A duplication-ligation origin of coded protein synthesis. The origin of coded protein synthesis from the duplication of a hairpin-binding ribozyme  to form the proposed ancestral peptidyl transferase ribozyme  and the duplication of a hairpin possessing a 3'-terminal CCA [30–32, 34] to form the first tRNA. Serendipitous binding of a single-stranded RNA (proto-mRNA) complementary to the tRNA anticodon loops enhanced the binding and positioning of the two tRNAs on the peptidyl transferase, and thereby, the rate of peptide synthesis. Adapted from the PDB files of the T. thermophilus 70S ribosome (with tRNAs and mRNA) taken from Voorhees et al. . PDB files rendered using MacPyMol .