140 research outputs found
The free energy cost of reducing noise while maintaining a high sensitivity
Living systems need to be highly responsive, and also to keep fluctuations
low. These goals are incompatible in equilibrium systems due to the Fluctuation
Dissipation Theorem (FDT). Here, we show that biological sensory systems,
driven far from equilibrium by free energy consumption, can reduce their
intrinsic fluctuations while maintaining high responsiveness. By developing a
continuum theory of the E. coli chemotaxis pathway, we demonstrate that
adaptation can be understood as a non-equilibrium phase transition controlled
by free energy dissipation, and it is characterized by a breaking of the FDT.
We show that the maximum response at short time is enhanced by free energy
dissipation. At the same time, the low frequency fluctuations and the
adaptation error decrease with the free energy dissipation algebraically and
exponentially, respectively
Error-speed correlations in biopolymer synthesis
Synthesis of biopolymers such as DNA, RNA, and proteins are biophysical
processes aided by enzymes. Performance of these enzymes is usually
characterized in terms of their average error rate and speed. However, because
of thermal fluctuations in these single-molecule processes, both error and
speed are inherently stochastic quantities. In this paper, we study
fluctuations of error and speed in biopolymer synthesis and show that they are
in general correlated. This means that, under equal conditions, polymers that
are synthesized faster due to a fluctuation tend to have either better or worse
errors than the average. The error-correction mechanism implemented by the
enzyme determines which of the two cases holds. For example, discrimination in
the forward reaction rates tends to grant smaller errors to polymers with
faster synthesis. The opposite occurs for discrimination in monomer rejection
rates. Our results provide an experimentally feasible way to identify
error-correction mechanisms by measuring the error-speed correlations.Comment: PDF file consist of the main text (pages 1 to 5) and the
supplementary material (pages 6 to 12). Overall, 7 figures split between main
text and S
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