10 research outputs found
Thermal Fluctuations of Elastic Filaments with Spontaneous Curvature and Torsion
We study the effects of thermal flucutations on thin elastic filaments with
spontaneous curvature and torsion. We derive analytical expressions for the
orientational correlation functions and for the persistence length of helices,
and find that this length varies non-monotonically with the strength of thermal
fluctuations. In the weak fluctuation regime, the persistence length of a
spontaneously twisted helix has three resonance peaks as a function of the
twist rate. In the limit of strong fluctuations, all memory of the helical
shape is lost.Comment: 1 figur
Fluctuating Filaments I: Statistical Mechanics of Helices
We examine the effects of thermal fluctuations on thin elastic filaments with
non-circular cross-section and arbitrary spontaneous curvature and torsion.
Analytical expressions for orientational correlation functions and for the
persistence length of helices are derived, and it is found that this length
varies non-monotonically with the strength of thermal fluctuations. In the weak
fluctuation regime, the local helical structure is preserved and the
statistical properties are dominated by long wavelength bending and torsion
modes. As the amplitude of fluctuations is increased, the helix ``melts'' and
all memory of intrinsic helical structure is lost. Spontaneous twist of the
cross--section leads to resonant dependence of the persistence length on the
twist rate.Comment: 5 figure
Twisting DNA with variable intrinsic curvature
We study the effect of applying a twist to an elastic rod with
intrinsic curvature distributed on segments spaced by elastic loops
without intrinsic curvature. This model describes the elastic
properties of DNA molecules with non-uniform roll-tilt distribution. A
novel numerical technique is introduced to compute the equilibrium
shape at fixed angle of torsion for a wide range of torque regimes.
It is shown that the strain associated with torsion is preferably
distributed on the segments with intrinsic curvature. An analytical
solution is obtained for small torques. We discuss our results in the
context of single-molecule experiments
Peeling model for cell detachment
In many experimental situations, the adhesion of cells to solid
substrates is due to non-covalent chemical bonds. It is the
thesis of this paper that many phenomena occurring in cell
detachment experiments, such as in I (E. Decavé, G. Garriver, Y. Brechet,
B. Fourcade, F. Bruckert, Biophys. J. 82, 2383 (2002)),
result from the static and dynamic
properties of the adhesive bridges at the extreme margin of the
cell. This region defines the adhesive belt where the
distribution of connected bonds crosses over to zero where the
membrane leaves the substrate. The theoretical model we introduce
in this paper discusses the threshold force together with the
peeling velocity in the same theoretical framework. In this
one-dimensional model, the threshold force results from a
non-homogeneous distribution of anchor proteins along the membrane
so that the adhesive belt increases its capacity to resist motion
with increasing the external force. Analyzing the kinetics of the
the contact line motion, we derive the characteristic
relationship speed versus external force and we describe the
non-equilibrium state of the adhesive belt as a function of the
speed. We discuss our model in view of the experimental results
obtained with D. discoideum for hydrodynamic shear
experiments. Our results could be also confronted to single-cell
observations
Coordination between Intra- and Extracellular Forces Regulates Focal Adhesion Dynamics
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