Transcript Chapter 3
Chapter 3 Bioenergetics EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6th edition Scott K. Powers & Edward T. Howley © 2007 McGraw-Hill Higher Education. All rights reserved. Introduction • Metabolism: total of all chemical reactions that occur in the body – Anabolic reactions • Synthesis of molecules – Catabolic reactions • Breakdown of molecules • Bioenergetics – Converting foodstuffs (fats, proteins, carbohydrates) into energy © 2007 McGraw-Hill Higher Education. All rights reserved. Objectives • Discuss the function of cell membrane, nucleus, and mitochondria • Define: endergonic, exergonic, coupled reactions, and bioenergetics • Describe how enzymes work • Discuss nutrients used for energy • Identify high-energy phosphates © 2007 McGraw-Hill Higher Education. All rights reserved. Objectives • Discuss anaerobic and aerobic production of ATP • Describe how metabolic pathways are regulated • Discuss the interaction of anaerobic and aerobic ATP production during exercise • Identify the rate limiting enzymes © 2007 McGraw-Hill Higher Education. All rights reserved. Cell Structure • Cell membrane – Protective barrier between interior of cell and extracellular fluid • Nucleus – Contains genes that regulate protein synthesis • Cytoplasm – Fluid portion of cell – Contains organelles (mitochondria) © 2007 McGraw-Hill Higher Education. All rights reserved. Structure of a Typical Cell Fig 3.1 © 2007 McGraw-Hill Higher Education. All rights reserved. Cellular Chemical Reactions • Endergonic reactions – Require energy to be added • Exergonic reactions – Release energy • Coupled reactions – Liberation of energy in an exergonic reaction drives an endergonic reaction © 2007 McGraw-Hill Higher Education. All rights reserved. The Breakdown of Glucose: An Exergonic Reaction Fig 3.3 © 2007 McGraw-Hill Higher Education. All rights reserved. Coupled Reactions Fig 3.4 © 2007 McGraw-Hill Higher Education. All rights reserved. Oxidation-Reduction Reactions • Oxidation: removing an electron • Reduction: addition of an electron • Oxidation and reduction are always coupled reactions • In cells, often involve the transfer of hydrogen atoms rather than free electrons – Hydrogen atom contains one electron – A molecule that loses a hydrogen also loses an electron and, therefore, is oxidized © 2007 McGraw-Hill Higher Education. All rights reserved. Enzymes • Catalysts that regulate the speed of reactions – Lower the energy of activation • Factors that regulate enzyme activity – Temperature – pH • Interact with specific substrates – Lock and key model © 2007 McGraw-Hill Higher Education. All rights reserved. Enzymes Lower the Energy of Activation Fig 3.6 © 2007 McGraw-Hill Higher Education. All rights reserved. EnzymeSubstrate Interaction Fig 3.7 © 2007 McGraw-Hill Higher Education. All rights reserved. Fuels for Exercise • Carbohydrates – Glucose • Stored as glycogen • Fats – Primarily fatty acids • Stored as triglycerides • Proteins – Not a primary energy source during exercise © 2007 McGraw-Hill Higher Education. All rights reserved. High-Energy Phosphates • Adenosine triphosphate (ATP) – Consists of adenine, ribose, and three linked phosphates • Formation ADP + Pi ATP • Breakdown ATP ATPase © 2007 McGraw-Hill Higher Education. All rights reserved. ADP + Pi + Energy Structure of ATP Fig 3.8 © 2007 McGraw-Hill Higher Education. All rights reserved. Model of ATP as the Universal Energy Donor Fig 3.9 © 2007 McGraw-Hill Higher Education. All rights reserved. Bioenergetics • Formation of ATP – Phosphocreatine (PC) breakdown – Degradation of glucose and glycogen (glycolysis) – Oxidative formation of ATP • Anaerobic pathways – Do not involve O2 – PC breakdown and glycolysis • Aerobic pathways – Require O2 – Oxidative phosphorylation © 2007 McGraw-Hill Higher Education. All rights reserved. Anaerobic ATP Production • ATP-PC system – Immediate source of ATP PC + ADP Creatine kinase ATP + C • Glycolysis – Energy investment phase • Requires 2 ATP – Energy generation phase • Produces ATP, NADH (carrier molecule), and pyruvate or lactate © 2007 McGraw-Hill Higher Education. All rights reserved. The Two Phases of Glycolysis © 2007 McGraw-Hill Higher Education. All rights reserved. Fig 3.10 Glycolysis Energy Investment Phase Fig 3.11 © 2007 McGraw-Hill Higher Education. All rights reserved. Glycolysis Energy Generation Phase Fig 3.11 © 2007 McGraw-Hill Higher Education. All rights reserved. Oxidation-Reduction Reactions • Oxidation – Molecule accepts electrons (along with H+) • Reduction – Molecule donates electrons • Nicotinomide adenine dinucleotide (NAD) NAD + 2H+ NADH + H+ • Flavin adenine dinucleotide (FAD) FAD + 2H+ FADH2 © 2007 McGraw-Hill Higher Education. All rights reserved. Production of Lactic Acid • Normally, O2 is available in the mitochondria to accept H+ (and electrons) from NADH produced in glycolysis – In anaerobic pathways, O2 is not available • H+ and electrons from NADH are accepted by pyruvic acid to form lactic acid © 2007 McGraw-Hill Higher Education. All rights reserved. Conversion of Pyruvic Acid to Lactic Acid Fig 3.12 © 2007 McGraw-Hill Higher Education. All rights reserved. Aerobic ATP Production • Krebs cycle (citric acid cycle) – Completes the oxidation of substrates and produces NADH and FADH to enter the electron transport chain • Electron transport chain – Oxidative phosphorylation – Electrons removed from NADH and FADH are passed along a series of carriers to produce ATP – H+ from NADH and FADH are accepted by O2 to form water © 2007 McGraw-Hill Higher Education. All rights reserved. The Three Stages of Oxidative Phosphorylation Fig 3.13 © 2007 McGraw-Hill Higher Education. All rights reserved. The Krebs Cycle Fig 3.14 © 2007 McGraw-Hill Higher Education. All rights reserved. Relationship Between the Metabolism of Proteins, Fats, and Carbohydrates Fig 3.15 © 2007 McGraw-Hill Higher Education. All rights reserved. Electron Transport Chain Fig 3.17 © 2007 McGraw-Hill Higher Education. All rights reserved. The Chemiosmotic Hypothesis of ATP Formation • Electron transport chain results in pumping of H+ ions across inner mitochondrial membrane – Results in H+ gradient across membrane • Energy released to form ATP as H+ diffuse back across the membrane © 2007 McGraw-Hill Higher Education. All rights reserved. The Chemiosmotic Hypothesis of ATP Formation Fig 3.16 © 2007 McGraw-Hill Higher Education. All rights reserved. Aerobic ATP Tally Metabolic Process High-Energy Products ATP from Oxidative ATP Subtotal Phosphorylation Glycolysis 2 ATP 2 NADH — 5 2 (if anaerobic) 7 (if aerobic) Pyruvic acid to acetyl-CoA 2 NADH 5 12 Krebs cycle — 15 3 14 29 32 2 GTP 6 NADH 2 FADH Grand Total 32 2.5 ATP per NADH 1.5 APT per FADH Table 3.1 © 2007 McGraw-Hill Higher Education. All rights reserved. Efficiency of Oxidative Phosphorylation • Aerobic metabolism of one molecule of glucose – Yields 32 ATP • Aerobic metabolism of one molecule of glycogen – Yields 33 ATP • Overall efficiency of aerobic respiration is 34% – 66% of energy released as heat © 2007 McGraw-Hill Higher Education. All rights reserved. Control of Bioenergetics • Rate-limiting enzymes – An enzyme that regulates the rate of a metabolic pathway • Levels of ATP and ADP+Pi – High levels of ATP inhibit ATP production – Low levels of ATP and high levels of ADP+Pi stimulate ATP production • Calcium may stimulate aerobic ATP production © 2007 McGraw-Hill Higher Education. All rights reserved. Action of Rate-Limiting Enzymes Fig 3.19 © 2007 McGraw-Hill Higher Education. All rights reserved. Control of Metabolic Pathways Pathway Rate-Limiting Enzyme Stimulators Inhibitors ATP-PC system Creatine kinase ADP ATP Glycolysis Phosphofructokinase AMP, ADP, Pi, pH ATP, CP, citrate, pH Krebs cycle Isocitrate dehydrogenase ++ ADP, Ca , NAD Electron transport Cytochrome Oxidase ADP, Pi chain ATP, NADH ATP Table 3.2 © 2007 McGraw-Hill Higher Education. All rights reserved. Control of Bioenergetics Glycogen ATP-PC System PC + ADP C + ATP Glucose 1 Rate Limiting Enzymes 1. Creatine kinase 2. Phosphofructokinase 3. Iscitrate dehydrogenase 4. Cytochrome oxidase Glucose 6-phosphate Glycerol Triglycerides 2 Phosphoglyceraldehyde Lactic Acid Glycolysis Pyruvic Acid -ox Acetyl CoA Fatty acids Ketone bodies Table 3.2 © 2007 McGraw-Hill Higher Education. All rights reserved. C4 Krebs Cycle 3 Amino Acids C6 C5 Proteins Urea NADH FADH ETS 4 Interaction Between Aerobic and Anaerobic ATP Production • Energy to perform exercise comes from an interaction between aerobic and anaerobic pathways • Effect of duration and intensity – Short-term, high-intensity activities • Greater contribution of anaerobic energy systems – Long-term, low to moderate-intensity exercise • Majority of ATP produced from aerobic sources © 2007 McGraw-Hill Higher Education. All rights reserved. Chapter 3 Bioenergetics © 2007 McGraw-Hill Higher Education. All rights reserved.