One nitrogen atom of each urea molecule is contributed by free ammonia. The second nitrogen atom is contributed by:
- A Glutamine
- B Glutamate
- C Aspartate ✓
- D Alanine
Correct answer: C. Aspartate
Explanation
Aspartate donates the second nitrogen when it condenses with citrulline in the argininosuccinate synthetase reaction, consuming one ATP to AMP. Aspartate itself derives its nitrogen from oxaloacetate transamination with glutamate, so dietary nitrogen ultimately funnels through both ammonia and aspartate. Glutamine carries ammonia for transport between tissues but does not directly donate nitrogen within the urea cycle.
Reference: Lippincott's Illustrated Reviews: Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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