Lecture24

Lecture24 - the membrane These lipid bilayers are highly...

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Lecture 24 11/30/11 Background reading: Berg, et al: Pages 351 – 354 Garrett and Grisham: Pages 267 - 272 Outline Phospholipids Liposomes Membranes Membrane proteins Membrane fluidity
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Phospholipids Head group Most phospholipids consist of a glycerol backbone that is esterified to two fatty acids and a phosphate. The phosphate is esterified to an alcohol (often called the head group). Three common head groups:
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Phospholipids are abundant in cell membranes. Four of the common phospholipids in membranes are shown below.
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Phospholipids are amphipathic and differ from fatty acids in that they have two long hydrophobic tails. When mixed in water they spontaneously form lipid bilayers with the hydrophobic tails of the fatty acids tucked inside. Liposomes These lipid bilayers become sealed compartments (vesicles) called liposomes , which are aqueous compartments enclosed by a lipid bilayer.
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Liposomes The permeability of lipid bilayers can be measured by preparing liposomes in the presence of a solute and then testing the ability of that solute to pass through
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Unformatted text preview: the membrane. These lipid bilayers are highly impermeable to ions and to most polar molecules as shown below. • Membranes Membranes are composed of about equal amounts of lipids and proteins. Our present model for membrane structure is the Fluid Mosaic Model of membranes proposed in the early 1970’s by Singer and Nicolson. • Membrane proteins Two classes of membrane proteins: 1) Integral membrane proteins These proteins are embedded in the membrane and can be only extracted with detergents. 2) Peripheral membrane proteins These proteins are attached to the membrane by noncovalent interaction with other proteins. They can be removed from the membrane by procedures such as treatment with high or low ionic strength or extreme pH Extend across membrane as α-helix of 20 – 30 amino acid residues • Membrane fluidity Both the phospholipids and proteins are fluid and can move only within the plane of the membrane....
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Lecture24 - the membrane These lipid bilayers are highly...

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