Biological motor molecules possess many of thecharacteristics required to power nanomachines. They cangenerate force and torque, transport specific cargoes overappropriate substrates, and the character and rate of their actioncan be controlled. In cilia and flagella, axonemal dynein motorsare attached to nine microtubule doublets arranged cylindricallyaround two microtubules. Each motor undergoes a cycle ofactivity, during which it forms a transient attachment to theneighbouring doublet, and pushes it towards the tip of the ciliumor flagellum. Dynein motors have been isolated, deposited on aglass slide, and reactivated by adenosine triphosphate. Underthese in vitro conditions, assemblies of these motors can propelmicrotubules across the slide with velocities that are found toincrease with microtubule length. Computer simulations havebeen developed to predict these velocities. Simulations allow usto investigate individual motor properties in addition tocharacterizing the coordination of activity within the assembly.Agreement between experiment and simulation results fromrandom or sequential activity within the motor assembly andmotility characteristics of an individual arm are thus predicted.The sliding which occurs when microtubules are extruded fromdisintegrating cilia and flagella has also been simulated to enablein vivo characteristics of dynein to be studied.
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