EMERGENCE OF TEMPLATE-AND-SEQUENCE-DIRECTED (TSD) SYNTHESES .2. A COMPUTER-SIMULATION MODEL

The initiation of the bio-geochemical scenario described in Part I ser ves in the present work as the basis for computer modeling, where the central process of the simulation algorithm, i.e., peptide-catalyzed o ligomeric growth, is based on mass action equations. The computer mode l starts with a minimal system in which catalyzed growth processes of proto-RNA templates and small peptides take place, starting from their building blocks. The emerging populations of random oligomers also in clude a very small fraction of proto-tRNAs and a small fraction of cat alytic peptides. Using simplifying assumptions regarding catalyzed pro to-RNA template-replication, as well as selectivity of certain molecul es and processes, the proportion of proto-tRNA in the proto-RNA molecu lar population increases rapidly; it is followed by TSD peptide synthe sis: based on an ad hoc genetic code and specific peptide catalysts al located for this synthesis. Consequently, a feedback system is initiat ed in which TSD peptides involved in the relevant catalytic reactions of the TSD syntheses also start to accumulate. The initial sporadic fo rmation of TSD peptides is thus replaced gradually by cycles of positi ve feedback and autocatalysis characterized by accumulation of catalyt ic peptides and Proto-tRNAs and TSD-Reaction-Takeover. The model syste m which can be considered a 'toy model' can synthesize its templates a nd catalysts under a wide range of reaction parameters and initial con centrations, thus demonstrating a robustness which is essential for mo lecular evolution processes. The critical stage of the buildup of a mo lecular mechanism for the initiation of. minimal TSD reaction cycle ha s thus been described; because of the centrality of TSD reaction cycle s in biology, it is assumed to be central also in the origin of life p rocesses.