mRNA codon
aminoacyl-tRNA
release factor
polypeptide
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This simulator zooms in on the last, often-overlooked step of protein synthesis: how a ribosome knows to stop. As the mRNA threads through a 3D ribosome model, aminoacyl-tRNAs deliver amino acids codon by codon to build a growing polypeptide chain — until a stop codon (UAA, UAG or UGA) reaches the A site. No tRNA exists for a stop codon, so instead a release factor shaped like one docks in its place, reads the codon through a short peptide loop, and swings its GGQ motif into the peptidyl transferase center to hydrolyse the finished chain free. Toggle between the three stop codons to see their different release-factor specificity and real biological "leakiness," dial up near-cognate tRNA competition to watch stop-codon readthrough happen live, and adjust the RF3·GTP hydrolysis rate that ejects the release factor and recycles the ribosome for another round.