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The amino acid sequence of a protein is referred to as its primary structure. The primary structure of the protein is critical to its unique three-dimensional structure, mechanism of action, and relationship to other proteins with similar physiological roles.

All proteins have multiple structural levels known as "primary, secondary, tertiary, and quaternary structure." A protein's "primary structure" is its sequence of amino acids. When portions of an amino acid chain take on a specific spatial orientation, such as an alpha helix or beta pleated sheet, the "secondary structure" occurs.

When a protein takes on secondary structure, hydrogen bonds connect the carbonyl oxygen atoms of one peptide linkage and the hydrogen atoms of the amino group of another peptide linkage. As a result, alpha helices or beta pleated sheets are formed.