This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Nitrogen-9 of purine ring is provided by ? 
Select and explain. 
A. Glycine, B. Aspaate, C. Glutamine, D. CO2
C: Glutamine
Answer: C: Glutamine 
Explanation: In de novo synthesis, purine ring is formed from variety of precursors is assembled on ribose-5-phosphate. Precursors for de novo synthesis are - i) Glycine provides C4, C5 and N7 ii) Aspaate provides N1 iii) Glutamine provides N3 and N9 iv) Tetrahydrofolate derivatives furnish C2 and C8 v) Carbon dioxide provides C6