Final answer:
Protrusion of filopodia and lamellipodia in migrating cells is driven by actin polymerization, supported by molecular motors like myosin, and is a key process in cell motility and directed movement.
Step-by-step explanation:
In a migrating cell, the protrusion of filopodia and lamellipodia are primarily driven by actin polymerization. Actin filaments, as a part of the cytoskeleton, are responsible for cell movement through a complex series of polymerization and depolymerization, allowing these structures to extend forward. This actin dynamics, in conjunction with molecular motors like myosin, enable cellular extensions to form and retract, facilitating cell motility on a substrate. The polymerization of actin not only pushes the cell membrane outward but is counterbalanced by adhesions and cytoskeletal interactions that regulate the cell's contact with its external environment, thereby contributing to a directed movement.
Lamellipodia, characterized by a network of actin filaments, grow and develop at the leading edge of the cell due to the polymerization of actin. Simultaneously, filopodia extend by assembling actin bundles along the direction of cell movement. Myosin motors also play a role by pulling on the actin filaments and contributing to cellular contraction and retraction.