Transcript Chapter 3
Chapter 3 Bioenergetics EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6th edition Scott K. Powers & Edward T. Howley Introduction • Metabolism – Sum 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 Cell Structure • Cell membrane – Semipermeable membrane that separates the cell from the extracellular environment • Nucleus – Contains genes that regulate protein synthesis • Cytoplasm – Fluid portion of cell – Contains organelles • Mitochondria A Typical Cell and Its Major Organelles Figure 3.1 Steps Leading to Protein Synthesis Figure 3.2 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 The Breakdown of Glucose: An Exergonic Reaction Figure 3.3 Coupled Reactions Figure 3.4 Oxidation-Reduction Reactions • Oxidation – Removing an electron • Reduction – Addition of an electron • Oxidation and reduction are always coupled reactions • Often involves 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 Oxidation-Reduction Reaction involving NAD and NADH Figure 3.5 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 Enzymes Catalyze Reactions Figure 3.6 The Lock-and-Key Model of Enzyme Action Figure 3.7 Diagnostic Value of Measuring Enzyme Activity in the Blood Enzyme Diseases Associated w/ High Blood Levels of Enzyme Lactate dehydrogenase (Cardiac-specific isoform) Myocardial infarction Creatin kinase Myocardial infarction, muscular dystrophy Alkaline phosphatase Carcinoma of bone, Paget’s disease, obstructive jaundice Amylase Pancreatitis, perforated peptic ulcer Aldolase Muscular dystrophy Table 3.1 Classification of Enzymes • Oxidoreductases – Catalyze oxidation-reduction reactions • Transferases – Transfer elements of one molecule to another • Hydrolases – Cleave bonds by adding water • Lyases – Groups of elements are removed to form a double bond or added to a double bond • Isomerases – Rearrangement of the structure of molecules • Ligases – Catalyze bond formation between substrate molecules Example of the Major Classes of Enzymes Example of Enzyme Enzyme Class within this Class Reaction Catalyzed Oxidoreducatases Lactate dehydrogenase Lactate + NAD <-->Pyruvate + NADH + H Transferases Hexokinase Glucose + ATP Glucose 6-phosphate + ADP Hydrolases Lipase Triglyceride + 3 H20 Glycerol + 3 Fatty acids Lyases Carbonic anhydrase Carbon dioxide + H20 Carbonic acid Isomerases Phosphoglycerate mutase 3-Phosphoglycerate 2-Phosphoglycerate Ligases Pyruvate carboxylase Pyruvate + HC03 + ATP Oxaloacetate + ADP Table 3.2 Factors That Alter Enzyme Activity • Temperature – Small rise in body temperature increases enzyme activity • pH – Changes in pH reduces enzyme activity The Effect of Body Temperature on Enzyme Activity Figure 3.8 The Effect of pH on Enzyme Activity Figure 3.9 Fuels for Exercise • Carbohydrates – Glucose – Glycogen • Storage form of glucose in liver and muscle • Fats – Fatty acids – Triglycerides • Storage form of fat in muscle and adipose tissue • Proteins – Not a primary energy source during exercise High-Energy Phosphates • Adenosine triphosphate (ATP) – Consists of adenine, ribose, and three linked phosphates • Synthesis ADP + Pi ATP • Breakdown ATP ATPase ADP + Pi + Energy Structure of ATP Figure 3.10 Model of ATP as the Universal Energy Donor Figure 3.11 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 Anaerobic ATP Production • ATP-PC system – Immediate source of ATP PC + ADP Creatine kinase ATP + C • Glycolysis – Glucose 2 pyruvic acid or 2 lactic acid – Energy investment phase • Requires 2 ATP – Energy generation phase • Produces 4 ATP, 2 NADH, and 2 pyruvate or 2 lactate The Two Phases of Glycolysis Figure 3.12 Interaction Between Blood Glucose and Muscle Glycogen in Glycolysis Figure 3.14 Glycolysis: Energy Investment Phase Figure 3.15 Glycolysis: Energy Generation Phase Figure 3.15 Hydrogen and Electron Carrier Molecules • Transport hydrogens and associated electrons – To mitochondria for ATP generation (aerobic) – To convert pyruvic acid to lactic acid (anaerobic) • Nicotinamide adenine dinucleotide (NAD) NAD + 2H+ NADH + H+ • Flavin adenine dinucleotide (FAD) FAD + 2H+ FADH2 Conversion of Pyruvic Acid to Lactic Acid Figure 3.16 Aerobic ATP Production • Krebs cycle (citric acid cycle) – Completes the oxidation of substrates – 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 The Three Stages of Oxidative Phosphorylation Figure 3.17 The Krebs Cycle Figure 3.18 Fats and Proteins in Aerobic Metabolism • Fats – Triglycerides glycerol and fatty acids – Fatty acids acetyl-CoA • Beta-oxidation – Glycerol is not an important muscle fuel during exercise • Protein – Broken down into amino acids – Converted to glucose, pyruvic acid, acetyl-CoA, and Krebs cycle intermediates Relationship Between the Metabolism of Proteins, Carbohydrates, and Fats Figure 3.19 Beta-oxidation Figure 3.21 The Electron Transport Chain Figure 3.20 Aerobic ATP Tally Per Glucose Molecule 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 Grand Total 2 GTP 6 NADH 2 FADH 32 Table 3.3 Efficiency of Oxidative Phosphorylation • One mole of ATP has energy yield of 7.3 kcal • 32 moles of ATP are formed from one mole of glucose • Potential energy released from one mole of glucose is 686 kcal/mole • Overall efficiency of aerobic respiration is 34% – 66% of energy released as heat 32 moles ATP/mole glucose x 7.3 kcal/mole ATP 686 kcal/mole glucose x 100 = 34% Control of Bioenergetics • Rate-limiting enzymes – An enzyme that regulates the rate of a metabolic pathway • Modulators of rate-limiting enzymes – 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 Action of Rate-Limiting Enzymes Figure 3.24 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 Effect of Event Duration on the Contribution of Aerobic/Anaerobic ATP Production Figure 3.24