Final answer:
Protein synthesis stops when a stop codon is encountered during translation.
Step-by-step explanation:
Protein synthesis stops when a stop codon (UAA, UAG, or UGA) is encountered during the translation process. When the ribosome encounters the stop codon, the growing polypeptide is released, and the ribosome subunits dissociate from the mRNA. This allows for the termination of protein synthesis. Protein synthesis stops when a stop codon (UAA, UAG, or UGA) enters the ribosome. Termination occurs because the stop codons do not code for an amino acid, and instead, they signal release factors to help release the newly formed polypeptide chain from the translational machinery. This concludes the elongation of the protein. Once this has occurred, the ribosomal subunits, mRNA, and tRNAs dissociate and can be reused for translating other mRNAs. The stop codons, which are also known as termination or nonsense codons (Amber, Ochre, and Opal respectively), are integral to ending the translation process, and they are located at the end of the coding sequence of mRNA, right before the 3' untranslated region (3'UTR). The AUG codon serves as the start codon and also encodes for the amino acid methionine, establishing the reading frame for protein synthesis. The universality of this genetic code, with few exceptions across different species, is a potent indicator that all life on Earth shares a common origin. This shared genetic code is crucial for the accurate synthesis of proteins across various forms of life.