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Cell Membrane Structure & Permeability. Plasma Membrane
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Cell Membrane Structure & Permeability • Plasma Membrane • The plasma membrane that surrounds the cell is a fluid mosaic of phospholipids and proteins that separates the living cell from its nonliving surroundings. The membrane is selectively permeable consisting of a amphipathic (both hydrophilic and hydrophobic) bilayer of phosphate molecules. The layers are held together by hydrophobic interactions of the fatty acid tails.
Membrane Proteins • Membrane proteins • float freely with their hydrophilic regions in the center of the molecules and their hydrophilic regions extending outwards • some directed or held rigid by internal cytoskeleton fibers • 2 classes • Integral Proteins • has imbedded regions (can be transmembrane or partially imbedded) • Peripheral Proteins • loosely held only at the surface of the membrane
Cholesterol • Cholesterol • makes the membrane more rigid • lowers the temperature at which the membrane solidifies