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As mentioned before, dynamic polymer chains are often described by the WLC.This model, however, would oversimplify the anisotropic threedimensional interactions between neighboring protein monomers that contribute to the macroscopic mechanical properties of the tubular lament.Various experiments provide evidence for nonisotropic responses to mechanical stress.Recent studies further reported a lament lengthdependent persistence length for mirotubules deviating from the simplied wormlike chain behavior with short laments appearing more exible than long ones. These ndings are ascribed to anisotropies in the spatial alignment of the molecular monomers as well as in the binding strength between these subunits.In the latter case, a higher exibility was attributed to structural defects in the tubulin lattice, which are more likely to occur Dabigatran during fast polymerization phases.Departing from the WLC, different approaches have been pursued in order to t experimental data from uctuation and deformation measurements.They modied their wormlike bundle model, which was initially applied to describe actin bundle mechanics and dynamics. A large variety of crosslinkers and other associated proteins has been identied which can cause bundling, inuence polymerization speed, or stabilize the whole lament via altered binding and unbinding dynamics.The resistance against breakage is dominated by strain hardening occurring above a certain threshold, which is different for each lament type. Presumably, those properties enable cells to bear large stresses and deformations.At rst, many of the more dynamic cellular processes such as cell migration and division are mostly attributed to the more dynamic actin and MT structures. Depending on the lament density, one typically distinguishes between dilute, semidilute, and concentrated solutions.In dilute solutions, laments show all forms of translational and rotational motions nearly without any interactions.In the semidilute solution, however, these movements are conned by other laments, which due to the densepacking cross and entangle each other.In concentrated solutions, laments start to show liquidcrystalline phases with increasing orientational order. The focus in this section will be on isotropic actin networks which fall into the semidilute regime.We will distinguish three fundamentally different situations: entangled networks formed in the absence of specic crosslinkers, rigidly crosslinked networks showing permanent connection points, and transiently crosslinked networks Yohimbine hydrochloride allowing crosslinkers to bind and unbind.A common tool to characterize biopolymer networks is to investigate their mechanical behavior by rheological measurements.To investigate semiexibility, homogenous actin structures are especially suitable since actin is considered a model for semiexible polymers and hence will be discussed in this section.In the absence of crosslinkers, single lament uctuations are restricted only by the surrounding laments forming a conning cage or tube. The tube model proposes that a polymers movement within a semidilute solution is conned by other laments.Experiments also proved that the tube displays substantial heterogeneities regarding the tube radius.This was taken into account by computer simulations. When lament density increases further, the solution undergoes a transition from the isotropic or entangled phase to a nematic phase.Single lament diffusion within nematic regions was shown to be qualitatively different from entangled network diffusion. Rodlike polymers show accelerated longitudinal diffusion in the nematic phase which can possibly be assigned to the tube dilation effect.

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