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

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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

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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!

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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)

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Learning outcomes (cont)

• 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

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Metabolism

• 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

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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

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The Breakdown of Glucose An Exergonic
Reaction
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Coupled Reactions
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Enzymes

• 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

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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

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High-Energy Phosphates

• Adenosine triphosphate (ATP)
• Consists of adenine, ribose, and three linked
  phosphates
• Formation
• Breakdown

ADP Pi ? ATP
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Model of ATP as the Universal Energy Donor
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Carbohydrate
w Readily available (if included in diet) and
easily metabolized by muscles
w Ingested, then taken up by muscles and liver
and converted to glycogen
w Glycogen stored in the liver is converted back
to glucose as needed and transported by the
blood to the muscles to form ATP
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Fat (triglycerides)
w Provides substantial energy during prolonged,
low-intensity activity- light weight (little
water in storage)
w Body stores of fat are larger than carbohydrate
reserves
w Less accessible for metabolism because it must
be reduced to glycerol and free fatty acids (FFA)
w Only FFAs are used to form ATP- triglycerides-
must be broken down by process of lipolysis
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Protein - Body uses little protein during rest
and exercise (less than 5 to 10).
w Can be used as energy source if converted to
glucose via glucogenesis (or gluconeogenesis)
w Can generate FFAs in times of starvation
through lipogenesis

• w Only basic units of proteinamino acidscan be
  used for energy- via transamination feed into
  Krebs cycle
• waste produce is ammonia - must be excreted (as
  urea)

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Oxidation of Fat- FFA via ?- oxidation
w Lypolysisbreakdown of triglycerides into
glycerol and free fatty acids (FFAs).
w FFAs travel via blood to muscle fibers and are
broken down by enzymes in the mitochondria into
acetyl CoA.
w Acetyl CoA enters the Krebs cycle and the
electron transport chain.
w Fat oxidation requires more oxygen and
generates more energy than carbohydrate oxidation.
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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
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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 (lactate)
• Aerobic pathways- only occur in mitochondria
• Electron transport system (ETS) -Requires O2
• Oxidative phosphorylation

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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

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RECREATING ATP WITH PCr
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ATP AND PCr DURING SPRINTING
What does this show?
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The Two Phases of Glycolysis
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Glycolysis Energy Investment Phase
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Glycolysis Energy Generation Phase
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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
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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

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Conversion of Pyruvic Acid to Lactic Acid
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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

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3 Stages of Oxidative Phosphoryl-ation
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The Krebs Cycle
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Glycogen Breakdown and Synthesis
GlycolysisBreakdown of glucose may be anaerobic
or aerobic
GlycogenesisProcess by which glycogen is
synthesized from glucose to be stored in the liver
GlycogenolysisProcess 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)
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Relationship Between the Metabolism of Proteins,
Fats, and Carbohydrates
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The Chemiosmotic Hypothesis of ATP Formation
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Aerobic ATP yield from glucose
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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.
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Summary (cont) ?- Oxidation of Fat
w Lypolysisbreakdown of triglycerides into
glycerol and free fatty acids (FFAs).
w FFAs travel via blood to muscle fibers and are
broken down by enzymes in the mitochondria into
acetic acid which is converted to acetyl CoA.
w Acetyl CoA enters the Krebs cycle and the
electron transport chain.
w Fat oxidation requires more oxygen and
generates more energy than carbohydrate oxidation.
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Stop for 10 min break

• Any questions?

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Kilocalorie and other units (SI)
w Energy in biological systems is measured in
kilocalories.
w 1 kilocalorie is the amount of heat energy
needed to raise 1 kg of water 1C 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
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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?)
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CARBOHYDRATE vs FAT 1 gram of CHO--gt 4 kcal 1
gram of FFA (palmitic acid)--gt 9 kcal
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Body Stores of Fuels and Energy
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Oxygen consumption for Carbohydrate (glucose
from glycogen)
(C6H1206)n 6 O2 --gt 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
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Aerobic ATP yield from FFA (free fatty acid -
palmitic acid (16C)
16C ? 7 Acyl coA ? 7 acetyl coA (C16H3202) 23
O2 --gt 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
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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?

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Control of Bioenergetics

• Rate-limiting enzymes
• An enzyme that regulates the rate of a metabolic
  pathway
• Levels of ATP and ADPPi
• High levels of ATP inhibit ATP production
• Low levels of ATP and high levels of ADPPi
  stimulate ATP production
• Calcium may stimulate aerobic ATP production

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Action of Rate-Limiting Enzymes
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Control of Metabolic Pathways
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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

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Maximal capacity and power of three energy systems
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Contribution of energy systems
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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

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The Oxygen Deficit
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Differences in VO2 Between Trained and Untrained
Subjects- Why?
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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)

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Oxygen Deficit and Debt During Light-Moderate and
Heavy Exercise
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Factors Contributing to EPOC
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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

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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

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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

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Changes in Oxygen Uptake With Incremental
Exercise- explain?
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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

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Exercise Intensity and Fuel Selection

• Low-intensity exercise (lt30 VO2max)
• Fats are primary fuel
• High-intensity exercise (gt70 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

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Illustration of the Crossover Concept
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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

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Shift From CHO to Fat Metabolism During Prolonged
Exercise
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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

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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

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Effect of Exercise Intensity on Muscle Fuel Source
What does this graph show?
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Effect of Exercise Duration on Muscle Fuel
Source- summarise
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Summary

• 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