What is a start codon responsible for initiating protein synthesis?

The start codon responsible for initiating protein synthesis is AUG. In the process of translation, the ribosome recognizes the start codon, which is crucial for the assembly of the ribosomal complex at the beginning of the mRNA to begin protein synthesis. AUG codes for the amino acid methionine, which is typically the first amino acid incorporated into a nascent polypeptide chain during translation.

The significance of AUG as the start codon lies in its unique role; it sets the reading frame for the ribosome, ensuring that the subsequent codons are properly translated into the correct sequence of amino acids. The function of the start codon is essential for forming functional proteins, as a misreading of the frame could lead to entirely different proteins being synthesized, ultimately affecting cellular functions and organismal development.

In contrast, the other codons listed—UGA, UAA, and UAG—are known as stop codons. They signal the termination of protein synthesis, indicating to the ribosome that the polypeptide chain is complete and that the process should cease.