Chapter 3

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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