Chapter 32: Amino Acid Catabolism, Disposal of the Carbon Skeleton Flashcards
Consider amino acids in two halves
- Carbon skeleton
- Amino group
Carbon atoms from amino acids enter metabolic pathways
- After the amino group is removed (first step)
AAs that enter glycolysis or the CAC are called
- Glucogenic amino acids
AAs that are converted to FAs or to the keto acids (acetoacetic acid or acetate) are considered
- Ketogenic amino acids
Thirteen amino acids are
- Purely glucogenic
Only AAs that are purely ketogenic
- Leucine
- Lysine
AAs that are both glucogenic and ketogenic can be metabolized to
- Oxaloacetate
- Acetyl-CoA
Surplus AAs are used as
- Metabolic fuel
Alanine, serine, and cysteine are converted to
- Pyruvate
The carbon skeletons of tryptophan, glycine, and threonine can also be converted to
- Pyruvate
Some of the C5 family (glutamine, proline, arginine, and histidine) are converted to
- Glutamate
- Then alpha-ketoglutarate (via oxidative deamination)
Alpha-ketoglutarate is an intermediate of
- The CAC
Aspartate and asparagine (C4) can both be metabolized to
- Oxaloacetate
Asparagine is hydrolyzed to aspartate by
- L-asparaginase
Aspartate can also be converted to
- Fumarate
Three amino acids are converted to fumarate
- Phenyalanine
- Tyrosine
- Aspartate
Phenylalanine and tyrosine are degraded by
- Oxygenases
- Degraded to acetoacetate and ….
In mammals, there is no net mechanism for
- Reconverting acetyl-SCoA or acetoacetyl CoA back to glucose
The keto acids generated from these ketogenic amino acids can be
- Funneled
Amino acids that are both glucogenic and ketogenic
- Phenylalanine
- I
- T
- T
- T
Phenylalanine and tyrosine are examples of
- Amino acids that are both glucogenic and ketogenic
Metabolism of phenylalanine and other aromatic amino acids follows a common sequence of
- Oxidation
- Deamination
- Ring opening hydrolysis
Branched-chain amino acids
- Isoleucine
- Leucine
- Valine
All branched-chain amino acids are
- Essential amino acids
