purines are one of the two types of nitrogenous heterocyclic bases, which are one of the three components of the nucleotides that make up nucleic acids. synthesis can be de novo or salvage - air synthetase is a component of the "de novo" pathway. the first committed step of the de novo pathway begins with phosphoribosyl pyrophosphate (prpp) and the end product is inosine monophosphate (imp). imp is eventually converted to either amp or gmp purines. the purine ring structure is composed by the attachment of 1 or 2 atoms at a time to the ribose sugar. the "de novo" pathway tends to be conserved across most organisms.