In de novo purine synthesis, the nitrogen atoms of the purine ring are derived from all of the following EXCEPT:
- A Glutamine
- B Alanine ✓
- C Aspartate
- D Glycine
Correct answer: B. Alanine
Explanation
De novo purine ring atoms originate from glutamine (N3, N9), aspartate (N1), glycine (C4, C5, N7), CO2, and formyl-THF (C2, C8). Alanine does not contribute to the purine ring. This is a critical distinction from pyrimidine synthesis, which uses aspartate as the nitrogen donor for the ring itself alongside carbamoyl phosphate.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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