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    Membrane structure and function master 2011 Membrane structure and function master 2011 Presentation Transcript

    • Chapter 5: Cell Transport: Membrane Structure and Function
    • Chapter Objectives
      • Describe the fluid mosaic model of membrane structure and explain the underlying reasons for this structure.
      • Outline the roles of phospholipids, cholesterol, glycolipids, proteins and glycoproteins in membranes.
      • Outline the roles of the plasma membrane, and the roles of membranes within cells.
      • Describe and explain how molecules can get in and out of cells (cross cell membranes) by the processes of diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis.
      • Describe the effects on animal and plant cells of immersion in solutions of different “water potential”.
    • Chapter – Key Vocabulary
      • Selectively permeable
      • Phospholipid
      • Hydrophobic
      • Hydrophilic
      • Passive Transport
      • Active Transport
      • Diffusion
      • Osmosis
      • Concentration Gradient
      • Hypertonic
      • Hypotonic
      • Isotonic
      • Turgor
      • Plasmolysis
      • Facilitated diffusion
      • Exocytosis
      • Endocytosis
      • Phagocytosis
      • Pinocytosis
      • Fluid Mosaic Model
      • Equilibrium
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      • Membranes organize the chemical activities of cells.
        • They separate cells from their outside environments.
        • They control the passage of molecules from one side of the membrane to the other.
        • Membranes are selectively permeable ; that is, they allow some substances to cross more easily than others and blocks passage of some substances altogether.
      • Membrane phospholipids form a bilayer.
      • Phospholipids are:
        • fats with two nonpolar fatty acid “tails”
        • one polar phosphate “head”
        • attached to glycerol.
      • In water , thousands of individual molecules form a “stable bilayer”, aiming their heads out and their tails in.
      • The hydrophobic interior of this bilayer offers an effective barrier to the flow of most hydrophilic molecules.
      • The membrane is a Fluid Mosaic of phospholipids and proteins. WHY?
        • There are proteins embedded in the lipid bilayer.
            • Attached to the outer surface: Peripheral Protein
            • Running through the whole membrane: Integral Protein
        • The cell membrane appears to show some fluidity…lipids and proteins moving sideways in response to functions and surrounding conditions.
        • Cholesterol helps stabilize the fluidity at different temperatures.
    • Fluid-mosaic model of plasma membrane structure Slide number: 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside cell Outside cell glycolipid glycoprotein carbohydrate (sugar) chain phospholipid bilayer integral protein cholesterol peripheral protein filaments of the cytoskeleton hydro- phobic tails hydrophilc heads hydrophilc heads
    • Fluid-mosaic model of plasma membrane structure Slide number: 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside cell Outside cell glycoprotein carbohydrate (sugar) chain
    • Fluid-mosaic model of plasma membrane structure Slide number: 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside cell Outside cell glycolipid glycoprotein carbohydrate (sugar) chain
    • Fluid-mosaic model of plasma membrane structure Slide number: 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside cell Outside cell glycolipid glycoprotein carbohydrate (sugar) chain integral protein
    • Fluid-mosaic model of plasma membrane structure Slide number: 5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside cell Outside cell glycolipid glycoprotein carbohydrate (sugar) chain integral protein cholesterol
    • Fluid-mosaic model of plasma membrane structure Slide number: 6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside cell Outside cell glycolipid glycoprotein carbohydrate (sugar) chain integral protein cholesterol peripheral protein
    • Fluid-mosaic model of plasma membrane structure Slide number: 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside cell Outside cell glycolipid glycoprotein carbohydrate (sugar) chain integral protein cholesterol peripheral protein filaments of the cytoskeleton
    • Fluid-mosaic model of plasma membrane structure Slide number: 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside cell Outside cell glycolipid glycoprotein carbohydrate (sugar) chain phospholipid bilayer integral protein cholesterol peripheral protein filaments of the cytoskeleton
    • Fluid-mosaic model of plasma membrane structure Slide number: 9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside cell Outside cell glycolipid glycoprotein carbohydrate (sugar) chain phospholipid bilayer integral protein cholesterol peripheral protein filaments of the cytoskeleton hydro- phobic tails hydrophilc heads hydrophilc heads
    • Fluid-mosaic model of plasma membrane structure Slide number: 10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inside cell Outside cell glycolipid glycoprotein carbohydrate (sugar) chain phospholipid bilayer integral protein cholesterol peripheral protein filaments of the cytoskeleton hydro- phobic tails hydrophilc heads hydrophilc heads
    • Functions of Membrane Proteins
      • Channel – moves materials
      • Carrier – combines with a substance to move
      • Cell Recognition – glycoproteins – helps cells find molecules
      • Receptor – specific to a certain molecule
      • Enzyme – carries out metabolic functions
    • Chart from Textbook Fig. 4.2
    • Transport through cell membranes
      • The phospholipid bilayer is a good barrier around cells, especially to water soluble molecules. However, for the cell to survive some materials need to be able to enter and leave the cell.
      • There are 5 basic mechanisms:
      • Passive Transport
      • DIFFUSION
      • OSMOSIS
      • FACILITATED DIFFUSION
      • _______________________________________
      • Active Transport
      • 4. ENDOCYTOSIS
      • 5. EXOCYTOSIS
    • Fig. 4.3
    • Passage Through The Phospholipid Bilayer
      • What molecules can pass through the phospholipids bilayer?
      • Small non polar (O2)
      • Large non polar (lipids)
      • Small polar (water and CO2)
      • What molecules cannot pass freely through the bilayer?
      • Large polar (starch, glucose, and proteins)
      • Ions (Na+, K+)
    • Diffusion of liquids
    • Fig. 4.4
    • Fig. 4.4.a
    • Fig. 4.4.b
    • Fig. 4.4.c
    • Diffusion through a membrane Cell membrane Inside cell Outside cell
    • Diffusion through a membrane Cell membrane Inside cell Outside cell diffusion
    • Diffusion through a membrane Cell membrane Inside cell Outside cell EQUILIBRIUM
    • Simple Diffusion
      • Diffusion is the net movement of molecules (or ions) from a region of their high concentration to a region of their lower concentration.
      • molecules move down a concentration gradient .
      • Molecules have kinetic energy , which makes them move about randomly.
      • As a result of diffusion, molecules reach an equilibrium where they are evenly spread out.
      • Equilibrium = no net movement of molecules from either side.
    • REMEMBER…..
      • DIFFUSION refers to the movement (or non) of the SOLUTE (glucose, starch, gases across the membrane!
    • Molecules that diffuse through cell membranes!
    • Osmosis
    • Osmosis
      • ‘ The diffusion of water from an area of high concentration of water molecules to an area of low concentration of water across a semi permeable membrane.
    • Osmosis Cell membrane partially permeable. Inside cell Outside cell VERY High conc. of water molecules. VERY Low conc. of water molecules. Sugar molecule DILUTE SOLUTION CONCENTRATED SOLUTION
    • Osmosis Cell membrane partially permeable. Inside cell Outside cell High conc. of water molecules. Lower water potential. Low conc. of water molecules. High water potential. OSMOSIS
    • Osmosis Cell membrane partially permeable. Inside cell Outside cell OSMOSIS EQUILIBRIUM. Equal water concentration on each side. Equal water potential has been reached. There is no net movement of water
    •  
      • Tonicity
      • Movement of water in response to the amount of solute on either side of a membrane.
      • The Rule -
      • Water will always move toward the side of the membrane with the most solute!
    • Tonicity
      • Tonicity comes -in 3 types:
      • Hypertonic – the side the membrane or part of the solution with the greater amount of solute
      • Hypotonic – side/part with the lower amount of solute
      • Isotonic – equal solute content
    • ? ? Which side is hypotonic and which side is hypertonic? A B Draw THIS U-TUBE as it will appear after osmosis takes place.
    • Which way will the water move?
    • WHY?
    •  
      • A solution is made of a solute and solvent.
        • OSMOSIS: solvent is WATER.
        • Solute is what is dissolved in water.
        • THE DIRECTION OF WATER’S CONCENTRATION GRADIENT IS ALWAYS OPPOSITE TO THE DIRECTION OF THE SOLUTE’S CONCENTRATION GRADIENT .
      LOW SOLUTE CONCENTRATION HIGH SOLUTE CONCENTRATION HYPOTONIC HYPERTONIC HIGH WATER CONCENTRATION LOW WATER CONCENTRATION LOW OSMOTIC POTENTIAL HIGH OSMOTIC POTENTIAL DILUTE CONCENTRATED
      • Remember: A hypertonic solution is always relative to a hypotonic solution
    • TONICITY IN CELLS
      • Osmosis
    • Water Movement in the Cell
      • This is an Osmosis tutorial…for the smart board….
      • osmosis#Osmosis#Osmosis#Osmosis
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    • Hypotonic vs. Hypertonic Cells placed in a:
      • Hypotonic
      • animal cell will gain water – LYSE
      • Plant cell will swell and become TURGID
      • Hypertonic
      • animal cell will lose water – shrivel
      • Plant will lose water – plant cell membrane will detach from cell wall - plasmolysis
    • Do Water Molecules Stop Moving in Isotonic Conditions ?
      • No.
      • They continue to diffuse, however there is no net movement.
      • Equal does not mean STOP
    • Facilitated Diffusion
      • Large polar molecules such as glucose and amino acids , cannot diffuse across the phospholipid bilayer. Also ions such as Na + or Cl - cannot pass.
      • These molecules pass through protein channels instead. Diffusion through these channels is called FACILITATED DIFFUSION.
      • Movement of molecules is still PASSIVE just like ordinary diffusion, the only difference is, the molecules go through a protein channel instead of passing between the phospholipids.
    • Facilitated Diffusion Animation
    • Facilitated Diffusion through a membrane Cell membrane Inside cell Outside cell Protein channel
    • Facilitated Diffusion through a membrane Cell membrane Inside cell Outside cell Protein channel diffusion
    • Facilitated Diffusion through a membrane Cell membrane Inside cell Outside cell Protein channel diffusion EQUILIBRIUM
    • Facilitated Diffusion: Molecules will randomly move through the opening like pore, by diffusion. This requires no energy, it is a PASSIVE process . Molecules move from an area of high concentration to an area of low conc.
    • Active Transport
      • Cells expend energy for active transport .
        • Active transport involves the aid of a transport protein in moving a solute up a concentration gradient (from an area of low concentration to an area of high concentration).
        • Energy is required to help the protein to move the solute molecule.
        • What molecular form does this energy usually have?
            • ATP – usable cellular energy!
    •  
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      • Exocytosis and Endocytosis transport large molecules.
        • In exocytosis , membrane-bound vesicles (tiny membrane-bounded sacs) containing large molecules fuse with the plasma membrane and release their contents outside the cell.
    • Exocytosis
        • In endocytosis , the plasma membrane surrounds materials outside the cell, closes around the materials, and forms membrane-bound vesicles to contain the materials.
          • Two important types of endocytosis are
            • phagocytosis (“cell eating”) and
            • pinocytosis (“cell drinking”).
    • a) Phagocytosis
      • The “engulfing” of material by the cell
    • b) Pinocytosis
      • The “cell drinking” of material by the cell
      Phagocytosis takes in solid particles. Pinocytosis takes in liquids.
      • Active transport is used to:
      • Generate charge gradients. Ex. In the mitochondrion, hydrogen ion pumps, pump hydrogen ions into the “intermembrane” space of the organelle as part of making ATP. 
      • 2. Concentrate ions , minerals and nutrients inside the cell that are in low concentration outside. 
      • 3. Move sodium and potassium ions in and out of the cell. VERY important for nerve function.
    • Review of passive and active transport: ?
    • Review of passive and active transport: ?
    • Review of passive and active transport: ?
    • Review of passive and active transport: ?
    • Review of passive and active transport:
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