Energy Systems and Bioenergetics
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Ex biochem c4-energetics
Energy systems and bioenergetics
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Skeletal muscles, especially in elite athletes, can
generate incredible work, during a marathon:
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Expend ~3000 Kcal, Oxidize >700 g CHO and >30 g fat
Utilize >600 L oxygen, Break down and reform >150
mol ATP (63 kg)
[ATP] in muscle very low
Skeletal muscle can suddenly increase rate of ATP
use to > 100 times of rest
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Myosin-actin cross-bridge
~1/3 ATP hydrolyzed in contracting muscle is used in
Ca2+ uptake by SERCA (sarcoplasmic-endoplasmic
reticulum calcium ATPase)
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Ex biochem c4-energetics
Overview of muscle contraction
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Ex biochem c4-energetics
ATP utilization during exercise
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Ex biochem c4-energetics
Myosin and muscle contraction
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Myosin consists of 6 polypeptide chains
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Myosin head also act as enzyme to hydrolyze
ATP
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2 myosin heavy chains (MHC), tail and head,
form cross bridges with actin
2 regulatory light chains, can be phosphorylated
by accepting a Pi from ATP
2 essential light chains
Myosin ATPase
ATP + H2O  ADP + Pi
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Ex biochem c4-energetics
Thick and thin filaments
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Ex biochem c4-energetics
Myosin ATPase
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By itself, myosin ATPase activity low, but
increased by ~100 X when binds to actin
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Actin-activated myosin ATPase, actomyosin ATPase
Different kinds of skeletal muscle MHC
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Different ATPase activity, different rate of ATP
hydrolysis, myosin isoenzymes (myosin isoforms,
different molecular forms of same enzyme, catalyzed
same reaction with different speed)
Human: MHC I, IIA, IIX
Smaller animals also have MHC IIB
Fast- and slow-twitch fibers
Muscle fibers have many nuclei, each express MHC
genes: single muscle fiber may have >2 different MHCs
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Ex biochem c4-energetics
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Histochemical Staining of Fiber Type
Type IIa
Type IIb
Type I
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Ex biochem c4-energetics
Energy-rich phosphates
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ATP regeneration: ADP + Pi  ATP + H2O
Nucleotide: base + ribose + phosphate(s)
ATP: energy-rich compound
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Anhydride bonds between alpha and beta phosphates,
and beta and gamma phosphates
Analogy of a spring
In cell, [ATP]/[ADP] very high, ~500
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Ensure ATP hydrolysis
Muscle ATP utilization rate = regeneration rate in most
exercise situations
Muscle [ATP] could decrease by 60-80% in very severe
exercise, but very short-lived, replenished very rapidly
soon after exercise
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Ex biochem c4-energetics
ATP structure
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Ex biochem c4-energetics
Nucleosides
Nucleoside: a compound that consists of Dribose or 2-deoxy-D-ribose bonded to a
nucleobase by a -N-glycosidic bond
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u raci l O
HN
-D-ribos ide
O
5'
H OCH2
4'
H
1
N
O
H
3'
H
2'
HO
OH
Uridi ne
a -N-glycosi dic
bon d
1'
H
an ome ri c
carbon
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Ex biochem c4-energetics
Nucleotide
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Nucleotide: a nucleoside in which a molecule
of phosphoric acid is esterified with an -OH
of the monosaccharide, most commonly
either the 3’-OH or the 5’-OH
N H2
N
O
-
5'
O
-
H
H
N
O
O-P- O-CH2
3'
H
N
N
1'
H
HO
OH
Ade n os i n e 5'-mon oph os ph ate
(5'-AMP)
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Ex biochem c4-energetics
Phosphocreatine, creatine phosphate
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[ATP] in most tissues low
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Energy turnover rate in muscle
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3-8 mmol/L cell water, 2-6 mmol/kg tissue
1 mmol ATP/kg/min at rest
240 mmol/kg/min in sprinting in elite athletes, ~
180 mmol/kg/min in normally active subjects
ATP in muscle consumed in ~ 2s if not
regenerated
ATP regeneration rate < maximal ATP
hydrolyzed rate
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Sprint speed at maximal at start
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Ex biochem c4-energetics
Phosphocreatine
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ADP + PCr + H+ < ATP + Cr
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[PCr] in muscle 18-20 mmol/kg
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Catalyzed by creatine kinase (very rich in muscle),
fastest and most abundant among all muscle enzymes
Ensure ATP regeneration = break down near beginning
of sprint-type activities
Act as temporary ATP buffer until other ATPregenerating processes reach max rates
Forward direction in exercise, also consume H+
Backward direction in recovery
92-96% PCr in human skeletal muscles
CK: MB isoenzyme in cardiac muscle, MM
isoenzyme in skeletal muscle
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Ex biochem c4-energetics
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Ex biochem c4-energetics
Energy systems
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MgATP2- + H2O  MgADP- + n H2PO4- +
(1-n) HPO4 2- + (1-n) H+
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All cellular ATP in cells associated to Mg2+
ATP regeneration
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PCr
Oxidative phosphorylation
Glycolysis
Only glycolysis in red blood cell (erythrocyte)
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Ex biochem c4-energetics
Energy systems
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Ex biochem c4-energetics
Oxidative phosphorylation
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Aerobic system, aerobic metabolism, cellular
respiration, respiration
Electrons transferred from substrate (CHO, fat) 
carrier (NAD+, FAD+)  O2
Measure disappearance of O2 as rate of oxidative
phosphorylation
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Can not quickly reach max rate because O2 transfer
require time
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O2 consumption 1 L/min ~ 5 kcal/min
Require 15-20s to double the rate
High capacity: large fuel tank
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Ex biochem c4-energetics
Oxidative phosphorylation
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Ex biochem c4-energetics
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Ex biochem c4-energetics
Glycolysis
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Glucose + 2 ADP + 2 Pi + 2 NAD+  2
pyruvate + 2 ATP + 2 NADH + 2 H+
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Pyruvate + NADH + H+ < lactate +
NAD+
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Catalyzed by lactate dehydrogenase (LDH)
Pyruvate can enter TCA cycle
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Anaerobic glycolysis
Aerobic glycolysis
Net production of ATP from PCr and
glycolysis: substrate-level phosphorylation
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Ex biochem c4-energetics
Glycolysis and lactate
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Glycolysis has higher activities than oxidative
phosphorylation
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Generate more pyruvate than TCA cycle can oxidize
Pyruvate converted to lactate, also regenerate NAD+
Capacity of generating ATP: PCr < glycolysis <
oxidative phosphorylation
↓pH in very rapid rates of anaerobic glycolysis
Glycolysis can be quickly started at beginning
exercise, reach max rate in 5-10 sec in intensive
exercise
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Ex biochem c4-energetics
PCr system, Anaerobic alactic system
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ADP + PCr + H+ > ATP + Cr
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Low capacity: limited supply of PCr
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[PCr] in muscle 18-20 mmol/kg, or 23-26 mmol/L
[PCr] can decrease >90% in all-out exercise
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Consumption of H+ can be beneficial to muscle during
high-intensity exercise
CK activity so high, can maintain ATP level remarkable
well even during intense exercise
Regeneration of PCr during recovery by oxidative
phosphorylation
Half-time for PCr recovery ~ 30 sec
Persons with higher capacity for oxidative ATP
formation recovery PCr at faster rate
[PCr] and [TCr] Type II muscle fiber > Type I
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Ex biochem c4-energetics
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Ex biochem c4-energetics
PCr recovery after exercise
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Ex biochem c4-energetics
Excess postexercise oxygen
consumption (EPOC)
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Ex biochem c4-energetics
Creatine supplementation
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Increase [Cr], [PCr], [Total Cr]
PCr/TCr ratio in rested muscle constant at 0.6-0.7,
even after supplementation
Most effective in short-term high-intensity exercise
lasting up to 3 min in duration
Especially helpful if high-intensity activity is
repeated with only brief recovery period
Increase body weight and strength gains along with
resistance training
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Allow to train harder
Upregulate expression of some genes in muscles,
especially involved in intracullular signaling
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Ex biochem c4-energetics
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Ex biochem c4-energetics
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Ex biochem c4-energetics
Energy sources in different exercise
intensities
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Ex biochem c4-energetics
Energy sources in prolonged
moderate-intensity exercise
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Ex biochem c4-energetics
Energy source during maximal
exercise with different durations
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Ex biochem c4-energetics
Energy sources during repeated
high-intensity exercise
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Ex biochem c4-energetics
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Ex biochem c4-energetics
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Ex biochem c4-energetics
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Ex biochem c4-energetics
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Ex biochem c4-energetics
Adenylate kinase, AMP deaminase
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2 ADP > ATP + AMP
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AMP + H2O  IMP + NH3
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Low at rest, activated by↓pH, ↑[ADP]
The 2 reactions maintain optimal energy status in muscle
fiber during intense exercise
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AMP deaminase (adenylate deaminase)
NH4+ (ammonia) in blood
AMP deaminase activity higher in Type II fibers
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Catalyzed by adenylate kinase (adenylyl kinase)
Prevent [ADP] accumulation, maintain high [ATP]/[ADP], ensure
ATP hydrolysis
Irreversible AMP deaminase reaction drives reversible adenylate
kinase reaction to the right
During recovery, IMP converted back to AMP, or form
inosine and hypoxanthine
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Ex biochem c4-energetics
3
4
N
2
N
5
N
6
O
1
Pyri mi din e
6
1
N
2
O
H
C ytos i ne (C )
(DNA an d
s om e RNA)
N
3
4
N
H
Pu rin e
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N
N
O
H
Th ymin e (T)
(DNA an d
s om e RNA)
H
Uraci l (U)
(in RN A)
O
N
N
HN
N
N H2
8
N
O
CH3
HN
N
7
5
O
N H2
N
H
Ade n in e (A)
(DNA an d RNA)
N
HN
H 2N
N
N
H
Gu an in e (G)
(DNA an d RNA)
Inosine
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Ex biochem c4-energetics
Purine nucleotide cycle
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Ex biochem c4-energetics
Purine nucleotide cycle
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Ex biochem c4-energetics
Plasma lactate and NH3 after intensive ex
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Ex biochem c4-energetics
Muscle metabolism in exercise
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Techniques to measure muscle metabolism
Biopsy: invasive
Phosphorus 31 (31P) nuclear magnetic
resonance (NMR) spectroscopy
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Magnetic resonance imaging (MRI)
Identify ATP, PCr, Pi, estimate ADP, AMP
Expensive, limited type of exercise
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Ex biochem c4-energetics
Identification of high-energy
phosphate with 31P NMR
Jung & Dietze, 1999
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Ex biochem c4-energetics
31P-NMR
in PCr metabolism study
Slade JM, 2007
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Ex biochem c4-energetics
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Ex biochem c4-energetics
Muscle ATP, PCr, LA in exercise
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Epigenetics
Ex biochem c4-energetics
表觀遺傳學, 擬遺傳學, 後遺傳學
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heritable change in gene expression in the absence
of changes to the sequence of the genome
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沒有細胞核 DNA 序列改變的情況時， 基因功能的可
逆的、可遺傳的改變
環境, 飲食, 運動/訓練…
muscles cultured from endurance athletes had
significantly higher glucose uptake (a traininginduced adaptation) than muscles cultured from
untrained subjects (Berggren et a1. 2005).
Factors that regulate epigenetic regulation of
muscle-gene expression can be affected by exercise
training
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histone acetylation and methylation…
Inheritable? unclear
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