Thin filaments are composed of Group of answer choicesactinmyosintroponindystrophin

Thin filaments in muscle fibers are primarily composed of the protein actin. Additionally, they also contain two other proteins: tropomyosin and troponin.

Here's a step-by-step breakdown:

1. Actin: This is the main component of thin filaments. Each actin molecule is a globular subunit that assembles into a long polymer chain. Two of these chains twist around each other to form the thin filament.

2. Tropomyosin: This is a protein that winds around the chains of the actin filament. It blocks the myosin binding sites on actin when the muscle is not contracting.

3. Troponin: This is a complex of three proteins attached to tropomyosin. It has a binding site for calcium ions, which, when bound, cause a change in the position of tropomyosin, exposing the myosin binding sites on actin.

Dystrophin is not a component of thin filaments. It is a protein that helps to strengthen muscle fibers and protect them from injury.