Final answer:
A release factor recognizes stop codons on an mRNA molecule, triggering the termination of protein synthesis and the release of the newly formed polypeptide chain.
Step-by-step explanation:
Stop codons in an mRNA are recognized by a release factor, not by a specialized tRNA or the 3′ poly-A tail. When the ribosome reaches a stop codon during translation, which can be UAA, UAG, or UGA, the release factor binds to the A site of the ribosome. This event signals the termination phase of protein synthesis, where the polypeptide is released, and the translational complex dissociates.
The release factor's role is crucial as it helps to halt the translation process, ensuring that the protein is synthesized correctly. Stop codons are also known as nonsense codons because they do not code for any amino acids but instead signal the end of the polypeptide chain. Incorrect recognition of stop codons can lead to the production of incomplete or nonfunctional proteins.