BILD 1 chapter seven

BILD 1 chapter seven - Chapter seven Membrane structure and...

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Chapter seven Membrane structure and function 7.1 Fluidity of membranes A membrane remains fluid as temp. decreases until it becomes a solid Membranes remain fluid to a lower temp if it is rich in phospholipids with unsaturated hydrocarbon tails Cholesterol is a temp buffer for the membrane, resisting changes in membrane fluidity that can be caused by changes in temperature Membranes must be fluid to work properly; when membrane solidifies the permeability changes and enzymatic proteins in membrane may become inactive Membrane proteins and their functions A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer phosopholipds form the main fabric of the membrane, but the proteins and the various membranes within a cell each have a unique collection of proteins two major populations of membrane proteins o integral proteins penetrate the hydrophobic core of the lipid bilayer. Many are transmembrane proteins which completely span the membrane. The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, usually coiled into alpha helices. o Peripheral proteins are not embedded in the lipid bilayer at all; they are appendages loosely bound to the surface of the membrane, often to the exposed parts of integral proteins Sometimes membrane proteins are held in place by cytoskeleton on the cytoplasmic side On the exterior side, certain membrane proteins are attached to fibers of the extracellular matrix, which give animal cells a stronger framework than plasma membrane itself could provide The role of membrane carbohydrates in cell-cell recognition The way cells recognize other cells is by binding to surface molecules, often carbohydrates, on the plasma membrane o Carbohydrates Glycolipids Lipid and carbohydrate covalently bonded together Glycoproteins Protein and carbohydrate covalently bonded together Synthesis and sidedness of membranes 1) process starts with synthesis of membrane proteins and lipids in ER. Carbohydrates are added to proteins to make glycoproteins. 2) inside Golgi, glycoproteins undergo further carbohydrate modification and lipids acquire
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BILD 1 chapter seven - Chapter seven Membrane structure and...

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