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The Cell Membrane
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The Cell Membrane

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  • 1. The Cell Membrane
  • 2. Function
    • Regulates the movement of materials from one environment to the other.
    • Transports raw materials into the cell and waste out of the cell.
    • Prevents the entry of unwanted matter and the escape of needed materials.
    • Maintain a steady environment: Homeostasis
  • 3. Structure:
    • Composed of a phospholipid bilayer with a collage of many different proteins, lipids and carbohydrates.
    • A Phospholipid is composed of 1 glycerol molecule, 2 fatty acids and 1 phosphate group. This structure causes hydrophilic and hydrophobic regions.
  • 4.  
  • 5. The Fluid-Mosaic Membrane Model
    • Membranes are not static; they have a fluid consistency.
    • Most membrane lipids and proteins can drift about laterally in the plane of the membrane.
    • Cholesterol enhances membrane fluidity, allows animal membranes to function in a wide range of temperatures and also makes the membrane less permeable to biological molecules.
  • 6. Membrane Proteins:
    • Two Types:
    • Integral: Proteins that insert into the membrane (transmembrane proteins)
    • Peripheral: Proteins attached to the surface of the cell membrane.
    • Function:
    • Transportation
    • Enzymes
    • Receptor sites
    • Cell adhesion
    • Attachment to the cytoskeleton
  • 7. Carbohydrates:
    • Usually branched molecules of 15 or less sugar units.
    • Some are bonded to lipids: Glycolipids.
    • Most are bonded to proteins: Glycoproteins.
    • Function: Cell-cell recognition.
  • 8.  
  • 9. Construction of a Cell Membrane
    • Copy the link below to create your own cell
    • membrane.
    • http://www.wisc-online.com/objects/index_tj.asp?objID=AP1101
  • 10. Through the Cell Membrane
    • Diffusion
    • Osmosis
    • Facilitated Diffusion
    • Active Transport
    • Bulk Transport
  • 11. 1. Diffusion:
    • Passive movement of molecules from a region of high concentration to a region of low concentration.
    • ( Concentration gradient is the difference in concentration between the two regions)
    • Small, uncharged molecules like O 2 , CO 2 and H 2 O can move easily through the membrane.
    • Works well over short distances. Once molecules enter the cell the rate of diffusion slows.
    • Limits cell size.
  • 12. Passive Transport
  • 13. 2. Osmosis
    • Diffusion of the solvent across a semi-permeable membrane separating two solutions. (Diffusion of water)
    • Water molecules move from a region of high concentration to a region of low concentration.
    • Direction depends on the relative concentration of water molecules on either side of the cell membrane.
  • 14.
    • Isotonic: Water inside the cell equals the water outside the cell and equal amounts of water move in and out of the cell.
    • Hypotonic: Water outside the cell is greater than that inside the cell, water moves into the cell, may cause cell to burst (lysis)
    • Hypertonic: Water inside the cell is greater than outside. Water moves out of the cell, may cause the cell to shrink (plasmolysis)
  • 15.  
  • 16. Osmosis: Hypotonic
  • 17. 3. Facilitated Diffusion
    • Assists with the movement of large molecules like glucose.
    • Passive movement of a substance into or out of the cell by means of carrier proteins or channel proteins.
  • 18.
    • Moves molecules from high to low regions of concentration.
    • Carrier proteins: Transports non-charged molecules with a specific shape.
    • Channel proteins: Tunnel shape that transports small charged molecules.
  • 19. 4. Active Transport
    • The process of moving substances against their concentration gradients. Requires energy.
    • Examples:
    • Kidney cells pump glucose and amino acids out of the urine and back into the blood.
  • 20.
    • Intestinal cells pump in nutrients from the gut.
    • Root cells pump in nutrients from the soil.
    • Gill cells in fish pump out sodium ions.
  • 21.
    • Active Transport Pump:
      • Sodium-potassium pump
      • 3 sodium ions inside the cell and 2 potassium ions outside the cell bind to the pump.
      • This allows the release of energy from ATP and causes the protein complex to change shape.
      • The change in shape allow the Na + and K+ ions to move across and be released.
  • 22. Active Transport Pump
  • 23. 5. Bulk Transport
    • 1. Endocytosis: The cell membrane folds inward, traps and encloses a small amount of matter from the extracellular fluid. 3 types:
  • 24. Endocytosis
      • Pinocytosis: The intake of a small droplet of extracellular fluid. This occurs in nearly all cell types.
      • Phagocytosis: The intake of a large droplet of extracellular fluid. This occurs in specialized cells.
  • 25.
      • Receptor-assisted endocytosis: The intake of specific molecules that attach to special proteins in the cell membrane. These proteins are uniquely shaped to fit the shape of a specific molecule.
  • 26. Bulk Transport
    • 2. Exocytosis: The reverse of endocytosis: A vesicle from inside the cell moves to the cell membrane. The vesicle fuses to the membrane and the contents are secreted

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