This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
Amino acid used in the synthesis of purines 
Select and explain. 
A. Glycine, B. Ornithine, C. Alanine, D. Threonine
A: Glycine
Answer: A: Glycine 
Explanation: Purine contains glycine at 7th position and amino gp of aspaate at 1st position. No other amino acids present.Ref: Textbook of biochemistry for medical students, seventh edition, page no: 563, fig: 43.10