ABSTRACT
Efficient bacterial chromosome segregation typically requires the coordinated action of a three-component machinery, fueled by adenosine triphosphate, called the partition complex. We present a phenomenological model accounting for the dynamic activity of this system that is also relevant for the physics of catalytic particles in active environments. The model is obtained by coupling simple linear reaction-diffusion equations with a proteophoresis, or "volumetric" chemophoresis, force field that arises from protein-protein interactions and provides a physically viable mechanism for complex translocation. This minimal description captures most known experimental observations: dynamic oscillations of complex components, complex separation, and subsequent symmetrical positioning. The predictions of our model are in phenomenological agreement with and provide substantial insight into recent experiments. From a nonlinear physics view point, this system explores the active separation of matter at micrometric scales with a dynamical instability between static positioning and traveling wave regimes triggered by the dynamical spontaneous breaking of rotational symmetry.
Subject(s)
Adenosine Triphosphate/metabolism , Genome, Bacterial , Biophysical Phenomena , Catalysis , Diffusion , Models, Biological , Protein Interaction Domains and MotifsABSTRACT
A statistical model of homopolymer DNA, coupling internal base-pair states (unbroken or broken) and external thermal chain fluctuations, is exactly solved using transfer kernel techniques. The dependence on temperature and DNA length of the fraction of denaturation bubbles and their correlation length is deduced. The thermal denaturation transition emerges naturally when the chain fluctuations are integrated out and is driven by the difference in bending (entropy dominated) free energy between broken and unbroken segments. Conformational properties of DNA, such as persistence length and mean-square-radius, are also explicitly calculated, leading, e.g., to a coherent explanation for the experimentally observed thermal viscosity transition.
Subject(s)
DNA , Entropy , Base Pairing , Nucleic Acid Denaturation , TemperatureABSTRACT
We carry out a detailed experimental and theoretical study of the influence of temperature on nanofiltration performance using the Desal5DK membrane. Experimental results for the permeate volume flux density and rejection of four neutral solutes (glycerin, arabinose, glucose, and sucrose) are presented for temperatures between 22 and 50 degrees C. Solute rejection is modeled using a hindered transport theory that allows us to unveil the crucial role played by changes in the membrane structural parameters (effective pore radius and membrane thickness) due to changes in temperature.
ABSTRACT
The effects of three structurally related dopamine (DA) agonists (pergolide, lergotrile, bromocriptine) on motor activity and induction of cage climbing behavior were compared in mice. Pergolide stimulated activity and induced cage climbing that persisted for at least 5 h. Lergotrile depressed activity and failed to induce climbing over a wide range of doses. Bromocriptine produced stimulation and climbing, but only after a 2-3 h delay following injection. The qualitative differences among these drugs may represent an action involving different DA receptor subjects.
