Dr. Won Kyu Kim, Department of Physics, Pohang University of Science and Technology (POSTECH), Republic of Korea
Fluctuations due to thermal and athermal noises are essential to promote conformational transitions in biopolymers and thus a plethora of active processes can be produced in the cellular environment. To understand the effect of noises on biological processes, we studied how a small oscillatory force affects the thermally induced folding and unfolding transition of an RNA hairpin. Strikingly, our molecular simulationsperformed under overdamped condition show that even at a high (low) tension that renders the hairpin(un)folding improbable, a weak external oscillatory force at a certain frequency can synchronously enhancethe transition dynamics of RNA hairpin and increase the mean transition rate. Furthermore, the RNA dynamics can still discriminate a signal with resonance frequency even when the signal is mixed among other signals with non-resonant frequencies. Our findings, in fact, are direct realizations of the phenomena called stochastic resonance(SR) and resonant activation(RA). Also, we analytically studied viscoelastic responses and associated SR in a stretched single semi-flexible chain to a minute oscillatory force or electric field. Including hydrodynamic interactions between chain segments, we found power amplification factor of the response at a noise-strength (temperature) can attain the maximum that grows as the chain length increases, indicative of an entropic stochastic resonance (ESR). In particular for a charged chain under an electric field, we found ESR at an optimal chain length, a new feature of SR. The hydrodynamic interaction is found to enhance the ESR, representing unique polymer cooperativity to which the fluid background imparts despite its overdamping nature. These novel resonance phenomena suggest how a biopolymer self-organizes in a viscous environment, utilizing its flexibility and thermal fluctuations.
Nov 01, 2012 | 04:00 PM
Seminar Room T 2 (1.4.03)