Prebiotic synthesis of nucleotides.

If an RNA-only world preceded more complex forms of life, then it is essential that the process whereby the first nucleotides were made be considered. Presumably there were no enzymes and no templates to facilitate the synthesis of the first nucleotides so another form of chemical evolution must have been involved. Answers to problems of this sort were sought vigorously in the 1960s and the early 1970s but many issues were left unresolved. Progress made in the last few years has added to this early work and brings us closer to a satisfactory solution. In this article key results, old and new, and some ideas as to how further progress is likely to be made are discussed. There are reasons for optimism. Substantial progress has been made on the synthesis of purines and ribose, phosphorylation and polyphosphorylation. The outstanding problems at this juncture relate to the synthesis of ribose to the exclusion of the other aldopentoses and to the problem of linking ribose to the purine bases.