Biology

• Cell signaling


  The mechanisms by which cells communicate with one another
• Cell signaling


  • Cells may communicate by sending chemical signals over some distance
  • Cell signaling is precisely regulated
  • Cell signaling involves four main processes: signal transmission, reception, transduction, and response
• Cell signaling processes


  1. Signal transmission

  2. Signal reception

  3. Signal transduction

  4. Cellular response
• Signal transmission


  A cell must produce signaling molecules and release them
• Signal reception

  Target cells have receptors that bind to signaling molecules
• Signal transduction


  The process by which a cell converts an extracellular signal into an intracellular signal
• Cellular response

  The final response that results from the signaling pathway
• The term cell signaling refers to the mechanisms by which cells communicate with one another
• Cell signaling

  1. Signal transmission

  2. Reception

  3. Signal transduction

  4. Response
• Signal transmission - far away signal


  If the target cells are not in close proximity, the signal must be transported to them
• Reception


  Receptors are large proteins or glycoproteins that bind with signaling molecules, and many types of signaling molecules do not actually enter the target cell but bind to specific receptors on the surface of the target cell
• Signal transduction


  The process by which a cell converts an extracellular signal into an intracellular signal (or signals) that causes a response, typically involving a chain of molecules that relay information
• Response


  The final molecule in the signaling pathway converts the signal into a response that alters some cell process
• When insulin binds to an insulin receptor, the signal is relayed through several different signaling pathways
• Neurotransmitters


  Chemical compounds released by neurons to signal other neurons
• Neurotransmitters


  • More than 60 different neurotransmitters have been identified, including acetylcholine, norepinephrine, dopamine, serotonin, and several amino acids and peptides
• Neurotransmitter signaling


  Neurotransmitter molecules diffuse across synapses, tiny gaps between neurons
• Hormones


  Chemical signals produced by certain cells in animals and delivered to other parts of the body
• Local regulators


  Chemical signals produced by cells and acting on nearby cells
• Cells communicate in several ways, including directly through cell junctions, by way of electrical signals, temporary cell-to-cell contact, and chemical signals
• Gap junctions in animal cells allow rapid chemical and electrical communication between adjacent cells
• Plasmodesmata between adjacent plant cells allow signal molecules to pass quickly from one cell to another
• Some neurons communicate with electrical signals, but most neurons signal one another by releasing chemical compounds called neurotransmitters
• Cells in the immune system produce specific chemical compounds that are displayed on the cell surface, and these cells recognize the chemical signals and communicate with one another by making direct contact
• Hormones


  Signaling molecules produced by specialized cells in plants and animals
• Hormone production and transport

  1. Hormones may be synthesized by neighboring cells or by specialized organs/tissues

  2. Hormones diffuse into capillaries and are transported by the blood to target cells
• Endocrine glands


  Glands that secrete hormones into the surrounding interstitial fluid
• Local regulators


  Signaling molecules that diffuse through the interstitial fluid and act on nearby cells
• Histamine


  A local regulator stored in certain immune system cells and released in response to allergic reactions, injury, or infection. It causes blood vessels to dilate and capillaries to become more permeable.
• Nitric oxide (NO)


  A local regulator gas produced by many types of cells, including plant and animal cells. It relaxes smooth muscle in blood vessel walls, causing vasodilation and decreased blood pressure.
• Prostaglandins


  Local hormones that are paracrine regulators, modifying cAMP levels and interacting with other signaling molecules to regulate metabolic activities. Some stimulate smooth muscle contraction.
• Paracrine regulation


  Signaling between cells in close proximity through local regulators diffusing in the interstitial fluid
• Types of cell surface receptors


  • Ion channel-linked receptors
  • G protein-linked receptors
  • Enzyme-linked receptors
• Ligand


  A molecule, other than an enzyme, that binds specifically to a macromolecule (usually a protein), forming a macromolecule-ligand complex that triggers a biological response
• Intracellular receptors


  Receptors inside the cell that bind to small, hydrophobic signaling molecules that can pass through the plasma membrane
• Cell surface receptor

  • Has an external domain that is a docking site for a signaling molecule, a domain that extends through the plasma membrane, and a cytoplasmic tail that transmits the signal inside the cell
• Receptors are important in determining the specificity of cell communication
• Cells can synthesize different types of receptors at different stages in their life cycle or in response to different conditions
• The same signal can have different meanings for various target cells
• Phytochromes


  A family of blue-green pigment proteins in plants and some algae that are activated by red light, leading to changes such as flowering