Credit: INTELECOM /SCIENCE PHOTO LIBRARY

Caption: Calcium binds to troponin, causing the binding site on actin to be exposed. Myosin heads attach to this binding site, a power stroke is achieved, then ADP is released and the myosin heads relax. The high energy myosin head releases the inorganic phosphate ion and binds tightly to actin, forming a crossbridge. Myosin is unstable in this conformation and shifts to the low energy form, releasing the bound ADP, or adenosine diphosphate. This conformational shift results in a power stroke as the tightly bound myosin pulls on the actin filament. In this low energy conformation, myosin has a high affinity for ATP. As ATP is bound to the myosin head, actin is released, thus breaking the crossbridge. The ATPase activity of myosin triggers ATP hydrolysis and the myosin head is re-cocked to the high energy conformation, thus bringing the cycle back to the beginning. Because actin is tethered to structures located at the lateral ends of each sarcomere, called the z disc, any pulling of the actin filament results in a shortening of the sarcomere and thus the muscle.

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Keywords: actin, adenosine diphosphate, adp, cross bridge cycling, muscle, myofibril, myosin, myosin head, power stroke, sarcomere, troponin

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Calcium binding to troponin

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Duration: 00:01:08.03

Frame size: 1920x1080

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