  We propose that supercoiling energizes double-stranded DNA (dsDNA) so as to
facilitate thermal fluctuations to an unzipped state. We support this with a
model of two elastic rods coupled via forces that represent base pair
interactions. Supercoiling is shown to lead to a spatially localized higher
energy state in a small region of dsDNA consisting of a few base pairs. This
causes the distance between specific base pairs to be extended, enhancing the
thermal probability for their disruption. Our theory permits the development of
an analogy between this unzipping transition and a second order phase
transition, for which the possibility of a new set of critical exponents is
identified.
