This thesis discusses circularization and supercoiling of actin biofilaments, as well as the various examples of self-organization observed in a simple non-equilibrium system of microtubules, motor clusters, and a depletion agent (PEG).
When the ends of an actin filament approach each other, annealing can occur, resulting in the assumption of a circular conformation. In order to facilitate this experimentally, we dramatically reduce the space available for the ends to explore by confining the filaments to a quasi-2D region. This is accomplished through the use of a depletion attraction. In addition to the pronounced effects of this topological ring constraint on the statistical fluctuations of the filaments, we also observe a spontaneous supercoiling transition in fluorescently labeled actin rings that is directly driven by illumination. To better understand this transition in natural twist, we investigate real-time twist of a filament trapped between two beads, held by optical traps.
The main focus of this graduate work was on the behavior of non-equilibrium in vitro mixtures of microtubules, kinesin motor clusters, and a depletion agent. We observed several striking and distinct examples of self-organization on near-macroscopic length scales, due to the interactions of very simple components.
First we investigate the driving mechanism behind the beating of biological cilia and flagella, and find that this beating functionality can be reproduced in our vastly simpler system. This occurs only when minimalist components are reconstituted: motors, biofilaments, elastic links to hold the filaments together, and a basal attachment. Beyond the cooperativity of the motors to produce oscillatory beating in individual bundles, we also observe that active bundles in close proximity can synchronize their beating to produce stable, periodic metachronal waves that propagate along the bundle array.
By changing only the length distribution of the microtubules in our system, we find that basal attachments at the chamber edge no longer form. Rather, bundles become unstable and interact in bulk by merging, extending, buckling, breaking, and recombining. These interactions lead to the emergence of a steady-state bulk mixing process that causes the super-diffusive transport of tracer particles and enhanced mixing of fluid. This mixing bears some resemblance to other mixing processes, including the biological example of cytoplasmic streaming.
Finally, we show that a qualitatively new example of self-organization occurs when these active mixtures are put into water droplets in oil-water emulsions. The MT bundles migrate to the oil-water interface, forming a 2D active nematic. This active nematic exhibits a host of emergent properties, including the unbinding of +1/2 and -1/2 nematic defects from each other. The internal stresses of these active nematics also cause droplets to be self-propelled, leading to the possibility of studying a system of spherical swimmers, where new examples of self-organized behavior may occur.
|Commitee:||Hagan, Michael, Nicastro, Daniela|
|School Location:||United States -- Massachusetts|
|Source:||DAI-B 73/09(E), Dissertation Abstracts International|
|Subjects:||Condensed matter physics, Biophysics|
|Keywords:||Active matter, Cilia, Cytoskeleton, Microtubules, Non-equilibrium, Self-organization|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be