Amino acids enter the TCA cycle (also known as the citric acid cycle or Krebs cycle) by being converted into intermediates of the cycle. The exact entry point varies depending on the specific amino acid. Certain amino acids, termed "glucogenic," are converted into pyruvate or acetyl-CoA which then enter the cycle.
Glucogenic Amino Acids and Their Entry Points
Glucogenic amino acids are those that can be converted into glucose. These amino acids, after deamination (removal of the amino group), are transformed into various intermediates that participate in the TCA cycle.
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Pyruvate Route: Some glucogenic amino acids, such as alanine, cysteine, glycine, serine, and threonine, can be converted to pyruvate. Pyruvate can then be either converted into:
- Acetyl-CoA: This enters the TCA cycle, eventually being completely oxidized to CO2 and water.
- Oxaloacetate: This is a direct entry point into the TCA cycle, representing an anaplerotic reaction (a reaction that replenishes TCA cycle intermediates).
In summary, amino acids enter the TCA cycle through conversion into intermediates like pyruvate, acetyl-CoA, or oxaloacetate. The specific pathway and entry point depend on the individual amino acid's metabolic fate.
