Download Energy Systems

Objectives
• Bioenergetics ~ energy transfer
a) Within the body
b) During exercise
Energy Systems
• ATP regeneration
• Sources of energy during exercise:
a) Anaerobic
b) Aerobic
Energy Transfer
• Direct transfer of chemical energy required for
all forms of biological work
a) Energy = the capacity for work
Bioenergetics
9 Dynamic state related to change
9 As work load increases, energy transfer increases
• Bioenergetics & Thermodynamics
a) Process of converting food stuffs into “harnessed”
energy
1st Law of Thermodynamics
• Energy is neither created nor destroyed, but is
transformed from one form to another
a) As the body undergoes transformations, energy is
changed from one form to another
9 Conservation of energy
Energy in food
Heat
ATP
Potential & Kinetic Energy
Total (heat) energy of a system includes both:
1. Potential energy
• Bound in a specific form
2. Kinetic energy
Mechanical
Chemical
• Harnessing of potential energy (energy of motion)
• Biosynthesis results from harnessing energy
9 Individual atoms are joined to synthesize biologic
compounds
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Energy Release & Conservation
• Exergonic reactions (-∆G)
a) Physical or chemical release of energy
Energy Release & Conservation
• Endergonic reactions
a) Chemical processes that store or absorb energy
9 ‘Gibbs free energy’
b) Measurement of ‘free energy’
G = free energy
G = H - TS
• Processes may be coupled
a) Exergonic + Endergonic
∆G = ∆ H - T ∆ S
H = Enthalpy (potential energy)
T = Absolute temperature (ºC + 273)
S = Unavailable energy due to
randomness
ex:
H2 + O
H2O
~ -∆G 68kcal/mol
H2 + O
H2O
~ +∆G 68kcal/mol
Examples of ∆G for Important Molecules
2nd Law of Thermodynamics
• All reactions proceed in the direction of:
a) Increased entropy
b) The release of free energy
• The more –∆G, the greater the release of free
energy
• Direction & amount of free energy may be
modified by altering
a) Substrate concentration
b) Product concentration
Glucose-6-phosphate
-3.3 ∆G
Glucose-1-phosphate
-5.0 ∆G
ATP
-7.3 ∆G
Creatine Phosphate
-10.3 ∆G
Rate of Bioenergetics
• Enzymes function as:
a) Biological Catalysts – speed up chemical reactions
without being involved in the reaction or altering the
free energy release
b) Couplers – provide means to couple reactions
c) Regulators of metabolism
• Factors influencing enzyme function:
a) pH
b) Temperature
c) Availability of substrate and enzyme
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Major affects on enzyme activity
Figure 5.7
Enzymes (cont.)
• Mode of action
a) Lock and key mechanism (active site)
b) Enzyme-substrate complex
9 After entering active site catalyzes reaction & end product
produced
• Enzymes increase or decrease the likelihood of a
reaction occurring
a) Allosteric modification – can be activated or
inhibited
9 PFK (glycolysis) & Phosphorylase (glycogenolysis)
Figure 5.8
Alterations in enzyme concentration
Coenzymes
• Complex, non-protein organic substance
a) Iron
b) Zinc
c) B vitamins
• Require less specificity than enzymes
a) Affects various numbers of reactions
b) May serve as a temporary carrier
9 Nicotinamide adenine dinucleotide (NAD+)
9 Flavin adenine dinucleotide (FAD)
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Hydrolysis & Condensation Rx
1. Hydrolysis reactions
• Catabolizes complex organic molecules (CHO,
lipids, proteins)
9 Specific enzymes for each molecule
• Splits chemical bonds by adding H+ and OH9 Digestive enzymes
2. Condensation reactions
• Synthesis of molecules or anabolic process
• Reverse of hydrolysis
9 Peptide bonds
Figure 5.9
Electrons, protons & oxidation-reduction
reactions
• Electrons
a) Negatively charged subatomic particles circulating
around the atom nucleus
b) Essential for atoms to form covalent (sharing) bonds
c) During many chemical reactions
9 Electrons are either removed or added to molecules
• Molecules that lose 1 or more electrons are
oxidized, whereas molecules that gain electrons
are reduced
Figure 5.9
• Oxidation involves the loss of electrons, &
reduction involves the gaining of electrons
• Reactions occur together and often termed
oxidation-reduction or redox reactions
A:e + B
A + B:e
example:
Pyruvate + NADH + H+
lactate + NAD+
(Reduced)
(Oxidized)
Q – which molecule was reduced & which oxidized in the
direction of lactate production?
Figure 5.11
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Bioenergetics Review
• Law’s of Thermodynamics
• Exergonic & endergonic rx
Energy Transfer
a) Potential & kinetic energy
• Enzymes & coenzymes
• Hydrolysis, condensation & redox reactions
Adenosine Triphosphate (ATP)
ATP + H2O
ATPase
ADP + Pi
∆G = -7.3kcal/mol
Food Energy
Figure 6.2
ATP – Energy Currency of the Cell
ATP Regeneration
• Design & function of skeletal muscle metabolism
is to meet rapidly meet the ATP demand
• Skeletal muscle can produce the necessary ATP
for muscle contraction from 1 or a combination
of three metabolic reactions/pathways:
ex: Muscle contraction can ↑ cellular ATP demand by
100 fold
9 Could deplete resting [ATP] in as little as 2 – 3 seconds of
intense exercise
• Skeletal muscle has sensitive biochemical
controls of metabolic pathways involving the
sudden activation and inhibition of specific
enzymes
1. Phosphagen System
2. Glycolysis
3. Mitochondrial Respiration
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Anaerobic vs. Aerobic
Immediate Sources of
ATP
(Anaerobic)
Energy Reservoirs
Energy Reservoirs (cont.)
1. Phosphocreatine
2. Andenylate Kinase
• Most immediate means for ATP regeneration
•
CrP + ADP +
H+
ATP + Cr
• Actually 2 “coupled” reactions
CrP
Cr + Pi
ADP + H+ + Pi
exergonic
ADP + ADP
ATP
endergonic
• Responsive to immediate changes in ADP & ATP
concentrations
Important By-products of the
Phosphogen Systems
• PCr hydrolysis and adenylate kinase reaction
generate:
a) Pi
b) AMP
c) ADP
Reforms ATP using two ADP molecules
9 Results in ATP and AMP
9 Adenylate kinase drives this reaction
9 Requires only 1 enzyme, creatine kinase (CK)
CK
•
AK
ATP + AMP
AMP acts as an important regulator
9 Activator of the allosteric enzymes phosphorylase
(glycogenolysis) and phosphofructokinase (PFK)
Exercise Specifics
• ATP – PCr system
a) Provides ATP for short-term, high-intensity
movements & is rapidly depleted
By-products
• By-products stimulate:
a) Glycogenolysis
b) Glycolysis
c) Respiratory pathways of mitochondria
What type of exercises
include these systems?
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Glycogen & Glycogen Stores
1. Liver
Glycogenolysis &
Glycolysis
• Reservoir for blood glucose & brain
2. Muscle
• Does not release to blood (only for muscle
metabolism)
Biochemically efficient – no net ATP cost
Glucose requires one ‘extra’ ATP
Glycogenolysis
• Catabolism of glycogen requires
a) Removal of glucose units from glycogen
b) Addition of Pi
9 End product – glucose-6-phosphate
• Pi & Ca2+ major regulators of glycogenolysis
a) Epinephrine also ↑
• Major enzyme required is phosphorylase
Glycolysis
• Glucose (glucose-6-phosphate) → pyruvate
• Rapid rate of net 2 ATP
• Produces 2 NADH + 2 H+
• Provides substrate for other pathways
a) Pyruvate
b) Lactate
• Transported into the cell by GLUT proteins
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• Pyruvate reduction to lactate:
a) Lactate dehydrogenase (LDH)
Pyruvate + NADH + H+
LDH
lactate + NAD+
b) Depends on availability of NADH
9 NADH/NAD+ (redox potential)
Via glycerolphosphate
shuttle &
malateaspartate
shuttle
Via glycerolphosphate
shuttle &
malateaspartate
shuttle
c) Reduction of pyruvate to lactate helps to buffer the
solution
9 ‘absorbing’ excess protons (H+)
Sport Application
• Glycolysis resulting in lactate formation (lactic
lactic acid
system)
system
• Lactate accumulation
a) Blood Lactate Threshold (LT)
9 Lactate production exceeds clearance
9 Average for untrained = ~ 55% max aerobic
capacity (Davis JA et al., JAP 1979)
9 Training increases lactate threshold
Figure 6.12
Sport Application (cont.)
• Lactate-producing capacity increases with
anaerobic training
a) Increased intramuscular glycogen stores
9 Allows for increased glycolysis
b) Increased glycolytic enzymes
9 Training increases ~ 20%
c) Increased ability to recruit Type IIb fibers
Figure 7.2
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Lactate Is Not a Waste Product!
1. Lactate shuttle
• Converted to pyruvate and oxidized as an energy
source in another cell
2. Gluconeogenesis
• Converted back to glucose in the liver in Cori Cycle
Figure 6.13
Sources of ATP
(Aerobic & Steady-State)
Pyruvate Dehydrogenase Complex
acetyl CoA → TCA cycle
• Pyruvate entry into mitochondria is converted to
acetyl CoA by a series of linked enzymes known
collectively as pyruvate dehydrogenase
• Combined products of the TCA cycle from acetyl
CoA are:
Pyruvate dehydrogenase complex
Pyruvate + NAD+ + CoA
Acetyl CoA + NADH + H+ + CO2
• Glycolysis to TCA cycle
• Irreversible step
a) 2 CO2
b) 1 ATP
c) 3 NADH + H+
d) 1 FADH2
Support ATP regeneration during
oxidative phosphorylation
• All CO2 produced in energy metabolism are
accounted for from pyruvate dehydrogenase
reaction and 2 reactions of the TCA cycle
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TCA key points
• TCA cycle is ‘ultimate furnace’
a) Amino acids
b) Glucose
c) Fatty acids
d) Ketones
acetyl CoA
• Main electron transferring pathway (redox
reactions – energy conserved in NADH &
FADH)
Figure 6.15
TCA key points (cont.)
Electron Transport Chain (ETC)
• Each ‘turn of cycle’: one acetyl-CoA enters and 2
CO2 leave
• Involves the biochemical use of O2 to regenerate
ATP in mitochondria
• Synthesis of citrate which is an inhibitor for
glycolysis at PFK
a) Mainly during rest and post exercise recovery
• Oxaloacetate is regenerated with each turn
• ETC
a) Series of electron receivers located along the inner
mitochondrial membrane that sequentially receive
and transfer electrons to the final electron receiver –
oxygen
• Consumption of oxygen, and formation of water
and ATP during the ETC is termed oxidative
phosphorylation
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Summary
Summary (cont.) – Regulation of Energy
Metabolism
• Overall energy state dictates the direction of
metabolic pathways
• Rate-limiting modulators:
1.
2.
3.
4.
5.
6.
ATP
ADP
cAMP
NAD
Calcium
pH
• It is the relative concentrations that are
important: NADH/NAD+ & ATP/ADP
Sport Application & Concepts
Oxygen Consumption During Exercise:
Application &
Measurement of Energy
Metabolism
• Oxygen consumption (VO2)
a) Pulmonary oxygen uptake
b) Oxygen is measured at lung, not tissues (debatable)
c) Steady-state
9 When oxygen demand is met by oxygen delivery
9 Blood lactate doesn’t accumulate
9 Exercise may continue at this rate until limitations other
than oxygen alter performance
Sport Application & Concepts (cont.)
Oxygen Deficit:
• As exercise begins:
a) Oxygen demand increases immediately
b) Oxygen consumption lags behind
• Oxygen deficit
a) Quantitative expression of difference between
oxygen consumed and the amount that would have
been consumed had steady state been reached right
from the start.
Figure 7.3
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Sport Application & Concepts (cont.)
Sport Application & Concepts (cont.)
Oxygen Deficit (cont.):
Maximal Oxygen Consumption (VO2max):
• Trained Individuals
• Maximal volume of oxygen one can consume
a)Reach steady-state more rapidly
b)Have a smaller oxygen deficit
9 More rapid increase in cardiac output
9 Larger percentage of blood directed to active muscle
9 Training induced cellular adaptations
1. Increased capillary density
2. Increased number mitochondria
3. Increased oxidative enzymes
9 Maximal oxygen uptake
9 Maximal aerobic power
9 Aerobic capacity
• Provides a quantitative measure of capacity for
aerobic ATP resynthesis
Muscle Fiber Types
• Fast- and slow-twitch muscle fibers
a) Slow-twitch = Type I
9 Highest aerobic capacity
9 Lowest glycolytic capabilities
b) Fast-twitch = Type II
9 Type IIa: Medium glycolytic and aerobic capabilities
9 Type IIb: Highest glycolytic capacity & lowest aerobic
capacity
Figure 7.5
O2 Consumption During Recovery
• Metabolic dynamics of recovery oxygen
consumption
• Excess postexercise oxygen consumption
(EPOC):
Type II
Type I
a) Oxygen cost of adjustments in:
9
9
9
9
9
Ventilation
Circulating hormones
Blood circulation
Temperature
O2 reloading with muscle
Speed of recovery
depends on
recovery mode
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Energy from Fat
Energy Release From Fat
• Adipocytes
a) Site of fat storage and mobilization
b) Fat is stored primarily as triglycerides
• Mobilization
a) First step in utilizing fatty acids is Lipolysis
b) Triglycerides are split into:
9 Fatty acids
9 Glycerol
c) Hormone Sensitive Lipase (HSL) drives lipolysis
Transport and Uptake of Fatty Acids
• Fatty acids from Lipolysis are FFA
a) Bound to Albumin for transport in plasma
• FFA are taken up by muscle cells
a) FFA are activated to fatty Acyl CoA
b) Acyl CoA binds to Carnitine for transport into
mitochondria
c) Carnitine Acyltransferase drives this reaction
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Fatty Acids From Lipoproteins
• Lipoproteins also transport triglycerides
Circulating triglycerides
• Lipoprotein Lipase (LPL) catalyzes hydrolysis of
these triglycerides
• LPL is located on surface of surrounding
capillaries
Circulating triglycerides
Oxidation of fat w/in muscle
• Beta Oxidation
a) Cleaves two-carbon compounds from fatty Acyl
CoA molecule
b) Two-carbon acetyl groups enter Citric Acid Cycle
c) Oxidation produces NADH
• Fate of Glycerol
a) Conversion to Pyruvate via glycolytic action
b) Gluconeogenesis
9 Converted to Glucose in Liver
Hormonal Effects
• Lipolysis is stimulated by:
a) Epinephrine
b) Norepinephrine
c) Glucagon
d) Growth Hormone
Energy from Protein
• Intracellular mediator
a) cAMP activates hormone sensitive lipase
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Branched-chain Amino Acids
• AA play contributory role as energy substrates
during endurance and heavy resistance exercises
• Requires removal of nitrogen from AA
a) Liver – deamination
b) Muscle – transamination
• Depend on enzyme concentration (training)
Figure 1.25
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