Final answer:
In lamellipodia, actin polymerization is nucleated by the Arp2/3 complex, and depolymerization is catalyzed by proteins such as ADF/cofilin. These processes are crucial for cell motility by enabling the cell to extend its membrane and ensuring cytoskeletal turnover.
Step-by-step explanation:
In lamellipodia, actin polymerization is nucleated by the Arp2/3 protein complex, while depolymerization is catalyzed by proteins like ADF/cofilin. Actin polymerization at the leading edge of a cell involves the growth of actin filaments, which requires ATP-binding to globular actin (G-actin), leading to the elongation of these filaments primarily at their plus end. Depolymerization, in contrast, is driven by the hydrolysis of ATP to ADP within the filament, which weakens the bonds between monomers, particularly at the minus end, facilitating disassembly.
The dynamics of actin polymerization are essential for cell motility, as they allow the cell to extend its membrane outward in the form of lamellipodia. Conversely, actin depolymerization recycles actin monomers, maintaining a pool of G-actin for future polymerization events and ensuring the turnover of the cytoskeletal structure. Thus, both processes are critical for the forward movement of the cell.