What determines the primary structure of proteins?

The primary structure of proteins is determined by the sequence of amino acids in the polypeptide chain. This sequence is critical because it dictates how the protein will fold and ultimately function. Each amino acid has unique properties, and the order in which they are arranged influences interactions, such as hydrogen bonding and hydrophobic effects, leading to secondary, tertiary, and quaternary structures.

While other factors play important roles in a protein’s function and structure—such as the types of bonds formed (like hydrogen bonds, ionic bonds, disulfide bridges) and the presence of enzymes (which can facilitate folding or modifications)—these aspects do not establish the primary structure itself. The arrangement of nucleotides, relating to DNA or RNA, instead refers to nucleic acids, not proteins. Therefore, the sequence of amino acids is fundamentally what determines the protein's primary structure.