The Cell Membrane


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The Cell Membrane

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