  In this paper we investigate the use of path-integral formalism and the
concepts of entropy and traffic in the context of molecular motors. We show
that together with time-reversal symmetry breaking arguments one can find
bounds on efficiencies of such motors. To clarify this techinque we use it on
one specific model to find both the thermodynamic and the Stokes efficiencies,
although the arguments themselves are more general and can be used on a wide
class of models. We also show that by considering the molecular motor as a
ratchet, one can find additional bounds on the thermodynamic efficiency.
