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
[{'content': 'PRPP paicipates in purine biosynthesis in _____ \nSelect and explain. \nA. Serves as a scaffold for assembly of purine ring, B. Post assembly of purine ring, C. Both, D. None', 'role': 'user'}, {'content': 'Answer: A \nExplanation: PRPP serves as a scaffold for assembly of the purine ring in purine biosynthesis. Phosphoribosyl pyrophosphate (PRPP) paicipates in pyrimidine biosynthesis only subsequent to assembly of the pyrimidine ring. Reference: Harpers illustrated biochemistry 30th edition', 'role': 'assistant'}]