  We study the nonlinear dynamics of a deformed Deoxyribonucleic acid (DNA)
molecular chain which is governed by a perturbed sine-Gordon equation coupled
with a linear wave equation representing the lattice deformation. The DNA chain
considered here is assumed to be deformed periodically which is the
energetically favourable configuration, and the periodic deformation is due to
the repulsive force between base pairs, stress in the helical backbones and due
to the elastic strain force in both the strands. A multiple scale soliton
perturbation analysis is carried out to solve the perturbed sine-Gordon
equation and the resultant perturbed kink and antikink solitons represent open
state configuration with small fluctuation. The perturbation due to periodic
deformation of the lattice changes the velocity of the soliton. However, the
width of the soliton remains unchanged.
