Active polymer hydrodynamics: simulations and theory

Recent spectroscopy experiments on interphase chromatin have uncovered the existence of long-
ranged coherent motions on the scale of microns and persisting for seconds. These motions were found
to be ATP-dependent and thus driven by the cooperative activity of ATP-powered molecular motors.
Motivated by these observations, we use Brownian dynamics simulations to elucidate the effects of
motor activity on the dynamics of long flexible polymer chains in viscous solvents. We develop a coarse-
grained model where active events are modeled as stochastic force dipoles, which affect chain dynamics
and also drive long-ranged hydrodynamic flows. Numerical simulations in unconfined environments
demonstrate the key role played by hydrodynamic interactions in these systems, where extensile dipolar
activity is shown to result in chain stretching whereas contractile activity effectively enhances local
fluctuations. Our numerical results are explained theoretically based on a statistical model for an
active trimer.