PCB3134 - Exam 1 Review - Lipids and Membranes by Joyce Diwan

PCB3134 - Exam 1 Review - Lipids and Membranes by Joyce Diwan

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Copyright © 1999-2006 by Joyce J. Diwan. All rights reserved. Biochemistry of Metabolism
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Lipids are non-polar (hydrophobic) compounds, soluble in organic solvents. Most membrane lipids are amphipathic , having a non-polar end and a polar end. Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end. A 16-C fatty acid: CH3(CH2)14 - COO - Non-polar polar A 16-C fatty acid with one cis double bond between C atoms 9-10 may be represented as 16:1 cis 9 .
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Some fatty acids and their common names: 14:0 myristic acid; 16:0 palmitic acid; 18:0 stearic acid; 18:1 cis 9 oleic acid 18:2 cis 9,12 linoleic acid 18:3 cis 9,12,15 α -linonenic acid 20:4 cis 5,8,11,14 arachidonic acid 20:5 cis 5,8,11,14,17 eicosapentaenoic acid (an omega- 3) Double bonds in fatty acids usually have the cis configuration. Most naturally occurring fatty acids have an even number of carbon atoms.
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There is free rotation about C-C bonds in the fatty acid hydrocarbon, except where there is a double bond. Each cis double bond causes a kink in the chain. Rotation about other C-C bonds would permit a more linear structure than shown, but there would be a kink.
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Glycerophospholipids Glycerophospholipids (phosphoglycerides), are common constituents of cellular membranes. They have a glycerol backbone. Hydroxyls at C1 & C2 are esterified to fatty acids . An ester forms when a hydroxyl reacts with a carboxylic acid, with loss of H2O.
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Phosphatidate In phosphatidate : w fatty acids are esterified to hydroxyls on C1 & C2 w the C3 hydroxyl is esterified to Pi .
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In most glycerophospholipids (phosphoglycerides), Pi is in turn esterified to OH of a polar head group ( X ): e.g., serine, choline, ethanolamine, glycerol, or inositol . The 2 fatty acids tend to be non-identical. They may differ in length and/or the presence/absence of double bonds.
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Phosphatidylinositol , with inositol as polar head group, is one glycerophospholipid. In addition to being a membrane lipid, phosphatidylinositol has roles in cell signaling.
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Phosphatidylcholine , with choline as polar head group, is another glycerophospholipid. It is a common membrane lipid.
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Each glycerophospholipid includes w a polar region: glycerol , carbonyl O of fatty acids, Pi , & the polar head group ( X ) w non-polar hydrocarbon tails of fatty acids ( R1 , R2 ).
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Sphingosine may be reversibly phosphorylated to produce the signal molecule sphingosine-1-phosphate . Other derivatives of sphingosine are commonly found as constituents of biological membranes. Sphingolipids are derivatives of the lipid sphingosine , which has a long hydrocarbon tail, and a polar domain that includes an amino group.
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a polar “head group" is esterified to the terminal hydroxyl of the sphingosine moiety of the ceramide. The amino group of sphingosine can form an amide bond
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PCB3134 - Exam 1 Review - Lipids and Membranes by Joyce Diwan

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