Receptor (biochemistry)

In biochemistry and pharmacology, a receptor is a protein-molecule that receives chemical-signals from outside a cell. When such chemical-signals bind to a receptor, they cause some form of cellular/tissue-response, e.g. a change in the electrical-activity of a cell. In this sense, a receptor is a protein-molecule that recognises and responds to endogenous-chemical signals, e.g. an acetylcholine-receptor recognizes and responds to its endogenous-ligand, acetylcholine. However, sometimes in pharmacology, the term is also used to include other proteins that are drug-targets, such as enzymes, transporters and ion-channels.

Receptor-proteins are embedded in all cells' plasmatic-membranes; facing extracellular-(cell surface receptors), cytoplasmic (cytoplasmic-receptors), or in the nucleus (nuclear receptors). A molecule that binds to a receptor is called a ligand, and can be a peptide (short-protein) or another small molecule such as a neurotransmitter, hormone, pharmaceutical-drug, toxin, or parts of the outside of a virus or microbe. The endogenously designated-molecule for a particular receptor is referred to as its endogenous-ligand. E.g. the endogenous-ligand for the nicotinic-acetylcholine receptor is acetylcholine but the receptor can also be activated by nicotine and blocked by curare.

Sensory receptor

In a sensory system, a sensory receptor is a sensory nerve ending that responds to a stimulus in the internal or external environment of an organism. In response to stimuli, the sensory receptor initiates sensory transduction by creating graded potentials or action potentials in the same cell or in an adjacent one.

Functions

The sensory receptors involved in taste and smell contain receptor molecules that bind to specific chemicals. Odor receptors in olfactory receptor neurons, for example, are activated by interacting with molecular structures on the odor molecule. Similarly, taste receptors (gustatory receptors) in taste buds interact with chemicals in food to produce an action potential.

Other receptors such as mechanoreceptors and photoreceptors respond to physical stimuli. For example, photoreceptor cells contain specialized proteins such as rhodopsin to transduce the physical energy in light into electrical signals. Some types of mechanoreceptors fire action potentials when their membranes are physically stretched.

Immune receptor

An immune receptor (or immunologic receptor) is a receptor, usually on a cell membrane, which binds to a substance (for example, a cytokine) and causes a response in the immune system.

Types

The main receptors in the immune system are pattern recognition receptors (PRRs), Toll-like receptors (TLRs), killer activated and killer inhibitor receptors (KARs and KIRs), complement receptors, Fc receptors, B cell receptors and T cell receptors.

See also

References

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