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Cell Signaling

Cell Signaling. Communication between cells that are not directly connected. Cell Signaling involves a series of processes…. Sending a signal Transport to target cells Reception Often—signal transduction Response. Sending Signals. Cells synthesize signaling molecules Neurotransmittors

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Cell Signaling

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  1. Cell Signaling Communication between cells that are not directly connected

  2. Cell Signaling involves a series of processes… • Sending a signal • Transport to target cells • Reception • Often—signal transduction • Response

  3. Sending Signals • Cells synthesize signaling molecules • Neurotransmittors • Hormones (plant and animal) • Local regulators – growth factors, histamine, prostaglandins, nitric oxide

  4. Transport to target cell • Signaling molecules may: • Diffuse through interstitial fluid • Be carried by circulatory system to target organ • Endocrine glands • http://bcs.whfreeman.com/thelifewire/content/chp44/4403s.swf

  5. Reception • Cells have receptors that bind to signaling molecules that can’t enter cell • Proteins or glycoproteins • Different cell types have different receptors • Highly specific – bind to 1 ligand • Receptors have 3 domains • External – docking site for ligand • 2nd extends through membrane • “tail” – extends into cytoplasm

  6. Regulation of Reception • Cells synthesize and degrade receptors depending on needs • Down-regulation – cells decrease # of receptors • Reduces sensitivity to receptor (ex. Insulin) • Receptors transported to lysosome • Up-regulation • Response to low hormone conc. • Increase sensitivity, amplifies signaling molecules effects

  7. Types of receptors • Ion channel-linked • Signal binds to receptor, ion-gated channel opens • Changes chemical signal to electrical

  8. Types of receptors, cont. • Enzyme-linked receptors • Function as enzymes • Linked to enzymes

  9. Types of receptors, cont. • G protein-linked receptors**

  10. Signal Transduction • Cell converts extracellular signal to intracellular one resulting in response • Initiated by G protein-linked receptors • G protein made of 3 subunits (GDP) • Signal molecule binds to receptor & receptor associates with G protein –GTP replaces GDP • GTP subunit separates & binds to protein in cell, activating it, often creating 2nd message • http://entochem.tamu.edu/G-Protein/index.html

  11. Summing Up Signal Transduction

  12. Response • Change in cell as result of signal • 3 categories • Ion channels open/close • Change in enzyme activity/metabolism • Gene activated or repressed • Response can be amplified

  13. Signals must be terminated • Once signal has done its job, must be terminated • Often 2ndary signals (like cAMP) are quickly broken down

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