What is the quaternary structure of a protein comprised of?

The quaternary structure of a protein is defined by the arrangement and interaction of two or more polypeptide chains, also known as subunits. This structure represents the highest level of protein organization and is crucial for the protein's overall functionality. These subunits can be identical or different, and their interactions often involve various types of bonds, including hydrogen bonds, ionic bonds, and hydrophobic interactions, which contribute to the stability of the protein as a whole.

This multichain configuration is essential for many proteins to function correctly, as certain biological activities require multiple polypeptide chains to work in tandem. Examples of proteins with a quaternary structure include hemoglobin, which is made up of four polypeptide chains (two alpha and two beta subunits), each playing a critical role in oxygen transport in the blood.

Understanding the quaternary structure is vital in biochemistry and molecular biology, as the interactions between subunits can significantly affect the protein's activity, stability, and regulatory mechanisms.