Chapter 3Bioenergetics

EXERCISE PHYSIOLOGYTheory 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

Figure 3.6

Enzymes Catalyze Reactions

Figure 3.7

The Lock-and-Key Model of Enzyme Action

Table 3.1

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

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

ADP + Pi ATP

• Adenosine triphosphate (ATP)– Consists of adenine, ribose, and three linked

phosphates

• Synthesis

• Breakdown

High-Energy Phosphates

ADP + Pi + EnergyATP ATPase

Figure 3.10

Structure of ATP

Figure 3.11

Model of ATP as the Universal Energy Donor

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

• 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

ATP + CPC + ADPCreatine kinase

Figure 3.12

The Two Phases of Glycolysis

Figure 3.14

Interaction Between Blood Glucose and Muscle Glycogen in Glycolysis

Figure 3.15

Glycolysis: Energy Investment Phase

Figure 3.15

Glycolysis: Energy Generation Phase

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

Figure 3.16

Conversion of Pyruvic Acid to Lactic Acid

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

Figure 3.17

The Three Stages of Oxidative

Phosphorylation

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

Figure 3.19

Relationship Between the Metabolism of Proteins, Carbohydrates, and Fats

Figure 3.21

Beta-oxidation

The Electron Transport Chain

Figure 3.20

Metabolic Process High-Energy Products

ATP from Oxidative Phosphorylation

ATP Subtotal

Glycolysis 2 ATP 2 NADH

— 5

2 (if anaerobic) 7 (if aerobic)

Pyruvic acid to acetyl-CoA 2 NADH 5 12

Krebs cycle 2 GTP 6 NADH 2 FADH

— 15 3

14 29 32

Grand Total

32

Aerobic ATP Tally Per Glucose Molecule

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 glucosex 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