7,190 research outputs found
Polar features in the flagellar propulsion of E. coli bacteria
E. coli bacteria swim following a run and tumble pattern. In the run state
all flagella join in a single helical bundle that propels the cell body along
approximately straight paths. When one or more flagellar motors reverse
direction the bundle unwinds and the cell randomizes its orientation. This
basic picture represents an idealization of a much more complex dynamical
problem. Although it has been shown that bundle formation can occur at either
pole of the cell, it is still unclear whether this two run states correspond to
asymmetric propulsion features. Using holographic microscopy we record the 3D
motions of individual bacteria swimming in optical traps. We find that most
cells possess two run states characterised by different propulsion forces,
total torque and bundle conformations. We analyse the statistical properties of
bundle reversal and compare the hydrodynamic features of forward and backward
running states. Our method is naturally multi-particle and opens up the way
towards controlled hydrodynamic studies of interacting swimming cells
Quasi-saddles as relevant points of the potential energy surface in the dynamics of supercooled liquids
The supercooled dynamics of a Lennard-Jones model liquid is numerically
investigated studying relevant points of the potential energy surface, i.e. the
minima of the square gradient of total potential energy . The main findings
are: ({\it i}) the number of negative curvatures of these sampled points
appears to extrapolate to zero at the mode coupling critical temperature ;
({\it ii}) the temperature behavior of has a close relationship with the
temperature behavior of the diffusivity; ({\it iii}) the potential energy
landscape shows an high regularity in the distances among the relevant points
and in their energy location. Finally we discuss a model of the landscape,
previously introduced by Madan and Keyes [J. Chem. Phys. {\bf 98}, 3342
(1993)], able to reproduce the previous findings.Comment: To be published in J. Chem. Phy
Strategies against nonsense: oxadiazoles as translational readthrough-inducing drugs (TRIDs)
This review focuses on the use of oxadiazoles as translational readthrough-inducing drugs (TRIDs) to rescue the functional full-length protein expression in mendelian genetic diseases caused by nonsense mutations. These mutations in specific genes generate premature termination codons (PTCs) responsible for the translation of truncated proteins. After a brief introduction on nonsense mutations and their pathological effects, the features of various classes of TRIDs will be described discussing differences or similarities in their mechanisms of action. Strategies to correct the PTCs will be presented, particularly focusing on a new class of Ataluren-like oxadiazole derivatives in comparison to aminoglycosides. Additionally, recent results on the efficiency of new candidate TRIDs in restoring the production of the cystic fibrosis transmembrane regulator (CFTR) protein will be presented. Finally, a prospectus on complementary strategies to enhance the effect of TRIDs will be illustrated together with a conclusive paragraph about perspectives, opportunities, and caveats in developing small molecules as TRIDs
Hard sphere-like dynamics in a non hard sphere liquid
The collective dynamics of liquid Gallium close to the melting point has been
studied using Inelastic X-ray Scattering to probe lengthscales smaller than the
size of the first coordination shell. %(momentum transfers, , 15
nm). Although the structural properties of this partially covalent
liquid strongly deviate from a simple hard-sphere model, the dynamics, as
reflected in the quasi-elastic scattering, are beautifully described within the
framework of the extended heat mode approximation of Enskog's kinetic theory,
analytically derived for a hard spheres system. The present work demonstrates
the applicability of Enskog's theory to non hard- sphere and non simple
liquids.Comment: 5 pages, 2 figures, accepted in Phys. Rev. Let
P14ARF: The absence that makes the difference
P14ARF is a tumor suppressor encoded by the CDKN2a locus that is frequently inactivated in human tumors. P14ARF protein quenches oncogene stimuli by inhibiting cell cycle progression and inducing apoptosis. P14ARF functions can be played through interactions with several proteins. However, the majority of its activities are notoriously mediated by the p53 protein. Interestingly, recent studies suggest a new role of p14ARF in the maintenance of chromosome stability. Here, we deepened this new facet of p14ARF which we believe is relevant to its tumor suppressive role in the cell. To this aim, we generated a monoclonal HCT116 cell line expressing the p14ARF cDNA cloned in the piggyback vector and then induced aneuploidy by treating HCT116 cells with the CENP‐E inhibitor GSK923295. P14ARF ectopic re‐expression restored the near‐diploid phenotype of HCT116 cells, confirming that p14ARF counteracts aneuploid cell generation/proliferation
Vanishing conductivity of quantum solitons in polyacetylene
Quantum solitons or polarons are supposed to play a crucial role in the
electric conductivity of polyacetylene, in the intermediate doping regime. We
present an exact fully quantized calculation of the quantum soliton
conductivity in polyacetylene and show that it vanishes exactly. This is
obtained by applying a general method of soliton quantization, based on
order-disorder duality, to a Z(2)-symmetric complex extension of the TLM
dimerization effective field theory. We show that, in this theory,
polyacetylene solitons are sine-Gordon solitons in the phase of the complex
field.Comment: To appear in J. Phys. A: Math. Theor., 15 page
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