Thin filament

Thin Filament

The Thin Filament is a fundamental component of the sarcomere, the basic unit of muscle contraction. It is primarily composed of the proteins actin, tropomyosin, and troponin.

Structure

The thin filament is approximately 7 nm in diameter and is made up of two strands of actin molecules twisted around each other. Each actin molecule has a binding site for myosin, the motor protein that drives muscle contraction.

Wrapped around the actin strands are two strands of tropomyosin, a protein that blocks the myosin-binding sites on actin when the muscle is at rest. Attached to the tropomyosin are troponin complexes, which regulate the position of tropomyosin on the actin filament.

Function

The primary function of the thin filament is to interact with the thick filament to generate muscle contraction. This process is regulated by the calcium ions that bind to the troponin complexes on the thin filament.

When calcium ions bind to troponin, it causes a conformational change in the troponin-tropomyosin complex, exposing the myosin-binding sites on actin. This allows myosin heads on the thick filament to bind to actin, forming cross-bridges. The myosin heads then undergo a power stroke, pulling the thin filament towards the center of the sarcomere and shortening the muscle.

See Also

• Actin
• Tropomyosin
• Troponin
• Sarcomere
• Muscle Contraction
• Thick Filament