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Unformatted text preview: TEST 3 1. The lipid bilayer a. Forms spontaneously b/c of hydrophobic effect b. Feature of all cells and eukaryotic organelles c. Different lipids of the membranemostly derivatives of fatty acids i. Saturated fatty acids 1. Ex: Palmitate, Stearate ii. Unsaturated fatty acids 1. Ex: Oleate, Linoleate 2. Contain DB usually with a cis conformation 3. DB induces rigidity; much less flexible than sat. iii. Free fatty acids scarce in biological systemsusually esterified 1. Fats and oils in plants and animals are triacylglycerols ** neutral fats** a. The acyl groups (R-CO groups) of 3 fatty acids are esterified to the 3 hydroxyls groups of glycerol b. Do not form bilayers c. Aggregate in large globules to serve as storage for fatty acids to be broken down for energy d. Simple vs. mixed i. Mixed have DBput kink in molecule, affects interaction btwn tails. iv. In the membrane: 1. Glycerophospholipdsglycerol backbone w/ fatty acyl groups at position 1 and 2; phosphate derivative (head group) at pos 3 a. Phosphate bound to diff side chains b. Head groups give appropriate geometry and amphipathic nature to easily form bilayers 2. Sphingolipids a. Instead of glycerolsphingosine (derivative of serine and palmitate b. Have a 2 nd fatty acyl group attached via amide bond to serine nitrogen c. Sphingomyelin: phosphocholine or phosphoethanolamine head groups; sterically similar to glycerophospholipids. 3. Cholestrol a. Doesnt form bilayer on its own, b/c hydrophobic except for single polar hydroxyl group (sticks out) b. Planar ring structure inserts among the acyl chains of other lipids; all hydrophobic 4. Isoprenoids a. Not structural components but soluble in lipid bilayer b/c of hydrophobicity b. 5-carbon units w/ same skeleton as isoprene 5. EX: ubiquione: mitochondrial membrane; made of isoprenoid units 6. EX: lipid soluble vitamins: A, D, & K d. Fluidity of the membrane i. No defined geometry ii. Hydrophobic core 25 to 30 A thick.varies according to lengths of acyl chains & how they bend & intergrate iii. Dynamic assembly: heads bob up and down and tails in constant motion iv. Melting Point 1. For saturated chain: MP increases w/ increasing length 2. For unsaturated: less able to pack closely, MP decrease as length increases 3. Summation: @ constant Tlonger chains less mobile than short and sat less mobile than unsat v. Cholesterol helps maintain constant fluidity @ range of temps in 2 ways 1. its rigid and planar ring system restricts movement of acyl chains, decreasing fluidity 2. By inserting btwn membrane lipids, it prevents there close packing, which tends to increase fluidity e. Bilayers are asymmetric i. Distinct compositions of inner and outer leaflets ii. Preserved by the extremely slow rate of transverse diffusion or flip-flop 1. thermodynamically unfavorablepolar group has to pass through hydrophobic region 2. able to happen with assistance of enzymes. Flippases or translocases iii. Lipids undergo rapid lateral diffusion within one leaflet...
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This test prep was uploaded on 03/20/2008 for the course HDF 304 taught by Professor Gray during the Fall '08 term at University of Texas at Austin.
- Fall '08