In the urea cycle, the carbon skeleton of aspartate enters urea through its condensation with citrulline to form argininosuccinate. The fumarate released by argininosuccinate lyase links the cycle to which metabolic pathway?

• A Glycolysis via conversion to phosphoenolpyruvate
• B Beta oxidation via conversion to acetyl-CoA
• C The pentose phosphate pathway via ribulose-5-phosphate
• D The citric acid cycle after cytosolic conversion to malate ✓

Explanation

This is the aspartate-argininosuccinate shunt. Fumarate liberated in the cytosol is hydrated to malate by cytosolic fumarase, then transported into mitochondria where malate dehydrogenase regenerates oxaloacetate for the citric acid cycle. This shunt lets the same carbon flow serve both nitrogen disposal and energy production, and explains why urea cycle defects can cause secondary TCA cycle disruption.

Reference: Lehninger Principles of Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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