Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Chapter 6 Energy Transfer in the Body

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Phosphate Bond Energy Adenosine triphosphate: The energy currency –Powers all of cell’s energy-requiring processes –Potential energy extracted from food –Energy is stored in bonds of ATP –Energy is transferred to do work

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Harnessing ATP’s Potential Energy ADP forms when ATP joins with water –Outermost phosphate is released –Catalyzed by the enzyme ATPase –Energy is released (~ 7.3 kCal/mol) Limited currency –Low ATP levels in cells create sensitivity to ATP/ADP

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Phosphocreatine: The Energy Reservoir Anaerobic resynthesis of ATP Hydrolyzed by the enzyme, creatine kinase ADP is phosphorylated to ATP Creatine may be phosphorylated back to PCr Cells store ~ 4 – 6 times more PCr than ATP

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Adenylate Kinase Reaction Reforms ATP using two ADP molecules –Results in ATP and AMP –Adenylate kinase drives this reaction. –It is reversible.

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Cellular Oxidation Cellular oxidation – reduction constitutes the biochemical mechanism that underlies energy metabolism

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Electron Transport Cellular redox reactions underlie energy metabolism. NAD and FAD oxidize food. Carrier molecules transport electrons. Electrons are passed to cytochromes. Oxygen serves as the final electron acceptor. ATP is synthesized.

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Oxidative Phosphorylation Synthesizes ATP by transferring electrons from NADH and FADH 2 to oxygen

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Oxygen’s Role in Energy Metabolism Three prerequisites for continual resynthesis of ATP during coupled oxidative phosphorylation –Availability of reducing agent in tissue –Presence of oxidizing agent –Sufficient concentration of enzymes and mitochondria

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Energy Release from Macronutrients Carbohydrate –Glycolysis Occurs in cytosol Series of chemical reactions Glucose is oxidized NAD is reduced to NADH Limited quantities of ATP are generated Glucose is cleaved into 2 pyruvate molecules

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Energy Release from Carbohydrate Carbohydrate’s primary function is to supply energy for cellular work.

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Glycolysis Generates Anaerobic Energy from Glucose Glycolysis is illustrated in Figure 6-11.

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Citric Acid Cycle Also known as the Krebs cycle Continues oxidation of –Carbohydrates following glycolysis –Fatty acids following beta oxidation –Some amino acids following deamination

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Total Energy Transfer from Glucose Catabolism

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition What Regulates Energy Metabolism? Overall energy state dictates the direction of metabolic pathways Rate-limiting modulators –ATP –ADP –cAMP –NAD –Calcium –pH

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Energy Release from Fat Stored fat is the body’s most plentiful source of potential energy. Two sources –Triacylglycerol in fat cells (adipocytes) –Intramuscular triacylglycerol Mobilization –First step in utilizing fatty acids is lipolysis –Triacylglycerol is split into fatty acids and glycerol. Hormone-sensitive lipase drives lipolysis.

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Adipocytes: The Site of Fat Storage and Metabolism Dynamics of fatty acid mobilization and fat use are outlined in Figure 6-17.

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Hormonal Effects Lipolysis is stimulated by –Epinephrine –Norepinephrine –Glucagon –Growth hormone Intracellular mediator –cAMP activates hormone-sensitive lipase.

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Catabolism of Glycerol and Fatty Acids Pathways for degrading glycerol and fatty acids fragments of triacylglycerol are shown in Figure 6-18.

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Total Energy Transfer from Fat Catabolism

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Energy Release from Protein Deamination –Nitrogen removal from amino acid –Occurs in liver and muscles –Enter citric acid cycle for oxidation Transamination –Amine group transferred

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition Protein as a Fuel Source Glucogenic –May be used to form Pyruvate Oxaloacetate Malate Ketogenic –May be used to form Acetyl-CoA Acetoacetate

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition The Metabolic Mill Glucose conversion to fat –Lipogenesis –Citrate diverted to cytosol –Fatty acids are synthesized. Protein conversion to fat –Excess amino acids deaminated –Converted to acetyl-CoA –Fatty acids are synthesized.

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition The Metabolic Mill Fats burn in a carbohydrate flame. –Glycolytic production of pyruvate keeps required levels of oxaloacetate to maintain activity of beta oxidation.

Copyright © 2007 Lippincott Williams & Wilkins.McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition The Metabolic Mill Slower rate of energy release from fat –Rate of fat oxidation is slower than that for carbohydrate. –Carbohydrate oxidation helps maintain fat oxidation rates. –Carbohydrate depletion impairs exercise performance.