alleryStart learning →Why is the first step of the citric acid cycle irreversible?
ABecause it is highly exergonic
BBecause it needs no enzyme
CBecause it releases carbon dioxide
DBecause it consumes two ATP
Answer & Solution
Correct answer: A. Because it is highly exergonic
1. Step one is a condensation joining the two-carbon acetyl group to four-carbon oxaloacetate.
2. The step is irreversible because it is highly exergonic.
3. Its rate is controlled by negative feedback and by the amount of adenosine triphosphate available.
4. No carbon dioxide is released at step one, so that option describes a later step.
_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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