© 2007 McGraw-Hill Higher Education. All rights reserved. Chapter 3 Bioenergetics EXERCISE...

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

Chapter 3Bioenergetics

EXERCISE PHYSIOLOGY

Theory and Application to Fitness and Performance, 6th edition

Scott K. Powers & Edward T. Howley


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

• Breakdown

ADP + Pi ATP

ADP + Pi + EnergyATP ATPase


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 O2

– PC breakdown and glycolysis• Aerobic pathways

– Require O2

– Oxidative phosphorylation


Anaerobic ATP Production

• ATP-PC system– Immediate source of ATP

• Glycolysis– Energy investment phase

• Requires 2 ATP– Energy generation phase

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

PC + ADP ATP + CCreatine kinase


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)

• Flavin adenine dinucleotide (FAD)FAD + 2H+ FADH2

NAD + 2H+ NADH + H+


Production of Lactic Acid

• Normally, O2 is available in the mitochondria to accept H+ (and electrons) from NADH produced in glycolysis

– In anaerobic pathways, O2 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 O2 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


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

Table 3.1

2.5 ATP per NADH1.5 APT per FADH


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+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

Fig 3.19


Control of Metabolic Pathways

Pathway Rate-LimitingEnzyme

Stimulators Inhibitors

ATP-PC system Creatine kinase ADP ATP

Glycolysis Phosphofructokinase AMP, ADP, Pi, pH ATP, CP, citrate, pH

Krebs cycle Isocitratedehydrogenase

ADP, Ca++, NAD ATP, NADH

Electron transportchain

Cytochrome Oxidase ADP, Pi ATP

Table 3.2


Control of Bioenergetics

Glycogen

Glucose 6-phosphate

Phosphoglyceraldehyde

Pyruvic Acid

Acetyl CoA Amino Acids Proteins

Ketonebodies

Fatty acids

Triglycerides

Glycerol

Lactic Acid

Krebs Cycle

C6

C5

C4

Urea

Glucose

2

Rate Limiting Enzymes1. Creatine kinase2. Phosphofructokinase 3. Iscitrate dehydrogenase 4. Cytochrome oxidase

-ox

3 ETSNADHFADH

4

Glycolysis

1PC + ADP C + ATP

ATP-PC System

Table 3.2


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 3Bioenergetics

© 2007 McGraw-Hill Higher Education. All rights reserved. Chapter 3 Bioenergetics EXERCISE...

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