10,166 research outputs found
Stochastic thermodynamics for active matter
The theoretical understanding of active matter, which is driven out of
equilibrium by directed motion, is still fragmental and model oriented.
Stochastic thermodynamics, on the other hand, is a comprehensive theoretical
framework for driven systems that allows to define fluctuating work and heat.
We apply these definitions to active matter, assuming that dissipation can be
modelled by effective non-conservative forces. We show that, through the work,
conjugate extensive and intensive observables can be defined even in
non-equilibrium steady states lacking a free energy. As an illustration, we
derive the expressions for the pressure and interfacial tension of active
Brownian particles. The latter becomes negative despite the observed stable
phase separation. We discuss this apparent contradiction, highlighting the role
of fluctuations, and we offer a tentative explanation
Cdc6 ATPase activity disengages Cdc6 from the pre-replicative complex to promote DNA replication
© 2015, Chang et al.To initiate DNA replication, cells first load an MCM helicase double hexamer at origins in a reaction requiring ORC, Cdc6, and Cdt1, also called pre-replicative complex (pre-RC) assembly. The essential mechanistic role of Cdc6 ATP hydrolysis in this reaction is still incompletely understood. Here, we show that although Cdc6 ATP hydrolysis is essential to initiate DNA replication, it is not essential for MCM loading. Using purified proteins, an ATPase-defective Cdc6 mutant ‘Cdc6-E224Q’ promoted MCM loading on DNA. Cdc6-E224Q also promoted MCM binding at origins in vivo but cells remained blocked in G1-phase. If after loading MCM, Cdc6-E224Q was degraded, cells entered an apparently normal S-phase and replicated DNA, a phenotype seen with two additional Cdc6 ATPase-defective mutants. Cdc6 ATP hydrolysis is therefore required for Cdc6 disengagement from the pre-RC after helicase loading to advance subsequent steps in helicase activation in vivo
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