Asymmetry of the propagation of conformational excitations in a double-strand DNA molecule

A very simple model describing the conformational degrees of freedom of a d ouble-strand DNA molecule is proposed. It is shown that the characteristic modes of the model consist of an acoustic (longitudinal with respect to the axis of the double helix) and two transverse optical modes. The latter mod es are directly related with the deformations of the ideal structure of the double helix, which necessarily leads to softening of one of the optical m odes on a finite wave vector. It is found that the conformational excitatio ns propagating in DNA are asymmetric. (C) 1999 American Institute of Physic s. [S0021-3640(99)01223-2].