1MembranesMembranes
Ch. 5 Outline - MembranesCh. 5 Outline - Membranes
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
2MembranesMembranesStructure 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 phosphatephosphate heads heads
Cytoplasmic surface lined with hydrophilic Cytoplasmic surface lined with hydrophilic polar polar phosphate phosphate headsheads
Nonpolar, hydrophobic, fatty-acid tails Nonpolar, hydrophobic, fatty-acid tails sandwiched in betweensandwiched in between
3The Fluid Mosaic Model
4MembranesMembranes
Fluid-Mosaic ModelFluid-Mosaic Model
Four components:Four components:Basic membrane referred to as Basic membrane referred to as phospholipid phospholipid bilayerbilayer
Protein moleculesProtein molecules Float around like icebergs on a seaFloat around like icebergs on a sea Membrane proteins may be Membrane proteins may be peripheralperipheral or or integralintegral Peripheral proteinsPeripheral proteins are found are found onon the membrane the membrane
surfacesurface 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 – helps stiffen membrane – helps stiffen membrane
5Transmembrane Proteins
6Phospholipid & CholesterolMolecules
7MembranesMembranes
Fluid-Mosaic ModelFluid-Mosaic Model
Carbohydrate chains:Carbohydrate chains: Give the cell a “sugar coat”, Give the cell a “sugar coat”, glycocalyx.glycocalyx. Protects cellProtects cell Facilitates adhesion between cellsFacilitates adhesion between cells Facilitates reception of signal moleculesFacilitates reception of signal molecules Functions in cell-to-cell recognitionFunctions in cell-to-cell recognition
8The Fluid Mosaic Model
9MembranesMembranes
Fluidity of Plasma MembraneFluidity of Plasma Membrane
Fluidity of membrane is dependent on its lipid Fluidity of membrane is dependent on its lipid components and is critical to proper components and is critical to proper functioning.functioning. Body temperatureBody temperature – consistency of olive oil – consistency of olive oil.. More unsaturated fatsMore unsaturated fats = more fluid membrane = more fluid membrane Fluidity means that cells are Fluidity means that cells are pliable.pliable. Proteins free to “Proteins free to “driftdrift” laterally in phospholipid ” laterally in phospholipid bilayer.bilayer.
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 ProteinsProteins:: CarryCarry out metabolic reactions directly out metabolic reactions directly
12Membrane Protein Diversity
13MembranesMembranes
Permeability of MembranePermeability of Membrane
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 protein or help of vesiclesRequires carrier protein or help of vesiclesRequires 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 move both ways along gradientMolecules move 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:Osmosis – Passive transportOsmosis – Passive transport
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 Solution – normal cell environmentIsotonic Solution – normal cell environment 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 Creates Creates turgor pressureturgor pressure in plant cells in plant cells
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 – Plasmolysis (plants) & crenation (animals)Plasmolysis (plants) & crenation (animals)
21Osmotic Effects on Cells
22MembranesMembranesTypes of Transport:Types of Transport:Carrier ProteinsCarrier Proteins
Facilitated Transport – no cell energy neededFacilitated Transport – no cell energy needed Explains passage of small molecules like Explains passage of small molecules like glucose and amino acids (even though polar)glucose and amino acids (even though polar)
Can’t get through membrane lipidsCan’t get through membrane lipids
Combine with carrier proteinsCombine with carrier proteins
FollowFollow concentration gradient concentration gradientActive Transport – requires extra cell energyActive Transport – requires extra cell energy Moves molecules Moves molecules againstagainst concentration gradient concentration gradient
Molecules combine with carrier proteinMolecules combine with carrier protein
Example: sodium-potassium pumpExample: sodium-potassium pump
23Types of Membrane Transport:Facilitated Transport
24Active 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 vesicles = active transportcell inside vesicles = active transportExocytosisExocytosis – Vesicles fuse with plasma – Vesicles fuse with plasma membrane and membrane and secretesecrete contents outside contents outside
EndocytosisEndocytosis – Cells engulf substances into – Cells engulf substances into pouch which becomes a vesicle inside cellpouch which becomes a vesicle inside cell PhagocytosisPhagocytosis – Large, solid material taken into – Large, solid material taken into vesiclevesicle
PinocytosisPinocytosis – Liquid or small, solid particles go – Liquid or small, solid particles go into vesicleinto vesicle
Receptor-MediatedReceptor-Mediated –form of pinocytosis using a –form of pinocytosis using a receptor protein in a receptor protein in 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
JunctionsBetweenCellsJunctionsBetweenCells
AnchoringjunctionsattachadjacentcellsAnchoringjunctionsattachadjacentcells
Adhesion JunctionsAdhesion Junctions
Many intercellular filaments between cells (heart, Many intercellular filaments between cells (heart, bladder, stomach = tissues that get stretched)bladder, stomach = tissues that get stretched)
DesmosomesDesmosomes
Single point of attachment between cells (skin)Single point of attachment between cells (skin)
29MembranesMembranesCell Surface Modifications:Cell Surface Modifications:JunctionsJunctions
Cell Surfaces in AnimalsCell Surfaces in Animals
Tight JunctionsTight Junctions
Form impermeable barriers (like a zipper)Form impermeable barriers (like a zipper)
Serve as barriers (blood-brain barrier, intestines, Serve as barriers (blood-brain barrier, intestines, kidney tubules)kidney tubules)
Gap JunctionsGap Junctions
Two plasma membrane channels are joined. Two plasma membrane channels are joined. Allows communication when small molecules and Allows communication when small molecules and ions pass between two cells (muscle cells)ions pass between two cells (muscle cells)
30Cell-Surface Modifications:
Junctions
31MembranesMembranes
Cell Surface ModificationsCell Surface Modifications
Extracellular MatrixExtracellular MatrixExternalmeshworkofpolysaccharidesandExternalmeshworkofpolysaccharidesandproteins(collagen,elastin,cartilage,bone)proteins(collagen,elastin,cartilage,bone)
FoundincloseassociationwiththecellthatFoundincloseassociationwiththecellthatproducedthemproducedthem
PlantPlant Cell WallsCell WallsPlantshavefreelypermeablecellwall,withPlantshavefreelypermeablecellwall,withcellulosecelluloseasthemaincomponentasthemaincomponent PlasmodesmataPlasmodesmatachannelspenetratecellwallchannelspenetratecellwall EachcontainsstrandsofcytoplasmthatallowEachcontainsstrandsofcytoplasmthatallowpassageofsmallmoleculesbetweencellspassageofsmallmoleculesbetweencells
32Cell-Surface Modifications:
Extracellular Matrix
33Cell-Surface Modifications:
Plasmodesmata