<prompt> PRPP paicipates in purine biosynthesis in ___Serves as a scaffold for assembly of purine ringPost assembly of purine ringBothNone  <response>: 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 