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BP: Fachverband Biologische Physik

BP 11: Transport Processes

BP 11.2: Vortrag

Dienstag, 26. Februar 2008, 15:30–15:45, C 243

How Nature beats the central limit theorem: non-Brownian search from gene control to animal foraging — •Ralf Metzler and Michael Lomholt — Technical University of Munich, Physics Department T30g, James Franck Strasse, D-85747 Garching

Simple chemical reactands search for each other by three-dimensional diffusion until encounter. At low concentrations of reactands, pure 3D search is quite inefficient. Nature has come up with various active and passive solutions to speed up search. I will discuss two examples.

Facilitated diffusion of regulatory proteins in search for their specific binding site on a DNA combines 3D volume diffusion with 1D motion along the DNA. The combination of these two mechanisms significantly speeds up the search. In addition, intersegmental transfers that occur at contact points of chemically remote segments of the DNA due to looping gives rise to Levy flights along the DNA that further optimise the search. While this model holds for diluted solutions, in the cell molecular crowding occurs, leading to the subdiffusion of larger molecules. Consequences of this effect include a weak ergodicity breaking, that could allow low regulatory protein concentrations (Phys Rev Lett 95, 260603 (2005); Phys Rev Lett 98, 200603 (2007)).

Bacteria or higher animals perform an active search for food. It turns out that long-tailed distributions, that help avoiding the spell of the central limit theorem, lead to significantly higher search efficiency and significantly reduced sensitivity to a changing environment (E-print arXiv:0709.2352; compare also Phys Rev Lett 99, 160602 (2007)).