Chapter 7

Chapter 7 - Chapter 7 Membrane Structure and Function...

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Chapter 7 Membrane Structure and Function Plasma membrane exhibits selective permeability allows some substance to cross it more easily than others Cellular membranes are fluid mosaics of lipids and proteins A phospholipid is an amphipathic, meaning it has hydrophilic region and hydrophobic Fluid mosaic model, membrane is a fluid structure with a mosaic of various proteins embedded in or attached to a double layer of phospholipids Freeze fracture Cutaway view Hydrophobic are weaker then covalent bonds Proteins can shift laterally rapidly Some movie in a directed manner, driven by cytoskeletal fibers by motor proteins Remains fluid as temperature decreases until phospholipids settle and membrane solidifies Whenever it solidifies depends on the types of lipids it is made of Steroid cholesterol has different effects on membrane fluidity at different temperatures “fluidity buffer” Resists changes in membrane fluidity that can be caused by changes in temperature When a membrane solidifies its permeability changes and proteins may become inactive if they have to move around the membrane Membranes that are to fluid cannot support protein function either Evolution of Difference in Membrane Lipid Composition Membranes have the ability to change the lipid composition of cell membranes in response to changing temperatures When membranes have unsaturated hydrocarbon tails it prevents them packing enhancing membrane fluidity When membranes have saturated hydrocarbon tails they pack together increasing membrane viscosity Cholesterol reduce membrane fluidity at moderate temperatures but at low temperatures it hinders solidification Membrane Proteins and Their functions Phospholipids form main fabric of the membrane, but proteins determine most of the membranes
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Chapter 7 - Chapter 7 Membrane Structure and Function...

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