Final answer:
Arp2/3-dependent actin polymerization directly drives b) lamellipodia protrusion, a critical activity at the leading edge of crawling cells, contributing to cell movement by pushing the plasma membrane forward.
Step-by-step explanation:
The question pertains to the role of Arp2/3-dependent actin polymerization in cell motility. Specifically, Arp2/3 complex initiates the formation of branched actin networks at the leading edge of a crawling cell, contributing directly to lamellipodia protrusion. This is a key driver in the process of cell movement as the actin network pushes against the plasma membrane causing the cell to extend forward. New adhesions are formed under the lamellipodium which are then carried rearward with the actin flow, and may eventually mature into focal adhesions as they proceed towards the cell body.
The growth of a lamellipodium is supported by the polymerization of actin filaments, branching, capping, and crosslinking. The actin polymerization is mainly driven by the Arp2/3 complex which helps in creating a dendritic network with filaments branching off at a specific angle, thereby pushing the membrane outward and assisting the protrusion of lamellipodia.
Focal adhesions provide attachment to the extracellular matrix and are subjected to forces via contractile actin stress fibers. Adhesions can grow and mature if sufficient force is exerted, and Arp2/3-dependent actin dynamics contribute to the necessary tension and traction forces that sustain mature adhesions and facilitate cell crawling.