A
biological target is anything within a living organism to which some other entity, like an endogenous
ligand or a
drug is directed and/or binds. Examples of common classes of biological targets are
proteins and
nucleic acids. The definition is context-dependent and can refer to the biological target of a
pharmacologically active drug compound, the receptor target of a
hormone (like
insulin), or some other target of an external stimulus. The implication is that a target is "hit" by a signal and its behavior or function is then changed. Biological targets are most commonly proteins such as
enzymes,
ion channels, and
receptors.