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Molecular basis of muscle contraction
Structure of muscles
The tissues of muscle are composed of the muscle fibers, which are large as
well skinny cells which can be few inches long whilst few nuclei are found in
the skeletal muscle
...
Sarcoplasmic
reticulum stores calcium ions as well it surrounds the thick and thin
filaments
...

Moreover, myofibril is composed of repeating units known as the
sarcomeres, at its end a Z disc is found
...
Thin filaments are joined to the Z disc whilst the thick filaments
are enriched in the center of the sarcomere known as the M line
...
Myosin molecule consist of tail terminating as well with two
globular heads
...
Their heads are also known as the cross bridges because
they are interconnected with actin filaments during the contraction
...
Myosin proteins are
the most abundant in the muscles because they play an important role in
the muscle’s contraction
...
So, myosin molecules possess
the 2 heavy chains as well 4 light chains
...


Myosin II is involved in the muscle’s contraction; it has two heavy chains in
which head & tail is include
...
Myosin V functions microtubules, Myosin VI
travel to the end of the thin filament
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Myosin X, during
phagocytosis it is work as the downstream effector of the PI(3)K
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Myosin also contains two 220 kilodaltons heavy
chains which form the major of overall structure as well 2- pairs of light
chains that’s are different in size
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The molecular size is about 130 kilodaltons

of each globular head and 2 light chains
...

Moreover, the myosin is a protein which convert the chemical energy in the
form of adenosine triphosphate into mechanical energy, in the result force
generate as well the movement occurs
...
As well, myosin is involved in many functions such as
growth, reproduction even in the movement of hundred trillion of cells
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Thin filaments are arranged in 2- chains and coil together as
like the double stranded of pearls
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Whilst the troponin can bind with three other molecules
which are actin & myosin as well the calcium ions
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In all eukaryotic cells, actin is known as the

most abundant protein approximately 5-10% of total protein that is greatly
involved in the muscle contraction
...
Holmes, W
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Only one molecule of the actin which are globular proteins and
consists of about 375 amino acids
...

Each monomer of actin can rotate about 166o in the filaments, and appear
as the double stranded structure of helix
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Muscle contraction occur due to the interactions of myosin as well the actin
filaments which produce the movement
...
So, the actin protein is an important molecule of the
muscle cell which is greatly involved in the muscle contractions
...
Firstly, the motor neurons give the signals
to the muscle cell from brain, in the result acetylcholine is released which

causes the release of calcium ions to secrete out from the sarcoplasmic
reticulum
...
So, the shape of troponin changes when
calcium ions bind with it, tropomyosin travel from binding regions of
myosin on the thin filaments, & unblock them in result, myosin head bind
with the actin filament
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The hydrolysis reaction secreted the energy from adenosine triphosphate
& myosin act as motor change the chemical energy into the mechanical
energy
...
This movement results the thin filaments move to the center of
the sarcomere in result sarcomere become shorten as well contract and so
the contraction of sarcomere develop the muscle movement
...
In which, they described that
myosin and actin filaments are involved in the muscle contractions
...
F
...
E
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When the muscles contract their cells undergo with various

changes in which also the changes in actin and myosin filaments occur
...

This theory explained that the actin filaments slide past the myosin
filaments so, the thin and thick filaments overlapped in greater degree
...
In this procedure of the contraction of the muscles, the
cross bridges of the myosin filaments joined to the binding region of the
thin filament
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Controlling actin-myosin interaction via Ca++ ions
The nerve impulse starts or initiate the muscle contraction which is reached
at the neuromuscular junction
...

Sarcolemma (plasma membrane of the muscle cell) of the muscle cell
pierce deeply into the cell which form an elongated hollow tube that is
transverse tubule
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Transverse tubules & the terminal
region of envelop of the sarcoplasmic reticulum form the triads
...

And these binding regions are exposed as well the cross bridges with
myosin is formed and in the result contraction is happened
...
So, the
contraction is based on the number of fibers which take part in the
contraction
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These protein filaments include the myosin as well the actin
molecules
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Under light microscope via using various tricks, the process of the
actomyosin sliding can be perceived
...
Head of the myosin molecule is crystallized in
many conformations that suggests the bending of the neck portion, when the
head of myosin bound the actin molecule is can be responded for power stroke
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ATP is supplied to the muscles that is balanced in the muscles
via the aerobic breakdown of the glucose molecules, that get out from
stored glycogen
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When the oxygen is depleted or the high muscular activity, ATP
is come through the anaerobic breakdown of the glucose molecules into
the lactic acid, which can cause muscle fatigue
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Myosin and actin
filaments are the molecular basis of muscle contraction which permit
the myosin act as motor to drive the filament sliding, and actin &
myosin perform action together to create of force that generate the
muscle contraction, results in the stimulation of the movement of
muscles
...
ATP is supplied to the muscles that is
balanced in the muscles via the aerobic breakdown of the glucose
molecules
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References
▪ https://www2
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ac
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nature
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Myosin structure and
function
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1995;60:783-91
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Unconventional myosins
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2000;35:33-42
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Regulation of myosin II during cytokinesis in higher eukaryotes
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2005 Jul;15(7):371-7
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doi
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1016/j
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2005
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004

▪ https://www
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nlm
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gov/books/NBK9908/#:~:text=Individual%
20actin%20molecules%20are%20globular,actin)%20(Figure%2011
...
net/actin-and-myosin/



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