Model of elastic responses of single DNA molecules in collapsing transition.

We present a simple phenomenological model to describe elastic responses of a collapsed single DNA molecule. The model is represented by the elastic theory for the wormlike chain combined with the order-parameter equation, which accounts for the intramolecular transition kinetics. Our continuum and discrete model reproduces the force plateaus and the stick-release patterns in the force-extension curves, respectively. Both of the elastic responses have been observed experimentally by changing the concentration of the condensing agents.