Download Lecture 3 Nutrient Roles in Bioenergetics

BPK 312 Nutrition for Fitness & Sport
Lecture 3
Nutrient Roles in Bioenergetics
1. 
Learning Objectives for Lecture 3
2. 
Bioenergetics/Conservation of Energy
3. 
Redox Reactions
4. 
ATP/Phosphocreatine
5. 
Cellular Oxidation/Electron Transport/Oxidative
Phosphorylation
6. 
Energy Release from Macronutrients
7. 
The Metabolic Mill
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1. Lecture 3 Learning Objectives (LO3)
LO3-1: Define bioenergetics and give a description of the nutritionenergy interaction, energy transfer from macronutrients and cellular
respiration.
LO3-2: Define and explain oxidation-reduction reactions as well as how
they are important in energy transfer from macronutrients to ATP.
LO3-3: Explain how phosphocreatine and high energy phosphate bonds
allow short term, explosive activity.
LO3-4: Explain the details of how electron transport in the respiratory
chain and oxidative phosphorylation allow the transfer of energy from
macronutrients to ATP.
LO3-5: Explain and describe the steps of energy transfer from: (i)
glycogen and glucose to ATP in glycolysis, (ii) from coenzymes to high
energy phosphate bonds in the citric acid cycle and (iii) from lactate in
the Cori Cycle.
LO3-6: Name the sources of fat for catabolism and describe the steps
in transfer of energy from triacylglycerols in beta-oxidation to the
electron transport chain for ATP production.
LO3-7:Explain deamination, transamination and how the carbon
‘skeletons’ from amino acids are catabolized to give gluconeogenic as
2
well as ketogenic intermediates for energy transfer.
2. Bioenergetics & Conservation of Energy
§  Bioenergetics refers to flow of energy within a living
system.
§  Aerobic chemical reactions do & anaerobic chemical
reactions do not require oxygen.
§  Energy is transferred from the sun to plants by
photosynthesis using chlorophyll, H2O & CO2 to produce
carbohydrates (CHO) including glucose. Overall
equation for photosynthesis:
§  Cellular respiration in animals allows recovery of food
chemical energy stored in plants
§  Herbivores, carnivores and omnivores transfer energy
transfer from different food sources
§ 
Image Source: https://en.wikipedia.org/w/index.php?title=Photosynthesis&oldid=759051544
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2. Bioenergetics & Conservation of Energy
‘On engraisse pas les cochons à l'eau claire’
Jeanne Beauregard, né Archambault, Calixa-Lavallée, Qc, 1908-1985
Energy and Laws of Thermodynamics
§  First law – Energy is neither created nor destroyed, but instead,
transforms from one state to another without being used up.
§  There are six forms of interchangeable energy states:
• 
Chemical, Light, Electric, Mechanical, Heat, Nuclear
Biologic Work
Takes one of three forms:
§ 
• 
Mechanical work of muscle contraction
• 
Chemical work for synthesizing molecules
• 
Transport work that concentrates diverse
substances in body fluids
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2. Bioenergetics & Conservation of Energy
Recall Potential Energy and Kinetic Energy
§  Potential energy (PE) refers
to energy associated with a
substance’s structure or
position.
§  Kinetic Energy (KE) refers
to energy of motion.
§  PE and KE constitute the
total energy of any system.
§  Releasing PE transforms it
into KE of motion.
Energy transformation in the human body depend on:
•  (i) Oxidation-reduction (redox) reactions & (ii) Chemical reactions
that conserve & liberate energy in Adenosine Triphosphate (ATP)
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3. Redox Reactions
§  Oxidation–reduction reactions couple:
•  Oxidation = a substance loses H+, electrons or oxygen giving a ↑valence
•  Reduction = a substance gains electrons giving a ↓valence
§  Redox reactions power the body’s energy transfer processes.
LDH
MAXIMAL
STRENUOUS
MODERATE
LIGHT
LDH
(Lactate Dehydrogenase = LDH)
Fig 4-5:
Example of a
redox reaction
during intense
exercise
- the reduction
of pyruvate to
give lactate &
subsequent
oxidation of
lactate to give
pyruvate during
recovery cf slide
22
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4. Adenosine Triphosphate (ATP) &
Phosphocreatine (PCr)
•  ATP is the body’s
primary energy carrier
molecule that captures
free energy high energy
phosphate bonds
Examples of work
carried out in the body using ATP
Digestion
Circulation
2 outermost phosphate bonds are
‘high energy’ phosphate bonds.
•  Splits rapidly without O2
•  Only 80-100 g of ATP
stored in body ∴ there
is a continual
resynthesis of ATP
Nerve
Conduction
Glandular
Muscle
Contraction
Tissue
Synthesis
Fig 4-8: Adenosine Triphosphate (ATP), the body’s energy
currency that powers all biological work
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4. Adenosine Triphosphate (ATP)
& Phosphocreatine (PCr)
§  Adenosine TriPhosphate (ATP)
is the energy currency of body
cells & it contains high energy
phosphate bonds
§  Potential energy (PE) is extracted
from macronutrients in food &
conserved within phosphate bonds
within ATP.
§  Chemical PE in ATP powers all
biologic work.
•  Adenosine TriPhosphatase
(ATPase)
•  rapid anaerobic energy supply
ATP + H2O
ATPase
→
Fig 4-7: Simplified
image of ATP
ADP + Pi + 7.3 kcal/mole
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4. Adenosine Triphosphate (ATP) &
Phosphocreatine (PCr)
Phosphocreatine (PCr): The Energy Reservoir
§ In addition to ATP, PCr is
another high-energy phosphate
compound.
§ PCr quickly releases large
amounts of energy when bonds
between creatine & phosphate
are broken.
§ Cells store 4–6 x more PCr
than ATP
§ Is a reservoir of high-energy
phosphate bonds, for shortterm 8-10 s explosive, all out
muscular exercise
ATPase
Creatine
Phosphokinase
Fig 4-9: ATP & PCr sources of anaerobic
§ Phosphorylation gives energy phosphate bond energy. Energy released
transfer in phosphate bonds from splitting PCr helps resynthesize ATP
from ADP & Pi; Adenosine triphosphatase
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(ATPase)
5. Cellular Oxidation, Electron Transport
Chain (ETC) & Oxidative Phosphorylation
ACTIVATION ENERGY
sudden release
of all chemical
energy
BURNING OF GLUCOSE
ACTIVATION ENERGY
slow step-wise
release of
chemical energy
CELLULAR OXIDATON OF GLUCOSE
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Fig 4-6: Burning glucose in a fire vs. cellular oxidation of glucose
5. Cellular Oxidation, Electron Transport
Chain (ETC) & Oxidative Phosphorylation
§  Most energy for ATP phosphorylation is from oxidation of hydrogen
(H) from macronutrients, CHO, lipids & protein
§  Constitutes the mechanism for aerobic energy metabolism
§  Involves the transfer of hydrogen atoms & electrons
• 
Loss of hydrogen= oxidation & gain of hydrogen=reduction
•  Highly specific dehydrogenase co-enzymes are reduced with H
from macronutrients
•  Nicotinamide Adenine Dinucleotide (NAD+) from niacin (Vit B3)
•  Flavin Adenine Dinucleotide (FAD) from riboflavin (Vit B2)
•  NADH & FADH2 are 2 high energy molecules carrying H & their
electrons
§  Mitochondria contain cytochrome carrier molecules on their inner
membrane that remove electrons from H & pass them to O2
§  Electron transport by cytochromes is the ‘respiratory chain’
Chemical Reactions in Mitochondria Animation Button
nb change ‘create to ‘transfer’ of energy in this animation
http://download.lww.com/wolterskluwer_vitalstream_com/animation_library/HP-03-mitochondria/mitochondria.html
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5. Cellular Oxidation, Electron Transport
Chain (ETC) & Oxidative Phosphorylation
Oxidative
Phosphorylation
§  Refers to energy transfer
through phosphate bonds
§  Most of the energy for ATP
phosphorylation comes from
oxidation of carbohydrates,
lipids, and proteins.
§  Oxidative phosphorylation
synthesizes ATP by
transferring H & electrons
from NADH and FADH2 to
oxygen.
§  >90% of body’s ATP synthesis
Fig 4-10: Schematic diagram for oxidation of hydrogen from NADH
& FADH2 for subsequent electron transport for the reduction of O2. 12
5. Cellular Oxidation, Electron Transport
Chain (ETC) & Oxidative Phosphorylation
Electron Transport & Oxidative Phosphorylation
1
Cytochrome 2 e-
2
Cytochrome 2eCytochrome 2e-
3
Cytochrome 2eCytochrome 2e-
Electron
Transport
Animation
Button
http://download.lww.com/wolterskluwer_vitalstream_com/animation_library/HP-15-electron_transport/electron_transport.html
Fig 4-11: In the body chemical energy is liberated with each of 3 hydrogen/electron pairs
from NADH & FADH2 are shuttled by 5 mitochondrial cytochromes; cytochromes
are Fe
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containing proteins. This energy is conserved in ATP in high energy phosphate bonds.
5. Cellular Oxidation, Electron Transport &
Oxidative Phosphorylation
Electron Transport Chain (ETC) & Oxidative
Phosphorylation
•  Theoretical value for aerobic ATP production from
oxidation of H & subsequent phosphorylation is:
NADH + H+ + 3 ADP + 3 Pi + ½ O2 → NAD+ + H2O + 3 ATP
•  ATP needs to be transported out of the mitochondria at the
cost of some ATP
•  On average the net yield is 2.5 ATP synthesized per NADH,
when FADH2 donates H this gives on average a net yield of 1.5
ATP synthesized from each hydrogen pair
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5. Cellular Oxidation, Electron Transport
Chain (ETC) & Oxidative Phosphorylation
Efficiency of Electron Transport Chain (ETC) &
Oxidative Phosphorylation
•  Formation of each mole of ATP conserves ~ 7 kcal of energy
•  Since 2.5 moles ATP is produced per mole of NADH then 2.5 x
7 kcal = ~18 kcal is conserved as chemical energy
•  The relative efficiency is ~34% for transferring chemical
energy by ETC-oxidative phosphorylation since 1 mole of NADH
liberates 52 kcal, i.e. ~18 kcal/52 kcal x 100 = ~34%.
•  Remaining 66% of this energy is dissipated as heat
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5. Cellular Oxidation, Electron Transport
Chain (ETC) & Oxidative Phosphorylation
Role of Oxygen in Energy Metabolism
•  3 conditions for ATP re-synthesis using energy from macronutrients
–  Cond. 1: Availability of reduced NADH & FADH2 in tissues
–  Cond. 2: Presence of oxidizing agent O2 in the tissues
–  Cond. 3: Sufficient concentration of the enzymes &
mitochondria in the tissues to ensure energy transfer
reactions proceed at their appropriate rate
•  Oxygen is the final electron acceptor in the respiratory chain &
combines with hydrogen to form water.
•  Strenuous Exercise
–  In Cond. 2 if there is inadequate O2 in the tissues or in Cond 3 if
the rate of delivery of O2 is inadequate these give an imbalance
between H release & acceptance by O2, i.e. its reduction.
–  Electron flow down ETC backs up, H accumulates & lactate forms
as give in Fig 4-15 on a following slide in this lecture.
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6. Energy Release from Macronutrients
Sources for ATP formation
include:
i. 
Glucose derived from
liver glycogen
ii.  Triacylglycerol &
glycogen molecules
stored within skeletal
muscle cells/fibers
iii.  Free fatty acids (FFA)
derived from
triacylglycerol in liver
and adipocytes that
enter the bloodstream
for delivery to active
muscle
iv.  Intramuscular & liverderived carbon
skeletons of amino acids
Fig 4-12
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6. Energy Release from Macronutrients
Intramuscular Energy Stores
Fig 4-13: Macronutrient
Fuel Sources
Mitochondrion
Glycogen
Glucose
Citric Acid Cycle
aa
ATP
TAG
Glucose
Deaminated aa
FFA
• 
• 
• 
• 
• 
FFA
Liver produces rich sources of amino acids (aa) & glucose (glycogen)
Adipocytes give large amounts of free fatty acids (FFA)
These compounds are released into blood & are carried to skeletal m.
Most energy transfer takes place in mitochondria within skeletal m.
Intramuscular energy sources include ATP, PCr, Triacylglycerol (TAG),
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glycogen & carbon skeletons from aa’s
6. Energy Release from Macronutrients
Energy Release from Carbohydrates
C6H12O6 + 6 O2 → 6CO2 + 6H2O - 686 kcal/mol
§  1° function of CHO is to supply energy for cellular work.
§  in a bomb calorimeter the complete breakdown of 1 mol of
glucose of 180 g liberates 686 kcal of energy
•  Synthesis of 1 mol ATP needs 7.3 kcal of energy
•  All energy in glucose oxidation could give 94 mol of ATP
•  In muscle phosphate bonds conserve only 34%, i.e. 34%
of 686 kcal/mol = 233 kcal/mol of energy in ATP bonds
with the remainder dissipated as heat.
•  ∴ 1 mol of glucose breakdown gives 233 kcal/7.3 kcal x
mol-1 = 32 mol of ATP
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6. Energy Release from Macronutrients
Glucose Degradation
Occurs in two stages:
1.  Anaerobic: Glucose breaks down relatively rapidly to 2
molecules of pyruvate in the reactions of glycolysis
2.  Aerobic: Pyruvate degrades further to carbon dioxide and
water in the reactions of the citric acid cycle
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6. Energy Release
from Macronutrients
Glycolysis
1
1
§  Substrate-level
phosphorylation in glycolysis
gives net gain of 2 ATP
2.  Glucose 6Phosphate
isomerase
3
http://download.lww.com/wolterskluwer_vitalstream_com/animation_library/HP-02-glycolysis/
glycolysis.html
§  Glycolysis gives 5-10% of
total ATP from a glucose
molecule
1.  Hexokinase
2
Glycogen
phosphorylase
§  In cytosol & anaerobic cond.
Fig 4-13
ENZYMES
3. Phosphofructokinase
4
5
4. Aldolase
6
7
§  Hydrogen release in
glycolysis gives 2 NADH
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§  for max exercise <90 s
9
§  Glycogenolysis gives net gain
3 ATP b/c 1st step bypassed
§  Lactate formation
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5. Triosephosphate
isomerase
6. Glyceraldehyde
3- phosphate
dehydrogenase
7. Phosphoglycerate
kinase
8.Phosphoglycerom
utase
9. Enolase
10. Pyruvate
kinase
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6. Energy Release from Macronutrients
Lactate Formation & Use
•  In heavy exercise when energy
demand exceeds O2 supply,
ETC can’t process all NADH
•  Depends on reaction 6 in
glycolysis & for NAD+
availability to oxidize
‘3-phosphoglyceraldehyde’
Lactate Dehydrogenase = LDH
•  dramatically slows glycolytic
rate & ↑ lactic acid production
results
•  Lactate is a valuable source of
chemical energy in the Cori
Cycle
•  nb at physiological pH lactic
acid dissociates to lactate & H+
Fig 4-15: Lactic Acid Formation when excess H+ from NADH temporarily combines
with pyruvate. This frees NAD+ to accept more H+ from glycolysis, cf slide 6
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6. Energy Release from Macronutrients
Cori Cycle
•  Lactate is a valuable source of
chemical energy during exercise
1.  Lactic acid from skeletal muscle
enters venous circulation &
dissociates to lactate & H+
2.  Lactate enters liver where it is
converted to pyruvate & then via
gluconeogenesis, there is a
resynthesis of glucose.
3.  Blood glucose as well as muscle
& liver glycogen can
subsequently be maintained.
4.  Glucose is released from liver to
arterial blood to active skeletal
muscle.
http://download.lww.com/wolterskluwer_vitalstream_com/
animation_library/HP-25-cori_cycle/cori_cycle.html
3
2
Fig 4-16
Glucose
4
1
Cori Cycle
Animation
Button
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6. Energy Release from
Macronutrients
Citric Acid Cycle (CAC)
Fig 4-18
§  2nd stage of CHO breakdown is
the CAC.
§  Irreversible joining of pyruvate
with CoA, a Vit. B derivative,
from Vit B6 or pantothenic acid,
to acetyl-CoA
§  This releases 2 H atoms to
reduce both NAD+ & FAD
oxaloacetate
malate
Citric Acid
Cycle
Animation
citrate
Button
fumarate
isocitrate
Succinate
e.g. Pyruvate + NAD+ + CoA →
acetyl-CoA + CO2 + NADH + H+
§ The acetyl portion of acetyl-CoA
joins with oxaloacetate to form
citrate from citric acid.
§ Each acetyl-CoA gives 2 CO2 & 4
pairs of hydrogen atoms, plus 1
high energy Guanosine-5'triphosphate (GTP)
Succinyl-CoA
oxalosuccinate
α-ketoglutarate
http://download.lww.com/
wolterskluwer_vitalstream_
com/animation_library/
HP-16-citric_acid/
citric_acid_cycle.html
24
6. Energy Release from Macronutrients
Fig 4-17- Schematic Diagram of hydrogen formation &
subsequent oxidation during aerobic energy metabolism.
Phase 1: CAC generates H
atoms during breakdown of
acetyl CoA
Phase 2: ATP is reformed when
these H’s are oxidized via
aerobic electron transport oxidative phosphorylation
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6. Energy Release
from Macronutrients
Fig 4-19: Net Yield of 32
ATP molecules during
complete oxidation of 1
glucose molecule through
glycolysis, the CAC &
electron transport chain
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6. Energy Release from Macronutrients
Energy Release from Fat – Lipolysis
Lipolysis
Animation
§  Stored fat represents the body’s biggest source of PE.
§  Energy sources for fat catabolism include:
i.  Triacylglycerol stored directly in skeletal m. fiber
http://
download.lww.com/
wolterskluwer_vitalstr
eam_com/
animation_library/
HP-26-triacylglycerol/
triacylglycerol.html
ii. Circulating triacylglycerol (TAG) in lipoprotein complexes
iii. Circulating free fatty acids
Hormone Sensitive
Lipase
TAG + 3 H2O
→
3,5 cyclic monophosphate
(cAMP)
glycerol + 3 fatty acids
3 steps in lipoysis, steps 1&2 with HSL, Step 3 with HSL & monoglyceride lipase
•  cAMP Activation: stimulated by epinephrine, norepinephrine (e.g. exercise),
glucagon, growth hormone + inhibited by lactate, insulin & ketones
•  these circulating factors don’t enter cell but activate cAMP & Hormone
Sensitive Lipase
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6. Energy Release from Macronutrients
Adipocytes
Fig 4-20: Fat storage & mobilization or lipolysis
Fat Mobilzation
Animation
§  TAG fat droplets takeup to 95% of
adipocyte volume &is major FFA source
§  Lipase stimulates glycerol & FFA release
from adipocytes
Lipase
§  FFA bind to albumin in the plasma
http://
download.lww.com/
wolterskluwer_vitalstre
am_com/
animation_library/
HP-17-fat_mobilization/
fat_mobilization.html
§  Long chain fatty acids enter muscle
fibers by diffusion or by protein
mediated transport &:
(i) form intracellular TAG
(ii) bind to CoA & then to carnitine by actions of carnitineacyl-CoA transferase I & II fatty acids enter mitochondria
(iii) Carnitine + fatty acyl-CoA à acylcarnitine + CoA
(iv) end product is Acetyl-CoA à CAC & ETC to give ATP
(iv) ↑[Acetyl-CoA]/[CoA] ratio ↓FA transfer to mitoch.
§  Short & medium chain FA diffuse freely into the mitochondria
28
6. Energy Release from Macronutrients
Breakdown of Glycerol and Fatty Acids
§  Glycerol
• 
Provides carbon skeletons for glucose synthesis, enters
glycolytic pathway as 3-phosphoglyceraldehyde to give
ATP by substrate-level phosphorylation
§  Fatty acids
• 
Beta (ß)-oxidation for fatty acid oxidation converts a free
fatty acid to multiple acetyl-CoA molecules.
• 
H+ released during fatty acid catabolism is oxidized
through the respiratory chain.
•  Note CAC rate depends on concentration of its intermediates,
including oxaloacetate & malate, that are derived from CHO.
•  A low CHO diet can limit fatty acid oxidation, due a slow rate of
the citric acid cycle.
C15H32O2 + 23 O2 → 16CO2 + 16H2O + 2397 kcal
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6. Energy Release from Macronutrients
Breakdown of Glycerol and Fatty Acid Fragments
Electron transport chain accepts
pairs of hydrogen from glycolysis,
citric acid cycle and ß-oxidation
Fig 4-21: General scheme of glycerol & fatty acid fragment breakdown
30
6. Energy Release from Macronutrients
Energy Release from Protein
§  Protein plays a role as an energy substrate during
endurance activities and heavy trainings.
§  Deamination: Nitrogen is removed from the amino acid by
the liver
§  Transamination: when an amino acid is passed to another
compound
§  remaining carbon skeletons enter metabolic pathways to
produce ATP.
§  especially evident for the branched chained amino acids
leucine, isoleucine, valine, glutamine & aspartate
§  Excessive intake of protein is converted to body fat.
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6. Energy Release from Macronutrients
A. Alanine Structure
B. Transamination
•  The nitrogen
containing amine
group is transferred to
other compounds
•  Allows availability of
the carbon skeleton to
enter into energy
metabolism
•  e.g. the compound
enters into the citric
acid cycle
http://download.lww.com/
wolterskluwer_vitalstream_com/
animation_library/HP-23-transamination/
transamination.html
Transamination
Animation
Glutamate
Pyruvate
Glutamine
transaminase
α-ketoglutaric acid
Alanine
32
Fig. 1-16 A: Chemical structure of aa alanine B: Transamination
6. Energy Release from Macronutrients
Glucogenic & Ketogenic Amino Acids
•  Carbon skeletons of amino
acids that form pyruvate or
directly enter the citric acid
cycle are glucogenic because
they can form glucose
•  Carbon skeletons of amino
acids that form acetyl-CoA
are ketogenic because they
can’t form glucose molecules
but rather synthesize fat
Fig 4-21: Glucogenic and ketogenic amino acids.
33
6. Energy Release from Macronutrients
Deamination
Glucose–Alanine
Cycle Animation
Button
Gluconeogenesis
Alanine
Transaminase
•  In prolonged exercise this
cycle accounts for 10-15%
of total exercise energy
requirement
•  after 4 h of continuous
light exercise alaninederived glucose accounts
for 45% of the livers total
glucose release
Fig. 1-20: Glucose-Alanine Cycle
http://download.lww.com/wolterskluwer_vitalstream_com/animation_library/
HP-09-alanine_glucose/alanineglucose.html
34
7. The Metabolic Mill
§  The citric acid cycle is a
vital link between food
energy and the chemical
energy of ATP.
§  The citric acid cycle also
provides intermediates
that cross the
mitochondrial membrane
into the cytosol to
synthesize bio-nutrients.
35
BPK 312 Nutrition for Fitness & Sport
Lecture 3
Summary Slide
Nutrient Roles in Bioenergetics
1. 
Learning Objectives for Lecture 3
2. 
Bioenergetics/Conservation of Energy
3. 
Redox Reactions
4. 
ATP/Phosphocreatine
5. 
Cellular Oxidation/Electron Transport/Oxidative
Phosphorylation
6. 
Energy Release from Macronutrients
7. 
Metabolic Mill
36