Acetyl coenzyme A delivers its acetyl group to which four-carbon acceptor at the start of the citric acid cycle?
AThe molecule malate
BThe molecule fumarate
CThe molecule succinate
DThe molecule oxaloacetate
Answer & Solution
Correct answer: D. The molecule oxaloacetate
1. In the presence of oxygen the acetyl group is handed to a four-carbon acceptor.
2. That acceptor is oxaloacetate.
3. Two carbons plus four carbons give citrate, a six-carbon molecule with three carboxyl groups.
4. Malate, fumarate and succinate are all later intermediates of the same cycle, so they cannot be the entry point.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 7 "Cellular Respiration", section 7.3 Oxidation of Pyruvate and the Citric Acid Cycle_
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