Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1990. / Includes bibliographical references (leaves 216-228). / by Alan S. Feitelberg. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Transcription of mRNA appears to occur in random, intermittent bursts in a large variety of organisms. The statistics of mRNA expression can be described by two parameters: the frequency at which bursts occur (burst frequency) and the average number of mRNA produced within each burst (burst size). The mean steady-state abundance of mRNA is the product of the burst size and burst frequency. Although the experimental evidence for bursty gene transcription is abundant, little is known about its origins and consequences. We utilize single-molecule mRNA imaging and simple stochastic kinetic models to probe and understand both the mechanistic details and functional responses of transcriptional bursting in budding yeast. At the molecular level, we show that gene-specific activators can control both burst size and burst frequency by differentially utilizing kinetically distinct promoter elements. We also recognize the importance of activator residence time and nucleosome positioning on bursting. This investigation exemplifies how we can exploit spontaneous fluctuations in gene expression to uncover the molecular mechanisms and kinetic pathways of transcriptional regulation. At the network level, we demonstrate the important phenotypic consequences of transcriptional bursting by showing how noise itself can generate a bimodal, all-or-none gene expression profile that switches spontaneously between the low and high expression states in a transcriptional positive-feedback loop. Such bimodality is a hallmark in decision-making circuitry within metabolic, developmental, and synthetic gene regulatory networks. Importantly, we prove that the bimodal responses observed in our system are not due to deterministic bistability, which is an often-stated necessary condition for allor- none responses in positive-feedback loops. By clarifying a common misconception, this investigation provides unique biological insights into the molecular components, pathways and mechanisms controlling a measured phenotype. / by Tsz-Leung To. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1977. / MIT copy bound with: The effects of heparinization conditions on the antithrombin binding ability of heparin / by Jeffrey Maynard Swalchick [1977] jlh / Includes bibliographical references (leaves [89]-[92]). / by Wei Fun Sung. / B.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1983. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 117-119. / by Jayant Ghosh. / M.S.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1990. / Includes bibliographical references (leaves 182-195). / by Jirong Xiao. / Sc.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1984. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 102-103. / by Kevin G. Joback. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1994. / Includes bibliographical references (p. 209-222). / by Christine M.V. Moore. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1992. / Includes bibliographical references (leaves 203-209). / by Bhavik Ramesh Bakshi. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1989. / Includes bibliographical references (leaves 155-164). / by Julian Thomas McKinnon, Jr. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2007. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references. / Absorption of gases into a liquid is of crucial importance to multiphase reactions because diffusion of a sparingly soluble gas across a gas-liquid interface generally limits the relevant reaction rates. Pertinent examples of multiphase reactions that have found application in the chemical and biochemical industries include fermentation, water treatment, and hydrogenation reactions. Gas-liquid mass transfer is of particular importance in fermentation because productivity increases in aerobic cultures are often constrained by transport of oxygen, which is only slightly soluble in water. Previous approaches to enhance oxygen transfer consisted in adding emulsified organic phases in which oxygen has a greater solubility. However, these approaches have several limitations, the most important of which is the difficult recovery of the organic phase after the fermentation. The research presented in this thesis focuses on the use of functionalized magnetic nanoparticles to enhance gas-liquid oxygen transfer. The nanoparticles have a magnetic core and an organic coating. The magnetic core makes it possible to easily recover the fluid by passing it through a magnetic field, and the coating confers colloidal stability to the particle. / (cont.) Oxygen transfer enhancement has been observed in the presence of nanoparticles coated with oleic acid and a polymerizable surfactant. In cell-free media, nanoparticles improve gas-liquid oxygen mass transfer up to 6-fold (600%) in an agitated, sparged reactor. Furthermore, they show remarkable stability in high-ionic strength media over a wide pH range. In a fermentation of Escherichia coli, a nanoparticle weight fraction of 0.6% increases oxygen uptake rate and cell growth by 40%. Through a combination of experiments using both physical and chemical methods to characterize mass transfer, it has been shown that both the mass transfer coefficient (kL) and the gas-liquid interfacial area are enhanced in the presence of nanoparticles, the latter accounting for a larger fraction of the total enhancement. This insight has been used to propose a model of the enhancement that involves two separate mechanisms: one of area enhancement and the other of kL enhancement. It has been proposed that (i) the nanoparticles increase interfacial area by adsorbing on the gas bubble interface and stabilizing it against coalescence and (ii) the nanoparticles increase the mass transfer coefficient by causing microconvection in the surrounding fluid through Brownian motion. / (cont.) The methodology developed in this thesis shows several-fold gas-liquid mass transfer enhancements and at the same time allows for easier separation over previous approaches. In addition, the modeling effort resulted in correlations that can allow for extension of this methodology from laboratory-scale to industrial scale reactions across the variable space considered. / by Bernat Ollé Pocurull. / Ph.D.