  We show that a mesoscale model, with a minimal number of parameters, can well
describe the thermomechanical and mechanochemical behavior of homogeneous DNA
at thermal equilibrium under tension and torque. We predict critical
temperatures for denaturation under torque and stretch, phase diagrams for
stable DNA, probe/response profiles under mechanical loads, and the density of
dsDNA as a function of stretch and twist. We compare our predictions with
available single molecule manipulation experiments and find strong agreement.
In particular we elucidate the difference between angularly constrained and
unconstrained overstretching. We propose that the smoothness of the angularly
constrained overstreching transition is a consequence of the molecule being in
the vicinity of criticality for a broad range of values of applied tension.
