What is true about stop codons?

What is true about stop codons?

• A. They code for the amino acid methionine
• B. They signal the termination of translation and do not code for amino acids
• C. They are the only codons that code for start of translation
• D. They pair with tRNA carrying tryptophan

Answer: (B)

Stop codons mark the end of the protein-coding message and trigger termination of translation. They do not code for any amino acid. There are three of them in the genetic code: UAA, UAG, and UGA. When the ribosome encounters a stop codon, release factors recognize it and promote the release of the completed polypeptide, causing the ribosome to dissociate from the mRNA. Since there is no tRNA with an anticodon that pairs to a stop codon carrying an amino acid, no amino acid is added at this point. The start of translation is signaled by AUG, which typically codes for methionine, so stop codons cannot serve as start signals. The idea that a stop codon would pair with tRNA carrying tryptophan is incorrect because stop codons are recognized by release factors, not by tRNA.

Stop codons mark the end of the protein-coding message and trigger termination of translation. They do not code for any amino acid. There are three of them in the genetic code: UAA, UAG, and UGA. When the ribosome encounters a stop codon, release factors recognize it and promote the release of the completed polypeptide, causing the ribosome to dissociate from the mRNA. Since there is no tRNA with an anticodon that pairs to a stop codon carrying an amino acid, no amino acid is added at this point. The start of translation is signaled by AUG, which typically codes for methionine, so stop codons cannot serve as start signals. The idea that a stop codon would pair with tRNA carrying tryptophan is incorrect because stop codons are recognized by release factors, not by tRNA.