  Molecular motor proteins such as Myosin V, Dynein or Kinesin are no ratchets,
at least not with a flashing asymmetric potential; the crucial asymmetry is in
the dynamical activity. We make that explicit in terms of a simple Markov
model, emphasizing the kinetic (and non-thermodynamic) aspects of stochastic
transport. The analysis shows the presence of a fluctuation symmetry in that
part of the dynamical activity which is antisymmetric under reversal of
trailing and leading head of the motor. The direction of the motor motion is
determined by it.
