Localization phenomena in a DNA double-helix structure: a twisted ladder model

In this work we propose a model for the DNA double helix within the tight-binding framework that incorporates the helicity of the molecules. We have studied the localization properties of three DNA sequences, the periodic poly(dG)-poly(dC) and poly(dA)-poly(dT) sequences and the random ATGC sequence (where A is adenine, T is thymine, G is guanine, and C is cytosine), all of which are coupled to the backbone with random site energies representing the environmental fluctuations. We observe that due to the helicity of DNA, electron transport is greatly enhanced and there exists an almost disorder-strength-independent critical value of the hopping integral, which accounts for the helicity of DNA, for which the electronic states become maximally extended. We have also investigated the effect of backbone energetics on the transmission and I-V characteristics of DNA.