2006 MU dissertations - Access restricted to MU
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Item Gating of CFTR chloride channels : distinct closed states revealed by the action of AMP-PNP(University of Missouri--Columbia, 2006) Cho, Jeong Han, 1972-; Hwang, Tzyh-Chang[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] The CFTR chloride channel is gated by ATP through an irreversible gating cycle driven by an input of free energy of ATP hydrolysis. The open state of the CFTR chloride channel is associated with the dimerization of its two nucleotide binding domains (NBDs). Mutations of the glutamate 1371 residue (e.g., E1371S), the catalytic base for hydrolysis of ATP at CFTR's NBD2, dramatically prolong the lifetime of the open state ([tau]=~110 s) by abolishing the hydrolytic pathway for channel closing. Interestingly, when the E1371S mutant is opened by AMP-PNP, a non-hydrolysable ATP analog, the mean open time is less than 1 s, indicating that AMP-PNP alone cannot support a stable dimer configuration. Surprisingly, however, the macroscopic E1371S-CFTR channel currents do not decay upon ATP washout in the presence of AMP-PNP. Furthermore, when AMP-PNP was applied during the current decay after ATP washout, it not only reopened the closed E1371S channels, the AMP-PNP reopened channels have a lifetime of 113 s. These results indicate the presence of at least two different closed states that can be differentiated by their distinct responses to AMP-PNP. The relative amount of current induced by AMP-PNP during the ATP washout phase is decreased as the washout time increases. Quantitative analysis of these results using a simplified kinetic scheme yields a lifetime of ~85 s for the closed state, C2, which can be re-locked open by AMP-PNP. The lifetime of this closed state is prolonged when the channel is opened by N6 - phenylethyl-ATP, a high-affinity hydrolysable ATP analog, suggesting that at least one nucleotide remains bound in this closed state. WT-CFTR channels exhibiting a fast gating behavior ([tau]=0.45 s) presumably due to the hydrolysis of ATP were also examined. Consistently once the channels are locked-open by ATP and AMP-PNP, providing AMP-PNP during the current relaxation after the removal of all nucleotides derives significant numbers of channels to enter into the re-locked open state. This result hints that the different closed state is also present in WT-CFTR channels when they are closed through non-hydrolytic pathway.Item Mechanisms regulating skeletal muscle satellite cell cycle progression(University of Missouri--Columbia, 2006) Rathbone, Christopher R., 1977-; Booth, Frank W.[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Skeletal muscle fibers are multinucleated with each myonucleus capable of governing a finite cytoplasmic volume. In healthy skeletal muscle, myonuclear number decreases with muscle atrophy and fiber damage and increases with hypertrophy, to maintain a constant myonuclear to cytoplasmic ratio. Myonuclei are post-mitotic, therefore, the repair, regrowth, and hypertrophy of skeletal muscle relies on satellite cells, muscle precursor cells located between the basal lamina and plasmalemma of mature muscle fibers. Since decreased satellite cell proliferation may limit the regrowth of old skeletal muscle following atrophy or damage, it is important to understand the mechanisms that control satellite cell proliferation to enable the development of countermeasures to treat muscle atrophy that occurs with age. Adenoviral infection of primary satellite cells with the forkhead transcription factor FoxO3a decreased satellite cell cycle progression; this process occurred, in part, through increases in the promoter activity and protein levels of the cyclin dependent kinase (cdk) inhibitor p27superscript Kip1], without altering p21[superscript Waf/Cip1] or cyclin D1 -CDK 4/6 activity. Conversely, increases in satellite cell cycle progression following adenoviral infection of Sirt1 were associated with a decrease in the cyclin dependent kinase inhibitor p21[superscript Waf/Cip1], increased p27[superscript Kip1], and increased cyclin D1 -CDK4/6 activity. In summary, it is speculated that these studies suggest that increasing FoxO3a expression alters factors that would decrease cell cycle progression of primary satellite cells, and this inhibition is likely through the inhibition of cyclin E -CDK2 and/or cyclin A -CDK2 activities via increases in p27[superscript Kip1]. Also, increasing the expression of Sirt1 increases satellite cell cell cycle progression by decreasing the expression levels of p21[superscript Waf/Cip1]. These studies are important for the understanding of the mechanisms that regulate satellite cell proliferation, more specifically, these studies have contributed to the understanding of two molecules that control satellite cell proliferation, FoxO3a and Sirt1.Item Pencil or pen : the permanence of the writing center on the accountability watermark(University of Missouri--Columbia, 2006) Eaton, Thomas M., 1963-; Waddle, Jerry L. (Jerry Louis)[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] University writing centers have been around since the 1970's with the intent of assisting students in conducting writing assignments for their matriculation through college. The writing center paradigm has remained a program in the shadows, a condition which left the writing center to view itself and its tasks within its own belief system. However, in the advent of higher demands for matriculating students to be able to write within this global context, the writing center has become a key focus of both administrative personnel and the general populace who voice their demands through the form of educational policy. This study, using a Utilization Focus Evaluation (UFE) structure, contributes to writing center pedagogy through focusing on two primary objectives. The first element sought to discover whether the Southeast Missouri State University Writing Center was a student-services program or a learning-centered program based on its labor skill differentials and associated policies. References to technocratic characteristics throughout this research are identified within post-secondary education programs as student services whereas the use holistic characteristics are identified as a learning-centered approach in the postsecondary program vernacular. An identification of the Writing Center could then serve other writing centers at various institutions in determining their own identity since the writing center paradigm is consistent through all institutions. The second primary objective was to determine how the Writing Center was perceived by its user-constituents. This constituency was broken down into two categories: internal and external user constituents and then further categorized as direct or indirect user-constituents within the internal or external category. This study contributes to writing center discussion by examining perceptions of how the writing center is identified both internally and externally. This approach discovers areas of conflict between how the writing center program sees itself and how it is viewed by the population that interacts with it. These two primary elements became the cornerstone of discovery as they most accurately reflected the overall concerns of primary and secondary stakeholders involved in the UFE. These concerns were further broken down into five primary research questions which were then correlated with UFE procedures. From this correlation, three primary research methods were applied to gather data that would serve to address the two primary objectives and the associated stakeholders' concerns while providing representation of all user-constituents within the study. These three methods included historical documentation, single-focus observation, and dialogical-focus group interviews. Formative and summative committee input methods served as supplementary methods to the three dominant methods as a means of increasing reliability of the study. Historical documentation included an analysis of all written policies directing the Writing Center, as well as documentation regarding the Writing Center's planning and execution, including self-evaluation reports and specific forms and accountability reporting generated by the Writing Center. The single-focus observation method served this study in recognizing continuing patterns of interaction within the Writing Center as well as an opportunity to study both the cultural and physical aspects of the Writing Center facility. Dialogical-focus group interviews provided informal group input regarding perceptions of the Writing Center by encouraging open dialogue that was analyzed through descriptive analysis and coding techniques. The emerging perceptions were then compared to the findings resulting from the historical documentation and the single-focus observation methods to increase reliability of the resulting findings and recommendations. These findings and recommendations resulted from this study's focus upon the five primary research questions and the two overarching primary objectives that demanded the UFE strategy for accurate determination since the program was already in motion. The discussion of accountability played a major role in this research because accountability practices and associated pressures would have a strong affect on writing center identification. Internal self-identity as a learning-centered program is clearly challenged by external user-constituent perceptions that view the Writing Center as a student services program. Data analysis emerging from all three of the primary methods indicate that in terms of Writing Center procedures, environment, and interactions between Writing Center staff and University students all bear a student-service technocratic perception. This condition led to the key finding of this study and influenced the recommendations that conclude this study. The existing debate within the writing center paradigm as to whether the traditional ideal view or the pragmatic view is correct, will not address the actual situations that post-secondary writing centers face as accountability factors increase due to more attention regarding post-secondary student writing skills. Therefore, this study attempts to bring the debate out of its academic realm and introduce an understanding of writing program identity and the influence of use-constituent perceptions that can be applied toward program modifications. This study offers the conjecture that in order to generate a uniform learning-centered holistic perception that exists within the internal writing center program, the Writing Center will have to adopt a strong student-services approach in order to achieve a perception and identity that is both internally and externally harmonious.Item Development and evaluation of innovative iron-containing porous carbon adsorbents for arsenic removal(University of Missouri--Columbia, 2006) Gu, Zhimang, 1972-; Deng, Baolin[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Arsenic is of serious concern because of its marked negative impacts to human health. Of the various sources of arsenic in the environment, drinking water poses the greatest threat to human health. A variety of treatment processes have been examined for arsenic removal, and adsorption-based technology is one of best methods. Effectiveness of this method depends primarily on the adsorbent used. This dissertation is to develop of carbon based iron-containing adsorbents for arsenic removal. The development and characterization work is focused on two iron-containing carbon based adsorbents: (1) iron-containing granular activated carbon (As-GAC) and (2) iron-containing ordered mesoporous carbon (FeOMC). The investigation was conducted on optimizing the preparation conditions, including initial Fe concentration, oxidant type and dosage, and activated carbon or ordered mesoporous carbon types, etc. The ability of adsorbents for arsenic removal was evaluated by both batch and column studies. Effects of ionic strength, pH, and other competing constituents on the arsenic removal were also studied in batch systems. Redox transformation and surface characteristics of carbon based adsorbents were investigated. Meanwhile, the adsorbents were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and nitrogen adsorption-desorption analyses, etc. In the dissertation, As-GAC has been demonstrated as an excellent adsorbent for arsenic removal, and it is a cost efficient technology and potential commercial adsorbent for the arsenic removal. FeOMC was first explored for the environmental application of ordered mesoporous carbon. The advantages of high specific surface area, uniform porous, ordered structure potentially have the good application perspective, which will initiate the research of ordered nano-structured carbon materials for the environmental improvement.--From pulic.pdfItem The effects of conceptual description and search practice on users' mental models and information seeking in a case libray with a best match search mechanism(University of Missouri--Columbia, 2006) He, Wu, 1976-; Erdelez, Sanda, 1960-[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] The purpose of this study is to investigate the effects of conceptual description and search practice on users' mental models and information seeking in a case library with a best match search mechanism. This study also seeks to understand how the presence of a mental model affects the users' search performance and satisfaction in this case library. The study results reveal that the conceptual description and search practice treatments do not have significantly different effects on the types of user's mental models, search correctness, and search satisfaction. However, search practice group spent significantly less time than conceptual description group in finding the results. Qualitative analysis reveals that subjects in the conceptual description group seem to have more complete mental models of the best match system than those in the search practice group. This study also finds that subjects with the best match models have significantly higher search correctness and search result satisfaction than subjects without the best match models. However, best match mental models do not guarantee less search time in finding results. This study did not find significant correlation among search time, search correctness and search satisfaction.