The origin of the genetic code

Abstract

The problem of code origin is presented in the context of increasingly complex events in the origin of life. The likely sequence of events appears to progress from abiotic synthesis of biological monomers to polymers to formation of protocells, which would be capable of competition and further evolution. We propose that rate of polymer formation was a critical controlling parameter of rate of protocell propagation. This would lead to selection of autocatalytic and mutually catalytic reactions of polymer formation. Primitive proteins would catalyze polynucleotide formation, and polynucleotides could be used as anvils of noncoded polypeptide synthesis. Proteins that could catalyze this latter reaction (assignment catalysts) would play an important role in subsequent evolution of a genetic code. Competing populations of assignment catalysts would possess very nonlinear dynamics of production of the catalysts themselves. An analysis of this dynamics shows that it has a rich family of bifurications which would provide a pathway for gradual approach to a genetic code. The selection criterion in this process would be efficiency of utilization of monomers and energy for the production of assignment catalysts.