Final answer:
Stop codons are triplets of nucleotides in the mRNA molecule that signal the end of protein synthesis. Three of the 64 possible codons serve as stop codons, while another codon, AUG, serves as the initiation codon.
Step-by-step explanation:
The end of protein synthesis is specified by a stop codon, which is a triplet of nucleotides in the mRNA molecule. Three of the 64 possible codons serve as stop codons, signaling the termination of protein synthesis and releasing the polypeptide from the translation machinery. Another important codon, AUG, serves as the initiation codon to start translation.