receptor (biochemistry)

In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm that binds to a specific factor (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. As all receptors are proteins, their structure is encoded into the DNA. Most hormone genes contain a short sequence that signals to the cell whether it needs to be transported to the cell membrane or it is to remain in the cytoplasm.

Overview

Many genetic disorders involve hereditary defects in receptor genes. Often, it is hard to determine whether the receptor is nonfunctional or the hormone is produced at decreased level; this gives rise to the "pseudo-hypo-" group of endocrine disorders, where there appears to be a decreased hormonal level while in fact it is the receptor that is not responding sufficiently to the hormone. Receptors exist in different types, dependent on their ligand and function:

Some receptor proteins are peripheral membrane proteins;
Many hormone receptors and neurotransmitter receptors are transmembrane proteins, embedded in the lipid bilayer of cell membranes. These receptors are either coupled to G proteins or possess enzyme or ion channel activity that allow the activation of signal transduction pathways in response to the activation by the ligand.
Another major class of receptors are intracellular proteins such as those for steroid hormone receptors. These receptors often can enter the cell nucleus and modulate gene expression in response to the activation by the ligand.