Overview of catabolic pathways. Chapter 16 - Lipid Metabolism Triacylglycerols and glycogen are the...
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Transcript of Overview of catabolic pathways. Chapter 16 - Lipid Metabolism Triacylglycerols and glycogen are the...
![Page 1: Overview of catabolic pathways. Chapter 16 - Lipid Metabolism Triacylglycerols and glycogen are the two major forms of stored energy in vertebrates Glycogen.](https://reader033.fdocuments.in/reader033/viewer/2022061418/56649d935503460f94a79a71/html5/thumbnails/1.jpg)
Overview of catabolic pathways
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Chapter 16 - Lipid Metabolism
• Triacylglycerols and glycogen are the two major forms of stored energy in vertebrates
• Glycogen can supply ATP for muscle contraction for less than an hour
• Sustained work is fueled by metabolism of triacylglycerols
• Fatty acids (FA) and glycerol for metabolic fuels are obtained from triacylglycerols: (1) In the diet(2) Stored in adipocytes (fat storage cells)
• An enzyme (hormone-sensitive lipase) converts triacylglycerols to free fatty acids and glycerol
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Dietary Lipid (Triacylglycerol) Metabolism• In the small intestine, fat particles are coated with bile salts
and digested by pancreatic lipases
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Lipoproteins
• Triacylglycerols, cholesterol and cholesterol esters assemble with phospholipids and apolipoproteins to form spherical particles called lipoproteins with
• Hydrophobic cores: triacylglycerols and cholesteryl esters
• Hydrophilic surfaces: cholesterol, phospholipids, apolipoproteins
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Summary of lipoprotein metabolism
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Lipoproteins in human plasma
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Fig 16.27 Triacylglycerol degradation
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Activation and Transport of fatty acids into the mitochondria
• Fatty acids in the cytosol are activated by conversion to CoA thioesters costing two ATP equivalents
• The carnitine shuttle system transfers long-chain fatty acyl CoA from the cytosol into the mitochondria
• The b-oxidation cycle enzymes (mitochondrial) can then degrade the fatty acyl CoA
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Beta Oxidation of Fatty Acids
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Net yield of ATP per palmitate oxidized to 16 CO2
ATP generated
8 acetyl CoA 807 QH2 10.57 NADH 17.5
108 ATP
ATP expended to activate palmitate -2
Net yield: 106 ATP
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Ketone Bodies Are Fuel Molecules
• During fasting or starvation, glucose is decreased, and excess acetyl CoA from fat metabolism can be converted to ketone bodies:
b-HydroxybutyrateAcetoacetateAcetone
• Ketone bodies can fuel brain cells during starvation
• Synthesis in the liver
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Cholesterol Biosynthesis
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Lovastatin resembles mevalonate and inhibits the enzyme HMG-CoA reductase
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