What does the start codon do in translation?

• A. Signals the start of translation.
• B. Signals termination of translation.
• C. Initiates transcription.
• D. Codes for an amino acid other than methionine.

Answer: (A)

The start codon marks where translation begins and establishes the reading frame. It’s recognized by the initiator tRNA carrying methionine (fMet in bacteria), and together with initiation factors the ribosome assembles at this codon to start synthesizing the protein. This codon sets the frame for all subsequent codons and marks the transition from initiation to elongation. It does not terminate translation (that’s the stop codon) and it’s not related to transcription. The initiator codon is the one that directs methionine to start the polypeptide chain.