Chapter 7 - 12

Chapter 7 - 12 - Chapter 7 Membrane Structure and Function...

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Chapter 7 Membrane Structure and Function Selective Permeability: it allows some substances to cross it more easily than others. 7.1 Lipids, proteins, and carbs are staple ingredients of membranes. The most important lipid is the phospholipids. The phospholipids being amphipathic with a hydrophobic and hydrophilic region is important. Fluid mosaic model: a membrane model where the membrane is a fluid structure with a mosaic of various proteins embedded in or attached to a double layer of phospholipids. A membrane is held together primarily by hydrophobic interactions which are weaker than covalent bonds. The lipids and some of the proteins can shift laterally but they hardly ever flip-flop transversely from one phospholipids layer to the other. Lateral movement occurs about 10 7 times per second while the flip-flop occurs maybe once per month. Membrane remains fluid as temperature decreases until it then solidifies as the temperature goes cooler. It remains fluid to a lower temperature if it is rich in phospholipids with unsaturated hydrocarbon tails. Cholesterol, is a steroid which is wedged between phospholipids molecules in the plasma membranes of animal cell s and have different effects on membrane fluidity. At higher temps cholesterol makes membrane less fluid but it lowers the temp for the membrane to solidify too. More than 50 kinds of proteins have been found so far in the plasma membrane of red blood cells. They determine most of the membrane’s functions. There are 2 major types of membrane proteins Integral proteins They penetrate the hydrophobic core of the lipid bilayer. The inside of this protein has a hydrophobic region where it have 1 or more stretches of nonpolar amino acids usually coiled into a α -helix. The hydrophilic parts are exposed to the aqueous solution on either side of the membrane and some of these also have a hydrophilic channel through their center to allow passage of hydrophilic substances. Peripheral proteins These are not embedded in the lipid bilayer at all but are appendages loosely bound to the surface of the membrane often to parts of integral proteins. On the cytoplasmic side of plasma membrane, membrane proteins are held in place by attachment to cytoskeleton and on the extracellular side, they are attached to fibers of the extracellular matrix. Membrane Protein Functions Transport: can provide a hydrophilic channel across the membrane that is selective for a particular solute or can shuttle a substance from one side to the other by changing shapes. Some require hydrolysis of ATP to energize their pumps Enzymatic Activity: it can be a enzyme with its active site exposed to substance sin the adjacent solution. Signal Transduction: it can be a message relay where it receives message and transforms itself to releae
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This note was uploaded on 10/19/2008 for the course BILD 1 taught by Professor Boulanger during the Fall '08 term at UCSD.

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Chapter 7 - 12 - Chapter 7 Membrane Structure and Function...

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