Final answer:
The release factor binds to the ribosome when it encounters a nonsense codon, leading to the termination of translation and the release of the polypeptide chain.
Step-by-step explanation:
When the ribosome reaches a nonsense codon, the release factor binds to the A site of the ribosome. This signals the termination of translation, as the nonsense codon does not code for an amino acid but rather marks the end of the polypeptide chain. The release factors, which resemble tRNA molecules, cause the peptidyl transferase to add a water molecule to the carboxyl end of the P-site amino acid. This action leads to the release of the newly synthesized polypeptide chain from the tRNA. Consequently, the ribosomal subunits and the mRNA dissociate, completing the process of protein synthesis.