A relaxed sarcomere is cut across at four places…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A relaxed sarcomere is cut across at four places. Say which filaments you would see in each cut: thin only, thick only, or both.
- In the I band, close to the Z line.
- In the A band, just inside the end of a thick filament.
- In the H zone.
- At the M line.
Need a reminder? The key ideaShow
The sarcomere lies between two Z lines. The A band is as long as the thick filaments. The I band holds only thin filaments. The H zone is the part of the A band that the thin filaments do not reach. In the model, the thick filament is u and each thin filament 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.
Given. Four places.
Plan. Use the table of the zones.
Step 1. (a) The I band has the thin filaments only.
Step 2. (b) Just inside the end of the thick filament, the thin filaments overlap the thick ones. You see both.
Step 3. (c) The H zone has the thick filaments only.
Step 4. (d) The M line lies in the middle of the H zone. It has the thick filaments only, held together by the M line.
Answer: (a) thin only; (b) both; (c) thick only; (d) thick only.
Check. Only the part of the A band where the thin and the thick filaments overlap shows both.
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