In general, structures of proteins are studied under four levels of organization as followed by

Primary structure: It includes amino acid sequence and disulfide bonds.

Secondary structure: It includes α helix and β sheet conformation.

Tertiary structure: It provides the 3D structure of protein which referrers to orientation of prosthetic group. In addition, it provides information about the conformation of side chain groups to peptide chain in space and the distance between the polypeptide chains. The tertiary structures are stabilized by various non- covalent interactions.

Example: electrostatic forces, hydrophobic interaction, H bonding.