STEVEN CHU
William R. Kenan Jr. Professor, Professor of Molecular and Cellular Physiology and of Energy Science and Engineering
Stanford University
1997 Nobel Prize in Physics
Monday, April 24, 2023, @4:30pm
Jefferson Lab 250
Colloquium: "Entropy, molecular motors, and non-thermal equilibrium statistical physics"
The transport of molecular cargos in neuronal cells is analyzed in the context of new developments in entropy and statistical physics. Our development of very bright optical probes enabled the long-term single tracking of molecular cargos in live neurons. The number of active dynein motors transporting a cargo is found to switch stochastically from one to five dynein motors during the long-range transport in neurons. Our probes allowed the observation of individual molecular steps where the time between single steps is controlled by two temperature-dependent rate constants. This finding suggests that two ATP molecules are hydrolyzed sequentially during each dynein step.
The measured fluctuations can be described by a steady-state non-thermal equilibrium temperature, Teff as high as 30 × Tcell = 30 × 310 K, and inversely proportional to the number of motors. Using the Fluctuation Theorem (proven in 1993) is consistent an "uncertainty principle" limit, ΔQ ⋅ ϵ2 ≥ 2kB Teff, where ΔQ = Teff ΔS is the minimum heat entropy needed to achieve an outcome with a given statistical precision. This theorem sets a lower limit to the heat energy needed to achieve a given precision in any physical operation. In the context of intercellular molecular transport, a smaller variance in the displacement of the vesicle demands a greater expenditure of energy.
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Tuesday, April 25, 2023, @5:00pm
Jefferson Lab 250
2023 Lee Historical Lecture in Physics:
"A random walk into laser cooling, optical trapping and beyond"
A personal perspective of how laser cooling and optical trapping of atoms and biomolecules was developed. Emphasis will be given on how an elementary understanding of the physics at an undergraduate physics level led to success in initial successes. Once the basic tools of optical molasses and optical trapping were developed, more random walks into polymer physics and biology will be described.
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Steven Chu is Professor of Physics, Molecular and Cellular Physiology, and Energy Science and Engineering at Stanford University.
He received the 1997 Nobel Prize in Physics for laser cooling and trapping of atoms. Other contributions include the first optical tweezers manipulation of biomolecules, precision atom interferometry based on optical pulses of light, and single molecule FRET of biomolecules tethered to surfaces.
He is now developing and applying new methods in molecular biology and medical imaging, materials science, and batteries.
Previously he was U.S. Secretary of Energy, where he began ARPA-E, the Energy Innovation Hubs, and was tasked by President Obama to help BP stop the Macondo Oil spill. Previously, he was director of Lawrence Berkeley National Laboratory and Professor of Physics and Applied Physics at Stanford, and help initiate Bio-X, that linked the physical and biological sciences with engineering and medicine. Before Stanford, he was a department head at Bell Laboratories. He was past president of the American Association for the Advancement of Science, a Senior Advisor to the Directors of the NIH and the NNSA. He received an A.B. degree in mathematics and a B.S. degree in physics from the University of Rochester, a Ph.D. in physics from the University of California, Berkeley, has 35 honorary degrees, and is a member of the U.S. National Academy of Sciences and 8 foreign academies.
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David M. Lee Historical Lectures in Physics are sponsored by the Marvin and Annette Lee Fund
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