Molecular motors are protein enzymes that can use the free energy of the non-equilibrium chemical reaction (such as ATP hydrolysis) they catalyze to move a cargo (load) along a periodic molecular track. The main biochemical pathway that a motor goes through for each ATP hydrolyzed when interacting with the track is called the “mechanochemical” cycle of the motor. This cycle defines how ATP hydrolysis is coupled to the translocation of the motor on the track at a non-equilibrium steady state and is important in understanding how a motor works at the molecular level. In the absence of a load, the mechanochemical cycle of a motor can be elucidated using conventional enzyme biochemistry methods. In contrast, if the motor is carrying a cargo this cycle can only be obtained by theoretical modeling using measured motility data (such as the force-velocity curve, etc). In this talk, I’ll show, with some simple examples, how to model the motility of an ensemble of non-processive myosin motors in muscles and the motility of single processive kinesin motors carrying a microscopic cargo. I’ll emphasize the general kinetic and thermodynamic principles the model has to obey in both cases. Formalism for a chemically driven Brownian-Ratchet model will also be presented to show explicitly how the chemical free energy and the charge fluctuations are coupled to the movement of the Brownian particle in an asymmetric ratchet.
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