A dual approach for studying the dynamics and function of DNA is proposed. Soliton-like excitations may occur under certain conditions and, via an electromagnetic signal that can modulate the soliton energy, the transition B-DNA (resting state) ? A-DNA (active state) can take place. On the other hand, the Hamiltonian describing this transition can be used to construct an entropy operator for DNA and thus assess its state of relative disorder and its relationship to DNA function. Biological and medical applications of this study are put forward, as well as predictions for experimentally testing the model.