Final answer:
The long tail of myosin II is made up of myosin monomer assemblies that interact with actin filaments to facilitate muscle contraction through a process that includes a power stroke driven by ATP hydrolysis.
Step-by-step explanation:
The long tail of myosin II is formed by the assembly of myosin monomers. These monomers are large protein molecules that can be dissociated into heavy chains known as S1 (head) and tail fragments. Through electron microscopy and experiments involving proteins like actin and myosin, it's been shown that these myosin molecules can bind to actin microfilaments, and the binding is catalyzed by the energy from adenosine triphosphate (ATP) hydrolysis. During muscle contraction, myosin heads bind to actin filament sites, hydrolyze ATP, go through a power stroke, and pull the actin along with it, which results in the shortening of the sarcomere and the contraction of muscle fibers. The power stroke is the critical step where myosin releases stored energy and moves towards the center of the sarcomere, known as the M line.