Drugs usually interact with biomolecules such as carbohydrates, lipids, proteins and nucleic acids. These are called target molecules or drug targets. These perform various functions in the body. For example, proteins which perform the role of biological catalysts in the body are called enzymes and those which are crucial to communication system in the body are called receptors. Nucleic acids have coded genetic information for the cell. Lipids and carbohydrates are structural parts of the cell membrane.