alleryStart learning →Citrate is converted into its isomer isocitrate in step two. How does this happen?
AIt gains two phosphate groups at once
BIt loses one water molecule and gains another
CIt loses a carboxyl group as carbon dioxide
DIt joins with a second acetyl group
Answer & Solution
Correct answer: B. It loses one water molecule and gains another
1. An isomer has the same atoms arranged differently, so no atoms may be gained or lost overall.
2. In step two citrate loses one water molecule and gains another.
3. The net effect is a rearrangement, giving the isomer isocitrate.
4. Losing a carboxyl group would change the carbon count and so could not give an isomer.
_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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