Domains and Subunits

Proteins are built from the monomer Amino Acids and have primary, secondary, tertiary and quaternary levels of structure. A base overview shows that primary structure includes the chemical structure of the protein, secondary involves beta sheets and alpha helices and tertiary combines secondary structure with other folds. Quaternary structure is where the polypeptide is built as it combines different proteins of tertiary structure. A further way to separate protein structure once there are many polymers is to look at functional domains. A domain is a discrete function and/or structural section of a polypeptide. This differs from a subunit, which is a single polypeptide in a protein which is in turn composed of multiple polypeptides. It is important to note that subunits can have domains.