What is the start codon for protein synthesis?

The start codon for protein synthesis is AUG. This codon is crucial because it signals the ribosome to initiate the translation process, which is the synthesis of proteins from messenger RNA (mRNA). AUG codes for the amino acid methionine, which is often the first amino acid incorporated into a newly synthesized protein in eukaryotes.

In mRNA, the sequence of nucleotides is read in triplets, known as codons, and AUG together not only serves as the starting point but also establishes the reading frame for the ribosome. Without the AUG codon, the ribosome would not know where to begin translating the mRNA into a polypeptide chain, leading to an incomplete or incorrect protein synthesis process.

Other codons listed, such as UAG, GUA, and CAA, do not function as start codons. UAG is actually a stop codon, which signals the termination of protein synthesis, while GUA and CAA correspond to different amino acids and do not carry the function of initiating the process. Thus, recognizing AUG as the start codon is fundamental to understanding how proteins are synthesized in cells.