Protein structure

primary structure: the linear sequence of amino acids in a polypeptide chain, which determines the protein's unique characteristics.

secondary structure: the local folding of the polypeptide chain into alpha-helices and beta-pleated sheets, stabilized by hydrogen bonds between the backbone atoms.

tertiary structure: the overall three-dimensional shape of a polypeptide, resulting from interactions between the side chains of the amino acids, including hydrophobic interactions, ionic bonds, and disulfide bridges.

quaternary: the assembly of multiple polypeptide chains into a single functional protein complex, which can include interactions such as van der Waals forces, hydrogen bonds, and ionic interactions that stabilize the overall structure.