This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nucleotides, Subject name: Biochemistry
Which one of the following is the major site for Purine nucleotide biosynthesis? 
Select and explain. 
A. Liver, B. Erythrocytes, C. Polymorphonuclear leukocytes, D. Brain
A: Liver
Answer: A: Liver 
Explanation: Liver is the major site for Purine nucleotide biosynthesis. Erythrocytes, Polymorphonuclear leukocytes and Brain cannot produce purines. The purines are built upon a pre-existing ribose 5-phosphate.