| Force generation by actin polymerization is investigated via both molecular-level simulation and continuum rate equations. The passive processive growth of actin filaments with barbed ends attaching to a moving obstacle is investigated first. The required binding energy and the force-velocity relation of a single filament are obtained via Brownian dynamics simulations of a three-dimensional energy-based model. This passive processive growth model, together with other two single-filament force-generation models in the literature, are compared within a multi-filament framework which includes both the filaments' orientations and deformations. We find that all three models give similar force-velocity relations and force-filament number relations. However, the zero-force velocity of the obstacle as a function of capping rate and detachment rate differs significantly between the models, and the assumption of the filament creation mechanism makes distinct predictions for the filament orientation distribution. We also study the symmetrization of filaments in a mother-daughter filament pair, caused by filaments' internal stress. The symmetrization time is obtained from both numerical simulations of a bead-spring model, and analytical calculations of the growth velocities of the filaments. |
