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The Cell Membrane

The Cell Membrane






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    The Cell Membrane The Cell Membrane Presentation Transcript

    • The Cell Membrane
    • 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
    • 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.
    • 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.
    • 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
    • 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.
    • 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
    • Through the Cell Membrane
      • Diffusion
      • Osmosis
      • Facilitated Diffusion
      • Active Transport
      • Bulk Transport
    • 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.
    • Passive Transport
    • 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.
      • 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)
    • Osmosis: Hypotonic
    • 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.
      • 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.
    • 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.
      • Intestinal cells pump in nutrients from the gut.
      • Root cells pump in nutrients from the soil.
      • Gill cells in fish pump out sodium ions.
      • 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.
    • Active Transport Pump
    • 5. Bulk Transport
      • 1. Endocytosis: The cell membrane folds inward, traps and encloses a small amount of matter from the extracellular fluid. 3 types:
    • 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.
        • 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.
    • 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