213 research outputs found
Molecular motors: design, mechanism and control
Biological functions in each animal cell depend on coordinated operations of
a wide variety of molecular motors. Some of the these motors transport cargo to
their respective destinations whereas some others are mobile workshops which
synthesize macromolecules while moving on their tracks. Some other motors are
designed to function as packers and movers. All these motors require input
energy for performing their mechanical works and operate under conditions far
from thermodynamic equilibrium. The typical size of these motors and the forces
they generate are of the order of nano-meters and pico-Newtons, respectively.
They are subjected to random bombardments by the molecules of the surrounding
aqueous medium and, therefore, follow noisy trajectories. Because of their
small inertia, their movements in the viscous intracellular space exhibits
features that are characteristics of hydrodynamics at low Reynold's number. In
this article we discuss how theoretical modeling and computer simulations of
these machines by physicists are providing insight into their mechanisms which
engineers can exploit to design and control artificial nano-motors.Comment: 11 pages, including 8 embedded EPS figures; Invited article, accepted
for Publication in "Computing in Science and Engineering" (AIP & IEEE
100 years of Einstein's theory of Brownian motion: from pollen grains to protein trains
Experimental verification of the theoretical predictions made by Albert
Einstein in his paper, published in 1905, on the molecular mechanisms of
Brownian motion established the existence of atoms. In the last 100 years
discoveries of many facets of the ubiquitous Brownian motion has revolutionized
our fundamental understanding of the role of {\it thermal fluctuations} in the
exotic structures and complex dynamics exhibited by soft matter like, for
example, colloids, gels, etc. The domain of Brownian motion transcends the
traditional disciplinary boundaries of physics and has become an area of
multi-disciplinary research. Brownian motion finds applications also in earth
and environmental sciences as well as life sciences. Nature exploits Brownian
motion for running many dynamical processes that are crucial for sustaining
life. In the first one-third of this article I present a brief historical
survey of the initial period, including works of Brown and Einstein. In the
next one-third I introduce the main concepts and the essential theoretical
techniques used for studying translational as well as rotational Brownian
motions and the effects of time-independent potentials. In the last one-third
of this article I discuss some contemporary problems on Brownian motion in
time-dependent potentials, namely, {\it stochastic resonance} and {\it Brownian
ratchet}, two of the hottest topics in this area of interdisciplinary research.Comment: 15 pages, LATEX, Based on the inaugural lecture in the Horizon
Lecture Series organized by the Physics Society of I.I.T. Kanpur, in the
"World Year of Physics 2005
Collective effects in intra-cellular molecular motor transport: coordination, cooperation and competetion
Molecular motors do not work in isolation {\it in-vivo}. We highlight some of
the coordinations, cooperations and competitions that determine the collective
properties of molecular motors in eukaryotic cells. In the context of
traffic-like movement of motors on a track, we emphasize the importance of
single-motor bio-chemical cycle and enzymatic activity on their collective
spatio-temporal organisation. Our modelling strategy is based on a synthesis-
the same model describes the single-motor mechano-chemistry at sufficiently low
densities whereas at higher densities it accounts for the collective flow
properties and the density profiles of the motors. We consider two specific
examples, namely, traffic of single-headed kinesin motors KIF1A on a
microtubule track and ribosome traffic on a messenger RNA track.Comment: 9 pages including LATEX text and 9 EPS figure
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