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Final

Biochemistry of Muscle Function and Energy Systems in Muscle Section of the course examining the energy systems used by muscle including the high energy phosphate transfer, glycolysis and aerobic phosphorylation. Also looks at contribution of various sour


Department
Biomedical Physio & Kines
Course Code
BPK 205
Professor
Russ Tupling
Study Guide
Final

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Biochemistry of Muscle Function Energy Systems in Muscle
ATP + H20 ------------ ADP + Pi + energy (7.3 kcal/mol ATP, under ideal conditions)
Skeletal muscle is capable of enormous increases in force and velocity and consequently
in the rate of ATP hydrolysis or demand
Ie. ATP demand at rest may increase 200-fold during contraction
Problem: in skeletal muscle tissue the concentration of ATP is low, in fact only sufficient
to sustain maximal muscle contraction for an estimated 2 to 3 seconds
Therefore NOT surprising that skeletal possesses a very sophisticated energy metabolic
assembly that is able to respond to the highly variable ATP requirements as dictated by
exercise intensity (ie. ATP is continuously regenerated as it is needed for work)
↑ATP supply  ATP demand↑
Bioenergetics
Bioenergetics: the study of how energy is generated in the cell. It refers to the metabolic
process of converting foodstuffs (substrates) into ATP
Carbohydrates (CHOs): glucose (stored as glycogen)
Fats: primarily fatty acids (stored as triglycerides)
Proteins: not a primary energy source during exercise
There are 3 energy (ATP) delivery systems in muscle
High energy phosphate transfer (HEPT): transfer of a phosphate group from
phosphocreatine (PCr) to ADP to regenerate ATP
Glycolysis: degradation of glucose or glycogen (glycogenolysis: found in cyto.)
Ox Phosphorylation: complete combustion of fats and/or CHOs
Anaerobic pathways
Do not involve O2
HEPT and glycolysis
Aerobic pathways
Require O2
Oxidative phosphorylation

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1. High energy phosphate transfer (HEPT): anaerobic alactic, phosphagen system
(2-3s) ATP + H20 --------------------- ADP + Pi + H+ + Energy (7.3 kcal/mole ATP)
Stored ATP
Pi does not recombine with ADP
(8-10s) ADP + PCr + H+ ------------------------------ ATP + Cr
↓PCr by 50, Pi and Cr ↑ by 50
PCr stores 3-4X greater than stored ATP
Enzyme creatine kinase responds to ↓ATP, ↑ADP and Pi
ADP + ADP ---------------------- ATP + AMP
Lose one net ATP (took 2 to make 2 ADP, we only make one ATP back)
AMP ------------------- IMP + NH3
IMP: inosine monophosphate
This reaction gets rid o AMP to keep reaction above moving to the right
EPOC used to replenish PCr levels
More on this reaction: ADP + PCr + H+ ------------------------------ ATP + Cr
PCr is a valuable energy source early in exercise
PCr stores limited in muscle, therefore low capacity for producing ATP
Creatine kinase activity is very high in muscle (higher than ATPase activity) and will
repleish ATP rapidly as it is hydrolyzed during exercise, therefore high power (rate of
ATP production high) for producing ATP
Near equilibrium reaction therefore all you need is a very small decrease in [ATP] to start
the reaction going to the right
Uses an H+ to help buffer pH
More on this reaction: ADP + ADP ---------------------- ATP + AMP
Enzyme turned on by ADP
Reversible reaction functions to ↑[ATP] especially during very intense exercise such that
the rate of ATP hydrolysis is very high resulting in increases in [ADP]
Reversible in order to bring AMP back to ADP and then to ATP
Helps keep [ADP] levels low to maintain a high free energy for the hydrolysis of ATP
and to minimize fatigue prevent ADP build up (by-product build up)
Increases [AMP] which can be useful for activating other metabolic pathways (ie.
glycolysis and ox phos)
More on this reaction: AMP ------------------- IMP + NH3

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Very useful during intense muscular work by helping to keep [AMP] low, which will
keep the adenylate kinase reaction moving to the right, therefore ultimately prevents
[ADP] build-up (maintaing high [ATP]/[ADP])
Ammonia quickly reduced to an ammonium ion (NH3 + H+ NH4+)
This effectively removes an H+ to help buffer pH
Ammonium ion also known to stimulate glycolysis
General PCr system functions:
Supply ATP
Ratio of ADP to ATP high (↓ADP)
Provides metabolic signals to turn on other pathways NH4+, AMP
Purine Nucleotide Cycle: helps to preserve the adenine nucleotide pool in skeletal
muscle since IMP and downstream metabolites are trapped inside the cell whereas in
heart AMP in converted to adenosine which easily diffuses out of the cel which reduces
the total adenine pool inside the cell (ie. loss of ATP)- important for cell survival
following ischemia
In skeletal muscle: use ATP but then restores it vs. in the heart: adenosine diffuses so it
cannot be restored lost adenosine pool must remake from scratch
This is the reason why we can reattach limbs because when reattached, ATP pool is ↑;
ischemia repurfusion
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