3,124 research outputs found
Cooperative protein transport in cellular organelles
Compartmentalization into biochemically distinct organelles constantly
exchanging material is one of the hallmarks of eukaryotic cells. In the most
naive picture of inter-organelle transport driven by concentration gradients,
concentration differences between organelles should relax. We determine the
conditions under which cooperative transport, i.e. based on molecular
recognition, allows for the existence and maintenance of distinct organelle
identities. Cooperative transport is also shown to control the flux of material
transiting through a compartmentalized system, dramatically increasing the
transit time under high incoming flux. By including chemical processing of the
transported species, we show that this property provides a strong functional
advantage to a system responsible for protein maturation and sorting.Comment: 9 pages, 5 figure
Living on the edge of chaos: minimally nonlinear models of genetic regulatory dynamics
Linearized catalytic reaction equations modeling e.g. the dynamics of genetic
regulatory networks under the constraint that expression levels, i.e. molecular
concentrations of nucleic material are positive, exhibit nontrivial dynamical
properties, which depend on the average connectivity of the reaction network.
In these systems the inflation of the edge of chaos and multi-stability have
been demonstrated to exist. The positivity constraint introduces a nonlinearity
which makes chaotic dynamics possible. Despite the simplicity of such minimally
nonlinear systems, their basic properties allow to understand fundamental
dynamical properties of complex biological reaction networks. We analyze the
Lyapunov spectrum, determine the probability to find stationary oscillating
solutions, demonstrate the effect of the nonlinearity on the effective in- and
out-degree of the active interaction network and study how the frequency
distributions of oscillatory modes of such system depend on the average
connectivity.Comment: 11 pages, 5 figure
Non-equilibrium dynamics of gene expression and the Jarzynski equality
In order to express specific genes at the right time, the transcription of
genes is regulated by the presence and absence of transcription factor
molecules. With transcription factor concentrations undergoing constant
changes, gene transcription takes place out of equilibrium. In this paper we
discuss a simple mapping between dynamic models of gene expression and
stochastic systems driven out of equilibrium. Using this mapping, results of
nonequilibrium statistical mechanics such as the Jarzynski equality and the
fluctuation theorem are demonstrated for gene expression dynamics. Applications
of this approach include the determination of regulatory interactions between
genes from experimental gene expression data
Methods applied to investigage the major UVCE that occured in the TOTAL refiner's Fluid Catalytic Cracking Unit at La Mède, France
International audienceOn monday November 9, 1992 at 5:20 a.m. a major U. V.C.E, occured in the Gas Plant of the TOTAL refinery's Fluid Catalytic Cracking unit at La Mede, France. The origin was a 25 cm2 break in the 8" by-pass of the absorber stripper column cooler; an amount of about 15 tons of LPG and light naphtha was released within 10 minutes, covering an area of 14000m2 including Gas Plant, cryogenic, propene and Merox units before being ignited on the FCC main furnace
Quasiparticle Chirality in Epitaxial Graphene Probed at the Nanometer Scale
Graphene exhibits unconventional two-dimensional electronic properties
resulting from the symmetry of its quasiparticles, which leads to the concepts
of pseudospin and electronic chirality. Here we report that scanning tunneling
microscopy can be used to probe these unique symmetry properties at the
nanometer scale. They are reflected in the quantum interference pattern
resulting from elastic scattering off impurities, and they can be directly read
from its fast Fourier transform. Our data, complemented by theoretical
calculations, demonstrate that the pseudospin and the electronic chirality in
epitaxial graphene on SiC(0001) correspond to the ones predicted for ideal
graphene.Comment: 4 pages, 3 figures, minor change
Mass spectrometry captures off-target drug binding and provides mechanistic insights into the human metalloprotease ZMPSTE24.
Off-target binding of hydrophobic drugs can lead to unwanted side effects, either through specific or non-specific binding to unintended membrane protein targets. However, distinguishing the binding of drugs to membrane proteins from that of detergents, lipids and cofactors is challenging. Here, we use high-resolution mass spectrometry to study the effects of HIV protease inhibitors on the human zinc metalloprotease ZMPSTE24. This intramembrane protease plays a major role in converting prelamin A to mature lamin A. We monitored the proteolysis of farnesylated prelamin A peptide by ZMPSTE24 and unexpectedly found retention of the C-terminal peptide product with the enzyme. We also resolved binding of zinc, lipids and HIV protease inhibitors and showed that drug binding blocked prelamin A peptide cleavage and conferred stability to ZMPSTE24. Our results not only have relevance for the progeria-like side effects of certain HIV protease inhibitor drugs, but also highlight new approaches for documenting off-target drug binding
Enzyme kinetics for a two-step enzymic reaction with comparable initial enzyme-substrate ratios
We extend the validity of the quasi-steady state assumption for a model double intermediate enzyme-substrate reaction to include the case where the ratio of initial enzyme to substrate concentration is not necessarily small. Simple analytical solutions are obtained when the reaction rates and the initial substrate concentration satisfy a certain condition. These analytical solutions compare favourably with numerical solutions of the full system of differential equations describing the reaction. Experimental methods are suggested which might permit the application of the quasi-steady state assumption to reactions where it may not have been obviously applicable before
Electrostatic control of quantum dot entanglement induced by coupling to external reservoirs
We propose a quantum transport experiment to prepare and measure
charge-entanglement between two electrostatically defined quantum dots.
Coherent population trapping, as realized in cavity quantum electrodynamics,
can be carried out by using a third quantum dot to play the role of the optical
cavity. In our proposal, a pumping which is quantum mechanically
indistinguishable for the quantum dots drives the system into a state with a
high degree of entanglement. The whole effect can be switched on and off by
means of a gate potential allowing both state preparation and entanglement
detection by simply measuring the total current.Comment: 5 pages, 4 figures, Latex2e with EPL macros, to appear in Europhysics
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