Chapter 3 Energy Metabolism and Metabolic Adaptations to Training

Energy metabolism Energy from the food we eat is stored in the form of ATP ATP is broken down to liberate the energy used to cause muscle contractions Anabolism— “to build up”; such as the use of amino acids to make proteins, which contribute to muscle mass Catabolism— “to break down”; such as breaking down glycogen to glucose molecules

Physical educators, coaches, and exercise scientists should have a basic understanding of energy metabolism because ATP is the source of energy for muscle contraction Producing enough ATP is essential to performance Adaptations to exercise training involve energy metabolism The metabolic demands of training are important in designing training or exercise prescriptions

Definitions of anaerobic and aerobic metabolism Aerobic metabolism is the production of ATP with oxygen. Anaerobic metabolism is the production of ATP without oxygen.

ATP production ATP can be produced aerobically or anaerobically Most physical activities involve both aerobic and anaerobic metabolism

Approximate percentages of aerobic and anaerobic contributions to ATP production

Approximate percentages of aerobic and anaerobic contributions to ATP production (cont.)

The three characteristics of enzymes Speed up or catalyze a reaction Are not changed by the reaction they cause Do not change the result of the reaction

Lock-and-key method The enzymes are specific to the reactant to which they bind. The enzyme must fit precisely with the reactant to catalyze the reaction.

What is the respiratory chain? The Krebs cycle and the electron transport system (ETS), where ATP is produced and oxygen is utilized.

Summary of aerobic metabolism Of carbohydrates –Anaerobic glycolysis precedes aerobic phases of ATP production Of fats (fatty acid oxidation) 1.Fatty acids are liberated from storage as a part of triglycerides 2.Long carbon chain fatty acids are metabolized through beta oxidation into two carbon acetyl coenzyme A molecules 3.These enter the Krebs cycle and go through the ETS for ATP production Of protein 1.Amino acids are converted into keto acids by the liver or muscle 2.Keto acids form substances that produce ATP through the Krebs cycle and ETS

Fat, carbohydrate, and protein can be used to produce ATP aerobically

Factors that affect the turnover rate of an enzyme Temperature and pH of the cellular environment Concentration and activity of reactants and enzymes Allosteric inhibition Availability and concentrations of cofactors and coenzymes

Selected coenzymes in energy metabolism

Anaerobic ATP production ATP can be produced anaerobically through two pathways: ATP-PC system Anaerobic glycolysis Visit Biological Energy Conversion, Review of Anaerobic Metabolism at

The three primary enzymatic reactions that occur in the ATP-PC system 1.ATPADP + inorganic phosphate (Pi) + energy 2.PC + ADPATP + C 3.2ADP ATP + AMP Myosin ATPase Creatine Kinase (CK) Adenylate Kinase (AK)

Anaerobic glycolysis The primary system for ATP production for activities that last from approximately 20– 30 seconds to two to three minutes The breakdown of glucose to lactate without the use of oxygen

Anaerobic glycolysis involves the breakdown of glucose to lactate.

The reactants, enzymes, and products for the two steps in glycolysis where ATP is produced Step 1 –Reactant: 1, 3-bisphosphoglycerate –Enzyme: phosphoglycerate kinase (PGK) –Product: 3-phosphoglycerate Step 2 –Reactant: phosphoenolpyruvate –Enzyme: pyruvate kinase (PK) –Product: pyruvate

The reactants, enzymes, and products for the two steps in glycolysis where ATP is used Step 1 –Reactant: blood glucose –Enzyme: hexokinase (HK) –Product: glucose-6-phosphate Step 2 –Reactant: fructose-6-phosphate –Enzyme: phosphofructokinase (PFK) –Product: fructose-1, 6-bisphosphate

The reactant, enzyme, and product for the step in glycolysis where NAD is reduced Reactant: glyceraldehyde 3-phosphate Enzyme: glyceraldehyde 3-phosphate dehydrogenase Product: 1,3-bisphosphoglycerate

Reactant: pyruvate Enzyme: lactate dehydrogenase Product: Lactate The reactant, enzyme, and product for the step in glycolysis where NAD is oxidized

The role of Phosphofructokinase (PFK) It is the rate-limiting enzyme in glycolysis It is the weak link—the rate of conversion of the reactant to product through enzymatic steps can proceed no faster than the rate-limiting enzyme will allow.

Aerobic metabolism of carbohydrates In the presence of sufficient oxygen, pyruvate from glycolysis enters muscle fiber mitochondria There, ATP is produced in the Krebs cycle and ETS Produces 38 molecules of ATP per molecule of glucose

The Krebs cycle occurs within the mitochondria of the muscle fiber

The four steps where NAD is reduced during the aerobic metabolization of carbohydrates Step 1 –Reactant: pyruvate –Enzyme: pyruvate dehydrogenase complex –Product: acetyl coenzyme A Step 2 –Reactant: isocitrate –Enzyme: isocitrate dehydrogenase –Product: alpha- ketoglutarate Step 3 –Reactant: alpha- ketoglutarate –Enzyme: alpha- ketoglutarate –Product: succinyl coenzyme A Step 4 –Reactant: malate –Enzyme: malate dehydrogenase –Product: oxaloacetate

The reactant, enzyme, and product for the step in the Kreb’s cycle where FAD is reduced Reactant: succinate Enzyme: succinate dehydrogenese Product: fumarate

The reactant, enzyme, and product in the Kreb’s Cycle where ATP is produced Reactant: succinyl coenzyme A Enzyme: succinyl coenzyme A synthetase Product: succinate

The electron transport system The part of aerobic metabolism where 34 of the 38 ATP are produced Visit Electron Transport System at

Most ATP is produced in the electron transport system

Anaerobic breakdown of glucose results in the net production of only 2 ATP, while aerobic metabolism nets 38 ATP

The net chemical reaction of the aerobic metabolism of glucose C 6 H 12 O 6 + 6O ADP + 38P  6CO 2 + 6H ATP

Comparison of the power and capacity of the various energy production systems The ATP-PC system has low capacity because there is a limited store of phosphagens available. Carbohydrate oxidation is limited by glycogen depletion. Fatty acid metabolism has the greatest capacity because, under normal conditions, each person has an inexhaustible supply of energy-rich fats.

There is an inverse relationship between the power and capacity of energy production systems

The main metabolic adaptations that result from endurance training myoglobin mitochondrial size and number mitochondrial enzymes lactate production and the role of the Glucose-Alanine-Glucose Cycle glycolytic enzymes fatty acid use

Effects of sprint training on anaerobic metabolism enzymes phosphocreatine stores in the muscle

Metabolic effects of resistance training enzymes phosphocreatine and ATP stores in the muscle