Question:
The urea cycle and the Krebs cycle are linked at which intermediate?
The urea cycle and the Krebs cycle are linked at which intermediate?
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Splitting argininosuccinate releases this Krebs intermediate.
Updated On: Jun 24, 2026
- Arginine
- Ornithine
- Oxaloacetate
- Fumarate
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The Correct Option is D
Solution and Explanation
Step 1: In the urea cycle, argininosuccinate is split by argininosuccinate lyase into arginine and fumarate. This releases fumarate into the cytosol and mitochondria.
Step 2: Fumarate is itself an intermediate of the citric acid (Krebs) cycle. It is hydrated to malate and then oxidised to oxaloacetate within the Krebs cycle.
Step 3: Because fumarate produced by the urea cycle feeds directly into the Krebs cycle, fumarate is the common molecule that links the two pathways. This bridge is sometimes called the aspartate-argininosuccinate shunt or Krebs bi-cycle. Hence option 4 is correct.
Step 4: Arginine and ornithine are pure urea cycle intermediates and oxaloacetate, although a Krebs intermediate, is not the molecule directly handed over from the urea cycle, so options 1, 2 and 3 are wrong.
Step 2: Fumarate is itself an intermediate of the citric acid (Krebs) cycle. It is hydrated to malate and then oxidised to oxaloacetate within the Krebs cycle.
Step 3: Because fumarate produced by the urea cycle feeds directly into the Krebs cycle, fumarate is the common molecule that links the two pathways. This bridge is sometimes called the aspartate-argininosuccinate shunt or Krebs bi-cycle. Hence option 4 is correct.
Step 4: Arginine and ornithine are pure urea cycle intermediates and oxaloacetate, although a Krebs intermediate, is not the molecule directly handed over from the urea cycle, so options 1, 2 and 3 are wrong.
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