Molecular motors are the proteins that translate the free energy/electrochemical gradient into mechanical work. They are generally divided into two classes: one is linear motor, including myosin, kinesin, dynesin, RNA polymerase and DNA helicase, the other is rotary motor, such as F₁-ATPase and the bacterial flagellar motor. The molecular motors play an important role in the cell transport,DNA replication, transcription, and ATP synthesis.