Question:medium
The urea cycle and the Krebs cycle are linked at which intermediate?
The urea cycle and the Krebs cycle are linked at which intermediate?
Show Hint
Splitting argininosuccinate releases this Krebs intermediate.
Updated On: Jun 24, 2026
- Arginine
- Ornithine
- Oxaloacetate
- Fumarate
Show Solution
The Correct Option is D
Solution and Explanation
Step 1: The phrase Krebs bi-cycle describes how the urea cycle and the tricarboxylic acid cycle share a metabolite. To find it, follow the carbon released when arginine is generated.
Step 2: When argininosuccinate is cleaved, two products appear: arginine, which continues in the urea cycle, and fumarate, which leaves it. That fumarate is the export point.
Step 3: Fumarate slots straight into the citric acid cycle, where fumarase converts it to malate and malate dehydrogenase makes oxaloacetate. So the molecule shuttling between the two cycles is fumarate.
Step 4: Ornithine and arginine never leave the urea cycle, and oxaloacetate is downstream within the TCA cycle rather than the shared hand-off point, so they are not the linking intermediate.
\[\boxed{\text{Fumarate}}\]
Step 2: When argininosuccinate is cleaved, two products appear: arginine, which continues in the urea cycle, and fumarate, which leaves it. That fumarate is the export point.
Step 3: Fumarate slots straight into the citric acid cycle, where fumarase converts it to malate and malate dehydrogenase makes oxaloacetate. So the molecule shuttling between the two cycles is fumarate.
Step 4: Ornithine and arginine never leave the urea cycle, and oxaloacetate is downstream within the TCA cycle rather than the shared hand-off point, so they are not the linking intermediate.
\[\boxed{\text{Fumarate}}\]
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