Question

List five proteins of the myofilaments and describe their physical arrangement

Answer 1

The five proteins of the myofilaments in muscle fibers are actin, myosin, tropomyosin, troponin, and alpha-actinin. Actin is the main component of thin filaments, while myosin is the main component of thick filaments. Tropomyosin blocks the binding sites on actin, troponin regulates the interaction between actin and myosin, and alpha-actinin attaches thin filaments to the Z disc.

Step-by-step explanation:

The myofilaments in muscle fibers are composed of various proteins. The five proteins of the myofilaments are:

1. Actin: Actin is the primary component of thin filaments. It has binding sites for myosin attachment.
2. Myosin: Myosin is the main component of thick filaments. The tail of a myosin molecule connects with other myosin molecules to form the central region of a thick filament near the M line, while the heads align on either side of the thick filament where the thin filaments overlap.
3. Tropomyosin: Tropomyosin is a protein that blocks the binding sites on actin, preventing actin-myosin interactions when the muscles are at rest.
4. Troponin: Troponin consists of three globular subunits. One subunit binds to tropomyosin, one subunit binds to actin, and one subunit binds Ca²+ ions.
5. Alpha-actinin: Alpha-actinin is a protein that attaches thin filaments to the Z disc.

Answer 2

The five proteins of the myofilaments are the following:

1. Myosin, shaped like a golf club, with two polypeptides intertwined to form a shaftlike tail and a double globular head, or cross-bridge, projecting from it at an angle.

2. Fibrous actin is like a bead necklace—a string of subunits called globular (G) actin. Each G actin has an active site that can bind to the head of a myosin molecule.

3. Tropomyosin. It blocks the active sites of six or seven G actins and prevents myosin cross-bridges from binding to them when a muscle fiber is relaxed.

4. Troponin a smaller calcium-binding protein bound to each tropomyosin molecule.

5. Titin (connectin), run through the core of a thick filament, emerge from the end of it, and connect it to a structure called the Z disc.