  We present a phenomenological dynamical model able to describe the stretching
features of the curve of DNA length vs applied force. As concerns the chain,
the model is based on the discrete wormlike chain model with elastic
modifications, which properly describes the elongation features at low and
intermediate forces. The dynamics is developed under a double-well potential
with a linear term, which, at high forces, accounts for the narrow transition
present in the DNA elongation (overstretching). A quite good agreement between
simulation and experiment is obtained.
