Dynamical Study On Molecular Motor's Motion Mechanism

In the organism cells, hundreds of molecular motors carry out various functions in the process of contraction of muscles, cellular transportation, DNA duplication, mitosis and so on. These motors are a kind of enzyme proteins that can efficiently convert chemical energy into mechanical energy directly. When the motion of the motor is coordinated, the macroscopic directed motion is brought. Especially, kinesin, which has the feature of the directivity and stepping motion, has been focused on its particular dynamical mechanism. Firstly the biology research progress of molecular motor is introduced in the paper, including their categories, biochemical research on kinesin and ATPase, and motor's biophysical research.The kinesin's directed motion is analyzed theoretically in the paper, three necessary conditions of directed motion are proposed, and how kinesin satisfies these conditions is discussed in detail. Two new viewpoints are proposed that may provide a possible explanation for kinesin's directed movement.As molecular motor lies in liquid environment, it can be regarded as Brownian ratchet in physics, and its motion can be analyzed and calculated by Langevin equation or Fokker-Planck equation in nonequilibriumstatistical physics. Through computer simulation and Monte Carlo method, Langevin equations are calculated for molecular motor systems in different environment, and their directed movement abilities are compared. And conclusions are as follow: under white noise without external force, the noise can't drive motor's directed movement;with constant or sinusoidal external force, molecular motor can move directionally under white noise, but with sinusoidal force the directed motion ability is much less than that with constant force;colored noise can drive directed motion in asymmetric periodic potential without force, but can't in symmetric periodic potential.The dwell time during motor's directed motion is also studied in this paper. According to the result of directed motion abilities in different systems, the diffusion model including colored noise and constant force is proposed. Through Monte Carlo simulation, the relationships between dwell time and the parameters such as colored noise correlation time, noise intensity and external force are calculated and analyzed. Compared dwell time with corresponding jump time, the reasons of producing these results are respectively analyzed and explained.In the paper, considered more of kinesin's two-headed structure, two-headed coupling interaction potential is introduced for proposing the two-headed coupling model under colored noise and constant external force. Through second order Runge-Kutta algorithm and Monte Carlo simulation, influences of the potential's coupling strength and depth parameter both on motor's two-headed motion and directed motion are calculated. The results indicate: (1) coupling strength can determine the ability to trap molecular motor in the potential wells, the larger coupling strength, the stronger trap ability, so the weaker motor's directed motion ability;(2) depth parameter determines not only the ability to trap motor, but also the ability to restricttwo-headed motion. The larger depth parameter, the stronger trap ability, but the weaker restriction ability. So these are two opposite effects, and they determine motor's directed motion ability.