Which codons are the standard stop codons?

Which codons are the standard stop codons?

• A. UAA, UAG, UGA.
• B. AUG, UAG, UGA.
• C. UAA, UGA, UGG.
• D. UAG, UGA, UAA.

Answer: (A)

Stop signals in translation terminate the growing protein chain. In the standard genetic code, the stop codons are UAA, UAG, and UGA. When one of these appears, no amino acid is added because no tRNA recognizes it. Release factors bind to the ribosome, hydrolyze the bond between the polypeptide and the tRNA, and trigger ribosome disassembly to finish translation. This set is the best answer because each of these trinucleotides functions specifically as a termination signal. Other codons don’t stop translation: AUG codes for methionine and often marks the start of translation, and UGG codes for tryptophan, so they do not terminate the protein-synthesis process. (Note: there are rare exceptions in some organisms, but these are the standard stop codons.)

Stop signals in translation terminate the growing protein chain. In the standard genetic code, the stop codons are UAA, UAG, and UGA. When one of these appears, no amino acid is added because no tRNA recognizes it. Release factors bind to the ribosome, hydrolyze the bond between the polypeptide and the tRNA, and trigger ribosome disassembly to finish translation. This set is the best answer because each of these trinucleotides functions specifically as a termination signal. Other codons don’t stop translation: AUG codes for methionine and often marks the start of translation, and UGG codes for tryptophan, so they do not terminate the protein-synthesis process. (Note: there are rare exceptions in some organisms, but these are the standard stop codons.)