4pp_3.Cholesterol - 12/29/2009 Cholesterol makes...

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12/29/2009 1 3. Cholesterol & lipoproteins Cholesterol makes phospholipid membranes more plastic with HO cholesterol Temperature cholesterol without cholesterol Cholesterol associates with sphingolipids and certain proteins to form “rafts” in the plasma membrane lipid raft protein with glycosyl- phosphatidylinositol (GPI) anchor at carboxyl end hl t sphingolipids & other phospholipids other Lipids probably are more ordered in rafts than elsewhere in the membrane because sphingolipids usually have long, saturated fatty acid side chains cholesterol phospholipids Cholesterol serves as a precursor for steroid hormones & bile acids HO O O OH cholesterol progesterone HO O OC H 2 OH O OH testosterone estradiol cortisone cholate CO 2 - HO OH OH O
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12/29/2009 2 Steroids are members of a large group of natural products with structures based on isoprene CH 2 H 2 C CH 3 cholesterol (27 carbons) squalene (30 carbons) HO isoprene CH 3 O CH 3 CH 3 O O O ubiquinone-7 (35-carbon side chain) β -carotene (40 carbons) Experiments with radioactive tracers showed that rats synthesize cholesterol and squalene from acetate. tt CH 3 CO 2 - squalene The labeling patterns in squalene and cholesterol were similar, supporting the hypothesis that squalene is an intermediate in cholesterol biosynthesis. HO cholesterol acetate The 5-carbon isoprenoid building block is synthesized from acetate by way of a 6-carbon intermediate, mevalonate C CH 3 CH 2 H 2 C CH 3 HO CH 2 CH 2 C CO 2 - CH 3 CH CH three molecules of acetate mevalonate isopentenyl- pyrophosphate CH 2 O P P CO 2 - CH 2 OH CO 2 - 3 CO 2 - 3 CO 2 Mevalonate is synthesized from three molecules of acetylCoA via β -hydroxy- β -methylglutarylCoA (HMG-CoA) CoA-SH CO -SCoA CH 3 CO -SCoA CH 3 CH 3 HO CO 2 - CO -SCoA CH 2 CH 2 C C=O CH 3 CO -SCoA CH 3 CO -SCoA CH 3 CoA-SH HMG-CoA mevalonate CH 3 HO CO 2 - CH 2 OH CH 2 CH 2 C 2 NADPH + 2H + 2 NADP + + CoA-SH HMG-CoA reductase key control point for cholesterol biosynthesis acetoacetylCoA 2 acetylCoA
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12/29/2009 3
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This note was uploaded on 02/08/2010 for the course LING 100 taught by Professor Kova during the Spring '10 term at University of Warsaw.

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4pp_3.Cholesterol - 12/29/2009 Cholesterol makes...

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