We study the static and dynamical properties of DNA in the vicinity of its melting transition, i.e. the separation of the two strands upon heating. The investigation is based on a simple mechanical model which includes the helicoidal geometry of the molecule and allows an exact numerical evaluation of its thermodynamical properties. Dynamical simulations of long-enough molecular segments allow the study of the structure factors and of the properties of the denaturated regions. Simulations of

more »

... ite chains display the hallmarks of a first order transition for sufficiently long-ranged stacking forces although a study of the model's "universality class" strongly suggests the presence of an "underlying" continuous transition.