Question:medium
In the Krebs cycle and the urea cycle, the linking amino acid is which of the following?
In the Krebs cycle and the urea cycle, the linking amino acid is which of the following?
Show Hint
Its keto acid partner is oxaloacetate, a TCA intermediate.
Updated On: Jun 23, 2026
- Fumarate
- Alanine
- Arginine
- Aspartate
Show Solution
The Correct Option is D
Solution and Explanation
Step 1: Look for a molecule that has a foot in both the urea cycle and the citric acid cycle. Aspartate fits because of its transamination partner oxaloacetate.
Step 2: On the urea side, aspartate donates its nitrogen by joining citrulline to make argininosuccinate, the step that introduces the second nitrogen of urea.
Step 3: On the Krebs side, removing the amino group from aspartate gives oxaloacetate, a hub intermediate of the TCA cycle, so aspartate is effectively oxaloacetate carrying an amino group.
Step 4: This dual membership, urea cycle directly and Krebs cycle via oxaloacetate, makes aspartate the bridging amino acid.\[\boxed{\text{Aspartate}}\]
Step 2: On the urea side, aspartate donates its nitrogen by joining citrulline to make argininosuccinate, the step that introduces the second nitrogen of urea.
Step 3: On the Krebs side, removing the amino group from aspartate gives oxaloacetate, a hub intermediate of the TCA cycle, so aspartate is effectively oxaloacetate carrying an amino group.
Step 4: This dual membership, urea cycle directly and Krebs cycle via oxaloacetate, makes aspartate the bridging amino acid.\[\boxed{\text{Aspartate}}\]
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