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Overview of catabolic pathways

Overview of catabolic pathways. 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

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Overview of catabolic pathways

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  1. Overview of catabolic pathways

  2. 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

  3. Dietary Lipid (Triacylglycerol) Metabolism • In the small intestine, fat particles are coated with bilesalts and digested by pancreatic lipases

  4. Lipoproteins • Triacylglycerols, cholesterol and cholesterol esters assemble with phospholipids and apolipoproteinsto form spherical particles called lipoproteins with • Hydrophobiccores: triacylglycerols and cholesterylesters • Hydrophilicsurfaces: cholesterol, phospholipids, apolipoproteins

  5. Summary of lipoprotein metabolism

  6. Lipoproteins in human plasma

  7. Fig 16.27 Triacylglycerol degradation

  8. Activation and Transport of fatty acids into the mitochondria • Fatty acids in the cytosol are activated by conversion to CoAthioesterscosting twoATPequivalents • The carnitine shuttle system transfers long-chain fatty acylCoA from the cytosol into the mitochondria • The b-oxidation cycle enzymes (mitochondrial) can then degrade the fatty acylCoA

  9. Beta Oxidation of Fatty Acids

  10. 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

  11. 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-Hydroxybutyrate Acetoacetate Acetone • Ketone bodies can fuel brain cells during starvation • Synthesis in the liver

  12. Cholesterol Biosynthesis

  13. Lovastatinresembles mevalonate and inhibits the enzyme HMG-CoAreductase

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