Which protein is listed as a component of thin filaments along with actin, troponin, and tropomyosin?

• A. Nebulin
• B. Myosin
• C. TitIn
• D. Desmin

Answer: (A)

Nebulin acts as a structural component of thin filaments, running alongside actin to help determine filament length and stabilize the filament by anchoring to the Z-disc and binding along the actin strand. This role fits with the other thin-filament components—actin, troponin, and tropomyosin—forming the regulatory and structural complex that controls thin-filament function during contraction. In contrast, myosin is part of thick filaments that generate force, titin connects Z-discs to M-lines and provides elasticity for thick filaments, and desmin is an intermediate filament that helps link and organize sarcomeres. Therefore, nebulin is the protein listed as a component of thin filaments.