What is the start codon that codes for methionine?

The start codon that codes for methionine is AUG. In the process of protein synthesis, the ribosome recognizes AUG as the signal to begin translation. This codon not only serves as the starting point for assembling amino acids into a polypeptide chain but also specifies the amino acid methionine. As a result, every newly synthesized protein begins with methionine, unless it is later removed in post-translational modifications.

The other choices represent stop codons rather than start codons; UAA, UAG, and UGA signal the termination of protein synthesis, indicating that the ribosome should stop translating the mRNA into a peptide chain. Therefore, AUG is unique in its role as the initiator codon and the first codon translated into an amino acid in a new protein.