How many moles of ATP are directly generated by substrate-level phosphorylation during one complete turn of the citric acid cycle?
Answer and explanation
Correct answer: B. 1 (in the form of GTP or ATP)
In the citric acid cycle, succinyl-CoA synthetase (succinate thiokinase) couples the cleavage of the high-energy thioester bond in succinyl-CoA to the phosphorylation of GDP to GTP (or ADP to ATP in some tissues). This represents the only direct substrate-level phosphorylation step in the cycle, producing exactly 1 high-energy nucleoside triphosphate per acetyl-CoA.
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