Browsing by Subject "Brownian Dynamics"
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Item Modeling complex structures in nucleic acids.(2012-04) Linak, Margaret C.Since the discovery of DNA, researchers have been attempting to decode the detailed structure, properties, and abilities of this molecule. At first approximation, DNA can be thought of as a long, regular, double-stranded helix encoding the genomic information of life. However, on closer analysis DNA has been found to take on a wide variety of complex shapes and functions both in vitro and in vivo. DNA can be single-, double-, triple-, and even quadruple-stranded in nature and can bind in both the Watson-Crick conformations and also in a variety of non-canonical con- figurations that add to its inherent flexibility, structure, and activity. Elucidating the varied structures and behaviors of DNA has historically been an experimental endeavor, due in large part to the difficulties in capturing nucleic acid's complex mo- tions and function in a tractable computational model. However, as the applications of DNA expand and computation power increases, simulation models are playing an increasingly important role in DNA understanding and engineering. In this thesis, we simulate short DNA and RNA (less than 100 nucleotides) and examine their complex structures. In particular, we will (i) experimentally evaluate previous DNA coarse grained models for their ability to capture complex nucleic acid structures, and (ii) develop a new model that can better capture both canonical and non-canonical in- teractions and show its utility in the study of several known structures. Further, we will use our understanding of the intricate interactions of short oligonucleotides to unravel a hereto experimentally inaccessible mechanistic pathway for a catalytically active DNA molecule. The model developed and the importance of non-canonical interactions in nucleic acid systems will be useful in the continued understanding and engineering of DNA and RNA molecules for nanotechnology, genetic engineering, and therapeutic applications.Item The predicted role of stereospecificity in crowding-mediated effects on reversible association: a Brownian Dynamics investigation(2013-08) Powers, Joseph DanielMacromolecular crowding refers to the presence of inert molecules in close proximity to other reacting molecules, and is often discussed in the context of biochemical reactions in the cytoplasm. This phenomenon has been proposed to cause alterations in the intrinsic kinetics and thermodynamics of chemical reactions, which has led to certain undefined caveats when relating biochemical characteristics observed in vitro to those seen in vivo. In this work, the effects of macromolecular crowding were studied by means of a computational, Monte Carlo simulation using Brownian Dynamics, where generalized chemical association and dissociation reaction kinetics of varying degrees of stereospecificity were modeled both in the absence and presence of crowding molecules of different sizes. It was found that crowded environments impose energetic contributions to reactant pairs through depletion forces, which bias their translational and rotational diffusion in such a way that overall net assembly is favored, with stronger effects on reactants with higher degrees of stereospecificity than for those with low stereospecificity. These favorable forces are insufficient to overcome the slowing of translational diffusion by crowders for low stereospecificity reactions, but more than compensate for the translational slowing for high stereospecificity reactions. In general, the effects observed in the simulation are relatively modest, with kon decreasing by 2-fold for low stereospecificity reactions, and increasing by 3-fold for high stereospecificity reactions. In addition, koff decreases by ~30-60% in the presence of crowders (depending on the strength of the bond between the reactant pair), so that the equilibrium constant is increased by at most ~3.5-fold (ΔΔGo = -1.3kBT). The moderate effects of crowding predicted in this work through strictly geometric constraints suggest that any effects observed in vitro larger than those found here are due to other energetic effects, such as solvent reordering. More generally, the results suggest that reactions in the cytoplasm are fundamentally insensitive to the physical presence of crowders over a large range of volume fractions (0-0.3).