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lecture 17 - 17-1 MCB 354 Lecture 17 Structure and...

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17-1 MCB 354 Lecture 17 Structure and Properties of Lipids Lipid Bilayers Reading in Lehninger : Chapter 10 , pp. 343-357 Chapter 11 , pp. 380-381
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Membranes and their components Membranes….. 1. = Organized assemblies of lipids and proteins + covalently associated carbohydrate 2. Surround all cells (= plasma membrane ) surround organelles in eukaryotes (nuclei, mitochondria, chloroplasts, ER, Golgi, vacuole) 3. Provide a 2D scaffolding for certain enzymes, for proteins involved in energy generation, for receptor proteins that detect extracellular signals 4. Regulate composition of intracellular spaces by controlling flow of nutrients, ions, waste products in and out of the cell and its organelles 5. Characteristic feature of membrane lipids : a m p h i p a t h i c : one end of molecule is highly hydrophobic , the other, hydrophilic 6. Three general types of membrane lipid: i) glycerophospholipids ii) sphingolipids iii) sterols 17-2
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Fatty acids 1. Carboxylic acids with long hydrocarbon chains 2. Chain can be fully saturated , or contain one or more double bonds (a few have 3-C rings, -OH groups, or methyl group branches) 3. Nomenclature: specifies chain length and # double bonds, separated by colon: eg. 16-C saturated palmitic acid = 16:0 18-C oleic acid (w. one double bond = 18:1) Position of double bond specified by superscript #’s following (e.g. 20-C FA with double bonds between C-9 & C-10 and between C-12 and C-13 = 20:2 ( 9,12) 4. The most commonly occurring FA have even #s of carbons in unbranched chains (even # results from biosynthesis from C2 units) 5. FA are rarely free in nature: usually ester- or amide-linked to other components of lipids (in vertebrates, free FA circulate in blood bound non-covalently to a carrier protein, serum albumin) 17-3 18:0
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Unsaturated fatty acids 17-4 Double bond introduces rigid 30° bend 18:3 ( 9,12,15) Generalizations : 1. In monounsaturated FA, double bond is usually between C-9 and C-10 ( 9) 2. Other double bonds of polyunsaturated FA usually 12 and 15 3. Double bonds in FA chains almost never conjugated (i.e. not -CH=CH-CH=CH-) 4. Double bonds almost always have cis configuration 18:1 ( 9)
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