BIOL 101 Chp 7: Membrane Structure and Function

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This is a lecture presentation for my BIOL 101 General Biology I students on Chapter 7: Membrane Structure and Function. (Campbell Biology, 10th Ed. by Reece et al).

Rob Swatski, Associate Professor of Biology, Harrisburg Area Community College - York Campus, York, PA. Email: rjswatsk@hacc.edu

Please visit my website for more anatomy and biology learning resources: http://robswatski.virb.com/

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BIOL 101 Chp 7: Membrane Structure and Function

  1. 1. Membrane Structure & Function BIOL 101: General Biology I Chapter 7 Rob Swatski Associate Professor of Biology HACC – York Campus 1
  2. 2. 2
  3. 3. 3 Plasma Membrane Fluid mosaic Lipids & proteins Selective permeability
  4. 4. Fibers of extracellular matrix (ECM) Glyco- protein Microfilaments of cytoskeleton Cholesterol Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE Glyco- lipid EXTRA- CELLULAR SIDE OF MEMBRANE Carbo- hydrate 4
  5. 5. 5
  6. 6. 6
  7. 7. 7 Phospholipid Bilayer Amphipathic Hydrophilic Hydrophobic
  8. 8. 8
  9. 9. Phospholipids Cell structure & function Polar phosphate head Nonpolar fatty acid tails 9
  10. 10. 10
  11. 11. 11 Membrane Models Sandwich model (Davson & Danielli, 1935): 2 outer protein layers with the phospholipid bilayer on the inside Fluid mosaic model (Singer & Nicolson, 1972): proteins dispersed within phospholipid bilayer
  12. 12. 12
  13. 13. 13 Freeze- Fracture Specialized preparation technique Splits membrane along the middle of the bilayer Confirmed fluid mosaic model
  14. 14. Knife Plasma membrane Cytoplasmic layer Proteins Extracellular layer Inside of extracellular layer Inside of cytoplasmic layer TECHNIQUE RESULTS 14
  15. 15. 15
  16. 16. 16
  17. 17. 17
  18. 18. Membrane Fluidity Flip-flop ( once per month) Lateral movement (107 times per second) 18
  19. 19. Membrane proteins Mouse cell Human cell Hybrid cell Mixed proteins after 1 hour 19
  20. 20. 20 Membrane Fluidity Essential for proper functioning Colder temp.  viscous Unsaturated fatty acids = more fluid Saturated fatty acids = less fluid
  21. 21. 21
  22. 22. 22 Cholesterol Membrane steroid that plays important role in membrane fluidity Warm temp.  restrains movement Cool temp.  maintains fluidity by preventing tight packing
  23. 23. Cholesterol in plasma membrane 23
  24. 24. 24 Membrane Proteins Membrane = collage of proteins Embedded in plasma membrane Determine most of membrane’s specific functions
  25. 25. 25
  26. 26. 26 Membrane Proteins Peripheral proteins Integral proteins Transmembrane proteins Alpha helices (nonpolar amino acids)
  27. 27. Fibers of extracellular matrix (ECM) Glyco- protein Microfilaments of cytoskeleton Cholesterol Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE Glyco- lipid EXTRA- CELLULAR SIDE OF MEMBRANE Carbo- hydrate 27
  28. 28. N-terminus C-terminus  Helix Trans- membrane protein 28
  29. 29. Major Functions of Membrane Proteins Transport Enzymatic activity Signal transduction Cell-to-cell recognition Intercellular joining Attachment to cytoskeleton & extracellular matrix (ECM) 29
  30. 30. (a) Transport (b) Enzymatic activity (c) Signal transduction ATP Enzymes Signaling molecule Receptor 30
  31. 31. 31 Sucrose porin (Transport protein)
  32. 32. 32 Succinate dehydrogenase (Enzyme)
  33. 33. 33 Cytochrome C Oxidase (Enzyme)
  34. 34. 34 G protein (Signal transduction)
  35. 35. (d) Cell-to-cell recognition Glyco- protein (e) Intercellular joining (f) Attachment to cytoskeleton & ECM 35
  36. 36. 36 HIV ligand receptor binding (Cell-to-cell recognition) HIV gp120 ligand CD4 gp receptor Antibody protein
  37. 37. 37 Adherens junction
  38. 38. 38 Bacterial ECM on 1 grain of sand
  39. 39. 39 Membrane Carbohydrates Surface sugars Cell-to-cell recognition Glycolipids Glycoproteins Variation: species, individual, cell types Cell membrane WBC membrane
  40. 40. Receptor (CD4) Co-receptor (CCR5) HIV Receptor (CD4) but no CCR5 Plasma membrane HIV can infect a cell that has CCR5 on its surface, as in most people. HIV cannot infect a cell lacking CCR5 on its surface, as in resistant individuals. 40
  41. 41. 41 Membrane Sidedness Outside = extracellular face Inside = cytoplasmic face Asymmetrical distribution of proteins, lipids, & sugars determined by ER & Golgi
  42. 42. Transmembrane glycoproteins ER ER lumen Glycolipid Plasma membrane: Cytoplasmic face Extracellular face Secretory protein Golgi apparatus Vesicle Transmembrane glycoprotein Secreted protein Membrane glycolipid 42
  43. 43. 43 Selective Permeability Regulates the cell’s molecular traffic Hydrophobic nonpolar molecules: dissolve & rapidly move across membrane [hydrocarbons] Hydrophilic polar molecules: do not easily move across membrane [sugars]
  44. 44. 44 Transport Proteins Allow passage of specific hydrophilic substances across membrane Channel proteins (hydrophilic tunnel for ions) Aquaporins (water transport) Carrier proteins (bind to molecules & change shape)
  45. 45. 45 K+ Channel Protein
  46. 46. 46
  47. 47. 47 Diffusion Tendency for molecules to spread out evenly into the available space Each molecule moves randomly A population of molecules exhibits a net movement in one direction Dynamic equilibrium
  48. 48. 48 Diffusion
  49. 49. 49 Concentration gradient
  50. 50. 50 Passive Transport Substances diffuse down their concentration gradient Move from an area of higher to lower concentration No energy required = Passive Transport
  51. 51. Net diffusion Net diffusion Equilibrium 51 Diffusion of one solute
  52. 52. Net diffusion Net diffusion Net diffusion Net diffusion Equilibrium Equilibrium 52 Diffusion of two solutes
  53. 53. 53 Osmosis Diffusion of water across a selectively permeable membrane Water moves from an area of lower to higher solute concentration Solutes cannot cross membrane
  54. 54. Low solute concentration H2O High solute concentration Selectively permeable membrane Equal solute concentration Osmosis 54 Osmosis
  55. 55. Tonicity: the ability of a surrounding solution to cause a cell to gain or lose water Isotonic Hypotonic Hypertonic 55
  56. 56. 56 Isotonic
  57. 57. 57 Hypotonic
  58. 58. 58 Hypertonic
  59. 59. Hypotonic solution Lysis Normal Isotonic solution Shriveled Hypertonic solution 59 Tonicity in Animal Cells
  60. 60. 60 Osmo- regulation Hypotonic & hypertonic environments create osmotic problems for organisms Osmoregulation = the control of solute concentrations & water balance Paramecium & contractile vacuoles
  61. 61. 61 Contractile Vacuoles
  62. 62. Hypotonic solution Turgid (normal, firm) Isotonic solution Flaccid (limp) Plasmolysis Hypertonic solution 62 Tonicity in Plant Cells
  63. 63. 63 Facilitated Diffusion Transport proteins help speed up passive transport Ion channels Gated channels Aquaporins Carrier proteins
  64. 64. 64 Channel Protein
  65. 65. 65 Carrier Protein
  66. 66. 66 Active Transport Requires ATP Moves substances against their concentration gradient Ions, amino acids, glucose Aided by specific membrane proteins Sodium-potassium pump ATP
  67. 67. EXTRACELLULAR FLUID [Na+] high [K+] low Na+ Na+ Na+ [Na+] low [K+] high CYTOPLASM Cytoplasmic Na+ binds to the sodium-potassium pump. 1 67
  68. 68. Na+ binding stimulates phosphorylation by ATP. Na+ Na+ Na+ ATP P ADP 2 68
  69. 69. Phosphorylation causes the protein to change its shape. Na+ is expelled to the outside. Na+ P Na+ Na+ 3 69
  70. 70. K+ binds on the extracellular side and triggers release of the phosphate group. P P 4 70
  71. 71. Loss of the phosphate restores the protein’s original shape. 5 71
  72. 72. K+ is released, and the cycle repeats. 72
  73. 73. 73 Electro- chemical Gradient Voltage: created by differences in distribution of +/- ions Membrane potential = voltage difference Electrochemical gradient = combination of chemical & electrical forces
  74. 74. 74 Electrogenic Pumps Transport proteins that generate voltage across a membrane Help store energy that can be used for cellular work Sodium- potassium pump (major pump in animal cells) Proton pump (major pump in plants, fungi, bacteria) H+ H+
  75. 75. H+ H+ H+ H+ + + + H+ + + H+ – – – – ATP – 75 Proton Pump
  76. 76. 76 Cotransport Active transport of a solute indirectly drives transport of another solute Also called coupled transport Plants use H+ gradient from proton pumps to actively transport nutrients into cells
  77. 77. Proton pump – – – – – – + + + + + + ATP H+ H+ H+ H+ H+ H+ H+ H+ Diffusion of H+ Sucrose-H+ cotransporter Sucrose Sucrose LOW HIGH LOW HIGH 77
  78. 78. Bulk Transport: Endocytosis & Exocytosis – requires energy Phagocytosis (“cell eating”) Pinocytosis (“cell drinking”) Receptor- Mediated Endocytosis 78
  79. 79. Pseudopodium Solutes “Food” or other particle Food vacuole CYTOPLASM EXTRACELLULAR FLUID Pseudopodium of amoeba Bacterium Food vacuole An amoeba engulfing a bacterium via phagocytosis (TEM). Phagocytosis 1 m 79
  80. 80. 80 Phagocytosis
  81. 81. Pinocytosis vesicles forming in a cell lining a small blood vessel (TEM). Plasma membrane Vesicle 0.5 m Pinocytosis 81
  82. 82. Top: A coated pit. Bottom: A coated vesicle forming during receptor-mediated endocytosis (TEMs). Receptor 0.25 m Receptor-Mediated Endocytosis Ligand Coat proteins Coated pit Coated vesicle Coat proteins Plasma membrane 82
  83. 83. 83 Exocytosis Secretory vesicles Enzymes, hormones, NT’s, wastes

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