page_title: Cell surface receptor
section_title: Signal transduction
hierarchical_section_title: Cell surface receptor / Signal transduction
caption_attribution_description: English: The External Reactions and the Internal Reactions of
context_page_description: Cell surface receptors are receptors that are embedded in the plasma membrane of cells. They act in cell signaling by receiving 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.
context_section_description: Signal transduction processes through membrane receptors involve the external reactions, in which the ligand binds to a membrane receptor, and the internal reactions, in which intracellular response is triggered.
  Signal transduction through membrane receptors requires four parts:
  Extracellular signaling molecule: an extracellular signaling molecule is produced by one cell and is at least capable of traveling to neighboring cells.
  Receptor protein: cells must have cell surface receptor proteins which bind to the signaling molecule and communicate inward into the cell.
  Intracellular signaling proteins: these pass the signal to the organelles of the cell. Binding of the signal molecule to the receptor protein will activate intracellular signaling proteins that initiate a signaling cascade.
  Target proteins: the conformations or other properties of the target proteins are altered when a signaling pathway is active and changes the behavior of the cell.
  Membrane receptors are mainly divided by structure and function into 3 classes: The ion channel linked receptor; The enzyme-linked receptor; and The G protein-coupled receptor.
  Ion channel linked receptors have ion channels for anions and cations, and constitute a large family of multipass transmembrane proteins. They participate in rapid signaling events usually found in electrically active cells such as neurons. They are also called ligand-gated ion channels. Opening and closing of ion channels is controlled by neurotransmitters.
  Enzyme-linked receptors are either enzymes themselves, or directly activate associated enzymes. These are typically single-pass transmembrane receptors, with the enzymatic component of the receptor kept intracellular. The majority of enzyme-linked receptors are, or associate with, protein kinases.
  G protein-coupled receptors are integral membrane proteins that possess seven transmembrane helices. These receptors activate a G protein upon agonist binding, and the G-protein mediates receptor effects on intracellular signaling pathways.
caption: External reactions and internal reactions for signal transduction (click to enlarge)
exif: {}