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A-level Biology Muscle contraction exam question (AQA)

Hi,

I am a bit confused about what ATP is needed for in muscle contraction. My textbook says it is needed for bending the myosin head and thus pulling the actin filament, and then when ATP binds to the myosin head it detaches. But this question seems to suggest that it is also needed to form the cross bridge? And return to resting state?

Any help greatly appreciated. Thanks.
______________
(c) People who have McArdle’s disease produce less ATP than healthy people. As a result,
they are not able to maintain strong muscle contraction during exercise. Use your
knowledge of the sliding filament theory to suggest why.

(Idea ATP is needed for)
1. Attachment / cross bridges between actin and myosin;
Accept the role of ADP in attachment
2. ‘Power stroke’ / movement of myosin heads / pulling of actin;
Not just ‘filaments slide’ as given in the question stem
3. Detachment of myosin heads;
4. Myosin heads move back / to original position / ‘recovery stroke’
(edited 1 year ago)
I don't remember completely, but these are the main steps if that helps?

1. Tropomyosin molecule prevents myosin head from attaching to the binding site on the actin molecule. (image for this step is attached)
2. Calcium ions released from the endoplasmic reticulum cause the tropomyosin molecule to change shape and so pull away from the binding sites on the actin molecule.
3. Myosin head now attaches to the binding site on the actin filament.
4. Head of myosin changes angle, moving the actin filament along as it does so. The ADP molecule is released.
5. ATP molecule fixes to myosin head, causing it to detach from the actin filament.
6. Hydrolysis of ATP to ADP by ATPase provides the energy for the myosin head to resume to its normal position.
7. Head of myosin reattaches to a binding site further along the actin filament and the cycle is repeated.
(edited 1 year ago)
Reply 2
Original post by simxne_
I don't remember completely, but these are the main steps if that helps?

1. Tropomyosin molecule prevents myosin head from attaching to the binding site on the actin molecule. (image for this step is attached)
2. Calcium ions released from the endoplasmic reticulum cause the tropomyosin molecule to change shape and so pull away from the binding sites on the actin molecule.
3. Myosin head now attaches to the binding site on the actin filament.
4. Head of myosin changes angle, moving the actin filament along as it does so. The ADP molecule is released.
5. ATP molecule fixes to myosin head, causing it to detach from the actin filament.
6. Hydrolysis of ATP to ADP by ATPase provides the energy for the myosin head to resume to its normal position.
7. Head of myosin reattaches to a binding site further along the actin filament and the cycle is repeated.

This is great thanks !

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