  We consider the motion of overdamped particles on random potentials subjected
to a Gaussian white noise and a time-dependent periodic external forcing. The
random potential is modeled as the potential resulting from the interaction of
a point particle with a random polymer. The random polymer is made up, by means
of some stochastic process, from a finite set of possible monomer types. The
process is assumed to reach a non-equilibrium stationary state, which means
that every realization of a random polymer can be considered as an
out-of-equilibrium structure. We show that the net flux of particles on this
random medium is non-vanishing when the potential profile on every monomer is
symmetric. We prove that this ratchet-like phenomenon is a consequence of the
irreversibility of the stochastic process generating the polymer. On the
contrary, when the process generating the polymer is at equilibrium (thus
fulfilling the detailed balance condition) the system is unable to rectify the
motion. We calculate the net flux of the particles in the adiabatic limit for a
simple model and we test our theoretical predictions by means of Langevin
dynamics simulations. We also show that, out of the adiabatic limit, the system
also exhibits current reversals as well as non-monotonic dependence of the
diffusion coefficient as a function of forcing amplitude.
