08 ge lecture presentation

Slide 1

Cell Membranes

BIOLOGYA Global Approach

Campbell Reece Urry Cain Wasserman Minorsky Jackson 2015 Pearson Education LtdTENTH EDITION

Global Edition

Lecture Presentation by Nicole Tunbridge andKathleen Fitzpatrick8

2015 Pearson Education Ltd

Life at the EdgeThe plasma membrane is the boundary that separates the living cell from its surroundingsThe plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others


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Figure 8.1

2015 Pearson Education Ltd3Figure 8.1 How do cell membrane proteins help regulate chemical traffic?

Figure 8.1a

2015 Pearson Education Ltd4Figure 8.1a How do cell membrane proteins help regulate chemical traffic? (part 1: ion channel)

Video: Structure of the Cell Membrane


Video: Water Movement Through an Aquaporin


Concept 8.1: Cellular membranes are fluid mosaics of lipids and proteinsPhospholipids are the most abundant lipid in the plasma membranePhospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regionsA phospholipid bilayer can exist as a stable boundary between two aqueous compartments


Figure 8.2

Hydrophilic headHydrophobic tailWATERWATER

2015 Pearson Education Ltd8Figure 8.2 Phospholipid bilayer (cross section)

The fluid mosaic model states that a membrane is a fluid structure with a mosaic of various proteins embedded in itProteins are not randomly distributed in the membrane


Figure 8.3Glyco-protein

CarbohydrateGlycolipidEXTRACELLULARSIDE OFMEMBRANEMicrofilamentsof cytoskeletonFibers of extra-cellular matrix (ECM)CholesterolPeripheralproteinsIntegralproteinCYTOPLASMICSIDE OFMEMBRANE

2015 Pearson Education Ltd10Figure 8.3 Updated model of an animal cells plasma membrane (cutaway view)

Figure 8.3aGlyco-protein

CarbohydrateMicrofilamentsof cytoskeletonFibers of extra-cellular matrix (ECM)Cholesterol

2015 Pearson Education Ltd11Figure 8.3a Updated model of an animal cells plasma membrane (cutaway view) (part 1)

Figure 8.3b

GlycolipidEXTRACELLULARSIDE OFMEMBRANEIntegralproteinCYTOPLASMICSIDE OFMEMBRANEPeripheralproteins

2015 Pearson Education Ltd12Figure 8.3b Updated model of an animal cells plasma membrane (cutaway view) (part 2)

The Fluidity of MembranesPhospholipids in the plasma membrane can move within the bilayerMost of the lipids, and some proteins, drift laterallyRarely, a lipid may flip-flop transversely acrossthe membrane


Figure 8.4-1Membrane proteinsMouse cellHuman cell

2015 Pearson Education Ltd14Figure 8.4-1 Inquiry: Do membrane proteins move? (step 1)

Figure 8.4-2

Membrane proteinsMouse cellHuman cellHybrid cell


Figure 8.4-3

Membrane proteinsMouse cellHuman cellHybrid cellMixed proteinsafter 1 hour


As temperatures cool, membranes switch from a fluid state to a solid stateThe temperature at which a membrane solidifies depends on the types of lipidsMembranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acidsMembranes must be fluid to work properly; they are usually about as fluid as salad oil


The steroid cholesterol has different effects on membrane fluidity at different temperaturesAt warm temperatures (such as 37C), cholesterol restrains movement of phospholipidsAt cool temperatures, it maintains fluidity by preventing tight packing


Figure 8.5FluidViscousUnsaturated tailsprevent packing.Saturated tails packtogether.CholesterolCholesterol reducesmembrane fluidity atmoderate temperatures,but at low temperatureshinders solidification.(a) Unsaturated versus saturated hydrocarbon tails(b) Cholesterol within the animal cell membrane

2015 Pearson Education Ltd19Figure 8.5 Factors that affect membrane fluidity

Evolution of Differences in Membrane Lipid CompositionVariations in lipid composition of cell membranes of many species appear to be adaptations to specific environmental conditionsAbility to change the lipid compositions in response to temperature changes has evolved in organisms that live where temperatures vary


Membrane Proteins and Their FunctionsA membrane is a collage of different proteins, often grouped together, embedded in the fluid matrix of the lipid bilayerProteins determine most of the membranes specific functions


Peripheral proteins are bound to the surface of the membraneIntegral proteins penetrate the hydrophobic core Integral proteins that span the membrane are called transmembrane proteinsThe hydrophobic regions of an integral protein consist of one or more stretches of nonpolaramino acids, often coiled into alpha helices


Figure 8.6

N-terminusC-terminus helixEXTRACELLULARSIDECYTOPLASMICSIDE

2015 Pearson Education Ltd23Figure 8.6 The structure of a transmembrane protein

Six major functions of membrane proteinsTransportEnzymatic activitySignal transductionCell-cell recognitionIntercellular joiningAttachment to the cytoskeleton and extracellular matrix (ECM)


Figure 8.7

(a) Transport(b) Enzymatic activity(c) Signaltransduction(d) Cell-cell recognition(e)Intercellular joining(f)Attachment tothe cytoskeletonand extracellularmatrix (ECM)EnzymesATPSignalingmoleculeReceptorSignal transductionGlyco-protein

2015 Pearson Education Ltd25Figure 8.7 Some functions of membrane proteins

Figure 8.7a

(a) TransportEnzymesATPReceptorSignal transduction(b)Enzymaticactivity(c) SignaltransductionSignalingmolecule

2015 Pearson Education Ltd26Figure 8.7a Some functions of membrane proteins (part 1: transport, enzymatic activity, and signal transduction)

Figure 8.7b

(d) Cell-cellrecognition(e) Intercellularjoining(f)Attachment tothe cytoskeletonand extracellularmatrix (ECM)Glyco-protein

2015 Pearson Education Ltd27Figure 8.7b Some functions of membrane proteins (part 2: cell-cell recognition, intercellular joining, and attachment to the cytoskeleton and ECM)

HIV must bind to the immune cell surface protein CD4 and a co-receptor CCR5 in order to infecta cell HIV cannot enter the cells of resistant individuals that lack CCR5


Figure 8.8

HIVReceptor(CD4)Co-receptor(CCR5)Receptor (CD4)but no CCR5Plasmamembrane(a)(b)

2015 Pearson Education Ltd29Figure 8.8 The genetic basis for HIV resistance

The Role of Membrane Carbohydrates in Cell-Cell RecognitionCells recognize each other by binding to molecules, often containing carbohydrates, on the extracellular surface of the plasma membraneMembrane carbohydrates may be covalently bonded to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins)Carbohydrates on the external side of the plasma membrane vary among species, individuals, and even cell types in an individual


Synthesis and Sidedness of MembranesMembranes have distinct inside and outside facesThe asymmetrical distribution of proteins, lipids, and associated carbohydrates in the plasma membrane is determined when the membrane is built by the ER and Golgi apparatus


TransmembraneglycoproteinsFigure 8.9SecretoryproteinGolgiapparatusVesicleAttachedcarbohydrateER lumenGlycolipidTransmembraneglycoproteinPlasma membrane: Cytoplasmic face Extracellular faceMembraneglycolipidSecretedprotein

2015 Pearson Education Ltd32Figure 8.9 Synthesis of membrane components and their orientation in the membrane

Concept 8.2: Membrane structure results in selective permeabilityA cell must exchange materials with its surroundings, a process controlled by theplasma membranePlasma membranes are selectively permeable, regulating the cells molecular traffic


The Permeability of the Lipid BilayerHydrophobic (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidlyHydrophilic molecules including ions and polar molecules do not cross the membrane easily


Transport ProteinsTransport proteins allow passage of hydrophilic substances across the membraneSome transport proteins, called channel proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnelChannel proteins called aquaporins facilitate the passage of water


Other transport proteins, called carrier proteins, bind to molecules and change shape to shuttle them across the membraneA transport protein is specific for the substanceit moves


Concept 8.3: Passive transport is diffusion of a substance across a membrane with no energy investmentDiffusion is the tendency for molecules to spread out evenly into the available spaceAlthough each molecule moves randomly, diffusion of a population of molecules may be directionalAt dynamic equilibrium, as many molecules cross the membrane in one direction as in the other


Figure 8.10

Molecules of dyeMembrane (cross section)WATER(a) Diffusion of one solute(b) Diffusion of two solutesNet diffusionNet diffusionNet diffusionNet diffusionNet diffusionNet diffusionEquilibriumEquilibriumEquilibrium

2015 Pearson Education Ltd38Figure 8.10 The diffusion of solutes across a synthetic membrane

Animation: Diffusion


Animation: Membrane Selectivity


Substances diffuse down their concentration gradient, the region along which the density of a chemical substance increases or decreasesNo work must be done to move substances down the concentration gradientThe diffusion of a substance across a biological membrane is passive transport because no energy is expended by the cell to make it happen


Effects of Osmosis on Water BalanceOsmosis is the diffusion of water across a selectively permeable membraneWater diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration until the solute concentration is equal on both sides


Figure 8.11

Lower concentrationof solute (sugar)Higher concentrationof soluteMore similarconcentrations of soluteSugarmoleculeH2OSelectivelypermeablemembraneOsmosis

2015 Pearson Education Ltd43Figure 8.11 Osmosis

Figure 8.11a

SelectivelypermeablemembraneOsmosisWatermolecules canpass throughpores, but sugarmoleculescannot.Water moleculescluster aroundsugar molecules.This side hasmore solutemolecules,fewer freewater molecules.This side hasfewer solutemolecules,more freewater molecules.

2015 Pearson Education Ltd44Figure 8.11a Osmosis (part 1: detail of membrane)

Animation: Osmosis


Water Balance of Cells Without Cell WallsTonicity is the ability of a surrounding solution to cause a cell to gain or lose waterIsotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membraneHypertonic solution: Solute concentration is greater than that inside the cell; cell loses waterHypotonic solution: Solute concentration is less than that inside the cell; cell gains water


Figure 8.12

HypotonicIsotonicHypertonicH2OLysedNormalShriveledPlasmamembraneCellwallTurgid (normal)FlaccidPlasmolyzed(a) Animal cell(b) Plant cellPlasmamembraneH2OH2OH2OH2OH2OH2OH2O

2015 Pearson Education Ltd47Figure 8.12 The water balance of living cells

Video: Plasmolysis


Video: Turgid Elodea


Hypertonic or hypotonic environments create osmotic problems for organismsOsmoregulation, the control of solute concentrations and water balance, is a necessary adaptation for life in such environmentsThe protist Paramecium, which is hypertonic to its pond water environment, has a contractile vacuole that acts as a pump


Figure 8.13

Contractile vacuole50 m

2015 Pearson Education Ltd51Figure 8.13 The contractile vacuole of Paramecium caudatum

Video: Chlamydomonas


Video: Paramecium Vacuole


Water Balance of Cells with Cell WallsCell walls help maintain water balanceA plant cell in a hypotonic solution swells until the wall 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)


In a hypertonic environment, plant cells lose water The membrane pulls away from the cell wall causing the plant to wilt, a usually lethal effect called plasmolysis


Facilitated Diffusion: Passive Transport Aided by ProteinsIn facilitated diffusion, transport proteins speed the passive movement of molecules across the plasma membraneTransport proteins include channel proteins and carrier proteins


Channel proteins provide corridors that allow a specific molecule or ion to cross the membraneAquaporins facilitate the diffusion of waterIon channels facilitate the diffusion of ions Some ion channels, called gated channels, open or close in response to a stimulus


Figure 8.14

(a) A channel protein(b) A carrier proteinCarrier proteinChannel proteinSoluteSoluteEXTRACELLULARFLUIDCYTOPLASM

2015 Pearson Education Ltd58Figure 8.14 Two types of transport proteins that carry out facilitated diffusion

Carrier proteins undergo a subtle change in shape that translocates the solute-binding site across the membrane


Concept 8.4: Active transport uses energy to move solutes against their gradientsFacilitated diffusion is still passive because the solute moves down its concentration gradient, and the transport requires no energySome transport proteins, however, can move solutes against their concentration gradients


The Need for Energy in Active TransportActive transport moves substances against their concentration gradientsActive transport requires energy, usually in the form of ATPActive transport is performed by specific proteins embedded in the membranes


Active transport allows cells to maintain concentration gradients that differ from their surroundingsThe sodium-potassium pump is one type of active transport system


Figure 8.15

EXTRACELLULARFLUIDCYTOPLASM

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3[Na+] low[K+] high[Na+] high[K+] lowNa+K+K+K+K+K+K+Na+Na+Na+Na+Na+Na+Na+Na+ATPADPPPPiP

2015 Pearson Education Ltd63Figure 8.15 The sodium-potassium pump: a specific case of active transport

Figure 8.15aCYTOPLASM

2[Na+] low[K+] high[Na+] high[K+] lowNa+Na+Na+Na+Na+Na+ATPADPPEXTRACELLULARFLUID

1 Cytoplasmic Na+binds to the sodium-potassium pump. Theaffinity for Na+ is highwhen the proteinhas this shape. Na+ bindingstimulatesphosphorylationby ATP.

2015 Pearson Education Ltd64Figure 8.15a The sodium-potassium pump: a specific case of active transport (part 1: Na+ binding)

Figure 8.15b

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3 Phosphorylationleads to a change inprotein shape, reducingits affinity for Na+, whichis released outside. The new shape has ahigh affinity for K+, whichbinds on the extracellularside and triggers releaseof the phosphate group.Na+Na+PNa+K+K+PPi

2015 Pearson Education Ltd65Figure 8.15b The sodium-potassium pump: a specific case of active transport (part 2: K+ binding)

Figure 8.15c

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K+ is released;affinity for Na+ ishigh again, and thecycle repeats. Loss of thephosphate grouprestores the proteinsoriginal shape, whichhas a lower affinityfor K+.5K+K+K+K+

2015 Pearson Education Ltd66Figure 8.15c The sodium-potassium pump: a specific case of active transport (part 3: K+ release)

Animation: Active Transport


Video: Na+/K+ ATPase Cycle


Figure 8.16

ATPPassive transportActive transportDiffusionFacilitated diffusion

2015 Pearson Education Ltd69Figure 8.16 Review: passive and active transport

BioFlix: Membrane Transport


How Ion Pumps Maintain Membrane PotentialMembrane potential is the voltage difference across a membraneVoltage is created by differences in the distribution of positive and negative ions across a membrane


Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membraneA chemical force (the ions concentration gradient)An electrical force (the effect of the membrane potential on the ions movement)


An electrogenic pump is a transport protein that generates voltage across a membraneThe sodium-potassium pump is the major electrogenic pump of animal cellsThe main electrogenic pump of plants, fungi, and bacteria is a proton pumpElectrogenic pumps help store energy that can be used for cellular work


Figure 8.17

EXTRACELLULARFLUIDATPCYTOPLASMH+H+H+H+H+H+Proton pump++++

2015 Pearson Education Ltd74Figure 8.17 A proton pump

Cotransport: Coupled Transport by a Membrane ProteinCotransport occurs when active transport of a solute indirectly drives transport of other substances Plants commonly use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell


Figure 8.18

SucroseATPH+H+H+H+H+Proton pump++++Sucrose-H+cotransporterH+H+H+H+SucroseDiffusion of H+

2015 Pearson Education Ltd76Figure 8.18 Cotransport: active transport driven by a concentration gradient

Concept 8.5: Bulk transport across theplasma membrane occurs by exocytosis and endocytosisSmall molecules and water enter or leave the cell through the lipid bilayer or via transport proteinsLarge molecules, such as polysaccharides and proteins, cross the membrane in bulk via vesiclesBulk transport requires energy


ExocytosisIn exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents outside the cellMany secretory cells use exocytosis to exporttheir products


EndocytosisIn endocytosis, the cell takes in macromolecules by forming vesicles from the plasma membraneEndocytosis is a reversal of exocytosis, involving different proteinsThere are three types of endocytosisPhagocytosis (cellular eating)Pinocytosis (cellular drinking)Receptor-mediated endocytosis


Figure 8.19

PhagocytosisPinocytosisReceptor-MediatedEndocytosisSolutesPseudopodiumFoodorotherparticleFoodvacuoleCYTOPLASMEXTRACELLULARFLUIDPlasmamembraneCoated pitCoated vesicleCoatproteinReceptor

2015 Pearson Education Ltd80Figure 8.19 Exploring endocytosis in animal cells

Animation: Exocytosis


Animation: Exocytosis and Endocytosis Introduction


Figure 8.19a

PhagocytosisSolutesPseudopodiumFoodorotherparticleFoodvacuoleCYTOPLASMEXTRACELLULARFLUIDPseudopodiumof amoebaBacteriumFood vacuoleAn amoeba engulfing abacterium via phago-cytosis (TEM)1 m

2015 Pearson Education Ltd83Figure 8.19a Exploring endocytosis in animal cells (part 1: phagocytosis)

Animation: Phagocytosis


Video: Phagocytosis in Action


Figure 8.19aa

Pseudopodiumof amoebaBacteriumFood vacuoleAn amoeba engulfing abacterium via phago-cytosis (TEM)1 m

2015 Pearson Education Ltd86Figure 8.19aa Exploring endocytosis in animal cells (part 1a: phagocytosis TEM)

Figure 8.19b

PinocytosisPlasmamembraneCoated pitCoated vesicleCoatproteinPinocytotic vesiclesforming (TEMs)0.25 m

2015 Pearson Education Ltd87Figure 8.19b Exploring endocytosis in animal cells (part 2: pinocytosis)

Animation: Pinocytosis


Figure 8.19ba

Pinocytotic vesiclesforming (TEMs)0.25 m

2015 Pearson Education Ltd89Figure 8.19ba Exploring endocytosis in animal cells (part 2a: pinocytosis TEMs)

Figure 8.19c

Receptor-MediatedEndocytosisReceptorCoatproteinPlasmamembraneTop: A coated pit.Bottom: A coated vesicleforming during receptor-mediated endocytosis (TEMs)0.25 m

2015 Pearson Education Ltd90Figure 8.19c Exploring endocytosis in animal cells (part 3: receptor-mediated endocytosis)

Animation: Receptor-Mediated Endocytosis


Figure 8.19ca

CoatproteinPlasmamembraneTop: A coated pit.Bottom: A coated vesicleforming during receptor-mediated endocytosis (TEMs)0.25 m

2015 Pearson Education Ltd92Figure 8.19ca Exploring endocytosis in animal cells (part 3a: receptor-mediated endocytosis TEMs)

In phagocytosis a cell engulfs a particle in a vacuoleThe vacuole fuses with a lysosome to digest the particle


In pinocytosis, molecules dissolved in droplets are taken up when extracellular fluid is gulped into tiny vesicles


In receptor-mediated endocytosis, binding of ligands to receptors triggers vesicle formationA ligand is any molecule that binds specificallyto a receptor site of another molecule


Figure 8.UN01

Glucose Uptake Over Time in Guinea Pig Red Blood Cells15-day-old guinea pig1-month-old guinea pigIncubation time (min)Concentration ofradioactive glucose (mM)1008060402000 10 20 30 40 50 60

2015 Pearson Education Ltd96Figure 8.UN01 Skills exercise: interpreting a scatter plot with two sets of data

Figure 8.UN02

ChannelproteinCarrierproteinPassive transport:Facilitated diffusion

2015 Pearson Education Ltd97Figure 8.UN02 Summary of key concepts: facilitated diffusion

Figure 8.UN03

Active transportATP

2015 Pearson Education Ltd98Figure 8.UN03 Summary of key concepts: active transport

Figure 8.UN04

0.03 M sucrose0.02 M glucoseCell0.01 M sucrose0.01 M glucose0.01 M fructoseEnvironment

2015 Pearson Education Ltd99Figure 8.UN04 Test your understanding, question 6 (diffusion)

Figure 8.UN05

2015 Pearson Education Ltd100Figure 8.UN05 Test your understanding, question 11 (water balance)

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