In the context of sarcomere structure, which band contains both actin and myosin?

The A band is the correct choice because it contains the entire length of myosin filaments, which are thick filaments, and also intersects with overlapping regions of actin filaments, which are thin filaments. The A band represents the area where the myosin and actin overlap, crucial for muscle contraction as it is where cross-bridges form during the sliding filament mechanism.

In contrast, the I band consists solely of actin filaments and does not include myosin, making it distinct from the A band. The H zone, which is present within the A band, represents the region where there is only myosin, lacking actin overlap. The Z line marks the boundary between adjacent sarcomeres and is composed of proteins that anchor the actin filaments, but it does not contain either type of filament in entirety. Hence, the A band is unique in that it contains both actin and myosin, fulfilling the requirement of the question.