Thick filament

Thick Filament

The thick filament is a type of protein filament that is primarily composed of the protein myosin. It is one of the two types of filaments involved in the contraction of muscle fibers in muscle tissue, the other being the thin filament.

Structure

The thick filament is approximately 15 nanometers in diameter and is made up of several hundred myosin molecules. Each myosin molecule consists of a head and a tail. The heads form cross-bridges with the thin filaments during muscle contraction, while the tails align to form the central part of the thick filament.

Function

The primary function of the thick filament is to interact with the thin filament to bring about muscle contraction. This is achieved through the cross-bridge cycle, a process that involves the binding and unbinding of myosin heads to actin molecules in the thin filament. The energy for this process is provided by adenosine triphosphate (ATP).

Role in Muscle Contraction

During muscle contraction, the myosin heads of the thick filament form cross-bridges with the actin molecules of the thin filament. This is followed by a power stroke, during which the myosin head pivots and pulls the thin filament towards the center of the sarcomere, the basic unit of muscle contraction. This sliding of filaments is known as the sliding filament theory of muscle contraction.

Clinical Significance

Abnormalities in the structure or function of the thick filament can lead to various muscle disorders. For example, mutations in the myosin gene can result in myopathies, a group of diseases that cause muscle weakness and wasting.

See Also

• Thin filament
• Myosin
• Muscle contraction
• Sarcomere
• Sliding filament theory