  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 finite 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.
