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Membrane structure and function master

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  • 1. Membrane Structure and Function Help Us!
  • 2. The Cell Membrane
  • 3.  
  • 4.  
  • 5.
    • Generalised Functions:
      • Hold the cell together
      • Allows the cell to recognize and be recognized (signaling and immunity)
      • Binds to other cells and molecules
      • A site for biochemical reactions
      • Selectively permeable – controls what enters and leave
  • 6.
    • 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.
    • LIPOSOME ******
    • The hydrophobic interior of this bilayer offers an effective barrier to the flow of most hydrophilic molecules.
  • 7.
    • The membrane is a Fluid Mosaic of phospholipids and proteins:
      • 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 MOSIAC MODEL ANN’Y
  • 8. General Functions of Membrane Proteins
    • Glycoproteins
    • Glycolipids
    • Channels for passive transport
    • Pumps for active transport
    • Electron carriers
    • Enzymes
    • Hormone binding sites
    • SEE “RITA” PAGE 59 FOR SPECIFIC EXAMPLES!!
  • 9.  
  • 10.  
  • 11. Membrane Transport
  • 12. Transport through cell membranes – Overview
    • 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 – carrier assisted
    • ________________________________________
    • 4. ACTIVE TRANSPORT – carrier assisted
    • 5. VESICLE MEDIATED TRANSPORT
        • ENDOCYTOSIS
            • PINOCYTOSIS
            • PHAGOCYTOSIS
        • EXOCYTOSIS
    • _______________________________________
  • 13. Fig. 4.3
  • 14. Passage Through The Phospholipid Bilayer
    • Molecules can pass through the phospholipids bilayer:
      • Hydrocarbons
      • Small non polar (O 2 )
      • Small polar ( water and CO 2 )
      • Lipids (even though they are big)
    • Molecules cannot pass freely through the Bilayer:
      • Large macromolecules: starch, glucose, and proteins
      • Ions (Na+, K+)
  • 15. Simple Diffusion
  • 16. Diffusion of liquids
  • 17. Diffusion through a membrane Cell membrane Inside cell Outside cell
  • 18. Diffusion through a membrane Cell membrane Inside cell Outside cell diffusion
  • 19. Diffusion through a membrane Cell membrane Inside cell Outside cell EQUILIBRIUM
  • 20.  
  • 21. 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.
      • Each molecule has its own gradient
      • The molecules move down a concentration gradient.
    • As a result of diffusion, molecules reach an equilibrium where they are evenly spread out.
    • This is when there is no net movement of molecules from either side.
  • 22. Factors Affecting Diffusion Rate
    • Concentration Gradient –when there is a greater difference in concentration.
      • Distance – shorter distances = greater rate
      • Area – larger surface area for diffusion = greater rate
        • Aveoli, mitochondria, root hairs
      • Barriers – thicker barriers slow rate. Pores will enhance diffusion.
  • 23. REMEMBER…..
    • DIFFUSION refers to the movement (or non) of the SOLUTE (glucose, starch, gases) across the membrane!
  • 24.  
  • 25. Osmosis
  • 26. 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.
  • 27. 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
  • 28. Osmosis Cell membrane partially permeable. Inside cell Outside cell High conc. of water molecules. Lower water potential. OSMOSIS
  • 29. 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
  • 30.
    • 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!
  • 31. 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
  • 32. ? ? Which side is hypotonic and which side is hypertonic? A B
  • 33. Which way will the water move?
  • 34. WHY?
  • 35.  
  • 36.
    • 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
  • 37.
    • In comparing two solutions:
      • a HYPERTONIC is the solution with the greater solute concentration relative to the HYPOTONIC solution.
  • 38.  
  • 39.  
  • 40. Carrier Assisted Transport
  • 41. Facilitated Diffusion
    • Larger polar molecules such as glucose and amino acids , cannot diffuse across the phospholipid bilayer..
    • These molecules pass through protein channels instead.
    • Diffusion through these channels is called FACILITATED DIFFUSION.
    • Movement of these molecules is still PASSIVE.
  • 42.  
  • 43. Facilitated Diffusion through a membrane Cell membrane Inside cell Outside cell Protein channel
  • 44. Facilitated Diffusion through a membrane Cell membrane Inside cell Outside cell Protein channel diffusion
  • 45. Facilitated Diffusion through a membrane Cell membrane Inside cell Outside cell Protein channel diffusion EQUILIBRIUM
  • 46.  
  • 47. Active Transport
  • 48.
    • Cells expend energy for active transport .
        • Active transport involves the aid of a transport protein or transport vesicle 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.
        • ATP – molecule used
  • 49.
    • Some Molecules Moved:
    • Glucose more required in the cell
    • Sodium must be removed from cells to maintain fluid balance and for enzymes to function properly
    • Generate Charge Gradients
    • Sodium – Potassium Pump – particular to nerve cells; allows cells to generate impulses.
    • Proton Pumps – used to pump H+ ions in mitochondria, cellular respiration
  • 50. Vesicle Mediated Transport
  • 51. Vesicle Mediated - Making a Vesicle
    • 1. Protein is already synthesized and present in the rER.
    • 2. The protein is moved through the rER and modified.
    • 3. A spherical vesicle is formed from the end of the rER with the protein inside.
    • 4, The vesicle migrates to the Golgi apparatus.
    • 5. Vesicle and Golgi membranes fuse. The protein is released into the folds of the Golgi apparatus.
    • 6. The Golgi modifies the protein further.
    • 7. A new vesicle is formed from Golgi membrane which then breaks away.
    • 8. The vesicle migrates to the plasma membrane, fuses with the plasma membrane and secretes its content.
  • 52.  
  • 53.
    • Exocytosis and Endocytosis transport large molecules.
    • Active Transport
      • E xocytosis :
        • membrane-bound vesicles (tiny membrane-bounded sacs) containing large molecules fuse with the plasma membrane and release their contents outside the cell.
        • Removes waste materials
  • 54.  
  • 55. Exocytosis
  • 56.
      • E ndocytosis :
        • the plasma membrane:
          • surrounds materials outside the cell
          • closes around the materials
          • forms membrane-bound vesicles to contain the materials.
        • Three important types of endocytosis:
          • phagocytosis (“cell eating”)
          • pinocytosis (“cell drinking”)
          • Receptor Mediated
  • 57. Endocytosis
  • 58. Phagocytosis
    • The “engulfing” of material by the cell
    • Amoeba, white blood cells
  • 59. Pinocytosis
    • The “cell drinking” of material by the cell
    Pinocytosis takes in liquids. Many protozoa, some liver cells
  • 60. Receptor Mediated Endocytosis
    • Binding proteins on the surface of a membrane that act to attract SPECIFIC molecules.
  • 61.  
  • 62. To Compare…..
  • 63. END!!!
  • 64. Review of passive and active transport: ?
  • 65. Review of passive and active transport: ?
  • 66. Review of passive and active transport: ?
  • 67. Review of passive and active transport: ?
  • 68. Review of passive and active transport:
  • 69.  
  • 70.
    • Water balance between cells and their surroundings is crucial to organisms.
      • If a plant or an animal cell is isotonic with its surroundings , no osmosis occurs, and the cells do not change .
      • Cells in a hypotonic environment
        • An animal cell will gain water and lyse (pop).
        • A plant cell will swell and become turgid (stiff).
  • 71.
    • Cells in a hypertonic environment ………
    • An animal cell in a hypertonic solution will lose water and shrivel: CRENATE
    • A plant cell in a hypertonic solution:
      • will lose water past the cell membrane but not the cell wall.
      • The plasma membrane pulls away from the inside of the cell wall and cell as a whole losing turgor .
        • This process is called plasmolysis .

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