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Membrane Structure & Function: A Concise Overview
- 1. Membrane Structure & Function BIOL 101: General Biology I Chapter 7 Rob Swatski Associate Professor of Biology HACC – York Campus 1
- 2. 2
- 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
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- 8. 8
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- 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
- 13. 13 Freeze- Fracture Specialized preparation technique Splits membrane along the middle of the bilayer Confirmed fluid mosaic model
- 14. Knife Plasma membrane Cytoplasmic layer Proteins Extracellular layer Inside of extracellular layer Inside of cytoplasmic layer TECHNIQUE RESULTS 14
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- 17. 17
- 18. Membrane Fluidity Flip-flop ( once per month) Lateral movement (107 times per second) 18
- 20. 20 Membrane Fluidity Essential for proper functioning Colder temp. viscous Unsaturated fatty acids = more fluid Saturated fatty acids = less fluid
- 21. 21
- 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. Cholesterol in plasma membrane 23
- 24. 24 Membrane Proteins Membrane = collage of proteins Embedded in plasma membrane Determine most of membrane’s specific functions
- 25. 25
- 26. 26 Membrane Proteins Peripheral proteins Integral proteins Transmembrane proteins Alpha helices (nonpolar amino acids)
- 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
- 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. (a) Transport (b) Enzymatic activity (c) Signal transduction ATP Enzymes Signaling molecule Receptor 30
- 33. 33Cytochrome C Oxidase (Enzyme)
- 34. 34G protein (Signal transduction)
- 35. (d) Cell-to-cell recognition Glyco- protein (e) Intercellular joining (f) Attachment to cytoskeleton & ECM 35
- 36. 36 HIV ligand receptor binding (Cell-to-cell recognition) HIV gp120 ligand CD4 gp receptor Antibody protein
- 38. 38Bacterial ECM on 1 grain of sand
- 39. 39 Membrane Carbohydrates Surface sugars Cell-to-cell recognition Glycolipids Glycoproteins Variation: species, individual, cell types Cell membrane WBC membrane
- 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 Membrane Sidedness Outside = extracellular face Inside = cytoplasmic face Asymmetrical distribution of proteins, lipids, & sugars determined by ER & Golgi
- 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 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 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)
- 46. 46
- 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. 48Diffusion
- 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. Net diffusion Net diffusion Equilibrium 51 Diffusion of one solute
- 52. Net diffusion Net diffusion Net diffusion Net diffusion Equilibrium Equilibrium 52 Diffusion of two solutes
- 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. Low solute concentration H2O High solute concentration Selectively permeable membrane Equal solute concentration Osmosis 54Osmosis
- 55. Tonicity: the ability of a surrounding solution to cause a cell to gain or lose water Isotonic Hypotonic Hypertonic 55
- 56. 56 Isotonic
- 57. 57 Hypotonic
- 58. 58 Hypertonic
- 59. Hypotonic solution Lysis Normal Isotonic solution Shriveled Hypertonic solution 59 Tonicity in Animal Cells
- 60. 60 Osmo- regulation Hypotonic & hypertonic environments create osmotic problems for organisms Osmoregulation = the control of solute concentrations & water balance Paramecium & contractile vacuoles
- 62. Hypotonic solution Turgid (normal, firm) Isotonic solution Flaccid (limp) Plasmolysis Hypertonic solution 62 Tonicity in Plant Cells
- 63. 63 Facilitated Diffusion Transport proteins help speed up passive transport Ion channels Gated channels Aquaporins Carrier proteins
- 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. EXTRACELLULAR FLUID [Na+] high [K+] low Na+ Na+ Na+ [Na+] low [K+] highCYTOPLASM Cytoplasmic Na+ binds to the sodium-potassium pump. 1 67
- 68. Na+ binding stimulates phosphorylation by ATP. Na+ Na+ Na+ ATP P ADP 2 68
- 69. Phosphorylation causes the protein to change its shape. Na+ is expelled to the outside. Na+ P Na+ Na+ 3 69
- 70. K+ binds on the extracellular side and triggers release of the phosphate group. P P 4 70
- 71. Loss of the phosphate restores the protein’s original shape. 5 71
- 72. K+ is released, and the cycle repeats. 72
- 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 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+
- 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
- 78. Bulk Transport: Endocytosis & Exocytosis – requires energy Phagocytosis (“cell eating”) Pinocytosis (“cell drinking”) Receptor- Mediated Endocytosis 78
- 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 1m 79
- 80. 80 Phagocytosis
- 81. Pinocytosis vesicles forming in a cell lining a small blood vessel (TEM). Plasma membrane Vesicle 0.5m Pinocytosis 81
- 82. Top: A coated pit. Bottom: A coated vesicle forming during receptor-mediated endocytosis (TEMs). Receptor 0.25m Receptor-Mediated Endocytosis Ligand Coat proteins Coated pit Coated vesicle Coat proteins Plasma membrane 82