What does a start codon encode for in protein synthesis?

The start codon is a specific sequence of three nucleotides in mRNA that signals the beginning of protein synthesis. In nearly all organisms, the start codon is AUG, which codes for the amino acid methionine. This amino acid is essential because it serves as the first amino acid incorporated into a nascent polypeptide chain during translation.

When ribosomes bind to the mRNA at the start codon, they initiate the translation process that builds proteins, with methionine setting the stage for subsequent amino acids to form the protein. This universal role of the start codon emphasizes the importance of methionine in the initiation of protein synthesis across varied forms of life, highlighting its foundational position in the translation process.