Final answer:
After a ribosome encounters a stop codon during translation, protein synthesis is terminated, the newly formed protein is released, and the ribosome and mRNA dissociate.
Step-by-step explanation:
When a ribosome reaches a stop codon in an mRNA transcript, the process of protein synthesis is terminated. This termination occurs because a stop codon (UAA, UAG, or UGA) does not code for an amino acid and is not recognized by tRNA, but rather by release factors that instruct the ribosome to release the newly synthesized protein. The release factors bind in the A site of the ribosome, causing the release of the polypeptide chain and the dissociation of the ribosome subunits from the mRNA, after which they can be recruited for a new round of translation. Eventually, the mRNA is degraded so its nucleotides can be reused.