Chapter 17 - Early Developments in Polypeptide Synthesis

Abstract

This chapter discusses schemes that have been used to link amino acids into peptides and polypeptides with random sequences and cases where simple biochemical systems have been used for synthesis of peptides with defined sequences. Steps in the emergence of a translation system are: transfer RNAs were probably borrowed from other systems; large ribosomal subunit could have served as a binding surface for aminoacyl tRNAs and as a catalyst for polypeptide synthesis; and transition from a ribozyme-directed system to a template-directed system was probably a gradual process. Useful polypeptides probably had to have defined sequences. It seems highly likely that such polypeptides were not synthesized until ribozymes had evolved that could catalyze specific peptide linkages. The first tRNAs were probably borrowed from other systems. The first mRNAs were probably not very specific, but merely served as a stabilizing force for bringing tRNAs together on the ribosome surface. The interaction between anticodons on the tRNAs and codons on the mRNAs became so strong that the ribozyme specificity properties became redundant and gradually gave way to this new way of determining specificity of sequence.