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My_Ch8_lecture(2009030423470480) - Chapter 8 Membrane...

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Chapter 8: Membrane Structure & Function Purpose : to understand plasma membrane structure and function and movement of substances across membranes (AP Bio Major Theme: V; I: Science as a process—in regards to the historical development of the fluid mosaic model) What you MUST know from Ch 8: Membrane fluidity Membrane proteins Permeability of membranes Osmosis Tonicity Facilitated diffusion Active transport Bulk transport Membrane models have evolved and developed to better explain new data (pages 130-131). The current model is the fluid mosaic model , in which the plasma membrane is a mosaic of protein molecules that are embedded in a fluid phospholipid bilayer. (Fig 8.2 b, Fig 8.3, Fig 8.5)
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http://micro.magnet.fsu.edu/cells/plasmamembrane/plasmamembrane.html both the phospholipids and proteins move around (think salad oil) the phospholipid bilayer is amphipathic : it has a hydrophilic and a hydrophobic region the membrane remains fluid as temperature decreases; at a critical temp, the membrane solidifies, its permeability changes and its enzymes may become inactive. If it is high in unsaturated fatty acid tails, it will stay fluid at lower temps. Cholesterol stabilizes the animal cell membrane, and at 37 ° C makes the membrane less fluid. At the same time, it lowers the temp at which it becomes solid. There is a distinct inside and outside face of the membrane o Lipid layers differ in composition o Carbohydrates are on the exterior surface 2 major types of membrane proteins: Peripheral proteins —loosely attached to the inner or outer surface of the membrane, often bound to integral proteins
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Integral proteins —transmembrane proteins , which span across the membrane and appear at both surfaces Integral proteins are amphipathic : hydrophilic regions face the aqueous solutions bordering the membrane, while the hydrophobic regions are embedded in the membrane Functions of plasma membrane proteins: Transport proteins: o Channel proteins provide a hydrophilic channel for ions and polar molecules to pass through o Transport proteins use ATP to actively pump molecules across the membrane
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