1,872 research outputs found
Cooperative Cargo Transport by Several Molecular Motors
The transport of cargo particles which are pulled by several molecular motors
in a cooperative manner is studied theoretically. The transport properties
depend primarily on the maximal number, , of motor molecules that may pull
simultaneously on the cargo particle. Since each motor must unbind from the
filament after a finite number of steps but can also rebind to it again, the
actual number of pulling motors is not constant but varies with time between
zero and . An increase in the maximal number leads to a strong increase
of the average walking distance (or run length) of the cargo particle. If the
cargo is pulled by up to kinesin motors, e.g., the walking distance is
estimated to be micrometers which implies that seven or eight
kinesin molecules are sufficient to attain an average walking distance in the
centimeter range. If the cargo particle is pulled against an external load
force, this force is shared between the motors which provides a nontrivial
motor-motor coupling and a generic mechanism for nonlinear force-velocity
relationships. With increasing load force, the probability distribution of the
instantenous velocity is shifted towards smaller values, becomes broader, and
develops several peaks. Our theory is consistent with available experimental
data and makes quantitative predictions that are accessible to systematic in
vitro experiments.Comment: 24 pages, latex, 6 figures, includes Supporting Tex
Received Signal Strength for Randomly Distributed Molecular Nanonodes
We consider nanonodes randomly distributed in a circular area and
characterize the received signal strength when a pair of these nodes employ
molecular communication. Two communication methods are investigated, namely
free diffusion and diffusion with drift. Since the nodes are randomly
distributed, the distance between them can be represented as a random variable,
which results in a stochastic process representation of the received signal
strength. We derive the probability density function of this process for both
molecular communication methods. Specifically for the case of free diffusion we
also derive the cumulative distribution function, which can be used to derive
transmission success probabilities. The presented work constitutes a first step
towards the characterization of the signal to noise ratio in the considered
setting for a number of molecular communication methods.Comment: 6 pages, 6 figures, Nanocom 2017 conferenc
Brownian molecular motors driven by rotation-translation coupling
We investigated three models of Brownian motors which convert rotational
diffusion into directed translational motion by switching on and off a
potential. In the first model a spatially asymmetric potential generates
directed translational motion by rectifying rotational diffusion. It behaves
much like a conventional flashing ratchet. The second model utilizes both
rotational diffusion and drift to generate translational motion without spatial
asymmetry in the potential. This second model can be driven by a combination of
a Brownian motor mechanism (diffusion driven) or by powerstroke (drift driven)
depending on the chosen parameters. In the third model, elements of both the
Brownian motor and powerstroke mechanisms are combined by switching between
three distinct states. Relevance of the model to biological motor proteins is
discussed.Comment: 11 pages, 8 figure
Length control of long cell protrusions: Rulers, timers and transport
Living cells use long tubular appendages for locomotion and sensory purposes. Hence, assembling and maintaining a protrusion of correct length is crucial for survival and overall performance. Usually the protrusions lack the machinery for the synthesis of building blocks and imports them from the cell body. What are the unique features of the transport logistics which facilitate the exchange of these building blocks between the cell and the protrusion? What kind of 'rulers' and 'timers' does the cell use for constructing its appendages of correct length on time? How do the multiple appendages coordinate and communicate among themselves during different stages of their existence? How frequently do the fluctuations drive the length of these dynamic protrusions out of the acceptable bounds? These questions are addressed from a broad perspective in this review which is organized in three parts. In part-I the list of all known cell protrusions is followed by a comprehensive list of the mechanisms of length control of cell protrusions reported in the literature. We review not only the dynamics of the genesis of the protrusions, but also their resorption and regrowth as well as regeneration after amputation. As a case study in part-II, the specific cell protrusion that has been discussed in detail is eukaryotic flagellum (also known as cilium); this choice was dictated by the fact that flagellar length control mechanisms have been studied most extensively over more than half a century in cells with two or more flagella. Although limited in scope, brief discussions on a few non-flagellar cell protrusions in part-III of this review is intended to provide a glimpse of the uncharted territories and challenging frontiers of research on subcellular length control phenomena that awaits rigorous investigations.(c) 2022 Elsevier B.V. All rights reserved
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Geometry Matters for Cargos Navigating 3D Microtubule Intersections
Eukaryotic cells transport cargos along microtubules to control their distribution within the cell and deliver them to distant locations. While we understand how molecular motors can transport cargos along individual microtubules, the cell's microtubules are usually arranged in a complex 3D network. While traversing this network, cargos need to navigate intersections where microtubules cross at a wide variety of separation distances and angles. To gain insight into how cargos navigate these intersections, we have used a recently established 3D construction technique based on holographic optical trapping to build single 3D microtubule intersections in vitro with relevant nanoscale precision. We then used these fully suspended microtubule structures to perform motility assays on kinesin-1 coated cargos. We find that some intersection geometries influence cargos to pass along their current microtubule, while other geometries influence them to switch to the intersecting one. To understand how, we use a 3D Brownian dynamics simulation of cargo transport to investigate the mechanisms which give rise to the observed switching probabilities. Using these stochastic simulations, we find that switching probability is often determined by a competition between a stronger motor team on the primary microtubule and the intersecting microtubule sterically hindering that team's progress. This understanding of the basic mechanisms of switching at single intersections in 3D helps lay a foundation for understanding how the cell may regulate switching to control how cargos navigate the MT network and ultimately their spatial organization
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