1. 24.8 Fates of the Carbon Atoms from Amino Acids
Carbon atoms from degraded amino acids are converted to the intermediates of the citric acid cycle or other pathways.
Learning Goal Describe where carbon atoms from amino acids enter the citric acid cycle or other pathways.

2. Carbon Atoms from Amino Acids
We can classify the amino acids according to the number of carbon atoms.
Amino acids that provide three-carbon compounds are converted to pyruvate.
Amino acids with four carbon atoms are converted to oxaloacetate.
Five-carbon amino acids provide α-ketoglutarate.
Some amino acids are listed twice because they can enter different pathways to form citric acid cycle intermediates.

3. Amino Acid Pathways to Citric Acid Intermediates

4. Glucogenic and Ketogenic Amino Acids
Amino acids are classified as
glucogenic if they generate pyruvate, α-ketoglutarate, succinyl-CoA, fumarate, or oxaloacete, which can be used to synthesize glucose.
ketogenic if they generate acetoacetyl-CoA or acetyl-CoA, which can form ketone bodies or fatty acids.

5. Study Check
Match each of the following citric acid intermediates with the amino acid that provides its carbon skeleton: 1) pyruvate 2) fumarate 3) α-ketoglutarate A. cysteine B. glutamine C. aspartate D. serine

6. Solution
Match each of the following citric acid intermediates with the amino acid that provides its carbon skeleton: 1) pyruvate 2) fumarate 3) α-ketoglutarate A. cysteine B. glutamine C. aspartate D. serine
1) Pyruvate
3) α-ketoglutarate
2) Fumarate
1) pyruvate