Review of bioenergetics
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Review of Bioenergetics . SP5005 Physiology Alex Nowicky power point slides: Powers and Howley- Exercise Physiology Ch 3 and 4. What is bioenergetics?. Study of energy in living systems what it is? Where does it come from? How is it measured?

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Review of Bioenergetics

SP5005 Physiology

Alex Nowicky

power point slides: Powers and Howley- Exercise Physiology Ch 3 and 4

What is bioenergetics?

  • Study of energy in living systems

  • what it is?

  • Where does it come from?

  • How is it measured?

  • How is it produced and used by human body at rest and during exercise?

  • Part of science of biochemistry -studies conversion of matter into energy by living systems

For your own study use any ex physiology text and cover the following:

  • Energy sources

  • recovery from exercise

  • measurement of energy, work and power

  • This lecture is an overview of these!

Aim: review energy metabolism

Learning outcomes

  • ATP is central to all energy transactions

  • Oxidation (O2) (in mitochondria) central

  • define aerobic and anaerobic pathways - systems of enzymes and their regulation

  • fate of fuels - CHO, fats and proteins- relative yields of useful energy (ATP)

Learning outcomes (con’t)

  • role of glycogenolysyis, -oxidation, gluconeogenesis

  • indirect calorimetry for monitoring energy expenditure- oxygen consumption- (RER)

  • contribution of fuel supply during exercise (short vs. long duration)

  • role aerobic and anaerobic systems during exercise and recovery


  • Total of all chemical reactions that occur in the body

    • Anabolic reactions

      • Synthesis of molecules

    • Catabolic reactions

      • Breakdown of molecules

  • Bioenergetics- oxidation (O2)

    • Converting foodstuffs (fats, proteins, carbohydrates) into energy

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

Coupled Reactions


  • Catalysts that regulate the speed of reactions

    • Lower the energy of activation

  • Factors that regulate enzyme activity

    • Temperature (what happens with changes in T?)

    • pH ( what happens with changes in pH?)

  • Interact with specific substrates

    • Lock and key model

Fuels for Exercise

  • Carbohydrates

    • Glucose

      • Stored as glycogen in liver and muscle

  • Fats

    • Primarily fatty acids

      • Stored as triglycerides- adipose tissue and muscles

  • Proteins

    • Not a primary energy source during exercise


ADP + Pi+ Energy


High-Energy Phosphates

  • Adenosine triphosphate (ATP)

    • Consists of adenine, ribose, and three linked phosphates

  • Formation

  • Breakdown


Model of ATP as the Universal Energy Donor


wReadily available (if included in diet) and easily metabolized by muscles

wIngested, then taken up by muscles and liver and converted to glycogen

wGlycogen stored in the liver is converted back to glucose as needed and transported by the blood to the muscles to form ATP

Fat (triglycerides)

wProvides substantial energy during prolonged, low-intensity activity- light weight (little water in storage)

wBody stores of fat are larger than carbohydrate reserves

wLess accessible for metabolism because it must be reduced to glycerol and free fatty acids (FFA)

wOnly FFAs are used to form ATP- triglycerides- must be broken down by process of lipolysis

Protein -Body uses little protein during rest and exercise (less than 5% to 10%).

wCan be used as energy source if converted to glucose via glucogenesis (or gluconeogenesis)

wCan generate FFAs in times of starvation through lipogenesis

  • wOnly basic units of protein—amino acids—can be used for energy- via transamination feed into Kreb’s cycle

  • waste produce is ammonia - must be excreted (as urea)

Oxidation of Fat- FFA via - oxidation

wLypolysis—breakdown of triglycerides into glycerol and free fatty acids (FFAs).

wFFAs travel via blood to muscle fibers and are broken down by enzymes in the mitochondria into acetyl CoA.

wAcetyl CoA enters the Krebs cycle and the electron transport chain.

wFat oxidation requires more oxygen and generates more energy than carbohydrate oxidation.

What Determines Oxidative Capacity?

w Oxidative enzyme activity within the muscle

w Fiber-type composition and number of mitochondria

w Endurance training

w Oxygen availability and uptake in the lungs


  • 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 (lactate)

  • Aerobic pathways- only occur in mitochondria

    • Electron transport system (ETS) -Requires O2

    • Oxidative phosphorylation



Creatine kinase

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



What does this show?

The Two Phases of Glycolysis

Glycolysis: Energy Investment Phase

Glycolysis: Energy Generation Phase

Oxidation-Reduction Reactions

  • Oxidation

    • Molecule accepts electrons (along with H+)

  • Reduction

    • Molecule donates electrons

  • Nicotinomide adenine dinucleotide (NAD)

  • Flavin adenine dinucleotide (FAD)

NAD + 2H+ NADH + H+

FAD + 2H+ FADH2

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

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

    • 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

3 Stages of Oxidative Phosphoryl-ation

The Krebs Cycle

Glycogen Breakdown and Synthesis

Glycolysis—Breakdown of glucose; may be anaerobic or aerobic

Glycogenesis—Process by which glycogen is synthesized from glucose to be stored in the liver

Glycogenolysis—Process by which glycogen is broken into glucose-1-phosphate to be used by muscles

Gluco(neo)genesis- formation of glucose from lipids and proteins via intermediates (lactate, pyruvate, amino acids)

Relationship Between the Metabolism of Proteins, Fats, and Carbohydrates

The Chemiosmotic Hypothesis of ATP Formation

Aerobic ATP yield from glucose

Summary- Oxidation of Carbohydrate

1. Pyruvic acid from glycolysis is converted to acetyl coenzyme A (acetyl CoA).

2. Acetyl CoA enters the Krebs cycle and forms 2 ATP, carbon dioxide, and hydrogen.

3. Hydrogen in the cell combines with two coenzymes that carry it to the electron transport chain.

4. Electron transport chain recombines hydrogen atoms to produce ATP and water.

5. One molecule of glycogen can generate up to 39 molecules of ATP.

Summary (con’t) - Oxidation of Fat

wLypolysis—breakdown of triglycerides into glycerol and free fatty acids (FFAs).

wFFAs travel via blood to muscle fibers and are broken down by enzymes in the mitochondria into acetic acid which is converted to acetyl CoA.

wAcetyl CoA enters the Krebs cycle and the electron transport chain.

wFat oxidation requires more oxygen and generates more energy than carbohydrate oxidation.

Stop for 10 min break

Any questions?

Kilocalorie and other units (SI)

wEnergy in biological systems is measured in kilocalories.

w1 kilocalorie is the amount of heat energy needed to raise 1 kg of water 1°C at 15 °C. 1kcal= 1000cal

Work - energy - application of force through a distance

Should be using SI units

1 Joule (J) = 1 N-m/s2

1 kg-m = 1kg moved through 1 metre

1kcal = 426 kg-m = 4.186kiloJoules (kJ)

1 kJ = 0.2389 kcal ( 1kcal = 4.186kJ)

1 litre of O2 consumed = 5.05kcal= 21.14 kJ

(1ml of oxygen = .005kcal) - useful conversion factor

Power to perform uses up energy- how much oxygen consumption to supply energy?

Power - work/time (Watts or hp)

1hp = 745 watts= 10.7kcal/min

1L of oxygen/min consumption= 5.05kcal/min= 21 kJ/min

1MET = 3.5ml oxygen/kg/min= 0.0177kcal/kg/min

15 kcal/min= ? Oxygen/min (can you do this?)


1 gram of CHO--> 4 kcal

1 gram of FFA (palmitic acid)--> 9 kcal

g kcal

Carbohydratesgrams kcal

Liver glycogen110 451

Muscle glycogen2501,025

Glucose in body fluids1562






Note. These estimates are based on an average body weight of 65 kg (143 lb) with 12% body fat.

Body Stores of Fuels and Energy

Oxygen consumption for Carbohydrate (glucose from glycogen)

(C6H1206)n + 6 O2 --> 6 CO2 +6 H20 + 39 ATP

6 moles of O2 needed to break down 1 mole of glycogen

6 moles x 22.4 l/mole oxygen = 134.4 l

134.4l/39 moles of ATP = 3.45 l/mole ATP

at rest takes about 10-15 min,

during max exercise takes about 1 min

ratio (RQ) carbon dioxide/oxygen = 6/6 = 1

Aerobic ATP yield from FFA (free fatty acid - palmitic acid (16C)

16C  7 Acyl coA  7 acetyl coA

(C16H3202) + 23 O2 --> 16 CO2 +16 H20 + 130 ATP

23 moles of O2 needed to break down 1 of palmitic acid

23 moles x 22.4 l/mole oxygen = 512.2 l

512l/130 moles of ATP = 3.96 l O2/mole ATP

ratio of carbon dioxide/oxygen = 16/23 = 0.7

15% more oxygen than metabolising glycogen, but advantage is light weight (little water) storage

How do we determine efficiency of ox phos- respiration (metabolism of glucose)?

  • Efficiency =

    38moles ATP x 7.3kcal/mole ATP

    686 kcal/mole glucose

    = 0.4 x100% = 40% (60% lost heat)

    how does this compare to mechanical engine?

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

Control of Metabolic Pathways

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

System moles ATP/min power capacity

phosphagen 3.6 0.7

anaerobic glycolysis1.61.2

aerobic (from glycogen)1.090.0

at rest - aerobic system supplies ATP with oxygen consumption about 0.3L/min, blood lactate remains constant

Maximal capacity and power of three energy systems

Contribution of energy systems

Rest-to-Exercise Transitions

  • Oxygen uptake increases rapidly

    • Reaches steady state within 1-4 minutes

  • Oxygen deficit

    • Lag in oxygen uptake at the beginning of exercise

    • Suggests anaerobic pathways contribute to total ATP production

  • After steady state is reached, ATP requirement is met through aerobic ATP production

The Oxygen Deficit

Differences in VO2 Between Trained and Untrained Subjects- Why?

Recovery From Exercise: Metabolic Responses

  • Oxygen debt

    • Elevated VO2 for several minutes immediately following exercise

    • Excess post-exercise oxygen consumption (EPOC)

  • “Fast” portion of O2 debt

    • Resynthesis of stored PC

    • Replacing muscle and blood O2 stores

  • “Slow” portion of O2 debt

    • Elevated body temperature and catecholamines

    • Conversion of lactic acid to glucose (gluconeogenesis)

Oxygen Deficit and Debt During Light-Moderate and Heavy Exercise

Factors Contributing to EPOC

Metabolic Response to Exercise: Short-Term Intense Exercise

  • High-intensity, short-term exercise (2-20 seconds)

    • ATP production through ATP-PC system

  • Intense exercise longer than 20 seconds

    • ATP production via anaerobic glycolysis

  • High-intensity exercise longer than 45 seconds

    • ATP production through ATP-PC, glycolysis, and aerobic systems

Metabolic Response to Exercise: Prolonged Exercise

  • Exercise longer than 10 minutes

    • ATP production primarily from aerobic metabolism

    • Steady state oxygen uptake can generally be maintained

  • Prolonged exercise in a hot/humid environment or at high intensity

    • Steady state not achieved

    • Upward drift in oxygen uptake over time

Metabolic Response to Exercise: Incremental Exercise

  • Oxygen uptake increases linearly until VO2max is reached

    • No further increase in VO2 with increasing work rate

  • Physiological factors influencing VO2max

    • Ability of cardiorespiratory system to deliver oxygen to muscles

    • Ability of muscles to take up the oxygen and produce ATP aerobically

Changes in Oxygen Uptake With Incremental Exercise- explain?

Estimation of Fuel Utilization During Exercise- from overall equations

  • Respiratory exchange ratio (RER or R)

    • VCO2 / VO2

    • Indicates fuel utilization

      • 0.70 = 100% fat

      • 0.85 = 50% fat, 50% CHO

      • 1.00 = 100% CHO

  • During steady state exercise

    • VCO2 and VO2 reflective of O2 consumption and CO2 production at the cellular level

Exercise Intensity and Fuel Selection

  • Low-intensity exercise (<30% VO2max)

    • Fats are primary fuel

  • High-intensity exercise (>70% VO2max)

    • CHO are primary fuel

  • “Crossover” concept

    • Describes the shift from fat to CHO metabolism as exercise intensity increases

    • Due to:

      • Recruitment of fast muscle fibers

      • Increasing blood levels of epinephrine

Illustration of the “Crossover” Concept

Exercise Duration and Fuel Selection

  • During prolonged exercise there is a shift from CHO metabolism toward fat metabolism

  • Increased rate of lipolysis

    • Breakdown of triglycerides into glycerol and free fatty acids (FFA)

    • Stimulated by rising blood levels of epinephrine

Shift From CHO to Fat Metabolism During Prolonged Exercise

Interaction of Fat and CHO Metabolism During Exercise

  • “Fats burn in the flame of carbohydrates”

  • Glycogen is depleted during prolonged high-intensity exercise

    • Reduced rate of glycolysis and production of pyruvate

    • Reduced Krebs cycle intermediates

    • Reduced fat oxidation

      • Fats are metabolized by Krebs cycle

Sources of Fuel During Exercise

  • Carbohydrate

    • Blood glucose

    • Muscle glycogen

  • Fat

    • Plasma FFA (from adipose tissue lipolysis)

    • Intramuscular triglycerides

  • Protein

    • Only a small contribution to total energy production (only ~2%)

      • May increase to 5-15% late in prolonged exercise

  • Blood lactate

    • Gluconeogenesis in liver

Effect of Exercise Intensity on Muscle Fuel Source

What does this graph show?

Effect of Exercise Duration on Muscle Fuel Source- summarise


  • Aerobic and anaerobic systems

  • What regulates metabolic pathways?

  • What is the RER?

  • Describe how fuel utilisation is affected by intensity and duration of exercise

  • What happens during recovery from exercise?

  • A note about ATP yield- some sources say 38 some say 36 with aerobic resp

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