Presentation on theme: "Membrane Transport Nestor T. Hilvano, M.D., M.P.H."— Presentation transcript:
1 Membrane Transport Nestor T. Hilvano, M.D., M.P.H. (Images Copyright Discover Biology, 5th ed., Singh-Cundy and Cain, Textbook, 2012.)
2 Learning Objectives Describe plasma membrane and give its functions. Differentiate the types of transport of molecules across the membrane.Compare and contrast diffusion and osmosis.Discuss briefly what happens when a red bloodcells is placed in hypotonic solution? Inhypertonic solution?
3 Plasma Membrane Functions: Regulates passage of ions and macromolecules in and out of the cellAllows some substances to cross more easily than othersAllows information to be transferred across the membranePossesses devices for cell attachmentReceptors for hormonesIon pumps for regulating the internal environment
4 Components of Plasma Membrane The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in itSelectively permeableComposed mainly of Bilayer of phospholipids (selective barriers), and some proteins, cholesterol, carbohydrates
5 Fig. 7-7 Fibers of extracellular matrix (ECM) Glyco- Carbohydrate proteinCarbohydrateGlycolipidEXTRACELLULARSIDE OFMEMBRANEFigure 7.7 The detailed structure of an animal cell’s plasma membrane, in a cutaway viewCholesterolMicrofilamentsof cytoskeletonPeripheralproteinsIntegralproteinCYTOPLASMIC SIDEOF MEMBRANE
6 Transport of Molecules Across the Plasma Membrane Passive transport- move from [high] to [low]; requires no ATPActive transport- move from [low] to [high]; needs ATPFacilitated transport- via carrier proteinExocytosis and endocytosis
7 Passive Transport Cell does not expend energy Diffusion – particles spread out from area of high concentration to an area of low concentration gradient.i.e. O2 and CO2 are small and nonpolar molecules that easily cross the membrane.Osmosis – is the net diffusion of water across a selectively permeable membrane
8 Molecules of dye Membrane Pores Net diffusion Net diffusion Figure 5.3AMolecules of dyeMembranePoresFigure 5.3A Passive transport of one type of moleculeNet diffusionNet diffusionEquilibrium8
9 p. 76 Lower concentration of solute Higher concentration of solute Figure 5.4Lower concentration of soluteHigher concentration of soluteEqual concentrations of soluteH2OSolute moleculeSelectively permeable membraneWater moleculeFigure 5.4 Osmosis, the diffusion of water across a membraneSolute molecule with cluster of water moleculesOsmosisp. 769
10 TonicityTonicity is important in maintaining cell volume (ability to cause a cell to loss or gain water)Isotonic solution – solute concentration is the same both intracellular and extracellularAn animal cell (RBC) placed in:Hypotonic – will gain water, swell and lyseHypertonic – will lose water and crenate
11 Figure 7.5 Water Moves into and out of Cells by Osmosis Osmosis is the diffusion of water across a selectively permeable membrane. Cells lose water in a hypertonic solution and gain water in a hypotonic solution. Our cells are bathed in an isotonic fluid to prevent osmotic swelling and bursting.
12 Facilitated Transport Uses specific transport proteins in the membraneDoes not requires energySubstances move down its concentration gradientChannel proteins- ions channels (gated channel) that open or close in response to stimulusCarrier proteins- binds to protein and changes it’s shape
13 Channel protein Solute (a) A channel protein Solute Carrier protein Fig. 7-15EXTRACELLULAR FLUIDChannel proteinSoluteCYTOPLASM(a) A channel proteinFigure 7.15 Two types of transport proteins that carry out facilitated diffusionSoluteCarrier protein(b) A carrier protein
14 Figure 7.7 Passive Carrier Proteins The facilitated diffusion of glucose into our cells is mediated by a class of passive carriers called GLUT proteins. No energy is required for the transport of glucose by carrier proteins. The sugar moves from the side of the membrane where it is at high concentration to the side where it is at lower concentration.
15 Active Transport Requires expenditure of energy (ATP) Molecules move against the concentration gradienti.e. Na+ - K+ pump in nerve impulse transmission
16 Figure 7.8 Active Carrier Proteins Active carrier proteins use energy to move materials from regions of low concentration to regions of high concentration. When food arrives, proton pumps secrete hydrogen ions (H+) into your stomach.Faciliatated diffusion and active transport:
17 Figure 7.6 (part 1) The Plasma Membrane Controls What Enters and Leaves the Cell Proteins that span the plasma membrane (b, c) play an important role in moving materials into and out of cells. The flowchart summarizes the different types of processes that move materials across biological membranes.
18 Endocytosis and Exocytosis Transport of large moleculesExocytosis – export bulky materialsi.e. tearing, insulin release into the bloodstreamEndocytosis – cells take in macromolecules by forming vesicles/vacuoles from its plasma membrane.a) phagocytosis, b) pinocytosis
19 Figure 7.9 Cell Contents Are Exported through Exocytosis Exocytosis exports materials from the cell.
20 Figure 7.10a Extracellular Substances Are Imported through Endocytosis (a) Endocytosis brings material from the outside of the cell to the inside, wrapped in membrane vesicles. (d) Pinocytosis is nonspecific endocytosis of external fluid. (b) Receptor-mediated endocytosis is a highly selective process in which only certain extracellular molecules are recognized by, and bound to, special plasma membrane receptors. (c, e) Phagocytosis is endocytosis on a large scale. A macrophage (blue) engulfing an invading yeast cell (yellow) is seen in (e). Macrophages are part of the body’s defense system.
21 HomeworkDefine – diffusion, osmosis, endocytosis, exocytosis, channel proteins, carrier proteins, isotonic solution, hypotonic solution, and hypertonic solution.Describe the structure of plasma membrane and give its functions. What is it’s primary component?Compare and contrast passive transport, facilitated transport, and active transport across a membrane as to concentration gradients, energy expenditure, use of carrier/transport proteins, and cite an example of substances.Discuss the effect of hypotonic and hypertonic solution to red blood cells.