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Chapter 5
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MembranesChapter 05
2MembranesMembranes
OutlineOutline
Membrane ModelsMembrane ModelsFluid-MosaicFluid-Mosaic
Plasma Membrane Structure and FunctionPlasma Membrane Structure and FunctionPhospholipidsPhospholipidsProteinsProteins
Plasma Membrane PermeabilityPlasma Membrane PermeabilityDiffusionDiffusionOsmosisOsmosisTransport Via Carrier ProteinsTransport Via Carrier Proteins
Cell Surface ModificationsCell Surface Modifications
3MembranesMembranesStructure and Function:Structure and Function:The Phospholipid BilayerThe Phospholipid Bilayer
The plasma membrane is common to all cellsThe plasma membrane is common to all cellsSeparates:Separates:
Internal living cytoplasmic fromInternal living cytoplasmic fromExternal environment of cellExternal environment of cell
Phospholipid bilayerPhospholipid bilayer::External surface lined with hydrophilic polar External surface lined with hydrophilic polar headsheads
Cytoplasmic surface lined with hydrophilic Cytoplasmic surface lined with hydrophilic polar headspolar heads
Nonpolar, hydrophobic, fatty-acid tails Nonpolar, hydrophobic, fatty-acid tails sandwiched in betweensandwiched in between
4Unit Membrane
5MembranesMembranes
Membrane ModelsMembrane Models
Fluid-Mosaic ModelFluid-Mosaic ModelThree components:Three components:
Basic membrane referred to as Basic membrane referred to as phospholipid phospholipid bilayerbilayer
PProtein moleculesrotein molecules Float around like icebergs on a seaFloat around like icebergs on a seaMembrane proteins may be Membrane proteins may be peripheralperipheral or or integralintegral Peripheral proteinsPeripheral proteins are found are found onon the inner the inner
membrane surfacemembrane surface Integral proteinsIntegral proteins are partially or wholly embedded are partially or wholly embedded
((transmembranetransmembrane) in the membrane) in the membrane Some have carbohydrate chains attachedSome have carbohydrate chains attached
CholesterolCholesterol
6Membrane Models:Unit Membrane vs. Fluid Mosaic
Model
7The Fluid Mosaic Model
8Phospholipid & CholesterolMolecules
9Transmembrane Proteins
10Lateral Migration of
Membrane Proteins
11MembranesMembranes
Functions of Membrane ProteinsFunctions of Membrane Proteins
Channel ProteinsChannel Proteins:: TubularTubular AllowAllow passage of molecules through membrane passage of molecules through membrane
Carrier ProteinsCarrier Proteins:: Combine with substance to be transportedCombine with substance to be transported Assist passage of molecules through membraneAssist passage of molecules through membrane
Cell Recognition ProteinsCell Recognition Proteins:: Provides unique chemical ID for cellsProvides unique chemical ID for cells Help body recognize foreign substancesHelp body recognize foreign substances
Receptor ProteinsReceptor Proteins:: Binds with messenger moleculeBinds with messenger molecule Causes cell to respond to messageCauses cell to respond to message
Enzymatic Enzymatic Proteins:Proteins: CarryCarry out metabolic reactions directly out metabolic reactions directly
12Membrane Protein Diversity
13MembranesMembranesTypes of Transport:Types of Transport:Active vs. PassiveActive vs. Passive
Plasma membrane is Plasma membrane is differentially differentially ((selectivelyselectively)) permeable permeable Allows some material to passAllows some material to pass Inhibits passage of other materialsInhibits passage of other materials
Passive TransportPassive Transport::NoNo ATP requirement ATP requirementMolecules follow Molecules follow concentration gradientconcentration gradient
Active TransportActive TransportRequires carrier proteinRequires carrier proteinRequires energy in form of ATPRequires energy in form of ATP
14Types of Membrane Transport:Overview
15MembranesMembranesTypes of Transport:Types of Transport:DiffusionDiffusion
A A solutionsolution consists of: consists of:A A solventsolvent (liquid) , and (liquid) , andA A solutesolute (dissolved solid) (dissolved solid)
DiffusionDiffusionNet movement of solute molecules down a Net movement of solute molecules down a concentration gradientconcentration gradient
Molecules both ways along gradientMolecules both ways along gradientMore move from high to low concentration More move from high to low concentration than vice versathan vice versa
EquilibriumEquilibrium::When NET change stopsWhen NET change stops Solute concentration uniform – no gradientSolute concentration uniform – no gradient
16Types of Membrane Transport:Diffusion
17Types of Membrane Transport:Diffusion Across Lung
18MembranesMembranesTypes of Transport:Types of Transport:OsmosisOsmosis
OsmosisOsmosis:: Special case of diffusionSpecial case of diffusion Focuses on solvent (water) movement rather than Focuses on solvent (water) movement rather than
solutesolute Diffusion of water across a differentially (selectively) Diffusion of water across a differentially (selectively)
permeable membranepermeable membrane Solute concentration on one side high, but water Solute concentration on one side high, but water
concentration lowconcentration low Solute concentration on other side low, but water Solute concentration on other side low, but water
concentration highconcentration high Water diffuses both ways across membrane but Water diffuses both ways across membrane but
solute can’tsolute can’t Net movement of water is toward low water (high Net movement of water is toward low water (high
solute) concentrationsolute) concentrationOsmotic pressureOsmotic pressure is the pressure that develops due is the pressure that develops due
to osmosisto osmosis
19Types of Membrane Transport:Osmosis
20MembranesMembranesTypes of Transport:Types of Transport:OsmosisOsmosis
Isotonic SolutionIsotonic Solution Solute and water concentrations equal on both Solute and water concentrations equal on both sides of membranesides of membrane
Hypotonic SolutionHypotonic Solution Concentration of solute Concentration of solute lowerlower than on other side than on other side Cells placed in a hypotonic solution will swellCells placed in a hypotonic solution will swell May cause cells to break – May cause cells to break – LysisLysis
Hypertonic SolutionHypertonic Solution Concentration of solute Concentration of solute higherhigher than on other side than on other side Cells placed in a hypertonic solution will shrink –Cells placed in a hypertonic solution will shrink –
PlasmolysisPlasmolysis
21Osmotic Effects on Cells
22MembranesMembranesTypes of Transport:Types of Transport:Carrier ProteinsCarrier Proteins
Facilitated TransportFacilitated Transport Small moleculesSmall molecules
Can’t get through membrane lipidsCan’t get through membrane lipids
Combine with carrier proteinsCombine with carrier proteins
FollowFollow concentration gradient concentration gradientActive TransportActive Transport Small moleculesSmall molecules
Move Move againstagainst concentration gradient concentration gradient
Combining with carrier proteinsCombining with carrier proteins
Requires energyRequires energy
23Types of Membrane Transport:Facilitated Transport
24Facilitated Transport:The Sodium-Potassium
Pump
25MembranesMembranesTypes of Transport:Types of Transport:Membrane-Assisted TransportMembrane-Assisted Transport
Macromolecules transported into or out of the Macromolecules transported into or out of the cell inside vesiclescell inside vesiclesExocytosisExocytosis – Vesicles fuse with plasma – Vesicles fuse with plasma membrane and membrane and secretesecrete contents contents
EndocytosisEndocytosis – Cells engulf substances into – Cells engulf substances into pouch which becomes a vesiclepouch which becomes a vesicle PhagocytosisPhagocytosis – Large, solid material into – Large, solid material into vesiclevesicle
PinocytosisPinocytosis – Liquid or small, solid particles go – Liquid or small, solid particles go into vesicleinto vesicle
Receptor-MediatedReceptor-Mediated – Specific form of – Specific form of pinocytosis using a pinocytosis using a coated pitcoated pit
26Membrane-Assisted Transport:Exocytosis
27Membrane-Assisted Transport:Three Types of Endocytosis
28MembranesMembranesCell Surface Modifications:Cell Surface Modifications:JunctionsJunctions
Cell Surfaces in AnimalsCell Surfaces in Animals
Junctions Between CellsJunctions Between Cells
Adhesion JunctionsAdhesion Junctions
Intercellular filaments between cellsIntercellular filaments between cells
Tight JunctionsTight Junctions
Form impermeable barriersForm impermeable barriers
Gap JunctionsGap Junctions
Plasma membrane channels are joined (allows Plasma membrane channels are joined (allows communication)communication)
29Cell-Surface Modifications:
Junctions
30MembranesMembranes
Cell Surface ModificationsCell Surface Modifications
Extracellular MatrixExtracellular MatrixExternal meshwork of polysaccharides and External meshwork of polysaccharides and proteinsproteins
Found in close association with the cell that Found in close association with the cell that produced themproduced them
Plant Plant Cell WallsCell WallsPlants have freely permeable cell wall, with Plants have freely permeable cell wall, with cellulosecellulose as the main component as the main component PlasmodesmataPlasmodesmata penetrate cell wall penetrate cell wall Each contains a strand of cytoplasmEach contains a strand of cytoplasm Allow passage of material between cellsAllow passage of material between cells
31Cell-Surface Modifications:
Extracellular Matrix
32Cell-Surface Modifications:
Plasmodesmata
33MembranesMembranes
ReviewReview
Membrane ModelsMembrane Models
Fluid-MosaicFluid-Mosaic
Plasma Membrane Structure and FunctionPlasma Membrane Structure and Function
Protein FunctionsProtein Functions
Plasma Membrane PermeabilityPlasma Membrane Permeability
DiffusionDiffusion
OsmosisOsmosis
Transport Via Carrier ProteinsTransport Via Carrier Proteins
Cell Surface ModificationsCell Surface Modifications
MembranesEnding Slide Chapter 05