Chapter 3 Bioenergetics

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Chapter 3Bioenergetics

• EXERCISE PHYSIOLOGY
• Theory and Application to Fitness and
  Performance, 6th edition
• Scott K. Powers Edward T. Howley

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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

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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

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A Typical Cell and Its Major Organelles
Figure 3.1
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Steps Leading to Protein Synthesis
Figure 3.2
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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

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The Breakdown of Glucose An Exergonic Reaction
Figure 3.3
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Coupled Reactions
Figure 3.4
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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

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Oxidation-Reduction Reaction involving NAD and
NADH
Figure 3.5
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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

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Enzymes Catalyze Reactions
Figure 3.6
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The Lock-and-Key Model of Enzyme Action
Figure 3.7
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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, Pagets
  disease, obstructive jaundice
• Amylase Pancreatitis, perforated peptic ulcer
• Aldolase Muscular dystrophy

Table 3.1
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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

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Example of the Major Classes of Enzymes

• Example of Enzyme
• Enzyme Class within this Class Reaction Catalyzed
• Oxidoreducatases Lactate dehydrogenase
  Lactate NAD lt--gtPyruvate 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
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Factors That Alter Enzyme Activity

• Temperature
• Small rise in body temperature increases enzyme
  activity
• pH
• Changes in pH reduces enzyme activity

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The Effect of Body Temperature on Enzyme Activity
Figure 3.8
The Effect of pH on Enzyme Activity
Figure 3.9
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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

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High-Energy Phosphates

• Adenosine triphosphate (ATP)
• Consists of adenine, ribose, and three linked
  phosphates
• Synthesis
• Breakdown

ADP Pi ? ATP
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Structure of ATP
Figure 3.10
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Model of ATP as the Universal Energy Donor
Figure 3.11
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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

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Anaerobic ATP Production

• ATP-PC system
• Immediate source of ATP
• 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

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The Two Phases of Glycolysis
Figure 3.12
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Interaction Between Blood Glucose and Muscle
Glycogen in Glycolysis
Figure 3.14
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Glycolysis Energy Investment Phase
Figure 3.15
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Glycolysis Energy Generation Phase
Figure 3.15
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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)
• Flavin adenine dinucleotide (FAD)

NAD 2H ? NADH H
FAD 2H ? FADH2
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Conversion of Pyruvic Acid to Lactic Acid
Figure 3.16
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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

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The Three Stages of Oxidative Phosphorylation
Figure 3.17
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The Krebs Cycle
Figure 3.18
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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

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Relationship Between the Metabolism of Proteins,
Carbohydrates, and Fats
Figure 3.19
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Beta-oxidation
Figure 3.21
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The Electron Transport Chain
Figure 3.20
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Aerobic ATP Tally Per Glucose Molecule
Table 3.3
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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

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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 ADPPi
• High levels of ATP inhibit ATP production
• Low levels of ATP and high levels of ADPPi
  stimulate ATP production
• Calcium may stimulate aerobic ATP production

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Action of Rate-Limiting Enzymes
Figure 3.24
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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

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Effect of Event Duration on the Contribution of
Aerobic/Anaerobic ATP Production
Figure 3.24