Physiology, Cellular Receptor

Cellular receptors are proteins either inside a cell or on its surface, which receive a signal. In normal physiology, this is a chemical signal where a protein-ligand binds a protein receptor. The ligand is a chemical messenger released by one cell to signal either itself or a different cell. The binding results in a cellular effect, which manifests as any number of changes in that cell, including altering gene transcription or translation or changing cell morphology. Typically, a single ligand will have a single receptor to which it can bind and cause a cellular response. There are several different types of cellular signaling, all of which depend on different ligands and cellular receptors. The major categories of cellular signaling include autocrine, signal across a gap junction, paracrine, and endocrine. Autocrine signaling is when a cell releases a signal that then binds one of its receptors to change its functioning. Signaling across gap junctions is when small signaling molecules move directly across neighboring cells that are attached. Paracrine signaling is communication between cells that are nearby. Endocrine signaling is when cell signals travel to target cell receptors in a different part of the body through the bloodstream. Each type of signaling requires a ligand and a receptor. Cellular receptors can broadly categorize into internal receptors, cell-surface receptors, ion channel receptors, G-protein-coupled receptors (GPCRs), and enzyme-linked receptors. While most cell receptor binding is by a chemical ligand, two notable exceptions are viruses which are pathogenic cells that can bind host cellular receptors to infect a cell and bacterial components that can bind receptors on immune cells to cause an immune response.