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Cell surface receptors (membrane receptors, transmembrane receptors) are receptors that are embedded in the plasma membrane of cells. [1] 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.
Receptors may bind with some molecules (ligands) or may interact with physical agents like light, mechanical temperature, pressure, etc. Reception occurs when the target cell (any cell with a receptor protein specific to the signal molecule) detects a signal, usually in the form of a small, water-soluble molecule, via binding to a receptor ...
Receptor proteins can be classified by their location. Cell surface receptors, also known as transmembrane receptors, include ligand-gated ion channels, G protein-coupled receptors, and enzyme-linked hormone receptors. [1] Intracellular receptors are those found inside the cell, and include cytoplasmic receptors and nuclear receptors. [1]
These proteins have receptors that bind to specific molecules (e.g., glucose) and transport them across the cell membrane. Because energy is required in this process, it is known as 'active' transport. Examples of active transport include the transportation of sodium out of the cell and potassium into the cell by the sodium-potassium pump.
G protein–coupled receptors (GPCRs) are a family of integral transmembrane proteins that possess seven transmembrane domains and are linked to a heterotrimeric G protein. With nearly 800 members, this is the largest family of membrane proteins and receptors in mammals. Counting all animal species, they add up to over 5000. [26]
The membrane is semi-permeable, and selectively permeable, in that it can either let a substance (molecule or ion) pass through freely, to a limited extent or not at all. [citation needed] Cell surface membranes also contain receptor proteins that allow cells to detect external signaling molecules such as hormones. [9]
Receptor-mediated endocytosis is a form of pinocytosis where a cell takes in specific molecules or solutes. Proteins with receptor sites are located on the plasma membrane, binding to specific solutes. The receptor proteins that are attached to the specific solutes go inside coated pits, forming a vesicle.
Intracellular receptors are globular protein receptors located inside the cell rather than on its cell membrane. The word intracellular means "within or inside a cell." Molecules that cross a cell membrane to bind with a receptor are generally nonpolar and may be relatively small.