Which codon signals the start of translation and often codes for methionine?

• A. Start codon
• B. Stop codon
• C. Codon table
• D. Degenerate codon

Answer: (A)

The start codon marks where translation begins and usually codes for the amino acid methionine. Translation starts when the ribosome recognizes AUG, and an initiator tRNA brings methionine to pair with this codon, setting the reading frame for the entire protein. In eukaryotes, methionine is incorporated as the first amino acid, while in bacteria the initiator tRNA carries formylmethionine, which is later removed from the growing chain. This codon thus both signals where to start and establishes the first amino acid of the polypeptide. Stops codons are for termination, the codon table is a reference, and degenerate codons refer to redundancy in coding for the same amino acid.