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1st step

resting stage, no contraction. ADP + PI are bound to ATpase of mysosin. Myosin binding site of acti is covered by tropomyosin.

2nd step

ca2+ binds to troponin, pulls troponin-tropomyosin complex off the myosin binding site of actin. Actin binds to myosin.

3rd step

adp + pi are released from myosin atpase, acusing a change in the conformation of the myosin head. the thin filament is pulled toward the center of the sarcomere.

4th step

ATP binds to myosin ATPASE, which breaks the crossbridge

5th step

ATP is hydrolized into DP + PI and energy is released. This energy is used to swivel the myosin head back to its original conformation. myosin is now ready to form a new crossbridge with another actin protein if ca2+ and ATP are still available


are formed when ca2+ binds to troponin, troponin-tropomyosin complex is pulled off the binding site of actin. actin binds to myosin formin crossbridge

roles of atp and ca2+

ca2+ binds o troponin, which changes formation of tropomyosin, revealing binding site of actin. ATP binds to atpase and breaks crossbridge

asynchronous crossbridge formation

multiple crossbridges form and break asynchronously. keeps sarcomere shortening.

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