Question

Thick filaments composed of myosin extend along the entire length of the A band. The center point of the A band is the dense M line that contains a myosin-binding protein, myomesin. This protein links thick filaments together, forming the M line. The less-dense H zone that flanks the M line consists exclusively of thick filaments. The thin filament anchored to the Z line extends over one-half of the I band and, therefore, overlaps with a portion of the A band. Thus, portions of the A band that flank the H zone contain both thin and thick filaments. These thin and thick filaments are organized so that each thick filament is in contact with six thin filaments. During muscle contraction, longer portions of the thin filaments slide into the A bands. As result of these molecular changes, H zones become thinner and I bands become shorter during muscle contraction. True or False?

Answer 1

The provided statement is true; it accurately describes the organization of myofibrils and the process of how muscle contraction occurs at the molecular level.

Step-by-step explanation:

The statement given by the student about the structure of myofibrils and what happens during muscle contraction is true. Myofibrils are made of repeating units called sarcomeres, which are marked by Z discs at each end. The sarcomere contains thick filaments of myosin in the A band, including the M line in the center and the lighter H zone surrounding it. Thin filaments of actin are anchored to the Z line and extend through the I band into the A band, overlapping with the myosin filaments. During muscle contraction, these thin filaments slide toward the center of the sarcomere, reducing the length of the I band and the width of the H zone, causing the muscle to shorten without changing the length of the A band itself.