A student measures a relaxed sarcomere in the model…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student measures a relaxed sarcomere in the model. The A band is u, the I band is u (both halves) and the H zone is u.
- What is the length of the sarcomere?
- What is the length of one thin filament?
- Which part of the sarcomere does not change if the muscle later contracts: the A band, the I band or the H zone?
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. A band u, I band u, H zone u.
Plan. Add the A and I bands for the sarcomere. Take the H zone away, and share the rest between the two thin filaments.
Step 1. Sarcomere. u.
Step 2. The two thin filaments. u together.
Step 3. One thin filament. u.
Step 4. The part that does not change. The A band is as long as the thick filaments, and the thick filaments do not change their length. The A band stays at u.
Answer: u; u; the A band.
Check. Put u back: u.
Watch out. This method works only when the H zone is present. If the thin filaments meet in the middle, the H zone is zero, and the method gives a wrong, smaller length.
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