by123 chapter 7 - Chapter 7: the Plasma Membrane Structure...

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Chapter 7: the Plasma Membrane Structure and Functions The plasma membrane is the boundary that separates the living cell from its surroundings The plasma membrane has selective permeability; that is, allows some substances to cross it more easily than others A phospholid is an amphipathic molecule, meaning it has both a hydrophilic region and a hydrophobic region Fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in or attached to a double layer of phospholipids E. Gorter and F. Grendel reasoned that cell membranes must be phospholipid bilayers Hugh Davson and James Danielli suggested that there was a phospholipid bilayer between two layers of proteins J. Singer and G. Nicholson proposed that membrane proteins are dispersed, individiually inserted into the phospholipid bilayer with their hydrophilic regions protruding Membranes are held together primarily by hydrophobic interactions, which are much weaker than covalent bonds o Most of the lipids and some of the proteins can shift about laterally (switch from right side to left) o Unsaturated hydrocarbon tails with kinds makes the membrane fluid o Saturated hydrocarbon tails makes the membrane viscous o Cholesterol in animal cell membranes reduces membrane fluidity at moderate temperatures by reducing phospholipid movement, but in low temperatures it hinders solidification by disrupting the regular packing of phospholipids o Membranes have the fluidity of salad oil Integral proteins penetrate the hydrophobic core of the lipid bilayer. Many are transmembranes, which span the membrane; other integral proteins extend only partway into the hydrophobic core. Periphial proteins are not embedded in the lipid bilayer at all; they are appendages Six major functions of the membrane proteins o Transport- a protein can provide a hydrophilic channel across the membrane, or shuttle a substance from one side to
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This note was uploaded on 08/07/2009 for the course BY 123 taught by Professor Cusic during the Spring '07 term at University of Alabama at Birmingham.

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by123 chapter 7 - Chapter 7: the Plasma Membrane Structure...

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