A simple model for DNA denaturation

Following Poland and Scheraga, we consider a simplified model for the denat uration transition of DNA. The two strands are modeled as interacting polym er chains. The attractive interactions, which mimic the pairing between the four bases, are reduced to a ingle short-range binding term. Furthermore, base-pair misalignments are forbidden, implying that this binding term exis ts only for corresponding (same curvilinear abscissae) monomers of the two chains. We take into account the excluded-volume repulsion between monomers of the two chains, but neglect intrachain repulsion. We nd that the exclud ed-volume term generates an effective repulsive interaction between the cha ins, which decays as 1/r(d-2). Due to this long-range repulsion between the chains, the denaturation transition is rst order in any dimension, in agre ement with previous studies.