Download - Membranes Chapter 05. Membranes 2Outline Membrane Models Fluid-Mosaic Plasma Membrane Structure and Function Phospholipids Proteins Plasma Membrane.

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



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


Extracellular Matrix


Plasmodesmata


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


MembranesEnding Slide Chapter 05