Transmembrane receptors

Cell surface receptors (membrane receptors, transmembrane receptors) are receptors that are embedded in the membranes of cells. They act in cell signaling by receiving (binding to) extracellular molecules. They are specialized integral membrane proteins that allow communication between the cell and the extracellular space. The extracellular molecules may be hormones, neurotransmitters, cytokines, growth factors, cell adhesion molecules, or nutrients; they react with the receptor to induce changes in the metabolism and activity of a cell. In the process of signal transduction, ligand binding affects a cascading chemical change through the cell membrane.

Transmembrane receptors are typically classified based on their tertiary (three-dimensional) structure. But, if the three-dimensional structure is yet undiscovered, then they can be classified based on experimentally verifiable membrane topology. The simplest polypeptide chains are found to cross the lipid bilayer once; while others, such as the G-protein coupled receptors, cross as many as seven times. There are various kinds, such as glycoprotein and lipoprotein. Hundreds of different receptors are known and many more have yet to be studied. Many membrane receptors include transmembrane proteins. Each cell membrane can have several kinds of membrane receptor, in varying surface distribution. A specific receptor may also be differently distributed on different membrane surfaces, depending on the membrane sort and cell function. Since receptors usually cluster on the membrane surface, the placement of every receptor on each membrane surface is heterogeneous.

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