Investigating the energetics and functional properties of quinones and chlorophyll in photosynthetic reaction centers.
Item
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Title
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Investigating the energetics and functional properties of quinones and chlorophyll in photosynthetic reaction centers.
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Identifier
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AAI3187384
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identifier
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3187384
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Creator
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Madeo, Jennifer.
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Contributor
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Adviser: Marilyn Gunner
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Date
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2005
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Biomedical
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Abstract
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The first steps for the process of converting light into chemical energy in photosynthesis occur within membrane-bound proteins called the reaction centers (RCs). When the RC is excited by light a series of electron transfer reactions take place. The RC has bound co-factor compounds that are specifically tuned to accept and donate the electron in the reaction series. The protein is responsible for creating the right micro-environment for the proper co-factor orientations and tune the energy levels to drive the electron transfer reactions.;Three RCs are the focus of this work. The first RC is from the purple bacteria Rhodobacter sphaeroides. These RCs contain two chemically identical quinones (ubiquinone-10). Electron transfer between these two quinones is favorable because the protein modifies their environment such that Q A is lower potential than QB. The negatively charged semi-quinone binds more tightly and dissociates more slowly than the neutral quinone. The binding affinities and rate constants for thirteen quinones (eight neutral and five negatively charged) at the QA site were measured. It is shown that a negative charge leads to a different binding mechanism as well as slower binding rate.;The shift in pKa of hydroxyl containing quinones and the relative affinities of anionic quinones was determined and compared both experimentally and computationally. The computational method is Mulpti-Conformational Continuum Electrostatics (MCCE). The good agreement between experimental and computational results confirms that electrostatics is the dominant way that the QA site modifies quinone chemistry.;The second two RCs come from cyanobacteria, which contain two RCs (PSI and PSII). The primary electron donor, a chlorophyll a dimer, is the same for both PSI and PSII. Despite this the redox potentials of the co-factors bound to these RCs are very different (about 600mV). Only PSII has a high enough potential to oxidize water. MCCE was used to calculate the redox midpoint potentials of the co-factors bound to PSI and PSII in effort to understand the role that electrostatics plays in fine-tuning these midpoint potentials. These results are compared with experimental results in an effort to understand how the protein modifies the co-factor environment.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
