This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
All of the following molecules are a pa of the synthesis of a purine ring except? 
Select and explain. 
A. Lysine, B. Glycine, C. Glutamine, D. Aspaate
A: Lysine
Answer: A: Lysine 
Explanation: Reference: Harpers illustrated biochemistry 30th edition