Final answer:
Actin polymerization requires G-actin subunits to bind with ATP, which provides the energy for conformational changes and the addition of new monomers to the filament.
Step-by-step explanation:
In order for actin polymerization to occur, G-actin subunits must bind with ATP. Actin filaments are polar, and their polymerization is a non-equilibrium process, driven by ATP hydrolysis. G-actin monomers associated with ATP attach to the plus end of the actin filament, and after a brief period, ATP is hydrolyzed to ADP. This hydrolysis leads to a reduced binding strength between monomers, destabilizing the filament and promoting dynamic changes in polymer length through processes like treadmilling. The process is essential for the formation of various cellular structures, such as microfilaments and involved in cellular movements. ATP hydrolysis provides the energy necessary for the actin to change conformation and bond with additional monomers, thereby facilitating polymerization.