Which of the following options lists the stop codons?

• A. AUG
• B. UAA and UGA
• C. UAA, UAG, UGA
• D. UGC, UGA

Answer: (C)

Stop signals appear at the end of the coding sequence to terminate protein synthesis. They are not read as amino acids; instead, release factors bind and cause the ribosome to release the finished polypeptide. There are three stop codons: UAA, UAG, and UGA. AUG, on the other hand, is the start codon that sets the reading frame and codes for methionine, so it is not a stop signal. UGC codes for cysteine, which is an actual amino acid codon, not a termination signal. The option listing all three stop codons and excluding non-stop codons is the correct one because it precisely identifies the termination signals.