino acids giving rise to succinyl-CoA: Methionine, threonine