Figure 3From: The transition from noncoded to coded protein synthesis: did coding mRNAs arise from stability-enhancing binding partners to tRNA?A detailed scenario for the origin of genetic coding. 1. Synthesis of gly-gly peptide enhanced by a proto-mRNA complementary to the anticodon loops of tRNAGly, sets up positive feedback loop to further enhance gly-gly synthesis from two tRNAsGly, plus noncoded synthesis of gly-ser from tRNAGly and the hairpin specific for serine, respectively. 2. tRNAGly undergoes gene duplication, with one copy undergoing mutation of the acceptor stem to produce a tRNA with aminoacylation specificity for serine (ser). As a result, the synthesis of gly-ser is enhanced by the same proto-mRNA that enhances the synthesis of gly-gly. 3. Selection occurs for mutation of the anticodon loop of proto-tRNASer so that the synthesis of gly-ser is specifically enhanced. In this way, each new amino acid incorporated into the genetic code is specified by a different sequence (codon). Complementary proto-mRNA and tRNA anticodon loop sequences are represented by the same colour.Back to article page