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BioFlix: Roles of Calcium and ATP

by Pearson
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How do the myosin heads pull actin? In a relaxed muscle the myosin binding sites on actin are blocked by a protein complex and ADP and phosphate are bound to each myosin head An action potential causes the ER to release calcium ions which bind to the protein complex causing it to shift and expose the myosin binding sites The myosin head binds to actin When ADP and phosphate are released the myosin head bends pulling the actin This is called the power stroke Next, ATP binds to the myosin head causing it to detach from actin When the ATP is broken down to ADP and phosphate the myosin head extends The sequence repeats as long as calcium ions are present Bind Power stroke Detach Extend The combined work of many myosin heads causes the actin filaments to slide past the myosin filaments When the action potentials stop calcium ions are pumped back into the ER The mysosin binding sites on actin are again blocked and the muscle relaxes
How do the myosin heads pull actin? In a relaxed muscle the myosin binding sites on actin are blocked by a protein complex and ADP and phosphate are bound to each myosin head An action potential causes the ER to release calcium ions which bind to the protein complex causing it to shift and expose the myosin binding sites The myosin head binds to actin When ADP and phosphate are released the myosin head bends pulling the actin This is called the power stroke Next, ATP binds to the myosin head causing it to detach from actin When the ATP is broken down to ADP and phosphate the myosin head extends The sequence repeats as long as calcium ions are present Bind Power stroke Detach Extend The combined work of many myosin heads causes the actin filaments to slide past the myosin filaments When the action potentials stop calcium ions are pumped back into the ER The mysosin binding sites on actin are again blocked and the muscle relaxes