What are the three stop codons in the genetic code?

What are the three stop codons in the genetic code?

• A. UAA, UAG, and UGA
• B. UAC, UGC, UAA
• C. TAG, TAA, TGA
• D. UUU, UCU, UAU

Answer: (A)

Stop codons signal the ribosome to terminate protein synthesis. In the standard genetic code, there are three of them: UAA, UAG, and UGA. They don’t code for any amino acid and are recognized by release factors that trigger the end of translation, releasing the completed polypeptide. If you’re reading a gene as DNA, those same signals would appear as TAA, TAG, and TGA, but in RNA terms they’re UAA, UAG, and UGA. The other sequences shown code for actual amino acids (for example, UAC for tyrosine, UGC for cysteine, UUU for phenylalanine), so they wouldn’t terminate translation. Some of these stop codons even have historical names—ochre, amber, and opal—reflecting their long-standing recognition in genetics.

Stop codons signal the ribosome to terminate protein synthesis. In the standard genetic code, there are three of them: UAA, UAG, and UGA. They don’t code for any amino acid and are recognized by release factors that trigger the end of translation, releasing the completed polypeptide. If you’re reading a gene as DNA, those same signals would appear as TAA, TAG, and TGA, but in RNA terms they’re UAA, UAG, and UGA. The other sequences shown code for actual amino acids (for example, UAC for tyrosine, UGC for cysteine, UUU for phenylalanine), so they wouldn’t terminate translation. Some of these stop codons even have historical names—ochre, amber, and opal—reflecting their long-standing recognition in genetics.