Conjugated proteins function in association with non-protein chemical structures attached either covalently or non-covalently. The non-peptide section of a conjugated protein is called its prosthetic group. While glycoproteins are typically the most abundant conjugated proteins, those in which the prosthetic group contains a coordinated metal atom constitute an important class. Coordination chemistry is an important topic for understanding protein chemistry. Prosthetic groups often contain metal atoms such as zinc or magnesium, or organic molecular structures containing metal atoms, such as in heme.