MembranesChapter
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Membranes 2
Chapter 5 Outline
Membrane ModelsFluid-Mosaic
Plasma Membrane Structure and FunctionPhospholipidsProteins
Plasma Membrane PermeabilityDiffusionOsmosisTransport Via Carrier Proteins
Cell Surface Modifications
Membranes 3Structure and Function:The Phospholipid Bilayer
The plasma membrane is common to all cellsSeparates:
Internal living cytoplasmic fromExternal environment of cell
Phospholipid bilayer:External surface lined with hydrophilic polar heads
Cytoplasmic surface lined with hydrophilic polar heads
Nonpolar, hydrophobic, fatty-acid tails sandwiched in between
Membranes 4
Unit Membrane
Membranes 5
Membrane Models
Fluid-Mosaic ModelThree components:
Basic membrane referred to as phospholipid bilayer
Protein molecules Float around like icebergs on a seaMembrane proteins may be peripheral or integralPeripheral proteins are found on the inner membrane surface
Integral proteins are partially or wholly embedded (transmembrane) in the membrane
Some have carbohydrate chains attachedCholesterol
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Membrane Models:Unit Membrane vs. Fluid Mosaic Model
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The Fluid Mosaic Model
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Phospholipid & CholesterolMolecules
Membranes 9Transmembrane Proteins
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Lateral Migration ofMembrane Proteins
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Functions of Membrane Proteins
Channel Proteins: Tubular Allow passage of molecules through membrane
Carrier Proteins: Combine with substance to be transported Assist passage of molecules through membrane
Cell Recognition Proteins: Provides unique chemical ID for cells Help body recognize foreign substances
Receptor Proteins: Binds with messenger molecule Causes cell to respond to message
Enzymatic Proteins: Carry out metabolic reactions directly
Membranes 12
Membrane Protein Diversity
Membranes 13Types of Transport:Active vs. Passive
Plasma membrane is differentially (selectively) permeable Allows some material to pass Inhibits passage of other materials
Passive Transport:No ATP requirementMolecules follow concentration gradient
Active TransportRequires carrier proteinRequires energy in form of ATP
Membranes 14Types of Membrane Transport:Overview
Membranes 15Types of Transport:Diffusion
A solution consists of:A solvent (liquid) , andA solute (dissolved solid)
DiffusionNet movement of solute molecules down a concentration gradient
Molecules both ways along gradientMore move from high to low concentration than vice versa
Equilibrium:When NET change stops Solute concentration uniform – no gradient
Membranes 16Types of Membrane Transport:Diffusion
Membranes 17Types of Membrane Transport:Diffusion Across Lung
Membranes 18Types of Transport:Osmosis
Osmosis: Special case of diffusion Focuses on solvent (water) movement rather than solute
Diffusion of water across a differentially (selectively) permeable membrane Solute concentration on one side high, but water
concentration low Solute concentration on other side low, but water
concentration high Water diffuses both ways across membrane but solute can’t
Net movement of water is toward low water (high solute) concentration
Osmotic pressure is the pressure that develops due to osmosis
Membranes 19Types of Membrane Transport:Osmosis
Membranes 20Types of Transport:Osmosis
Isotonic SolutionSolute and water concentrations equal on both sides of membrane
Hypotonic Solution Concentration of solute lower than on other sideCells placed in a hypotonic solution will swellMay cause cells to break – Lysis
Hypertonic SolutionConcentration of solute higher than on other sideCells placed in a hypertonic solution will shrink – Plasmolysis
Membranes 21
Osmotic Effects on Cells
Membranes 22Types of Transport:Carrier Proteins
Facilitated Transport Small moleculesCan’t get through membrane lipidsCombine with carrier proteins Follow concentration gradient
Active Transport Small moleculesMove against concentration gradientCombining with carrier proteinsRequires energy
Membranes 23Types of Membrane Transport:Facilitated Transport
Membranes 24
Facilitated Transport:The Sodium-Potassium Pump
Membranes 25Types of Transport:Membrane-Assisted Transport
Macromolecules transported into or out of the cell inside vesiclesExocytosis – Vesicles fuse with plasma membrane and secrete contents
Endocytosis – Cells engulf substances into pouch which becomes a vesicle Phagocytosis – Large, solid material into vesicle Pinocytosis – Liquid or small, solid particles go into vesicleReceptor-Mediated – Specific form of pinocytosis using a coated pit
Membranes 26Membrane-Assisted Transport:Exocytosis
Membranes 27Membrane-Assisted Transport:Three Types of Endocytosis
Membranes 28Cell Surface Modifications:Junctions
Cell Surfaces in AnimalsJunctions Between Cells
Adhesion Junctions Intercellular filaments between cells
Tight JunctionsForm impermeable barriers
Gap JunctionsPlasma membrane channels are joined (allows communication)
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Cell-Surface Modifications:Junctions
Membranes 30
Cell Surface Modifications
Extracellular MatrixExternal meshwork of polysaccharides and proteins
Found in close association with the cell that produced them
Plant Cell WallsPlants have freely permeable cell wall, with cellulose as the main component Plasmodesmata penetrate cell wall Each contains a strand of cytoplasmAllow passage of material between cells
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Cell-Surface Modifications:Extracellular Matrix
Membranes 32
Cell-Surface Modifications:Plasmodesmata
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Review
Membrane ModelsFluid-Mosaic
Plasma Membrane Structure and FunctionProtein FunctionsPlasma Membrane PermeabilityDiffusion
Osmosis
Transport Via Carrier Proteins
Cell Surface Modifications
MembranesEnding Slide Chapter
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