2. Acetyl-CoA enters the citric acid cycle by combining with oxaloacetate to for

Question

2. Acetyl-CoA enters the citric acid cycle by combining with oxaloacetate to form citrate. One turn of the cycle evolves two CO2 molecules and regenerates oxaloacetate. Studies have shown that the CO2 carbons do not originate from acetyl-CoA after the initial cycle. However, it is often said that acetyl-CoA is fully oxidized via the CAC. How is this possible? (In short, assuming acetyl-CoA originates from glucose, and glucose ultimately ends up as CO2 via cellular respiration, explain how the CAC leads to the complete oxidation of glucose’s two carbon metabolite, acetyl-CoA.)

Explanation / Answer

Cac is an anabolic pathway. The CO2 evolved during the first cycle has the C from oxaloacetate back bone and acetyl CoA becomes a part of that back bone. Acetyl Co A is the only fuel to enter cac. With each cycle, a molecule of acetyl CoA combines with oxaloacetate is never regenerated. Oxidation of acetate group of acetyl Co A leads to the production of CO2 and water along with energy in the form of ATP.

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