permeability - connected to the other population of...

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To work properly with active enzymes and appropriate permeability, membranes must be fluid, about as fluid as salad oil. Cells can alter the lipid composition of membranes to compensate for changes in fluidity caused by changing temperatures. For example, cold-adapted organisms, such as winter wheat, increase the percentage of unsaturated phospholipids in the autumn. This allows these organisms to prevent their membranes from solidifying during winter. 2. Membranes are mosaics of structure and function A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer. Proteins determine most of the membrane’s specific functions. The plasma membrane and the membranes of the various organelles each have unique collections of proteins. There are two populations of membrane proteins. Peripheral proteins are not embedded in the lipid bilayer at all. Instead, they are loosely bounded to the surface of the protein, often
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Unformatted text preview: connected to the other population of membrane proteins. • Integral proteins penetrate the hydrophobic core of the lipid bilayer, often completely spanning the membrane (a transmembrane protein). • Where they contact the core, they have hydrophobic regions with nonpolar amino acids, often coiled into alpha helices. • Where they are in contact with the aqueous environment, they have hydrophilic regions of amino acids. • One role of membrane proteins is to reinforce the shape of a cell and provide a strong framework. • On the cytoplasmic side, some membrane proteins connect to the cytoskeleton. • On the exterior side, some membrane proteins attach to the fibers of the extracellular matrix. • Membranes have distinctive inside and outside faces. • The two layers may differ in lipid composition, and proteins in the membrane have a clear direction....
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This note was uploaded on 08/08/2009 for the course BIO 1406 taught by Professor Gomez during the Spring '09 term at Collin College.

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permeability - connected to the other population of...

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