Final answer:
After assembly, actin filaments serve as a track for motor proteins and enable cellular motion. In muscle cells, actin and myosin filaments sliding past each other leads to muscle contraction.
Step-by-step explanation:
After assembly of actin/tubulin molecules into a filament, the actin filaments serve as a track for the movement of motor proteins like myosin. This enables actin to engage in cellular events requiring motion, such as cell division and cytoplasmic streaming. In muscle cells, the sliding of actin and myosin filaments past each other causes muscle contraction.