For each event of the cross-bridge cycle, say what is needed or what happens…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
For each event of the cross-bridge cycle, say what is needed or what happens.
- What must bind to troponin before the myosin head can bind the actin?
- What breaks the cross-bridge after the pull?
- What does the head release at the end of the pull?
- What is made when the head binds the exposed site on the actin?
Need a reminder? The key ideaShow
In the sliding filament theory, the myosin heads bind the actin, pull it toward the centre of the A band and let go when a new ATP binds. The filaments keep their lengths. The A band stays the same, and the I band and the H zone get shorter. In the model, the thick filament is u, each thin filament is u and the relaxed sarcomere is u.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Calcium ions bind to troponin and uncover the sites.
Step 2. (b) A new ATP binds to the head and breaks the cross-bridge.
Step 3. (c) The head releases ADP and Pi and goes back to its relaxed state.
Step 4. (d) A cross-bridge.
Answer: (a) calcium ions; (b) a new ATP; (c) ADP and Pi; (d) a cross-bridge.
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