CHAPTER 11(Pictures)

CHAPTER 11(Pictures) - David L. Nelson and Michael M. Cox...

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1 Lehninger Principles of Biochemistry Fourth Edition Chapter 11: Biological Membranes and Transport David L. Nelson and Michael M. Cox
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2 The Molecular constituents of membranes Each type of membrane has characteristics lipid and proteins Table 11-1 Figure 11-2
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4 The Supramolecular architecture of membranes All biological membranes are: Impermeable to most polar or charged molecules, Permeable to nonpolar compounds They are 5 to 8 nm (50 to 80 Å) thick Fluid mosaic model ( Fig. 11-3 ): Phospholipids and sterols form lipid bilayer in which the nonpolar regions of the lipid molecules faces each other at the core of the bilayer and their polar head gps face outward In the bilayer, protein is embedded at irregular intervals, held by hydrophobic interactions btw the membrane lipids and hydrophobic domains of the proteins Some proteins protrude from one side of the membrane; other have domains exposed on both sides The membrane mosaic is fluid because most of interactions among its components are noncovalent, leaving individual lipid and protein molecule free to move laterally in the plane of the membrane
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6 The Supramolecular architecture of membranes (cont.) A lipid bilayer is the basic structural element of members: Glycerophospholipids, sphingolipids and sterols are virtually insoluble in water When mixed with water, they spontaneously form microscopic lipid aggregates in phase separate from the aqueous surroundings, clustering together with hydrophobic moieties in contact with each other and their hydrophilic group interacting with water Micelles : Are spherical structures containing molecules arranged with their hydrophobic tails aggregated in the interior, excluding water, and their hydrophilic heads at the surface, in contact with water ( Fig. 11-4a ) Are favored when the X-sectional area of the head is greater than the acyl side chians Bilayer : Two lipid monolayers form a two-dimensional sheet Favored when the X-sectional surface area of the head group and acy side chain are similar ( Fig. 11-4b ) Liposome (vesicle) :
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8 The Supramolecular architecture of membranes (cont.) Peripheral membrane proteins are easily solubilized ( Fig. 11-6): Membrane proteins are divided into two operation groups Integral (intrinsic) proteins are firmly associated with the membrane, removal only by agents that interfere with hydrophobic interactions (detergents, organic solvents, or denaturants) Peripheral (extrinsic) proteins associated with membrane through electrostatic interactions and H-bonding with hydrophilic domains of integral proteins with the polar head groups of membrane lipids They can be released by relatively mild treatments that interfere with electrostatic interaction or break H-bond They serve as regulators of membrane -bound enzymes or may limit the mobility of integral proteins by tethering them to intracellular structures
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10 Covelently attached lipids anchor some peripheral membrane proteins ( Fig. 11-14)
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This note was uploaded on 08/21/2008 for the course BIOCHEM 301 taught by Professor Vanes during the Spring '08 term at Rutgers.

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CHAPTER 11(Pictures) - David L. Nelson and Michael M. Cox...

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