Routinely navigating through an ever-changing and unsteady environment, andutilizing chemical energy, molecular motors transport the cell's crucialcomponents, such as neurotransmitters and organelles. They generate force andpull cargo, as they literally walk along the polymeric tracts, e.g.microtubules. However, using experimental data one may derive that the energyneeded for this pulling would take the most part of the 22 kT that ATPhydrolysis makes available. In such a case there would not be sufficient energyleft to drive the conformational changes in the catalytic cycle of the protein.Furthermore, the medium inside living cell is viscoelastic. Pulling cargo insuch an environment takes more energy than in aqueous buffer solution. Here wepropose a mechanism for the motor to more efficiently utilize chemical energy.In our model the energy is used to ratchet the cargo forward. The motor nolonger pulls, but only holds a bead or a vesicle, allowing for Brownian motionin a range limited by the elasticity of the motor-cargo-track system. Theconsequence of such a mechanism is the dependency of motion not only on themotor, but also on the cargo (especially it's size) and on the environment(i.e. it's viscosity and structure). However, current experimental works rarelyprovide this type of information for in vivo studies. We suggest that evensmall differences between assays can impact the outcome. Our results agree withthose obtained in wet laboratories and provide novel insight in the mechanismof a molecular motor's functioning.
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