Final answer:
The quaternary structure of a protein is the arrangement and interaction of the protein's multiple polypeptide chains or subunits, exemplified by hemoglobin's four polyptide subunits. The interactions holding these subunits together are similar to those maintaining the tertiary structure.
Step-by-step explanation:
Protein Quaternary Structure
The quaternary structure of a protein refers to the arrangement and interaction between multiple polypeptide chains, also known as subunits, within a protein complex. This level of structure is relevant for proteins that are made up of more than one polypeptide chain. Examples of quaternary structure can be seen in the protein hemoglobin, which consists of four polypeptide chains, forming a heterotetramer. The interactions that hold these subunits together are the same as those that maintain the tertiary structure, including hydrogen bonding, ionic bonding, dispersion forces, and sometimes disulfide linkages.
It is important to note that not all proteins exhibit quaternary structure; it is only present in oligomeric proteins. When a protein does have a quaternary structure, it allows for functionality that individual polypeptides cannot achieve alone. The specific arrangement of these polypeptides dictates the biological function of the protein complex.