Membrane structure and function master

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Membrane structure and function master

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

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