A band

Definition

Target type: cellularcomponent

The dark-staining region of a sarcomere, in which myosin thick filaments are present; the center is traversed by the paler H zone, which in turn contains the M line. [ISBN:0321204131]

The A band is a prominent feature of the sarcomere, the fundamental contractile unit of striated muscle. It is the darkest band under a microscope, and its name derives from anisotropic, referring to its birefringence property. The A band is characterized by its dense arrangement of thick filaments, primarily composed of the protein myosin. Myosin molecules have a long tail and two globular heads, which project out from the filament. These heads bind to actin filaments, the thin filaments found in the I band, during muscle contraction.

The A band can be further divided into distinct sub-regions:

- **M line:** Located at the center of the A band, the M line serves as an anchoring point for the thick filaments. It contains proteins like myomesin and M-protein, which help stabilize the thick filament structure.

- **H zone:** Flanking the M line, the H zone is the region within the A band where only thick filaments are present. It appears lighter than the rest of the A band because it lacks thin filaments.

- **Overlap zone:** This region is where both thick and thin filaments overlap. It extends from the edge of the H zone to the edge of the A band. The interaction between thick and thin filaments in this zone is crucial for muscle contraction.

- **Bare zone:** This is a small, central region within the H zone where the myosin heads are absent. This area is characterized by only the myosin tails.

Overall, the A band represents the core structural unit of the sarcomere, containing the thick filaments and providing the necessary scaffolding for muscle contraction. Its organization and composition contribute significantly to the efficient generation of force in muscle fibers.'
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Proteins (2)

Compounds (14)