1-423-08MembranesStudent

1-423-08MembranesStudent - Membrane Structure and Transport...

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Unformatted text preview: Membrane Structure and Transport Proteins OBJECTIVES Outline the structural features of membranes that are generally shared by all membranes: a. lipid bilayer b. fluid structure c. asymmetry d. transmembrane proteins e. receptors f. channels To know the basic structures of the phospholipids that are found in membranes and the importance of their amphipathic properties. To understand the fluid-mosaic concept of membranes. How are transporters similar to enzymes? How are they different? Describe the differences between, and give examples of Active (both primary and secondary) and passive transport Uniporters, Symporters and Antiporters Be able to describe the structure and function of:-the GluT1 transporter-the Na+K+ ATPase-the Na+ Glucose transporter OUTLINE I. Membrane functions A. Define the external boundary of cells B. Regulate transport in and out C. Divide internal space of cells into discrete compartments to segregate processes (example: fatty acid oxidation and synthesis segregated by mitochondrial membrane) D. Contain components responsible for energy generation (oxidative phosphorylation) E. Intra- and inter-cell communication (receptors, second messengers) F. Site of cellular component assembly (Ex: on ER) II. Membrane structure Necessary attributes: All these above functions require certain properties: tough but flexible; selectively permeable; 1 asymmetric; self-sealing A. Membranes are lipid bilayers... 1. lipids =~50% of mass of most animal cell membranes 2. Made of amphipathic lipids Forces responsible for the lipid aggregation are hydrophobic and van der waals interactions; and also some electrostatic ints, and H-bonds between the polar heads, and with water in surrounding solution. The Point: NO covalent bonds responsible for stability of lipid bilayer aggregate 3. Consequences of this lipid bilayer; It forms a permeability barrier; most ions and polar molecules are unable to broach that hydrophobic barrier due to energetic considerations Water is an exception; it is a very polar molecule, but small enough to cross the bilayer 4. Lipid composition in lipid bilayers vary with different types of cells B. Not simply lipid bilayers... have proteins associated with them-Membrane proteins are responsible for most membrane functions; receptors, enzymes, transport proteins C. Fluid Mosaic model Membranes are solutions of oriented lipids--as lipid bilayers, with polar heads out, nonpolar tails in; and proteins are embedded within or associated upon this bilayer in a mosaic fashion Membrane is fluid; lipids within the bilayer, and proteins, can move laterally within the plane of the bilayer, but do not (usually) rotate from one side of the bilayer to the other; that is, no flip-flop; D. Membranes are asymmetric So, the structure of the membrane maintains the direction of the lipids and proteins within it; the sidedness of the membrane is maintained Many of the functions of the membrane proteins are dependent upon this asymmetry; energy generation, transport, recognition and signal effectors 2 E. Membranes are fluidE....
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This note was uploaded on 04/05/2008 for the course BIOCHEM 423 taught by Professor Osgood during the Spring '08 term at New Mexico.

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1-423-08MembranesStudent - Membrane Structure and Transport...

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