  In order to interpret recent experimental studies of the dependence of
conductance of ds-DNA as the DNA is pulled from the 3'end1-3'end2 ends, which
find a sharp conductance jump for a very short (4.5 %) stretching length, we
carried out multiscale modeling, to predict the conductance of dsDNA as it is
mechanically stretched to promote various structural polymorphisms. We
calculate the current along the stretched DNA using a combination of molecular
dynamics simulations, non-equilibrium pulling simulations, quantum mechanics
calculations, and kinetic Monte Carlo simulations. For 5'end1-5'end2
attachments we find an abrupt jump in the current within a very short
stretching length (6 $ \AA $ or 17 %) leading to a melted DNA state. In
contrast, for 3'end1-3'end2 pulling it takes almost 32$ \AA $ (84 %) of
stretching to cause a similar jump in the current. Thus, we demonstrate that
charge transport in DNA can occur over stretching lengths of several
nanometers. We find that this unexpected behaviour in the B to S conformational
DNA transition arises from highly inclined base pair geometries that result
from this pulling protocol. We find that the dramatically different conductance
behaviors for two different pulling protocols arise from the nature of how
hydrogen bonds of DNA base pairs break.
