Multiscale modelling of DNA elasticity

The mechanical behaviour of double-stranded DNA at the mesoscopic scale is one of the best studied phenomena in biophysics. Several experimental and theoretical investigations have established that when a stretching force and/or torque is applied to a single molecule of DNA in solution, a competition between entropy and elasticity determines its typical size. From this information, it is possible to determine the values of the bending (lp~50nm) and twisting (lτ~120nm) persistence lengths usually reported in the literature. However, there is an aspect that remains elusive. Recent experiments have reported on the unexpected high flexibility of short DNA fragments, whose origin is difficult to reconcile using existing theories. In this talk, I will address this problem by combining analytical theory and all-atom simulations, that help us to elucidate the missing link between models of DNA elasticity at different length scales. Additionally, I will talk about our (ongoing) experimental and computational effort to characterise the elastic behaviour of equilibrium gels made of tri-functional DNAnanostars. I will show results from large scale molecular dynamics simulations, that compare favourable with microrheology experiments of hydrogels at different concentrations. By computing the mesh size and typical path length, we attempt to connect the gels elasticity to their network topology.