You decide to do an experiment with isolated myofibrils to explore the effects of ATP hydrolysis on myofibril function. You do this by bathing the myofibrils in a solution that contains a modified form of ATP, which cannot be split into ADP and Pi. At what step will myofibril function be arrested by using this compound instead of unmodified ATP?
A. Myosin heads will be unable to bind to the actin filaments.
B. There will be no block in the cycle, since ATP hydrolysis is not required for this process.
C. The myosin heads will remain attached to the actin filaments after the power stroke.
D. Myosin heads will bind to the actin filaments, but the power stroke will not occur and actin filaments will not slide over the myosin filaments.
E. Myosin molecules will be unable to assemble into thick filaments.
Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
Gather Content
· What do you know about the role of ATP hydrolysis in myofibril function? What other information is related to the question?
Choose Answer
· Given what you now know, what information is most likely to produce the correct answer?
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
A. Myosin heads will be unable to bind to the actin filaments.
Clarify Question
· What is the key concept addressed by the question?
o The question asks about the role of ATP hydrolysis in myofibril function.
· What type of thinking is required?
o You are being asked to analyze statements to explain the role of ATP hydrolysis in myofibril function.
Gather Content
· What do you know about the role of ATP hydrolysis in myofibril function? What other information is related to the question?
o The cross-bridge cycle involves hydrolysis of ATP by myosin causing a conformational change that moves the head into an energized state. The ADP and Pi remain bound to the myosin head, which can bind to actin. In the second step, myosin binds to actin, forming a cross-bridge. In the third step, the power stroke, myosin returns to its original conformation, releasing ADP and Pi. In the last step, ATP binds to the myosin head breaking the cross-bridge. ATP hydrolysis returns the myosin head to its energized conformation, allowing the cycle to begin again.
Choose Answer
· Given what you now know, what information is most likely to produce the correct answer?
o Without ATP hydrolysis, myosin heads will be unable to bind to the actin filaments.
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
o This question asked you to analyze statements to explain the role of ATP hydrolysis in myofibril function. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you think that ATP hydrolysis was necessary for breaking the bridge between actin and myosin? Did you think that ATP hydrolysis was necessary for the power stroke?
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