Anaplerotic reactions
When citric acid cycle intermediates are drawn off for biosynthesis, which enzyme most directly replenishes the cycle?
Answer A: explanation for every choice
A
Correct. Anaplerotic reactions refill cycle intermediates, and carboxylating pyruvate to oxaloacetate is the major one.
B
Citrate synthase uses oxaloacetate but doesn't add new carbon skeletons to the cycle.
C
Acetyl-CoA from pyruvate dehydrogenase is fully oxidized and makes no net intermediates.
D
Lactate dehydrogenase interconverts pyruvate and lactate.
TakeawayAcetyl-CoA can't refill the cycle. Pyruvate carboxylase can.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb159.