22 Lipids - Cholesterol Synthesis and Ketone Bodies

22 Lipids - Cholesterol Synthesis and Ketone Bodies -...

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Unformatted text preview: Lipids: Cholesterol Synthesis Ketone Bodies HNFE 3025 Fall 2009 FA are esterified at this location Cholesterol Structure 2 27 carbon molecule with the steroid (4 ring) core structure. Because of the OH group, cholesterol is less hydrophobic than its cholesterol ester form. Membrane component Provides rigidity and fluidity Steroid synthesis Precursor for glucocorticoids, mineralcorticoids, sex hormones Bile acid/salt precursor Cholic acid necessary for absorption of dietary lipids Vitamin D precursor Important compontent in maintaining serum Ca 2+ concentrations Roles of Cholesterol 3 Exogenous (dietary) sources Exclusively found in animal products dairy, eggs, meats Dietary cholesterol (~600 mg/d) Endogenous sources The average person synthesizes cholesterol in all nucleated cell (~1000 mg/d) Sources of Cholesterol Absorption is about 50% of intake Increase intake increased absorption Excrete 1 g/day (bile acids) Assume 400 mg intake/day 200 mg is absorbed 1000 mg is excreted 800 mg synthesized to maintain the same levels Lowering cholesterol in the diet has very little effect on blood cholesterol !!! Dietary Cholesterol 5 The Ins and Outs of Cholesterol 6 Diet (Chylomicrons) Hepatic synthesis Extrahepatic synthesis Free cholesterol in bile Conversion to bile salts/acids Secretion of HDL and VLDL Occurs in cytosol 20 % in liver Intestine, adrenal glands, reproductive organs Requires NADPH and ATP Highly regulated Allosteric, covalent and transcriptional Statin drugs are potent competitive inhibitors for hydroxymethylglutaryl CoA reductase (HMG CoA reductase) which catalyzes the rate-limiting step in cholesterol synthesis Cholesterol uptake into cells regulated by cell membrane LDL receptor Cholesterol Synthesis 7 At least 31 steps (64 reactions) are involved in producing cholesterol from acetyl CoA We are going to break this down into 4 stages Formation of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) from 3 acetyl CoA Conversion of HMG CoA to isoprenoids Conversion of isoprenoids to squalene Formation of cholesterol from squalene Cholesterol Synthesis 8 Acetyl CoA must be moved into the cytosol from the mitochondria via the citrate shuttle 3 acetyl CoA are combined with the use of 2 enzymes HMG CoA, a 6 carbon molecule, can be converted to ketone bodies or to cholesterol precursors isoprenoids This step is repeated 6 times to produce a total of 6 HMG CoA Formation of HMG CoA 9 Acetyl CoA Acetoacetyl CoA Thiolase Acetyl CoA CoA HMG-CoA HMG-CoA synthase Acetyl CoA, H 2 O CoA Palmitoyl CoA-oxidation...
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This note was uploaded on 03/23/2010 for the course HNFE 3025 taught by Professor Mwhulver during the Spring '10 term at Virginia Tech.

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22 Lipids - Cholesterol Synthesis and Ketone Bodies -...

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