Receptor (biochemistry)

Receptor (biochemistry)

In the field of biochemistry, a receptor is a molecule most often found on the surface of a cell, which receives chemical signals originating externally from the cell. Through binding to a receptor, these signals direct a cell to do something—for example to divide or die, or to allow certain molecules to enter or exit.

Receptors are protein molecules, embedded in either the plasma membrane (cell surface receptors) or the cytoplasm or nucleus (nuclear receptors) of a cell, to which one or more specific kinds of signaling molecules may attach. A molecule which binds (attaches) to a receptor is called a ligand, and may be a peptide (short protein) or other small molecule, such as a neurotransmitter, a hormone, a pharmaceutical drug, or a toxin.

Numerous receptor types are found within a typical cell and each type is linked to a specific biochemical pathway. Furthermore each type of receptor recognizes and binds only certain ligand shapes (in analogy to a lock and key where the lock represents the receptor and the key, its ligand). Hence the selective binding of a specific ligand to its receptor activates or inhibits a specific biochemical pathway.

Ligand binding stabilizes a certain receptor conformation (the three-dimensional shape of the receptor protein). This is often associated with gain of or loss of protein activity, ordinarily leading to some sort of cellular response. However, some ligands (e.g. antagonists) merely block receptors without inducing any response. Ligand-induced changes in receptors result in cellular changes which constitute the biological activity of the ligands.