Actin-Based Cell Motility: Myofibril Contraction

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Muscle contraction is a very important physiological behavior to human. All physical movement for example lifting arms, swallowing food, heart beating involved muscles contraction. The mechanism of muscle contraction is studied by a lot of researchers.


A skeletal muscle is made up of subunits called the fasicles. Fasicles are bundles of elongated muscle fibers which extend for the length of the muscle. The muscle fiber is segmented into distinct sectional bands. Within each muscle cell are numerous myofibrils, which also extend for the length of the muscle cell. Sarcomeres are the basic contractile subunit of myofibrils. Within the myofibrils subunit, there are thin and thick filaments. The thin filament is made up of actin while the thick filament is made up of myosin. These two filaments are the main constituent of the filament sliding model. During a muscle contraction, a crossbridge cycle was initiated. When the nervous system sends a synaptic signal to the muscle fiber through the release of acetylcholine into the synaptic clefts, it causes the sarcoplasmic reticulum to release calcium ion Ca2+. Ca2+ binds to the troponin. This activated the myosin ATPase and ATP is hydrolyzed by to ADP and Pi. ATP initially dissociates actomyosin into actin and myosin; i.e. the thick filaments will be detached from the thin filaments. It is bind to the myosin head in the thick filaments. When ATP is hydrolyzed, myosin is attached to the actin through the shift of tropomyosin to the actin site. A crossbridge is formed.It is believed that the angle of crossbridge attachment is 90o. ...
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