Question:medium
Why is the citric acid cycle called an amphibolic pathway?
Why is the citric acid cycle called an amphibolic pathway?
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Amphibolic means it bridges catabolism and anabolism.
Updated On: Jun 24, 2026
- Both exergonic and endergonic reactions take place
- Metabolites are utilized in other pathways
- It can proceed both in forward and backward direction
- Same enzymes can be used in reverse directions
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The Correct Option is A
Solution and Explanation
Step 1: Break the word amphibolic into amphi (both) and bolic (from metabolism). A pathway with this name simultaneously participates in catabolic and anabolic processes.
Step 2: Catabolism, such as oxidising acetyl CoA to carbon dioxide, releases energy and is exergonic. Anabolism, such as drawing off oxaloacetate or alpha-ketoglutarate to build glucose or amino acids, consumes energy and is endergonic. The citric acid cycle does both.
Step 3: Because the same cycle therefore contains reactions that release energy and reactions that demand it, the best statement of why it is amphibolic is that both exergonic and endergonic reactions occur within it.
Step 4: Feeding metabolites elsewhere is only part of the picture, and directional reversibility of enzymes is irrelevant to the definition, so the other options do not capture the amphibolic concept.
\[\boxed{\text{Both exergonic and endergonic reactions take place}}\]
Step 2: Catabolism, such as oxidising acetyl CoA to carbon dioxide, releases energy and is exergonic. Anabolism, such as drawing off oxaloacetate or alpha-ketoglutarate to build glucose or amino acids, consumes energy and is endergonic. The citric acid cycle does both.
Step 3: Because the same cycle therefore contains reactions that release energy and reactions that demand it, the best statement of why it is amphibolic is that both exergonic and endergonic reactions occur within it.
Step 4: Feeding metabolites elsewhere is only part of the picture, and directional reversibility of enzymes is irrelevant to the definition, so the other options do not capture the amphibolic concept.
\[\boxed{\text{Both exergonic and endergonic reactions take place}}\]
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