1. CAMPBELLBIOLOGYReece Urry Cain Wasserman Minorsky Jackson 2014 Pearson Education, Inc.TENTHEDITION7MembraneStructure andFunctionLecture Presentation byNicole Tunbridge andKathleen Fitzpatrick

2. Life at the Edge The plasma membrane is the boundary thatseparates the living cell from its surroundings The plasma membrane exhibits selectivepermeability, allowing some substances to cross itmore easily than others 2014 Pearson Education, Inc. 3. Video: Structure of the Cell Membrane 2014 Pearson Education, Inc. 4. Video: Water Movement Through an Aquaporin 2014 Pearson Education, Inc. 5. Concept 7.1: Cellular membranes are fluidmosaics of lipids and proteins Phospholipids are the most abundant lipid in theplasma membrane Phospholipids are amphipathic molecules,containing hydrophobic and hydrophilic regions A phospholipid bilayer can exist as a stableboundary between two aqueous compartments 2014 Pearson Education, Inc. 6. Figure 7.2 2014 Pearson Education, Inc.Hydrophilic headWATERWATERHydrophobic tail 7. The fluid mosaic model states that a membraneis a fluid structure with a mosaic of variousproteins embedded in it Proteins are not randomly distributed in themembrane 2014 Pearson Education, Inc. 8. Figure 7.3Fibers of extra-cellular 2014 Pearson Education, Inc.matrix (ECM)Glyco-proteinCarbohydrate GlycolipidEXTRACELLULARSIDE OFMEMBRANECholesterolMicrofilamentsof cytoskeletonPeripheralproteins Integralprotein CYTOPLASMICSIDE OFMEMBRANE 9. Figure 7.3a 2014 Pearson Education, Inc.Fibers of extra-cellularmatrix (ECM)Glyco-proteinCarbohydrateCholesterolMicrofilamentsof cytoskeleton 10. Figure 7.3b 2014 Pearson Education, Inc.GlycolipidEXTRACELLULARSIDE OFMEMBRANEIntegralproteinCYTOPLASMICSIDE OFMEMBRANEPeripheralproteins 11. The Fluidity of Membranes Phospholipids in the plasma membrane can movewithin the bilayer Most of the lipids, and some proteins, drift laterally Rarely, a lipid may flip-flop transversely acrossthe membrane 2014 Pearson Education, Inc. 12. Figure 7.4-1Membrane proteinsMouse cell 2014 Pearson Education, Inc.Human cell 13. Figure 7.4-2Membrane proteinsMouse cell 2014 Pearson Education, Inc.Human cellHybrid cell 14. Figure 7.4-3Membrane proteinsMouse cell 2014 Pearson Education, Inc.Human cellHybrid cellMixed proteinsafter 1 hour 15. As temperatures cool, membranes switch from afluid state to a solid state The temperature at which a membrane solidifiesdepends on the types of lipids Membranes rich in unsaturated fatty acids aremore fluid than those rich in saturated fatty acids Membranes must be fluid to work properly; theyare usually about as fluid as salad oil 2014 Pearson Education, Inc. 16. The steroid cholesterol has different effects onmembrane fluidity at different temperatures At warm temperatures (such as 37C), cholesterolrestrains movement of phospholipids At cool temperatures, it maintains fluidity bypreventing tight packing 2014 Pearson Education, Inc. 17. Figure 7.5(a) Unsaturated versus saturated hydrocarbon tails(b) Cholesterol within the animal cell membrane 2014 Pearson Education, Inc.Fluid ViscousUnsaturated tailsprevent packing.Saturated tails packtogether.CholesterolCholesterol reducesmembrane fluidity atmoderate temperatures,but at low temperatureshinders solidification. 18. Evolution of Differences in Membrane LipidComposition Variations in lipid composition of cell membranesof many species appear to be adaptations tospecific environmental conditions Ability to change the lipid compositions inresponse to temperature changes has evolved inorganisms that live where temperatures vary 2014 Pearson Education, Inc. 19. Membrane Proteins and Their Functions A membrane is a collage of different proteins,often grouped together, embedded in the fluidmatrix of the lipid bilayer Proteins determine most of the membranesspecific functions 2014 Pearson Education, Inc. 20. Peripheral proteins are bound to the surface ofthe membrane Integral proteins penetrate the hydrophobic core Integral proteins that span the membrane arecalled transmembrane proteins The hydrophobic regions of an integral proteinconsist of one or more stretches of nonpolaramino acids, often coiled into alpha helices 2014 Pearson Education, Inc. 21. Six major functions of membrane proteins Transport Enzymatic activity Signal transduction Cell-cell recognition Intercellular joining Attachment to the cytoskeleton and extracellularmatrix (ECM) 2014 Pearson Education, Inc. 22. Figure 7.7(a) Transport (b) Enzymatic 2014 Pearson Education, Inc.activity(c) Signaltransduction(d) Cell-cellrecognition(e) Intercellularjoining(f) Attachment tothe cytoskeletonand extracellularmatrix (ECM)EnzymesATPSignalingmoleculeReceptorSignal transductionGlyco-protein 23. Figure 7.7a(a) Transport 2014 Pearson Education, Inc.EnzymesATPSignalingmoleculeReceptorSignal transduction(b) Enzymaticactivity(c) Signaltransduction 24. Figure 7.7b(d) Cell-cellrecognition 2014 Pearson Education, Inc.(e) Intercellularjoining(f) Attachment tothe cytoskeletonand extracellularmatrix (ECM)Glyco-protein 25. HIV must bind to the immune cell surface proteinCD4 and a co-receptor CCR5 in order to infecta cell HIV cannot enter the cells of resistant individualsthat lack CCR5 2014 Pearson Education, Inc. 26. Figure 7.8 2014 Pearson Education, Inc.HIVReceptor(CD4)Co-receptor(CCR5)Receptor (CD4)but no CCR5 Plasmamembrane(a) (b) 27. The Role of Membrane Carbohydrates in Cell-Cell Recognition Cells recognize each other by binding tomolecules, often containing carbohydrates, on theextracellular surface of the plasma membrane Membrane carbohydrates may be covalentlybonded to lipids (forming glycolipids) or morecommonly to proteins (forming glycoproteins) Carbohydrates on the external side of the plasmamembrane vary among species, individuals, andeven cell types in an individual 2014 Pearson Education, Inc. 28. Synthesis and Sidedness of Membranes Membranes have distinct inside and outside faces The asymmetrical distribution of proteins, lipids,and associated carbohydrates in the plasmamembrane is determined when the membrane isbuilt by the ER and Golgi apparatus 2014 Pearson Education, Inc. 29. 2014 Pearson Education, Inc.TransmembraneglycoproteinsFigure 7.9SecretoryproteinGolgiapparatusVesicleAttachedcarbohydrateERlumenGlycolipidTransmembraneglycoproteinPlasma membrane:Cytoplasmic faceExtracellular faceMembraneglycolipidSecretedprotein 30. Concept 7.2: Membrane structure results inselective permeability A cell must exchange materials with itssurroundings, a process controlled by theplasma membrane Plasma membranes are selectively permeable,regulating the cells molecular traffic 2014 Pearson Education, Inc. 31. The Permeability of the Lipid Bilayer Hydrophobic (nonpolar) molecules, such ashydrocarbons, can dissolve in the lipid bilayer andpass through the membrane rapidly Hydrophilic molecules including ions and polarmolecules do not cross the membrane easily 2014 Pearson Education, Inc. 32. Transport Proteins Transport proteins allow passage of hydrophilicsubstances across the membrane Some transport proteins, called channel proteins,have a hydrophilic channel that certain moleculesor ions can use as a tunnel Channel proteins called aquaporins facilitate thepassage of water 2014 Pearson Education, Inc. 33. Other transport proteins, called carrier proteins,bind to molecules and change shape to shuttlethem across the membrane A transport protein is specific for the substanceit moves 2014 Pearson Education, Inc. 34. Concept 7.3: Passive transport is diffusion of asubstance across a membrane with no energyinvestment Diffusion is the tendency for molecules to spreadout evenly into the available space Although each molecule moves randomly,diffusion of a population of molecules may bedirectional At dynamic equilibrium, as many molecules crossthe membrane in one direction as in the other 2014 Pearson Education, Inc. 35. Figure 7.10Molecules of dye Membrane (cross section)Net diffusion Net diffusionNet diffusion Net diffusionNet diffusion Net diffusion 2014 Pearson Education, Inc.WATER(a) Diffusion of one solute(b) Diffusion of two solutesEquilibriumEquilibriumEquilibrium 36. Animation: Diffusion 2014 Pearson Education, Inc. 37. Animation: Membrane Selectivity 2014 Pearson Education, Inc. 38. Substances diffuse down their concentrationgradient, the region along which the density of achemical substance increases or decreases No work must be done to move substances downthe concentration gradient The diffusion of a substance across a biologicalmembrane is passive transport because noenergy is expended by the cell to make it happen 2014 Pearson Education, Inc. 39. Effects of Osmosis on Water Balance Osmosis is the diffusion of water across aselectively permeable membrane Water diffuses across a membrane from theregion of lower solute concentration to the regionof higher solute concentration until the soluteconcentration is equal on both sides 2014 Pearson Education, Inc. 40. Figure 7.11Lower concentrationof solute (sugar) 2014 Pearson Education, Inc.Higher concentrationof soluteMore similarconcentrations of soluteSugarmoleculeH2OSelectivelypermeablemembraneOsmosis 41. Figure 7.11a 2014 Pearson Education, Inc.SelectivelypermeablemembraneOsmosisWatermolecules canpass throughpores, but sugarmoleculescannot.Water moleculescluster aroundsugar molecules.This side hasmore solutemolecules,fewer freewater molecules.This side hasfewer solutemolecules,more freewater molecules. 42. Animation: Osmosis 2014 Pearson Education, Inc. 43. Water Balance of Cells Without Cell Walls Tonicity is the ability of a surrounding solution tocause a cell to gain or lose water Isotonic solution: Solute concentration is thesame as that inside the cell; no net watermovement across the plasma membrane Hypertonic solution: Solute concentration isgreater than that inside the cell; cell loses water Hypotonic solution: Solute concentration is lessthan that inside the cell; cell gains water 2014 Pearson Education, Inc. 44. Figure 7.12 2014 Pearson Education, Inc.Hypotonic Isotonic HypertonicH2OH2OLysed Normal ShriveledPlasmamembraneCellwallTurgid (normal) Flaccid Plasmolyzed(b) Plant cell (a) Animal cellPlasmamembraneH2H O 2OH2H O 2OH2H O 2O 45. Hypertonic or hypotonic environments createosmotic problems for organisms Osmoregulation, the control of soluteconcentrations and water balance, is a necessaryadaptation for life in such environments The protist Paramecium, which is hypertonic to itspond water environment, has a contractile vacuolethat acts as a pump 2014 Pearson Education, Inc. 46. Figure 7.13 2014 Pearson Education, Inc.Contractile vacuole50 m 47. Water Balance of Cells with Cell Walls Cell walls help maintain water balance A plant cell in a hypotonic solution swells until thewall opposes uptake; the cell is now turgid (firm) If a plant cell and its surroundings are isotonic,there is no net movement of water into the cell;the cell becomes flaccid (limp) 2014 Pearson Education, Inc. 48. In a hypertonic environment, plant cells lose water The membrane pulls away from the cell wallcausing the plant to wilt, a usually lethal effectcalled plasmolysis 2014 Pearson Education, Inc. 49. Facilitated Diffusion: Passive Transport Aidedby Proteins In facilitated diffusion, transport proteins speedthe passive movement of molecules across theplasma membrane Transport proteins include channel proteins andcarrier proteins 2014 Pearson Education, Inc. 50. Channel proteins provide corridors that allow aspecific molecule or ion to cross the membrane Aquaporins facilitate the diffusion of water Ion channels facilitate the diffusion of ions Some ion channels, called gated channels, openor close in response to a stimulus 2014 Pearson Education, Inc. 51. Figure 7.14Channel protein SoluteCarrier protein 2014 Pearson Education, Inc.(a) A channelprotein(b) A carrier proteinSoluteEXTRACELLULARFLUIDCYTOPLASM 52. Carrier proteins undergo a subtle change in shapethat translocates the solute-binding site across themembrane 2014 Pearson Education, Inc. 53. Concept 7.4: Active transport uses energy tomove solutes against their gradients Facilitated diffusion is still passive because thesolute moves down its concentration gradient, andthe transport requires no energy Some transport proteins, however, can movesolutes against their concentration gradients 2014 Pearson Education, Inc. 54. The Need for Energy in Active Transport Active transport moves substances against theirconcentration gradients Active transport requires energy, usually in theform of ATP Active transport is performed by specific proteinsembedded in the membranes 2014 Pearson Education, Inc. 55. Active transport allows cells to maintainconcentration gradients that differ from theirsurroundings The sodium-potassium pump is one type ofactive transport system 2014 Pearson Education, Inc. 56. Figure 7.15 2014 Pearson Education, Inc.EXTRACELLULARFLUID[Na+] high[K+] lowCYTOPLASM1 25643[Na+] low[K+] highNa+K+K+K+K+K+K+Na+Na+Na+Na+Na+Na+Na+Na+ATPPADPPPiP 57. Figure 7.15aCYTOPLASM 2014 Pearson Education, Inc.2[Na+] high[K+] low[Na+] low[K+] highNa+Na+Na+Na+Na+Na+ATPPADPEXTRACELLULARFLUID1 Cytoplasmic Na+binds to the sodium-potassiumpump. Theaffinity for Na+ is highwhen the proteinhas this shape.Na+ bindingstimulatesphosphorylationby ATP. 58. Figure 7.15b3 Phosphorylation 4leads to a change inprotein shape, reducingits affinity for Na+, whichis released outside. 2014 Pearson Education, Inc.The new shape has ahigh affinity for K+, whichbinds on the extracellularside and triggers releaseof the phosphate group.Na+Na+PNa+K+K+PP i 59. Figure 7.15c5 2014 Pearson Education, Inc.6 K+ is released;affinity for Na+ ishigh again, and thecycle repeats.Loss of thephosphate grouprestores the proteinsoriginal shape, whichhas a lower affinityfor K+. 60. Animation: Active Transport 2014 Pearson Education, Inc. 61. Figure 7.16Passive transport Active transport 2014 Pearson Education, Inc.ATPDiffusion Facilitated diffusion 62. BioFlix: Membrane Transport 2014 Pearson Education, Inc. 63. How Ion Pumps Maintain Membrane Potential Membrane potential is the voltage differenceacross a membrane Voltage is created by differences in the distributionof positive and negative ions across a membrane 2014 Pearson Education, Inc. 64. Two combined forces, collectively called theelectrochemical gradient, drive the diffusion ofions across a membrane A chemical force (the ions concentration gradient) An electrical force (the effect of the membranepotential on the ions movement) 2014 Pearson Education, Inc. 65. An electrogenic pump is a transport protein thatgenerates voltage across a membrane The sodium-potassium pump is the majorelectrogenic pump of animal cells The main electrogenic pump of plants, fungi, andbacteria is a proton pump Electrogenic pumps help store energy that can beused for cellular work 2014 Pearson Education, Inc. 66. Figure 7.17 2014 Pearson Education, Inc.EXTRACELLULARFLUIDATPH+CYTOPLASMH+H+H+H+H+Proton pump++++ 67. Cotransport: Coupled Transport by a MembraneProtein Cotransport occurs when active transport of asolute indirectly drives transport of othersubstances Plants commonly use the gradient of hydrogenions generated by proton pumps to drive activetransport of nutrients into the cell 2014 Pearson Education, Inc. 68. Figure 7.18SucroseATP 2014 Pearson Education, Inc.H+H+H+H+H+Proton pump++++Sucrose-H+cotransporterH+H+H+H+SucroseDiffusion of H+ 69. Concept 7.5: Bulk transport across theplasma membrane occurs by exocytosis andendocytosis Small molecules and water enter or leave the cellthrough the lipid bilayer or via transport proteins Large molecules, such as polysaccharides andproteins, cross the membrane in bulk via vesicles Bulk transport requires energy 2014 Pearson Education, Inc. 70. Exocytosis In exocytosis, transport vesicles migrate to themembrane, fuse with it, and release their contentsoutside the cell Many secretory cells use exocytosis to exporttheir products 2014 Pearson Education, Inc. 71. Endocytosis In endocytosis, the cell takes in macromoleculesby forming vesicles from the plasma membrane Endocytosis is a reversal of exocytosis, involvingdifferent proteins There are three types of endocytosis Phagocytosis (cellular eating) Pinocytosis (cellular drinking) Receptor-mediated endocytosis 2014 Pearson Education, Inc. 72. Figure 7.19Phagocytosis PinocytosisEXTRACELLULARFLUID 2014 Pearson Education, Inc.Receptor-MediatedEndocytosisSolutesPseudopodiumFoodorotherparticleFoodvacuoleCYTOPLASMPlasmamembraneCoatedpitCoatedvesicleCoatproteinReceptor 73. Animation: Exocytosis 2014 Pearson Education, Inc. 74. Animation: Exocytosis and EndocytosisIntroduction 2014 Pearson Education, Inc. 75. Figure 7.19a 2014 Pearson Education, Inc.PhagocytosisEXTRACELLULARFLUIDSolutesPseudopodiumFoodorotherparticleFoodvacuoleCYTOPLASMPseudopodiumof amoebaBacteriumFood vacuoleAn amoeba engulfing abacterium via phago-cytosis(TEM)1 m 76. Animation: Phagocytosis 2014 Pearson Education, Inc. 77. Animation: Pinocytosis 2014 Pearson Education, Inc. 78. Animation: Receptor-Mediated Endocytosis 2014 Pearson Education, Inc. 79. In phagocytosis a cell engulfs a particle in avacuole The vacuole fuses with a lysosome to digest theparticle 2014 Pearson Education, Inc. 80. In pinocytosis, molecules dissolved in dropletsare taken up when extracellular fluid is gulpedinto tiny vesicles 2014 Pearson Education, Inc. 81. In receptor-mediated endocytosis, binding ofligands to receptors triggers vesicle formation A ligand is any molecule that binds specificallyto a receptor site of another molecule 2014 Pearson Education, Inc.