Assistant Professor of Medical Biochemistry€¦ · Biochemistry . Myofibril . Muscle Proteins . Myosin-thick filament structure . Role of ATP in contraction & relaxation . Role of
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Muscle biochemistry
Assistant Professor of Medical
Biochemistry
Myofibril
Muscle Proteins
Myosin-thick filament structure
Role of ATP in contraction & relaxation
Role of Ca2+ and regulatory proteins
in contraction and relaxation
Role of Ca2+ and regulatory proteins
in contraction and relaxation
• Running required more energy than walking. (Med Sci Sports Exerc. 2004 Dec;36(12):2128-34.)
• ATP is important to performs muscle
contraction and relaxation.
• The ATP that exists at the start of
• contractile only support a few twitches.
• There is a need for continual production
of ATP by a muscle fiber
The three ways of production of ATP by a
muscle fiber
1. Some ATP is stored in a resting muscle. As
contraction starts, it is used up in seconds. More
ATP is generated from creatine phosphate for
about 15 seconds.
2. Each glucose molecule produces two ATP and
two molecules of pyruvic acid, which can be
converted to lactic acid If oxygen is not available,
which may contribute to muscle fatigue. This
occurs during strenuous exercise (oxygen cannot
be sufficiently delivered).
Glucose –lactate cycle (Cori cycle)
ADP represents the ‘last gasp’ of the
short-term energy stores:
3. Aerobic respiration is the breakdown of glucose or
fatty acids in the presence of oxygen (O2) to produce
carbon dioxide, water, and ATP. Approximately 95
percent of the ATP required for resting or
moderately active muscles is provided by aerobic
respiration, which takes place in mitochondria.
Substrate level phosphorylation and
oxidative phosporylation
Tissue Fuel utilized Fuel stored Fuel produced
for export
Resting
muscles
Fatty acids Glycogen None
Exercising
muscles
Glucose None Lactate and
alanine
Muscle tissues
fuel utilization stores and production
Types of skeletal muscle fiber
1. Slow-oxidative fibers (type I)
combine low myosin-ATPase activity
with high oxidative capacity.
2. Fast-oxidative fibers (type IIa)
combine high myosin-ATPase activity
with high oxidative capacity.
3. Fast-glycolytic fibers (type IIb)
combine high myosin-ATPase activity
with high glycolytic capacity.
Metabolic control during exercise
presents an excellent model for
explaining how body efficiently
responds to changes in
physiological processes.
Two different pattern of exercise:
1. The short duration, vigorous
exercise competitions (sprinting),
2. And the low power-output, long
distance running (marathon).
Sprinters muscle fiber
Sprinters possess a large muscle mass
mainly consisting of white muscle fibers
(Type IIb) that have high anaerobic
capacity, and store considerable larger
amount of glycogen, and creatine
phosphate.
marathon runners muscle fiber
While muscles in the marathon runners
are consisting mainly of the highly aerobic
red mucles, densly packed with
mitochondria and myoglobin. (Type I).
During the first seconds of a 100
meter sprint, the stimulation of the
myofibrillar ATPase by Ca 2+
decreasing the ATP level and
increasing ADP.
Metabolism in sprinters muscle fiber
ATP will rapidly be reformed at
expense of phosphocreatine
catalyzed by creatine kinase,
muscle content of phosphocreatine
may only last for few seconds
(15s).
Metabolism in sprinters muscle fiber
Metabolism in sprinters muscle fiber
Then the muscle turn to the stored
glycogen which will be anaerobically
degraded at a very rapid rate controlled by
the activity of myo-phosphorylase (enzyme
breaking glycogen→glucose).
Myophosphorylase is activated by
epinephrine and by high Ca levels.
In marathon running, (42,2 km),
ATP synthesis is mainly powered
by aerobic oxidation involving an
increased rate of fatty acid
mobilization and acetyl-CoA
oxidation, still a large proportion of
glucose will also be used
particularly in the first stage of the
exercise.
Metabolism in marathon runners
muscle fiber
Sustained exercise modulate the body
metabolism in a way that reduce the
muscle dependence on glucose and
gradually increases utilization of FA.
Metabolism in marathon runners
muscle fiber
Acetyl-CoA when increased as a result of
FA oxidation, it inhibits carbohydrate
(glucose) utilization.
Thereby prevent a severe hypoglycemia
that would occur if glucose utilization
went unchecked in marathon running.
Metabolism in marathon runners
muscle fiber
Atrophy
Nonfunctioning neuromuscular junctions,
lack of exercise and disuse lead to
atrophy of the muscle.
On the other hand exercise can produce
an increase in the size (hypertrophy) of
muscle fibers as well as changes in their
capacity for ATP production.
Hypertrophy
On the other hand exercise can produce
an increase in the size (hypertrophy) of
muscle fibers as well as changes in their
capacity for ATP production.
Effect of exercise
Low intensity but of long duration (aerobic
exercise), such as running and swimming,
produces increases in the number of
mitochondria in the muscle fibers. In
addition, there is an increase in the number
of capillaries around these fibers. These
changes lead to an increase in the capacity
for endurance activity with a minimum of
fatigue.
Effect of exercise
In contrast, short-duration, high-intensity
exercise (strength training), such as weight
lifting, affects primarily the fast- glycolytic
fibers (hypertrophy). In addition, the
glycolytic activity is increased . The result of
such exercise is an increase in the strength
of the muscle. Such muscles, although very
powerful, have little capacity for endurance,
and they fatigue rapidly.
LECTURE RESOURCES:
1. Harpers illustrated biochemistry. Robert K Murry,
Daryl K. Granner, Peter A Mayes, and Victor W.
Rodwell , 27th edition. ISBN: 978-0071461979.
Chapter 49.
2. Biochemistry . Stryer, L.; Berg, J. M.; Tymoczko,
J. L. (2002), New York: W. H. Freeman, 5th
ed. ISBN 0716746840. chapter 30 page=270-271
3. Vander, Sherman, Luciano's .Human Physiology:
The Mechanisms of Body Function. Information
center- chapter 9. the Muscle.
4. http://www.bmb.leeds.ac.uk/illingworth/muscle/
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