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Lecture #5

Lecture #5. Membrane Transport & Cell Communication. Membrane Transport. diffusion facilitated diffusion active transport. Diffusion. O 2. EXTRACELLULAR. INTRACELLULAR. CO 2. -molecules pass through membrane -movement is spontaneous -molecules travel down the concentration gradient

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Lecture #5

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  1. Lecture #5 Membrane Transport & Cell Communication

  2. Membrane Transport • diffusion • facilitated diffusion • active transport

  3. Diffusion O2 EXTRACELLULAR INTRACELLULAR CO2 -molecules pass through membrane -movement is spontaneous -molecules travel down the concentration gradient -goal: equlibrium -speed is limited by rate of diffusion

  4. Osmosis • movement of water down a concentration gradient • difference in concentration of solute across a membrane • intracellular [solute] vs. extracellular [solute] • osmotic, hyperosmotic, hyposmotic

  5. Facilitated Diffusion molecule is transported down its concentration gradient faster and more efficient than diffusion uses transport proteins 2 kinds: carrier proteins channel proteins

  6. GLUT – glucose transporter proteins GLUT1 – red blood cells, adipose cells, muscle cells GLUT4 – liver cells, adipose cells, muscle cells glucose EXTRACELLULAR after glucose uptake insulin INTRACELLULAR

  7. Active Transport • pumping a molecule against its concentration gradient • requires energy (ATP)

  8. Ca2+-ATPase – skeletal muscle Ca2+ Ca2+ Ca2+ CYTOPLASM ATP P Ca2+ Ca2+ Ca2+ ER LUMEN Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ Ca2+

  9. Na+-K+-ATPase – nerve stimulation and membrane potential EXTRACELLULAR Na2+ K2+ Na2+ Na2+ K2+ K2+ K2+ stimulation ATP ADP release of energy resting stimulated Na2+ Na2+ K2+ Na2+ Na2+ Na2+ Na2+ K2+ INTRACELLULAR

  10. Active Transport and Co-transport blood gut epithelial cell intestinal lumen glucose glucose glucose glucose Na2+ Na2+ Na2+ Na2+ Na2+ ATP ADP K2+ K2+ tight junctions

  11. Other forms of transport • Exocytosis • Endocytosis • phagocytosis • pinocytosis • receptor-mediated endocytosis

  12. Cell Signalling • Signals: • local regulators – e.g. growth factors • long-distance regulators – e.g. hormones • 3 stages: • Reception • Transduction • Response

  13. Non-hormonal cell-to-cell communication

  14. Reception – Plasma Membrane Receptors • 3 major types: • G-protein linked receptors • receptor tyrosine kinases • ion channel receptors

  15. G-protein linked receptors ligands: e.g. some hormones (epinephrine) neurotransmitters

  16. Epinephrine – adrenergic receptor • epinephrine – produced by the adrenal gland • enters the bloodstream during short-term stress response • liver - a1 receptors • blood vessels - b2 receptors

  17. Liver blood vessels - heart, lung, cerebral cortex a1 receptor b2 receptor adenylate cyclase adenylate cyclase GTP GTP a1 receptor b2 receptor adenylate cyclase adenylate cyclase cAMP cAMP GTP GTP ATP ATP PKA PKA inhibits MLCK – vasodilation glycogen breakdown – release glucose

  18. blood vessels – skin and gut a2 receptor adenylate cyclase GDP a2 receptor adenylate cyclase X cAMP GDP ATP vasoconstriction

  19. Receptor Tyrosine Kinases • kinase: an enzyme that phosphorylates another protein – catalyzes the transfer of phosphate groups • RTKs – catalyze the transfer of phosphate to side chain of tyrosine amino acid in a protein • ligands – e.g. growth factors – EGF, FGF, PDGF, etc.

  20. Transduction • protein phosphorylation – kinases • second messengers: • cAMP • Ca2+

  21. Transduction • phosphorylation - kinases – growth factors • stimulate cell division • cAMP – adenylate cyclase • activates PKA • various effects – e.g. glycogen breakdown or vasodilation • Ca2+ - PLC produces IP3 and DAG • activates PKC • various effects – e.g. muscle contraction

  22. Response • Cytoplasmic responses: • opening or closing of a gated ion-channel • alteration in metabolism • regulation of enzyme activity • change in cytoskeletal organization • Nuclear responses • activation or repression of gene expression • activation or inhibition of cell cycle • induction of differentiation • cell committment

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