Biophysics

Our group has significantly contributed to fields related to the study of fluctuations and fluctuation-induced phenomena, like thermodynamics of fluctuating systems or response of far from equilibrium systems. In the present, several research projects in our group aim at applying or generalizing these results to relevant biological problems.

In particular, the ear hair-bundles of bullfrog’s sacculus is one of the biological systems that we are interested in. The group of Frank Jülicher (MPI-PKS, Dresden, Germany) has found a method to distinguish wether the cells are dead or alive, or equivalently if there are active processes driving the movement (e.g. produced by molecular motors) [1]. The method however requires the analysis of both spontaneous and forced oscillations of the cells. We expect that using our technique to estimate the irreversibility of single stationary trajectories [2] we would be able to distinguish between passive and active hair bundles using only the information of the spontaneous oscillations.

The underlying active process in the hair-bundle manifests in a strong violation of the classical fluctuation-dissipation theorem. We have recently shown in collaboration with J.F. Joanny and P. Martin’s groups at Insitiut Curie, that the generalized Fluctuation-Dissipation theorem [3] can be restored for the hair-bundle if the adequate conjugate degree of freedom is used [4]. Our results support the validity of modelling the hair-bundle as a noisy oscillator with Markovian dynamics.

[1] P. Martin, A. J. Hudspeth, and F. Jülicher. Proc. Natl. Acad. Sci. U.S.A. 98, 14 380 (2001).

[2] É. Roldán and J. M. R. Parrondo. Estimating dissipation from single stationary trajectories. Phys. Rev. Lett. 105, 15 (2010).

[3] J. Prost, J.F. Joanny, and J.M.R. Parrondo, Generalized Fluctuation-Dissipation Theorem for Steady-State Systems. Physical Review Letters 103, 090601 (2009).

[4] L. Dinis, P. Martin, J. Barral, J. Prost, and J.F. Joanny. Physical Review Letters 109, 160602 (2012)