Copy and fill in the table. For each part of a sarcomere, write whether it gets longer, gets…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Copy and fill in the table. For each part of a sarcomere, write whether it gets longer, gets shorter or stays the same when the muscle contracts, and give a short reason.
| Part | Change | Reason |
|---|---|---|
| A band | ? | ? |
| I band | ? | ? |
| H zone | ? | ? |
| Thin filament | ? | ? |
| Distance between two Z lines | ? | ? |
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 band. Stays the same. It is as long as the thick filaments, and they do not shorten.
Step 2. I band. Gets shorter. The thin filaments slide toward the centre, and the Z lines come closer to the A band.
Step 3. H zone. Gets shorter, and it may vanish. The thin filaments move in until their tips meet.
Step 4. Thin filament. Stays the same. It slides, but it does not shorten.
Step 5. Distance between two Z lines. Gets shorter. This is the sarcomere.
Answer: A band: same. I band: shorter. H zone: shorter. Thin filament: same. Z line to Z line: shorter.
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