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The Cell Membrane
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The Cell Membrane






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    The Cell Membrane The Cell Membrane Presentation Transcript

    • Membrane Structure and Function
    • Plasma Membrane
      The membrane at the boundary of every cell.
      Functions as a selective barrier for the passage of materials in and out of cells.
    • Membrane Composition
    • Fluid Mosaic Model
      Refers to the way the lipids and proteins behave in a membrane.
    • “Fluid”
      Refers to the lipid bilayer.
      Molecules are not bonded together, so are free to shift.
      Must remain "fluid" for membranes to function.
    • “Mosaic”
      Proteins: float in a sea of lipids.
      Proteins form a collage or mosaic pattern that shifts over time.
    • Protein Function in Membranes
      Enzymatic activity.
      Receptor sites for signals.
      Cell adhesion.
      Cell-cell recognition.
      Attachment to the cytoskeleton.
    • Types of Membrane Proteins
      Integral - inserted into the lipid bilayer.
      Peripheral - not embedded in the lipid bilayer, but are attached to the membrane surface.
    • Membranes are Bifacial
      The lipid composition of the two layers is different.
      The proteins have specific orientations.
      Carbohydrates are found only on the outer surface.
    • Question
      How do materials get across a cell's membrane?
    • Problems
      Lipid bilayer is hydrophobic. Hydrophilic materials don't cross easily.
      Large molecules don't cross easily. Too big to get through the membrane.
    • Mechanisms
      1. Passive Transport
      2. Active Transport
    • Passive Transport
      Movement across membranes that does NOT require cellular energy.
    • Types of Passive Transport
      1. Diffusion
      2. Osmosis
      3. Facilitated Diffusion
    • Diffusion
      The net movement of atoms, ions or molecules down a concentration gradient.
      Movement is from:
      High Low
    • Equilibrium
      When the concentration is equal on both sides.
      There is no net movement of materials.
    • Factors that Effect Diffusion
      1. Concentration
      2. Temperature
      3. Pressure
      4. Particle size
      5. Mixing
    • Osmosis
      Diffusion of water.
      Water moving from an area if its high concentration to an area of its low concentration.
      No cell energy is used.
    • Tonicity
      The concentration of water relative to a cell.
      1. Isotonic (same)
      2. Hypotonic (below)
      3. Hypertonic (above)
    • Isotonic
      Isosmotic solution.
      Cell and water are equal in solute concentration.
      No net movement of water in or out of the cell.
      No change in cell size.
    • Hypotonic
      Hypoosmotic solution
      Cell's water is lower than the outside water (more solutes).
      Water moves into the cell.
      Cell swells, may burst or the cell is turgid.
    • Hypertonic
      Hyperosmotic solution
      Cell's water is higher than the outside water (less solutes)
      Water moves out of the cell.
      Cell shrinks or plasmolysis occurs.
    • Facilitated Diffusion
      Transport protein that helps materials through the cell membrane.
      Doesn't require energy (ATP).
      Works on a downhill concentration gradient.
    • Active Transport
      Movement across membranes that DOES require cellular energy.
    • Types of Active Transport
      1. Carrier-Mediated
      2. Endocytosis
      3. Exocytosis
    • Carrier-Mediated Transport
      General term for the active transport of materials into cells AGAINST the concentration gradient.
      Movement is:
      low high
    • Examples
      1. Na+- K+ pump
      2. Electrogenic or H+ pumps
      3. Cotransport
    • Exocytosis
      Moves bulk material out of cells.
      Example - secretion of enzymes.
    • Endocytosis
      Moves bulk materials into cells.
      Several types known.
    • Types
      1. Pinocytosis - liquids
      2. Phagocytosis - solids
      3. Receptor Mediated - uses receptors to "catch" specific kinds of molecules.