Chapter 5: Membrane Structure

1. 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

2. What causes Cystic Fibrosis? Mutation to “CFTR” “Cystic Fibrosis Transmembrane Conductance Regulator” -- a membrane Cl- channel Symptoms: -- Lungs & respiratory track -- infection and obstruction -- sweat glands -- excessive salt loss (3-5 X) -- other organs also Tick and Sick-2

3. How does CFTR mutation cause respiratory track ailments? Mutation alters water transport -- How? Why? Cilia and mucus Tick and Sick-2

4. Solutions are isotonic What is Osmosis? How does solute concentration affect osmosis? Tonicity Osmotic pressure How does osmotic pressure affect cells? Turgor pressure Osmosis Membrane Structure

5. What is the structure of cell membranes? Phospholipids “Amphipathic” Spontaneously form bilayer Models Membrane Structure

6. 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? Membrane Structure

7. What are some key characteristics of cell membranes? Selectively permeable Contain other components proteins other lipids cholesterol Fluidity -- a “2 dimensional fluid” Membrane Structure

8. 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 Fluidity Membrane Structure

9. Cholesterol How does Alcoholism affect RBC function? Cholesterol content Spur cell formation Function and circulation problems Membrane Structure

10. Why can some molecules diffuse through a membrane, and others cannot? Size Charge Hydrophobicity Membrane Structure

11. 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

12. What are some properties of membrane proteins? Transmembrane (Integral) vs peripheral What are some functions of membrane proteins? Hydrophilic & hydrophobic domains Models Membrane Structure

13. 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

14. 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 Membrane Structure

15. Example: glucose cotransport in intestine Na/glucose symport -- active glucose -- against gradient Na/K pump -- remove Na Glucose uniport -- down gradient Membrane Structure

16. 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

17. How is the structure of membranes studied – I ? Freeze-fracture electron microscopy Tissue frozen Etched Carbon-coated TEM Chloroplast thylakoid membranes Membrane Structure

18. How is the structure of membranes studied – II ? Detergents amphipathtic solubilize lipids/proteins Membrane Structure