Final answer:
Quaternary structure refers to the arrangement and interaction of multiple polypeptide chains in a protein. It involves subunits held together by non-covalent interactions. The protein hemoglobin is an example of a protein with quaternary structure.
Step-by-step explanation:
Quaternary structure is a term used in biology to describe the arrangement and interaction of multiple polypeptide chains in a protein. Proteins with quaternary structure are composed of two or more polypeptides called subunits. These subunits can exist in various forms such as dimers (two subunits), trimers (three subunits), or oligomers (more than three subunits).
For example, the protein hemoglobin has a quaternary structure consisting of two alpha-globin and two beta-globin subunits. The subunits are held together by non-covalent interactions such as hydrogen bonds, ionic bonds, and Van der Waals forces.