  By means of computer simulations of a coarse-grained DNA model we show that
the DNA hairpin zippering dynamics is anomalous, i.e. the characteristic time T
scales non-linearly with N, the hairpin length: T ~ N^a with a>1. This is in
sharp contrast with the prediction of the zipper model for which T ~ N. We show
that the anomalous dynamics originates from an increase in the friction during
zippering due to the tension built in the closing strands. From a simple
polymer model we get a = 1+ nu = 1.59 with nu the Flory exponent, a result
which is in agreement with the simulations. We discuss transition path times
data where such effects should be detected.
