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