CHAPTER 7-Fall'10 (1)

CHAPTER 7-Fall'10 (1) - CHAPTER 7 Membrane structure and...

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Unformatted text preview: CHAPTER 7 Membrane structure and function Cell Membrane and transport Systems http://www.youtube.com/watch?v=37KNBEfcbsA&feature=related http://www.youtube.com/watch?v=ULR79TiUj80 http://www.youtube.com/watch?v=moPJkCbKjBs&feature=related • The fluid Mosaic Model • http://www.youtube.com/watch?v=C7XliJVJhok&feature=related • http://www.youtube.com/watch?v=kfy92hdaAH0&feature=channel • Osmosis: http://www.youtube.com/watch?v=sdiJtDRJQEc&feature=related • Diffusion and Osmosis(18 minutes long) http://www.youtube.com/watch?v=aubZU0iWtgI&feature=fvw Overview: Life at the Edge • The plasma membrane is the boundary that separates the living cell from its nonliving surroundings. • The plasma membrane exhibits selective permeability , allowing some substances to cross it more easily than others. THE COMPLEXITY OF THE PLASMA MEMBRANE CELLULAR MEMBRANES ARE FLUID MOSAICS OF LIPIDS AND PROTEINS • Phospholipids are the most abundant lipid in the plasma membrane. • Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions. • The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it. Hydrophilic head Hydrophobic tail WATER WATER THE NATURE OF THE PHOSPHOLIPID BILAYER Hydrophilic region of protein Hydrophobic region of protein Phospholipid bilayer • Freeze-fracture studies of the plasma membrane supported the fluid mosaic model. • Freeze-facture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer. FREEZE FRACTURE STUDIES Knife Cytoplasmic layer Extracellular layer Cytoplasmic layer Plasma membrane Extracellular layer Proteins THE FLUIDITY OF MEMBRANES • Membranes are not static sheets of molecules locked rigidly in place. • Phospholipids in the plasma membrane can move within the bilayer. • Most of the lipids, and some proteins, drift laterally. • Rarely does a molecule flip-flop transversely across the membrane. Lateral movement (~10 7 times per second) Flip-flop (~ once per month) Movement of phospholipids • As temperatures cool, membranes switch from a fluid state to a solid state. • The temperature at which a membrane solidifies depends on the types of lipids. • Membranes rich in unsaturated fatty acids are more fluid that those rich in saturated fatty acids. • Membranes must be fluid to work properly; they are usually about as fluid as salad oil. EFFECT OF TEMPERATURE ON MEMBRANES Viscous Fluid Unsaturated hydrocarbon tails with kinks Membrane fluidity Saturated hydro- carbon tails LIQUID VS. SOLID • The steroid cholesterol has different effects on membrane fluidity at different temperatures....
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This note was uploaded on 03/30/2012 for the course BI 107 taught by Professor Fuller during the Fall '08 term at Montgomery College.

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CHAPTER 7-Fall'10 (1) - CHAPTER 7 Membrane structure and...

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