  We consider force-induced unzipping transition for a heterogeneous DNA model
with a correlated base-sequence. Both finite-range and long-range correlated
situations are considered. It is shown that finite-range correlations increase
stability of DNA with respect to the external unzipping force. Due to
long-range correlations the number of unzipped base-pairs displays two widely
different scenarios depending on the details of the base-sequence: either there
is no unzipping phase-transition at all, or the transition is realized via a
sequence of jumps with magnitude comparable to the size of the system. Both
scenarios are different from the behavior of the average number of unzipped
base-pairs (non-self-averaging). The results can be relevant for explaining the
biological purpose of correlated structures in DNA.
