Torque-winding interdependence for a flexible polymer chain wound around a cylinder in the presence of obstacles

Polymer chains winding around each other or around other objects occur in many natural systems; the physical consequences of this winding are therefore of significant interest. A polymer chain could be surrounded by various bulky objects (referred as obstacles), such as other macromolecules or macromolecular aggregates. Here we show that for a long flexible polymer chain wound around a cylinder, the presence of obstacles could modify the winding-torque interdependence, in some cases leading to phase-transition-like behavior in which the winding occurs only when the torque exceeds some critical value. Possible implications of this effect are discussed in relation to the biophysics of nucleic acids.