Final answer:
Translation ends when the ribosome encounters a stop codon (UAA, UAG, UGA), leading to polypeptide release and ribosome dissociation.
Step-by-step explanation:
Translation is terminated when the ribosome reaches a stop codon on the mRNA strand. This codon is recognized by a protein release factor that binds to the ribosome and causes the newly synthesized polypeptide chain to be released. The key stop codons are UAA, UAG, and UGA, which do not correspond to any tRNA molecule. Once the polypeptide is released, the ribosome subunits, the mRNA, and the tRNAs dissociate. The ribosomal subunits can then be recycled for new translation events, and the mRNA is eventually degraded. After many ribosomes have completed translation, the mRNA is degraded so the nucleotides can be reused in another transcription reaction.