Final answer:
The quaternary structure of a protein is the organization of multiple polypeptide chains that form a protein complex. It is stabilized by various interactions including hydrogen and ionic bonds, dispersion forces, and disulfide linkages.
Step-by-step explanation:
Quaternary Protein Structure
The quaternary structure of a protein is the association and arrangement of multiple polypeptide chains, or subunits. This level of structure is only present in proteins with more than one subunit. The interactions between the subunits in the quaternary structure are the same as those that stabilize a protein's tertiary structure. These interactions include hydrogen bonding, ionic bonding, dispersion forces, and disulfide linkages.
Examples of quaternary structures are visible in proteins like hemoglobin, which is a heterotetramer consisting of two alpha and two beta globin chains. Insulin, a globular protein, exhibits a quaternary structure stabilized by hydrogen and disulfide bonds resulting in a ball-like shape. Silk, in contrast, is a fibrous protein and its quaternary structure arises from hydrogen bonding that forms its β-pleated sheet structure.