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Résumé |
Molecule concentrations are the building blocks of information
transmission in living organisms. Thanks to their molecule receptors,
cells are able to sense concentration gradients with high accuracy.
For example, small motile bacteria such as E. coli detect spatial
gradients indirectly by measuring concentration ramps (temporal
concentration changes) as they swim, and can respond to concentrations
as low as 3.2 nM - about three molecules per cell volume. The noise
arising from the small number of detected molecules sets a fundamental
physical limit on the accuracy of concentration sensing, as originally
shown in the seminal work of Berg and Purcell, but up to now no theory
existed for the physical limit of ramp sensing, which is what bacteria
actually do. I will show how such a bound can be derived for different
measurement devices, from a single receptor to an entire cell. I will
then present a plausible implementation of that bound by a realistic
(bio)chemical network, similar to the adaptation system of E. coli.
Finally I will show how energy consumption at the level of the
receptors can be used to increase the accuracy by a twofold factor
over a passive scheme where no energy is consumed.
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