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Transcript
1. The Plasma Membrane And Membrane Potential 2. Plasma Membrane Functions Forms cell boundary, enclosing intracellular contents Determines composition of the cell Entry of nutrients Exit of wastes Exit of secretory products Maintain differences in ion concentration Joins cells together Ability to respond to environmental signals 3-4. Membrane Transport Semipermeable/selectively permeable Permeability Solubility in lipids Size Charge Polar vs. nonpolar Passive No energy expended Active ATP required 5-11. Passive Transport Diffusion Concentration difference or chemical gradient Random motion of particles in solution Net diffusion Steady state http://upload.wikimedia.org/wikipedia/commons/thu mb/c/cc/Scheme_simple_diffusion_in_cell_membra ne-en.svg/626pxScheme_simple_diffusion_in_cell_membraneen.svg.png http://www.williamsclass.com/SeventhScienceWork /ImagesCellBricks/Diffusion.gif ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 12-13. What Can Diffuse Through the Phopholipid Bilayer? Small molecules Nonpolar molecules Uncharged particles 14. Diffusion Rate of diffusion of a substance depends on: Magnitude of its concentration gradient Permeability of membrane to that substance Temperature Surface area of membrane Also Molecular weight of substance Thickness of membrane 15. Fick’s Law of Diffusion 16.Movement of Ions Electrical gradient Chemical gradient Electrochemical gradient 17. Electrochemical Gradient 18. Diffusion of Ions Channels Specific Size Charge # present determined permeability Leak – always open Gated – sometimes open, sometimes closed Chemical Stretch Voltage http://www.biologycorner.com/resources/cell _membrane.jpg 20 - 24. Osmosis Diffusion of water through selectively permeable membrane Through bilayer ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ Aquaporins H2O diffuses down its concentration gradient H2O concentration is less when there are more solutes Solutes have to be osmotically active cannot freely move across membrane H2O diffuses down its concentration gradient until its concentration is equal on both sides of a membrane Some cells have water channels called aquaporins to facilitate osmosis 25 - 30. Osmotic Pressure Force that would have to be exerted to stop osmosis How strongly H2O “wants” to diffuse Proportional to solute concentration 31-32. Molarity and Molality 1 molar solution (1.0M) 1 mole of solute dissolved in enough water to make 1L of solution Doesn't specify exact amount of H2O 1 molal solution (1.0m) 1 mole of solute dissolved in 1 kg H2O Molarity and Molality Osmolality (Osm) is total molality of a solution 1mole of NaCl yields a 2 Osm solution 1 mole of glucose yields a 1 Osm solution 33-37. Tonicity Effect on cell volume via osmotic movement of H20 Isotonic No change in volume Solutions have same osmotic pressure Hypertonic Have higher osmotic pressure Cells shrink/crenate Hypotonic ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ Have lower osmotic pressure Cells swell/lyse http://www.medicine.mcgill.ca/physio/vlab/bloodlab /images/crenate.gif http://www.medicine.mcgill.ca/physio/vlab/bloodlab /eryfrag1_n.htm 38-9. Carrier-Mediated Transport Molecules too large and polar to diffuse Protein carriers Specificity Saturation Transport maximum Competition Passive or active Facilitated diffusion Active transport 40. Facilitated Diffusion Carriers bind with passenger molecule on either side of membrane Binding induces conformational change 41. Transport of Glucose 42. Channel vs Carrier Proteins http://www.bio.miami.edu/~cmallery/150/memb/c8. 7x15.facilitated.diffusion.jpg 43. Active Transport Is transport of molecules against a concentration gradient ATP is required 44. Primary Active Transport Substance binds to recognition site Bonding stimulates phosphorylation of the carrier protein Carrier undergoes conformational change Transported molecule released on opposite side of membrane 45-47. Na+/K+ Pump 3 Na+ out ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 2 K+ in Against their gradients Uses ATP Energy for coupled transport of other molecules Electrochemical impulses Osmotic reasons 49-52. Secondary Active Transport Requires ATP to first move Na+ uphill to create a gradient Secondary active transport then uses energy from “downhill” movement of Na+ to drive “uphill” transport of another molecule Cotransport or symport Molecule moves in same direction as Na+ Countertransport or antiport Molecule moves in opposite direction to Na+ Secondary Active Transport 53-76. Vesicular Transport A.k.a. bulk transport Large polar molecules Multimolecular materials Membrane-enclosed vesicle Endocytosis Pinocytosis Receptor-mediated endocytosis Phagocytosis Exocytosis http://upload.wikimedia.org/wikipedia/commons/8/8 1/FAGOCITOSI_BY_RAFF_.gif Pinocytosis “cell drinking” ECF into cell Retrieve extra membrane Receptor-mediated endocytosis Selective Import specific large molecules Receptors on cell surface ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ Cholesterol, B12, insulin, iron 59-60. Transport Summary 61-5. Membrane Potential All living cells Separation of charges across membrane or difference in relative # of cations and anions in the ICF and ECF Millivolts (mV) Negative inside/positive outside Magnitude depends on degree of separation of charges 66. The Membrane Potential Na+/K+ pump Negatively charged proteins inside of cell Membrane more permeable to K+ than amy other cation 67. Equilibrium Potential Membrane potential at which net movement of ion across membrane ceases K+ -90mV Na+ +66mV 68-69. Ion Concentrations 70. Resting Membrane Potential Differences in concentration and permeability of key ions K+, Na+, AConcentration gradient Na+ - into cell K+ - out of cell Electrical gradient for both K+ and Na+ is toward the negatively charged side of membrane ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________