Lipids-a - Lipid Metabolism Lipid Metabolism Major roles of...

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Unformatted text preview: Lipid Metabolism Lipid Metabolism Major roles of lipids in cell structure and metabolism: triacylglycerols: major form of stored energy in mammals phospholipids, glycolipids, cholesterol: components of cell membranes cholesterol: precursor of steroid hormones and bile salts hormones and intracellular messengers: prostaglandins, prostacyclins, thromboxanes, leucotrienes, lipoxins protein targeting to membranes Fatty Acid Metabolism Fatty acids have 4 major physiological roles: components of phospholipids and glycolipids covalent attachment to proteins, protein targeting fuel and storage (triglycerides) hormones and intracellular messengers Note: double bonds when present are cis and unconjugated. CH 2 CH 2 CH OH OH OH Glycerol Triacylglycerol R 1 R 2 R 3 CH 2 CH 2 CH O O O C C C O O O Triacylglycerols, stored in adapose cells, are the major energy reserve in animals Fats provide about 6 times the energy/mass of carbohydrates Stored in an anhydrous state carbon atoms have low oxidation states Comparison of fatty acid biosynthesis and degradation Digestion of dietary lipids: emulsification with detergents Major bile acids and their glycine and taurine conjugates Bile acids: synthesized in liver, passed to gall bladder, secreted into small intestine, re-adsorbed, taken up by liver. The fraction that escape re-adsorption is the only route for cholesterol excretion. If bile acid production is defective due to liver disease, large amounts of fats are excreted into the feces (steatorrhea). Dietary lipids are digested by pancreatic lipases pancreatic lipase-colipase complex triacylglycerol-------> 1,2 diacylglycerol---------->2 acylglycerol interfacial activation: The enzyme is only active in complex with micelles. Phospholipids are degraded by pancreatic phospholipases hypothetical model Active site and catalytic mechanism of phospholipase A 2 cut-away view of active site with tetrahedral transition state analogue MJ33. Bound Ca 2+ participates in activation of reactive H 2 and stabilizes oxyanion of transition state. Bile salts micells with dispersion/digestion products and lipid-soluble vitamins are taken up by the cells of the intestinal mucosa rat fatty acid binding protein bound to palmitate. a beta clam Inside the cells of the intestinal mucosa, fatty acids are converted back to triacylglycerols and packaged into chylomicrons along with cholesterol and vitamins. Chylomicrons are released into lymphatic system and from there into the blood stream. Model for plasma triacylglycerol and cholesterol transport in humans. Lipids are transported in lipoprotein complexes QuickTime and a GIF decompressor are needed to see this picture. Cartoon of the LDL particle Glycerol from the breakdown of dietary and endogenous triacylglycerols is transported to the liver and used in glycolysis and gluconeogenesis Fatty acids released from adipose tissue is carried in the bloodstream by serum albumin human serum albumin in complex with 7 palmitate...
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Lipids-a - Lipid Metabolism Lipid Metabolism Major roles of...

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