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Entropy, molecular motors, and non-thermal equilibrium statistical physics
Date: Thursday, February 23rd
Time: 4:00 pm - 5:00 pm
Place: 2241 Chamberlin Hall
Speaker: Steven Chu, Stanford University
Abstract: The transport of molecular cargos in neuronal cells is analyzed in the context of new developments in statistical physics. We developed bright optical probes which enabled the long-term single tracking of molecular cargos in live neurons for tens of minutes. The number of dynein motors transporting a cargo in a neuron was found to switch stochastically from one to five motors. We were able to resolve individual molecular steps, and new a quantitative chemo-mechanical model where a single step requires the hydrolysis of two ATP molecules.

We also find that the movement approaches a steady-state non-thermal equilibrium with effective temperature, T_eff=〖6×T〗_cell=6×310 K. Also, the minimum “uncertainty principle” limit, ΔQ⋅ϵ^2≥2k_B T_eff, where ΔQ=T_eff ΔS is the heat entropy needed to achieve movement with a normalized precision 〖ϵ(x)〗^2≡((〈x^2 〉-〈x〉^2))⁄〈x〉^2 . This uncertainty limit sets the minimum heat energy needed to achieve a given precision in any physical operation. In the context of intercellular molecular transport, a more uniform motion of the cargo requires a greater expenditure of energy.

Host: Uwe Bergmann, Alessandro Senes
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