Exam Four Tables and Figures

Exam Four Tables and Figures - Exam Four Tables and Figures...

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Exam Four Tables and Figures Chapter 14 – Lipid Metabolism Table 14.1 Characteristics of lipoproteins Chylomicrons: 85-90% triacylglycerol VLDL: 50-65% triacylglycerol IDL: 40-45% cholesterol and cholesteryl ester LDL: 45-50% cholesterol and cholesteryl ester HDL: 40-55% protein Figure 14.3 Lipoprotein function Chylomicrons transport dietary lipids to the liver and other tissues. VLDL is produced by the liver.  They give up their triacylglycerols, becoming LDL. LDL is taken up by the tissues. HDL transport cholesterol from the tissues back to the liver. Triacylglycerol reaction Reactants: Triacylglycerol Enzyme: Lipoprotein lipase Products: Glycerol and fatty acyl groups Activation prior to degradation Fatty acid displaces diphosphate group of ATP  o Conserves free energy: phosphoanhydride bond Coenzyme A displaces AMP group to form acyl-CoA
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o Conserves free energy: thioester bond Figure 14.5 Acyl groups must enter the mitochondria via a shuttle system involving the small  molecule carnitine. o Cytosolic carnitine acyltransferase transfers an acyl group from CoA to carnitine. o The carnitine transporter allows the acyl-carnitine to enter the mitochondrial  matrix. o A mitochondrial carnitine acyltransferase transfers the acyl group to a  mitochondrial CoA molecule. o Free carnitine returns to the cytosol via the transport protein. B-oxidation Each round consists of four enzyme catalyzed steps that yield one molecule of acetyl- CoA and an acyl-CoA shortened by two carbons, which becomes the starting substrate  for the next round. Seven rounds of B oxidation degrade a C16 fatty acid to eight molecules of acetyl-CoA. o Number of carbons / 2 = molecules of acetyl-CoA o Molecules of acetyl-CoA – 1 = rounds of B oxidation Oxidation of unsaturated fatty acids Oleate and linoleate contain cis double bonds. Enoyl-Coa isomerase converts the cis to trans so that B oxidation can continue. Linoeate metabolism - 2 / - 3 ATP for reductase to convert double bonds to 3,4 trans bond.  (NADPH as  cofactor) o The QH2 dehydrogenase step is bypassed, so two less ATP is produced. o NADPH-dependent reductase consumes 3 ATP.
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Product is isomerized to produce the trans 2,3 double bond. Oxidation of odd-chain fatty acids The final round of B oxidation of these molecules leaves a three-carbon fragment,  propionyl-CoA, rather than the usual acetyl-CoA. Figure 14.7
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Exam Four Tables and Figures - Exam Four Tables and Figures...

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