Question 1
Multiple choiceMedium1 markDuring aerobic respiration, a 3C pyruvate is processed before its acetyl group enters a cycle containing 4C oxaloacetate. Which description correctly links pyruvate processing to the carbon product and outputs of one cycle turn?
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Answer: D. Oxidative decarboxylation of 3C pyruvate leaves a 2C acetyl group. CoA transfers it to 4C oxaloacetate, forming 6C citrate; Krebs cycle oxidations and decarboxylations yield ATP and reduced NAD while regenerating oxaloacetate. A: gives the link reaction and citrate formation but stops before stating the cycle’s outputs and regeneration of oxaloacetate. B: reverses the redox direction; pyruvate is oxidized, not reduced. C: treats oxaloacetate as a net reactant, rather than a molecule regenerated by the cycle. Remember: acetyl groups enter the Krebs cycle by combining with oxaloacetate, which is then regenerated.