13,084 research outputs found
Coexistence and efficiency of normal and anomalous transport by molecular motors in living cells
Recent experiments reveal both passive subdiffusion of various nanoparticles
and anomalous active transport of such particles by molecular motors in the
molecularly crowded environment of living biological cells. Passive and active
microrheology reveals that the origin of this anomalous dynamics is due to the
viscoelasticity of the intracellular fluid. How do molecular motors perform in
such a highly viscous, dissipative environment? Can we explain the observed
co-existence of the anomalous transport of relatively large particles of 100 to
500 nm in size by kinesin motors with the normal transport of smaller particles
by the same molecular motors? What is the efficiency of molecular motors in the
anomalous transport regime? Here we answer these seemingly conflicting
questions and consistently explain experimental findings in a generalization of
the well-known continuous diffusion model for molecular motors with two
conformational states in which viscoelastic effects are included
Fluctuating-friction molecular motors
We show that the correlated stochastic fluctuation of the friction
coefficient can give rise to long-range directional motion of a particle
undergoing Brownian random walk in a constant periodic energy potential
landscape. The occurrence of this motion requires the presence of two
additional independent bodies interacting with the particle via friction and
via the energy potential, respectively, which can move relative to each other.
Such three-body system generalizes the classical Brownian ratchet mechanism,
which requires only two interacting bodies. In particular, we describe a simple
two-level model of fluctuating-friction molecular motor that can be solved
analytically. In our previous work [M.K., L.M and D.P. 2000 J. Nonlinear Opt.
Phys. Mater. vol. 9, 157] this model has been first applied to understanding
the fundamental mechanism of the photoinduced reorientation of dye-doped liquid
crystals. Applications of the same idea to other fields such as molecular
biology and nanotechnology can however be envisioned. As an example, in this
paper we work out a model of the actomyosin system based on the
fluctuating-friction mechanism.Comment: to be published in J. Physics Condensed Matter
(http://www.iop.org/Journals/JPhysCM
Elastically coupled molecular motors
We study the influence of filament elasticity on the motion of collective
molecular motors. It is found that for a backbone flexibility exceeding a
characteristic value (motor stiffness divided through the mean displacement
between attached motors), the ability of motors to produce force reduces as
compared to rigidly coupled motors, while the maximum velocity remains
unchanged. The force-velocity-relation in two different analytic approximations
is calculated and compared with Monte-Carlo simulations. Finally, we extend our
model by introducing motors with a strain-dependent detachment rate. A
remarkable crossover from the nearly hyperbolic shape of the Hill curve for
stiff backbones to a linear force-velocity relation for very elastic backbones
is found. With realistic model parameters we show that the backbone flexibility
plays no role under physiological conditions in muscles, but it should be
observable in certain in vitro assays.Comment: REVTeX, 13 pages, 11 figures; presentation improved; to appear in
European Physical Journal B; a Java applet showing the simulation is
accessible at http://www.physik.tu-muenchen.de/~avilfan/ecmm
Traffic of Molecular Motors
Molecular motors perform active movements along cytoskeletal filaments and
drive the traffic of organelles and other cargo particles in cells. In contrast
to the macroscopic traffic of cars, however, the traffic of molecular motors is
characterized by a finite walking distance (or run length) after which a motor
unbinds from the filament along which it moves. Unbound motors perform Brownian
motion in the surrounding aqueous solution until they rebind to a filament. We
use variants of driven lattice gas models to describe the interplay of their
active movements, the unbound diffusion, and the binding/unbinding dynamics. If
the motor concentration is large, motor-motor interactions become important and
lead to a variety of cooperative traffic phenomena such as traffic jams on the
filaments, boundary-induced phase transitions, and spontaneous symmetry
breaking in systems with two species of motors. If the filament is surrounded
by a large reservoir of motors, the jam length, i.e., the extension of the
traffic jams is of the order of the walking distance. Much longer jams can be
found in confined geometries such as tube-like compartments.Comment: 10 pages, latex, uses Springer styles (included), to appear in the
Proceedings of "Traffic and Granular Flow 2005
Interaction of molecular motors can enhance their efficiency
Particles moving in oscillating potential with broken mirror symmetry are
considered. We calculate their energetic efficiency, when acting as molecular
motors carrying a load against external force. It is shown that interaction
between particles enhances the efficiency in wide range of parameters. Possible
consequences for artificial molecular motors are discussed.Comment: 6 pages, 8 figure
Theoretical Analysis of Dynamic Processes for Interacting Molecular Motors
Biological transport is supported by collective dynamics of enzymatic
molecules that are called motor proteins or molecular motors. Experiments
suggest that motor proteins interact locally via short-range potentials. We
investigate the fundamental role of these interactions by analyzing a new class
of totally asymmetric exclusion processes where interactions are accounted for
in a thermodynamically consistent fashion. Theoretical analysis that combines
various mean-field cal- culations and computer simulations suggests that
dynamic properties of molecular motors strongly depend on interactions, and
correlations are stronger for interacting motor proteins. Surprisingly, it is
found that there is an optimal strength of interactions (weak repulsion) that
leads to a maxi- mal particle flux. It is also argued that molecular motors
transport is more sensitive to attractive interactions. Applications of these
results for kinesin motor proteins are discussed
A Master equation approach to modeling an artificial protein motor
Linear bio-molecular motors move unidirectionally along a track by
coordinating several different processes, such as fuel (ATP) capture,
hydrolysis, conformational changes, binding and unbinding from a track, and
center-of-mass diffusion. A better understanding of the interdependencies
between these processes, which take place over a wide range of different time
scales, would help elucidate the general operational principles of molecular
motors. Artificial molecular motors present a unique opportunity for such a
study because motor structure and function are a priori known. Here we describe
use of a Master equation approach, integrated with input from Langevin and
molecular dynamics modeling, to stochastically model a molecular motor across
many time scales. We apply this approach to a specific concept for an
artificial protein motor, the Tumbleweed.Comment: Submitted to Chemical Physics; 9 pages, 7 figure
Toy model for molecular motors
A hopping model for molecular motors is presented consisting of a state with
asymmetric hopping rates with period 2 and a state with uniform hopping rates.
State changes lead to a stationary unidirectional current of a particle. The
current is explicitly calculated as a function of the rate of state changes,
including also an external bias field. The Einstein relation between the linear
mobility of the particle and its diffusion coefficient is investigated. The
power input into the system is derived, as well as the power output resulting
from the work performed against the bias field. The efficiency of this model is
found to be rather small.Comment: 11 pages Latex, 7 postscript figures, to be published in Physica
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