How many stop codons are there?

How many stop codons are there?

• A. 1
• B. 2
• C. 3
• D. 4

Answer: (C)

Stop codons are the signals that end translation. In the standard genetic code, there are three of them: UAA, UAG, and UGA. They don’t encode amino acids; instead, they’re recognized by release factors that trigger the release of the completed polypeptide from the ribosome and terminate protein synthesis. Because there are three distinct stop codons, the correct count is three. Having only one or two would leave some mRNAs without a termination signal, while four would imply an extra termination codon that isn’t used in the standard code.

Stop codons are the signals that end translation. In the standard genetic code, there are three of them: UAA, UAG, and UGA. They don’t encode amino acids; instead, they’re recognized by release factors that trigger the release of the completed polypeptide from the ribosome and terminate protein synthesis. Because there are three distinct stop codons, the correct count is three. Having only one or two would leave some mRNAs without a termination signal, while four would imply an extra termination codon that isn’t used in the standard code.