Practice question

Standard genetic code assigns three codons to termination: UAA ochre, UAG amber, UGA opal, recognized by release factor RF2 in bacteria and eRF1 in eukaryotes triggering peptidyl-tRNA hydrolysis and ribosome dissociation. Sixty-one codons encode amino acids, three terminate. In most transcripts UGA functions as stop, least frequent in highly expressed bacterial genes. Its dual use for selenocysteine illustrates conditional reassignment where mRNA context redefines meaning, yet default decoding terminates protein synthesis. This plasticity demonstrates evolutionary flexibility where infrequent stop codon allows occasional recoding without globally disrupting proteome termination fidelity essential for accurate translation.