Membrane Structure1 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 Structure2 What causes Cystic Fibrosis? Symptoms: -- Lungs: mucous accumulation infections -- affects other organs also Mutation to “CFTR” CF-Transmembrane- Conductance Regulator 1480 amino acids glycoprotein Membrane Cl - channel Mutation alters water transport -- How? -- Why?

Membrane Structure3 What is Osmosis? How does solute concentration affect osmosis? Tonicity Osmotic pressure How does osmotic pressure affect cells? Turgor pressure Solutions are isotonic Osmosis Question

Membrane Structure4 What is the structure of cell membranes? Phospholipids “ Amphipathic ” Spontaneously form bilayer ModelsQuestion

Membrane Structure5 How do we know that phospholipids are arranged as a bilayer? Langmuir Trough exp – creates monolayer Used RBCs: (lack internal membranes) Surface area of 1 ml of RBCs = 5x10 9 cells x 130 um 2 / cell = 650 mm 2 (~25 cm 2 ) Actually observed ~1300 mm 2 Why? Question

Membrane Structure6 What are some key characteristics of cell membranes? Selectively permeable Contain other components proteins other lipids cholesterol Fluidity -- a “2 dimensional fluid”

Membrane Structure7 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 Structure8 How does Alcoholism affect RBC function? Cholesterol content Spur cell formation Function and circulation problems Cholesterol Question

Membrane Structure9 Why can some molecules diffuse through a membrane, and others cannot? Size Charge Hydrophobicity

Membrane Structure10 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 Structure11 What are some properties of membrane proteins? Transmembrane (Integral) vs peripheral What are some functions of membrane proteins? Models Hydrophilic & hydrophobic domains Question

Membrane Structure12 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 Structure13 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 Structure14 Example: glucose cotransport in intestine Na/glucose symport -- active glucose -- against gradient Na/K pump -- remove Na Glucose uniport -- down gradient

Membrane Structure15 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 Vesicle Coating Receptors

Membrane Structure16 How is the structure of membranes studied – I ? Freeze-fracture electron microscopy Tissue frozen Etched Carbon-coated TEM Chloroplast thylakoid membranes

Membrane Structure17 How is the structure of membranes studied – II ? Detergents amphipathtic solubilize lipids/proteins Question