Chapter 3

Chapter 3

Bioenergetics

EXERCISE PHYSIOLOGY

Theory and Application to Fitness and Performance, 6 th edition

Scott K. Powers & Edward T. Howley

© 2007 McGraw-Hill Higher Education. All rights reserved.

Introduction

• Metabolism: total 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


Objectives

• Discuss the function of cell membrane, nucleus, and mitochondria

• Define: endergonic, exergonic, coupled reactions, and bioenergetics

• Describe how enzymes work

• Discuss nutrients used for energy

• Identify high-energy phosphates


Objectives

• Discuss anaerobic and aerobic production of

ATP

• Describe how metabolic pathways are regulated

• Discuss the interaction of anaerobic and aerobic ATP production during exercise

• Identify the rate limiting enzymes


Cell Structure

• Cell membrane

– Protective barrier between interior of cell and extracellular fluid

• Nucleus

– Contains genes that regulate protein synthesis

• Cytoplasm

– Fluid portion of cell

– Contains organelles (mitochondria)


Structure of a Typical Cell


Fig 3.1

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


Fig 3.3

Coupled Reactions

Fig 3.4


Oxidation-Reduction

Reactions

• Oxidation: removing an electron

• Reduction: addition of an electron

• Oxidation and reduction are always coupled reactions

• In cells, often involve 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


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 Lower the

Energy of Activation


Fig 3.6

Enzyme-

Substrate

Interaction


Fig 3.7

Fuels for Exercise

• Carbohydrates

– Glucose

• Stored as glycogen

• Fats

– Primarily fatty acids

• Stored as triglycerides

• Proteins

– Not a primary energy source during exercise


High-Energy Phosphates

• Adenosine triphosphate (ATP)

– Consists of adenine, ribose, and three linked phosphates

• Formation

ADP + P i

• Breakdown



ATP

ATP

ATPase

ADP + P i

+ Energy


Structure of ATP


Fig 3.8

Model of ATP as the Universal

Energy Donor


Fig 3.9

Bioenergetics

• Formation of ATP

– Phosphocreatine (PC) breakdown

– Degradation of glucose and glycogen (glycolysis)

– Oxidative formation of ATP

• Anaerobic pathways

– Do not involve O

2

– PC breakdown and glycolysis

• Aerobic pathways

– Require O

2

– Oxidative phosphorylation


Anaerobic ATP Production

• ATP-PC system

– Immediate source of ATP

PC + ADP ATP + C

Creatine kinase

• Glycolysis

– Energy investment phase

• Requires 2 ATP

– Energy generation phase

• Produces ATP, NADH (carrier molecule), and pyruvate or lactate


The Two

Phases of

Glycolysis


Fig 3.10

Glycolysis

Energy Investment Phase


Fig 3.11

Glycolysis

Energy Generation Phase


Fig 3.11

Oxidation-Reduction

Reactions

• Oxidation

– Molecule accepts electrons (along with H + )

• Reduction

– Molecule donates electrons

• Nicotinomide adenine dinucleotide (NAD)

NAD + 2H +



NADH + H +

• Flavin adenine dinucleotide (FAD)

FAD + 2H +



FADH

2


Production of Lactic Acid

• Normally, O

2 is available in the mitochondria to accept H + (and electrons) from NADH produced in glycolysis

– In anaerobic pathways, O

2 is not available

• H + and electrons from NADH are accepted by pyruvic acid to form lactic acid


Conversion of Pyruvic Acid to Lactic Acid

Fig 3.12


Aerobic ATP Production

• Krebs cycle (citric acid cycle)

– Completes the oxidation of substrates and 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

O

2 to form water


The Three

Stages of

Oxidative

Phosphorylation


Fig 3.13

The Krebs Cycle


Fig 3.14

Relationship Between the Metabolism of

Proteins, Fats, and Carbohydrates


Fig 3.15

Electron Transport Chain

Fig 3.17


The Chemiosmotic Hypothesis of ATP Formation

• Electron transport chain results in pumping of

H + ions across inner mitochondrial membrane

– Results in H + gradient across membrane

• Energy released to form ATP as H + diffuse back across the membrane


The Chemiosmotic Hypothesis of ATP Formation

Fig 3.16


Aerobic ATP Tally

Metabolic Process High-Energy

Products

ATP from Oxidative

Phosphorylation

ATP Subtotal

Glycolysis 2 ATP

2 NADH

—

5

Pyruvic acid to acetyl-CoA 2 NADH

Krebs cycle 2 GTP

6 NADH

2 FADH

Grand Total

5

—

15

3

2.5 ATP per NADH

1.5 APT per FADH

2 (if anaerobic)

7 (if aerobic)

12

14

29

32

32

Table 3.1


Efficiency of Oxidative

Phosphorylation

• Aerobic metabolism of one molecule of glucose

– Yields 32 ATP

• Aerobic metabolism of one molecule of glycogen

– Yields 33 ATP

• Overall efficiency of aerobic respiration is

34%

– 66% of energy released as heat


Control of Bioenergetics

• Rate-limiting enzymes

– An enzyme that regulates the rate of a metabolic pathway

• Levels of ATP and ADP+P i

– High levels of ATP inhibit ATP production

– Low levels of ATP and high levels of

ADP+P i stimulate ATP production

• Calcium may stimulate aerobic ATP production


Action of Rate-Limiting Enzymes


Fig 3.19

Control of Metabolic Pathways

Pathway Rate-Limiting

Enzyme

ATP-PC system Creatine kinase

Stimulators

ADP

Inhibitors

ATP

Glycolysis Phosphofructokinase AMP, ADP, P i

,  pH ATP, CP, citrate,  pH

Krebs cycle Isocitrate dehydrogenase

ADP, Ca

Electron transport chain

Cytochrome Oxidase ADP, P i

++

, NAD ATP, NADH

ATP

Table 3.2


Control of Bioenergetics

ATP-PC System

PC + ADP C + ATP

1

Glycogen

Glucose

Rate Limiting Enzymes

1. Creatine kinase

2. Phosphofructokinase

3. Iscitrate dehydrogenase

4. Cytochrome oxidase

Glucose 6-phosphate

2

Phosphoglyceraldehyde Glycerol Glycolysis

Triglycerides Lactic Acid Pyruvic Acid

Fatty acids



-ox

Acetyl CoA Amino Acids

Table 3.2

Ketone bodies

C

4

C

6

Krebs

Cycle

3

C

5


Proteins

NADH

FADH

Urea

ETS

4

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



Chapter 3

Bioenergetics

Chapter 3

Chapter 3

Bioenergetics

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