Fluctuating Filaments Under Tension - From Flexible Chains to Rigid Rods

We develop a novel biased Monte-Carlo simulation technique to measure the force-extension curves and the distribution function of the extension of fluctuating filaments stretched by external force. The method is applicable for arbitrary ratio of the persistence length to the contour length and for arbitrary forces. The simulation results agree with analytic expressions for the force-extension curves and for the renormalized length-scale-dependent elastic moduli, derived in the rigid rod and in the strong force limits. We find that orientational fluctuations and wall effects produce non-Gaussian distributions for nearly rigid filaments in the small to intermediate force regime. We compare our results to the predictions of previous investigators and propose new experiments on nearly rigid rods such as actin filaments.