Which level of protein structure refers to the sequence of amino acids?

The level of protein structure that refers to the sequence of amino acids is known as the primary structure. This is the most fundamental aspect of protein architecture. It determines how the protein will fold and function. The primary structure is described as a linear sequence of amino acids linked together by peptide bonds, and the specific sequence is dictated by the gene encoding the protein.

Understanding the primary structure is essential because even a small change in the amino acid sequence can significantly affect a protein's overall structure and function, potentially leading to various diseases. For example, in sickle cell anemia, a single mutation in the primary structure of hemoglobin alters the protein's properties and overall function.

The secondary structure refers to local folding of the polypeptide chain into structures such as alpha helices and beta sheets, which are stabilized by hydrogen bonds. The tertiary structure involves the overall three-dimensional shape of a single protein molecule, including interactions among various side chains. The quaternary structure refers to the assembly of multiple polypeptide chains into a functional unit. Each of these structures builds upon the primary structure but does not define the sequence of amino acids itself.