Brownian ratchet models of molecular motors

Brownian ratchet theory refers to the phenomenon that nonequilibrium fluctuations in an isothermal medium and anisotropic system can induce mechanical force and motion. This concept of noise-induced transport has motivated an abundance of theoretical and applied research. One of the exciting applications of the ratchet theory lies in the possible explanation of the operating mode of biological molecular motors. Biomolecular motors are proteins able of converting chemical energy into mechanical motion and force. Because of their dimension, the many small parts that make up molecular motors must operate at energies only a few times greater than those of the thermal baths. The description of molecular motors must be stochastic in nature. Here, we review the theoretical concepts of the Brownian ratchet theory and its possible link to the operation of biomolecular motors. We illustrate the principle of the ratchet theory with models of two molecular motors: a rotary motor (F0F1ATP synthase) and a linear motor (myosin II).