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Chapter 5: Membrane Structure Topics you are not responsible for: details of Na-K pump (fig 5-15) End of Chapter questions: Understand: all Apply: all Synthesize: 1 & 2 Do all mQuiz questions Membrane Structure 1 What causes Cystic Fibrosis? Symptoms: -- Lungs: mucous accumulation infections -- affects other organs also Mutation to “CFTR” CF-TransmembraneConductance Regulator 1480 amino acids glycoprotein Membrane Cl- channel Mutation alters water transport -- How? -- Why? Membrane Structure 2 What is Osmosis? Solutions are isotonic How does solute concentration affect osmosis? Tonicity Osmotic pressure How does osmotic pressure affect cells? Turgor pressure Osmosis Question Membrane Structure 3 What is the structure of cell membranes? Phospholipids “Amphipathic” Spontaneously form bilayer Question Models Membrane Structure 4 How do we know that phospholipids are arranged as a bilayer? Langmuir Trough exp – 1925 -- creates monolayer Used RBCs: (lack internal membranes) Surface area of 1 ml of RBCs = 5x109 cells x 130 um2 / cell = 650 mm2 (~25 cm2) Actually observed ~1300 mm2 Why? Question Membrane Structure 5 What are some key characteristics of cell membranes? Selectively permeable Contain other components proteins other lipids cholesterol Fluidity -- a “2 dimensional fluid” Membrane Structure 6 What factors determine how fluid a membrane is? Properties of P-lipids: Chain length and FA saturation Properties of membranes: Cholesterol content Temperature Models Membrane Structure Membrane Fluidity 7 How does Alcoholism affect RBC function? Cholesterol Cholesterol content Spur cell formation Function and circulation problems Question Membrane Structure 8 Why can some molecules diffuse through a membrane, and others cannot? Size Charge Hydrophobicity Membrane Structure 9 How do molecules pass Through the membrane? Protein transporters high selectivity Vesicular (bulk) transport -- discussed more later Specialized Pores gap-junctions & plasmodesmata nuclear pores Membrane Structure 10 What are some properties of membrane proteins? Transmembrane (Integral) vs peripheral What are some functions of membrane proteins? Hydrophilic & hydrophobic domains Models Question Membrane Structure 11 What is facilitated transport? Channel transport proteins a selective pore Carrier transport protein has binding sites Passive Down a concentration gradient Active Against a gradient Requires energy Direction Reversible Membrane transporter Membrane Structure 12 Where does the energy come from for active transport? ATP e.g. Na/ K pump Sunlight (unusual) e.g. bacteriorhodopsin Gradient via Cotransport Build and use a ion gradient Cotransport Question Membrane Structure 13 Example: glucose cotransport in intestine Na/glucose symport -- active glucose -- against gradient Na/K pump -- remove Na Glucose uniport -- down gradient Membrane Structure 14 What types of molecules pass membranes via “Bulk Transport”? Particulates/ dissolved molecules Various forms Endocytosis vs exocytosis Phagocytosis Pinocytosis Can be “Receptor mediated” Vesicle “coating” proteins Receptors Vesicle Coating Membrane Structure 15 How is the structure of membranes studied – I ? Freeze-fracture electron microscopy Tissue frozen Etched Carbon-coated TEM Chloroplast thylakoid membranes Membrane Structure 16 How is the structure of membranes studied – II ? Detergents amphipathtic solubilize lipids/proteins Question Membrane Structure 17
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