Final answer:
When a STOP codon is reached during translation, the process ends, the polypeptide chain is released, and the ribosomal subunits separate from the mRNA.
Step-by-step explanation:
During translation, when a STOP codon is reached (UAA, UAG, or UGA), several events take place. Rather than mRNA starting over, or tRNA placing a final amino acid, a release factor binds in the ribosome's A site, prompting termination of the translation process. The polypeptide chain is released, signifying the end of protein synthesis. Subsequently, the ribosomal subunits dissociate and leave the mRNA, and the mRNA may be degraded for nucleotide recycling. The termination of translation is a crucial step ensuring that the newly synthesized protein is freed to fold into its functional three-dimensional shape and begin its intended role within the cell.