  A molecular motor is made of either a single macromolecule or a
macromolecular complex. Just like their macroscopic counterparts, molecular
motors "transduce" input energy into mechanical work. All the nano-motors
considered here operate under isothermal conditions far from equilibrium.
Moreover, one of the possible mechanisms of energy transduction, called
Brownian ratchet, does not even have any macroscopic counterpart. But,
molecular motor is not synonymous with Brownian ratchet; a large number of
molecular motors execute a noisy power stroke, rather than operating as
Brownian ratchet. We review not only the structural design and stochastic
kinetics of individual single motors, but also their coordination, cooperation
and competition as well as the assembly of multi-module motors in various
intracellular kinetic processes. Although all the motors considered here
execute mechanical movements, efficiency and power output are not necessarily
good measures of performance of some motors. Among the intracellular
nano-motors, we consider the porters, sliders and rowers, pistons and hooks,
exporters, importers, packers and movers as well as those that also synthesize,
manipulate and degrade "macromolecules of life". We review mostly the
quantitative models for the kinetics of these motors. We also describe several
of those motor-driven intracellular stochastic processes for which quantitative
models are yet to be developed. In part I, we discuss mainly the methodology
and the generic models of various important classes of molecular motors. In
part II, we review many specific examples emphasizing the unity of the basic
mechanisms as well as diversity of operations arising from the differences in
their detailed structure and kinetics. Multi-disciplinary research is presented
here from the perspective of physicists.
