10/5/2011 MEMBRANE TRANSPORT MEMBRANE TRANSPORT Expected Learning Outcomes Explain what is meant by a selectively permeable membrane. Describe the various mechanisms for transporting material through the plasma membrane. membrane Define osmolarity and tonicity and explain their importance. Plasma membrane—a barrier and a gateway between the cytoplasm and ECF Passive transport mechanisms require no ATP Random molecular motion of particles provides the necessary energy Filtration, diffusion, osmosis Active transport mechanisms consumes ATP Selectively permeable—allows some things through, and prevents other things from entering and leaving the cell Active transport and vesicular transport Carrier-mediated mechanisms use a membrane protein to transport substances from one side of the membrane to the other 3-1 3-2 FILTRATION SIMPLE DIFFUSION Filtration—process in which particles are driven through a selectively permeable membrane by hydrostatic pressure (force exerted on a membrane by water) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Solute Water Capillary wall Filtration of nutrients through gaps in blood capillary walls into tissue fluids Filtration of wastes from the blood in the kidneys while holding back blood cells and proteins Simple diffusion—the net movement of particles from area of high concentration to area of low concentration Red blood cell Examples Blood pressure in capillary forces water and small solutes such as salts through narrow clefts between capillary cells. Clefts hold back larger particles such as red blood cells. Figure 3.13 Down gradient Due to their constant, spontaneous t motion ti Also known as movement down the concentration gradient—concentration of a substance differs from one point to another Up gradient Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 3.14 3-3 3-4 SIMPLE DIFFUSION Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slid S “Slide Sorter” t ” views. i All animations i ti will ill appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Factors affecting diffusion rate through a membrane Temperature: temp., motion of particles Molecular weight: larger molecules move slower Steepness of concentrated gradient: difference, difference rate Membrane surface area: area, rate Membrane permeability: permeability, rate 3-6 1 10/5/2011 OSMOSIS SIMPLE DIFFUSION Osmosis—flow of water from one side of a selectively permeable membrane to the other Diffusion through lipid bilayer Diffusion through channel proteins Nonpolar, hydrophobic, lipid-soluble substances diffuse through lipid layer Water and charged, hydrophilic solutes diffuse through channel proteins in membrane Cells control permeability by regulating number of channel proteins or by opening and closing gates From side with higher water concentration to side with lower water concentration Reversible attraction of water to solute particles forms hydration spheres Makes those water molecules less available to diffuse back to the side from which they came Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Side A Side B Solute Water (a) Start 3-7 3-8 OSMOSIS Aquaporins—channel proteins in plasma membrane specialized for passage of water Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Cells can increase the rate of osmosis by installing more aquaporins Decrease rate by removing them Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Side B Solute Water (a) Start Significant amounts of water diffuse even through the hydrophobic, phospholipid regions of the plasma membrane Side A Figure 3.15a 3-10 OSMOLARITY AND TONICITY OSMOSIS Osmotic pressure—amount of hydrostatic pressure required to stop osmosis Reverse osmosis—pressure applied to one side, overrides pressure, drives against concentration gradient Heart drives water out of capillaries by reverse osmosis—capillary filtration Tonicity—ability of a solution to affect fluid volume and pressure in a cell Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Osmotic pressure Hydrostatic pressure Depends on concentration and permeability of solute Hypotonic solution Has a lower concentration of nonpermeating solutes than intracellular fluid (ICF) Cells absorb water, swell, and may burst (lyse) (b) 30 minutes later Hypertonic solution Has a higher concentration of nonpermeating solutes Cells lose water + shrivel (crenate) Figure 3.15b Low water concentration Isotonic solution 3-11 High water concentration Concentrations in cell and ICF are the same Cause no changes in cell volume or cell shape Normal saline 3-12 2 10/5/2011 EFFECTS OF TONICITY ON RBCS Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after f viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. (a) Hypotonic (b) Isotonic (c) Hypertonic © Dr. David M. Phillips/Visuals Unlimited Figure 3.16a Figure 3.16b Figure 3.16c Hypotonic, isotonic, and hypertonic solutions affect the fluid volume of a red blood cell. Notice the crenated and swollen cells. 3-13 Transport proteins in the plasma membrane that carry solutes from one side of the membrane to the other Specificity Transport proteins specific for a certain ligand Solute binds to a specific receptor site on carrier protein Differs from membrane enzymes because carriers do not chemicallyy change g their ligand g Simply picks them up on one side of the membrane, and releases them, unchanged, on the other Saturation CARRIER-MEDIATED TRANSPORT Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Rate of so olute transport (molecule es/sec passing through plassma membrane) CARRIER-MEDIATED TRANSPORT As the solute concentration rises, the rate of transport rises, but only to a point—transport maximum (Tm) Figure 3.17 Two types of carrier-mediated transport Transport maximum (Tm) Concentration of solute Facilitated diffusion and active transport 3-15 Transport maximum—transport rate when all carriers are occupied 3-16 CARRIER-MEDIATED TRANSPORT Uniport Symport Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Carries two or more solutes simultaneously in same direction (cotransport) Antiport Carries only one solute at a time Carries two or more solutes in opposite directions (countertransport) Sodium-potassium pump brings in K+ and removes Na+ from cell Carriers employ two methods of transport Facilitated diffusion Active transport 3-17 3 10/5/2011 CARRIER-MEDIATED TRANSPORT Facilitated diffusion—carrier-mediated transport of solute through a membrane down its concentration gradient Does not consume ATP Solute attaches to binding site on carrier, carrier changes confirmation, confirmation then releases solute on other side of membrane Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ECF Figure 3.18 ICF 1 A solute particle enters the channel of a membrane protein (carrier). 2 The solute binds to a receptor site on the carrier and the carrier changes conformation. 3 The carrier releases the solute on the other side of the membrane. 3-19 CARRIER-MEDIATED TRANSPORT CARRIER-MEDIATED TRANSPORT Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Active transport—carrier-mediated transport of solute through a membrane up (against) its concentration gradient ATP energy consumed to change carrier Examples of uses: Each pump cycle consumes one ATP and exchanges three Na+ for two K+ Glucose Na+ Apical surface Keeps the K+ concentration higher and the Na+ concentration lower within the cell than in ECF Necessary because Na+ and K+ constantly leak through membrane SGLT Cytoplasm Sodium–potassium pump keeps K+ concentration higher inside the cell Bring amino acids into cell Pump Ca2+ out of cell Half of daily calories utilized for Na+−K+ pump Na+– K+ pump ATP ADP + Pi Basal surface Na+ 3-22 3-21 CARRIER-MEDIATED TRANSPORT Secondary active transport Steep concentration gradient maintained between one side of the membrane and the other (water behind a dam) Sodium–glucose transport protein (SGLT) simultaneously binds Na+ and glucose and carries both into the cell Does not consume ATP Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after ft viewing i i g iin P Presentation t ti M Mode d and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Regulation of cell volume “Fixed anions” attract cations causing osmosis Cell swelling stimulates the Na+−K+ pump to ion concentration, osmolarity and cell swelling 3-24 4 10/5/2011 VESICULAR TRANSPORT CARRIER-MEDIATED TRANSPORT Vesicular transport—processes that move large particles, fluid droplets, or numerous molecules at once through the membrane in vesicles—bubblelike enclosures of membrane Endocytosis—vesicular processes that bring material into the cell Maintenance of a membrane potential in all cells Pump keeps inside more negative, outside more positive Necessary for nerve and muscle function Phagocytosis—“cell eating,” engulfing large particles Pinocytosis—“cell drinking,” of ECF containingg y g, takingg in droplets p molecules useful in the cell Receptor-mediated endocytosis—particles bind to specific receptors on plasma membrane Heat production Na+−K+ Thyroid hormone increases number of pumps Consume ATP and produce heat as a by-product Pseudopods; phagosomes; macrophages Pinocytic vesicle Clathrin-coated vesicle Exocytosis—discharging material from the cell Utilizes motor proteins energized by ATP 3-25 3-26 VESICULAR TRANSPORT Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Particle 7 The indigestible residue is voided by exocytosis. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear pp after viewingg in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 1 A phagocytic cell encounters a particle of foreign matter. Pseudopod Residue 2 The cell surrounds the particle with its pseudopods. Nucleus Phagosome g 6 The phagolysosome fuses with the plasma membrane. 3 The particle is phagocytized and contained in a phagosome. Lysosome Vesicle fusing with membrane Phagolysosome 5 Enzymes from the lysosome digest the foreign matter. 4 The phagosome fuses with a lysosome and becomes a phagolysosome. 3-28 Phagocytosis keeps tissues free of debris and infectious microorganisms Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear pp after viewingg in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode d playing l i each h animation. i i M and Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 5 10/5/2011 VESICULAR TRANSPORT VESICULAR TRANSPORT Taking in droplets of ECF Occurs in all human cells Receptor-mediated endocytosis Pinocytosis or “cell-drinking” More selective endocytosis Enables cells to take in specific molecules that bind to extracellular receptors Clathrin-coated vesicle in cytoplasm Membrane caves in, then pinches off into the cytoplasm as pinocytotic vesicle Uptake of LDL from bloodstream Familial Hypercholesterolemia Receptor-mediated endocytosis 3-31 VESICULAR TRANSPORT 3-32 VESICULAR TRANSPORT Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Capillary endothelial cell Intercellular cleft Exocytosis Capillary lumen Pinocytotic vesicles Secreting material Replacement of plasma membrane removed by endocytosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Muscle cell Fusion pore Dimple Tissue fluid Secretion Plasma membrane Linking protein © Don Fawcett/Photo Researchers, Inc. 0.25 m Transport of material across the cell by capturing it on one side and releasing it on the other Receptor-mediated endocytosis moves it into the cell and exocytosis moves it out the other side Insulin 3-33 Secretory vesicle (a) 1 2 (b) 3-34 6
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