956 resultados para Helix-coil transition
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1929/11 (N18).
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1928/03.
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1930/06 (N19)- (N20).
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1927/06 (N3).
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1927/12.
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1929/02 (N15).
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1928/01.
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1927/04 (N1).
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1929/06 (N16)- (N17).
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1927/10.
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1928/02.
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In the work reported here, optically clear, ultrathin TEOS derived sol-gel slides which were suitable for studies of tryptophan (Trp) fluorescence from entrapped proteins were prepared by the sol-gel technique and characterized. The monitoring of intrinsic protein fluorescence provided information about the structure and environment of the entrapped protein, and about the kinetics of the interaction between the entrapped protein and extemal reagents. Initial studies concentrated on the single Trp protein monellin which was entrapped into the sol-gel matrices. Two types of sol-gel slides, termed "wet aged", in which the gels were aged in buffer and "dry-aged", in which the gels were aged in air , were studied in order to compare the effect of the sol-gel matrix on the structure of the protein at different aging stages. Fluorescence results suggested that the mobility of solvent inside the slides was substantially reduced. The interaction of the entrapped protein with both neutral and charged species was examined and indicated response times on the order of minutes. In the case of the neutral species the kinetics were diffusion limited in solution, but were best described by a sum of first order rate constants when the reactions occurred in the glass matrix. For charged species, interactions between the analytes and the negatively charged glass matrix caused the reaction kinetics to become complex, with the overall reaction rate depending on both the type of aging and the charge on the analyte. The stability and conformational flexibility of the entrapped monellin were also studied. These studies indicated that the encapsulation of monellin into dry-aged monoliths caused the thermal unfolding transition to broaden and shift upward by 14°C, and causedthe long-term stability to improve by 12-fold (compared to solution). Chemical stability studies also showed a broader transition for the unfolding of the protein in dry-aged monoliths, and suggested that the protein was present in a distribution of environments. Results indicated that the entrapped proteins had a smaller range of conformational motions compared to proteins in solution, and that entrapped proteins were not able to unfold completely. The restriction of conformational motion, along with the increased structural order of the internal environment of the gels, likely resulted in the improvements in themial and long-term stability that were observed. A second protein which was also studied in this work is the metal binding protein rat oncomodulin. Initially, the unfolding behavior of this protein in aqueous solution was examined. Several single tryptophan mutants of the metal-binding protein rat oncomodulin (OM) were examined; F102W, Y57W, Y65W and the engineered protein CDOM33 which had all 12 residues of the CD loop replaced with a higher affinity binding loop. Both the thermal and the chemical stability were improved upon binding of metal ions with the order apo < Ca^^ < Tb^"^. During thermal denaturation, the transition midpoints (Tun) of Y65W appeared to be the lowest, followed by Y57W and F102W. The placement of the Trp residue in the F-helix in F102W apparently made the protein slightly more thermostable, although the fluorescence response was readily affected by chemical denaturants, which probably acted through the disruption of hydrogen bonds at the Cterminal end of the F-helix. Under both thermal and chemical denaturation, the engineered protein showed the highest stability. This indicated that increasing the number of metal ligating oxygens in the binding site, either by using a metal ion with a higher coordinatenumber (i.e. Tb^*) which binds more carboxylate ligands, or by providing more ligating groups, as in the CDOM33 replacement, produces notable improvements in protein stability. Y57W and CE)OM33 OM were chosen for further studies when encapsulated into sol-gel derived matrices. The kinetics of interaction of terbium with the entrapped proteins, the ability of the entrapped protein to binding terbium, as well as thermal stability of these two entrapped protein were compared with different levels of Ca^"*^ present in the matrix and in solution. Results suggested that for both of the proteins, the response time and the ability to bind terbium could be adjusted by adding excess calcium to the matrix before gelation. However, the less stable protein Y57W only retained at most 45% of its binding ability in solution while the more stable protein CDOM33 was able to retain 100% binding ability. Themially induced denaturation also suggested that CDOM33 showed similar stability to the protein in solution while Y57W was destabilized. All these results suggested that "hard" proteins (i.e. very stable) can easily survive the sol-gel encapsulation process, but "soft" proteins with lower thermodynamic stability may not be able to withstand the sol-gel process. However, it is possible to control many parameters in order to successfully entrap biological molecules into the sol-gel matrices with maxunum retention of activity.
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The purpose of this study was to examine the perceived preparedness of college students for the transition from college to full-time employment. The study was concerned with the interest and rationale behind developing a required Exit Course for college students in order to improve the college to work transition. As well, possible content of an Exit Course was evaluated. The importance of addressing college to work transitions is highlighted by two phenomena. First, there are specific employability skills that employers in Canada are seeking in newly hired employees. Second, the provincial government in Ontario is determining college funding based on graduate employment statistics which are measured by graduate satisfaction, graduate employment, and employer satisfaction. The research concentrated on the following stakeholders involved in the transition from college to work: (a) current students, (b) recent graduates, (c) support staff who assist students in college to work transition (Career Educators), and (d) employers. Through qualitative research, including focus groups and interviews, these stakeholder groups participated in the research to determine if the Exit Course was a viable solution to facilitate the transition from college to work. Focus groups were conducted with current students, while one-on-one, semi-structured interviews were conducted with recent graduates, Career Educators, and employers. Common themes elicited from the participants included the following: (a) although students were perceived by the participants of this study to be technically prepared for employment, they were perceived to have weak job search skills and unrealistic expectations of the world of work unless they had received the benefits of a Co-operative Education experience; (b) an Exit Course was seen as a viable solution to the issues involved in college to work transition; (c) an Exit Course should be comprised of skills necessary to obtain and succeed in a job and the course should be taught by individuals with extensive qualifications in this area; and (d) there is a need to develop college and business partnerships to ensure that students are connected to employers. Educators within post secondary institutions, specifically colleges, can benefit from the information provided within this study to gain a better understanding of the perceived level of preparedness of students for the transition from college to work. Suggestions with regard to how to improve this transition were made, with specific reference to the addition of an Exit Course as one possible solution.
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This research responds to a pervasive call for our educational institutions to provide students with literacy skills, and teachers with the instructional supports necessary to facilitate this skill acquisition. Questions were posed to gain information concerning the efficacy ofteaching literacy strategies to students with learning difficulties, the impact of this training on their volunteer tutors, and the influence of this experience on these tutors' ensuing instructional practice as teacher candidates in a preservice education program. Study #1 compared a nontreatment group of students with literacy difficulties who participated in the program and found that program participants were superior at reading letter patterns and at comprehending the elements of story grammar. Concurrently, the second study explored the experiences of 19 volunteer tutors and uncovered that they acquired instructional skills as they established a knowledge base in teaching reading and writing, and they affirmed personal goals to become future teachers. Study #3 tracked 6 volunteer tutors into their pre-service year and identified their constructions, and beliefs about literacy instruction. These teacher candidates discussed how they had intended to teach reading and writing strategies based on their position that effective teaching ofthese skills in the primary grades is integral to academic success. The teacher candidates emphasized the need to build rapport with students, and the need to exercise flexibility in lesson plan delivery while including activities to meet emotional and developmental requirements of students. The teacher candidates entered their pre-service education with an initial cognition set based on the limited teaching context of tutoring. This foundational ii perception represented their prior knowledge of literacy instruction, a perception that appeared untenable once they were immersed in a regular instructional setting. This disparity provoked some of the teacher candidates to denounce their teacher mentors for not consistently employing literacy strategies and individualized instruction. This critical perspective could have been a demonstration of cognitive dissonance. In the end, when the teacher candidates began to look toward the future and how they would manage the demands of an inclusive classroom, they recognized the differences in the contexts. With an appreciation for the need for balance between prior and present knowledge, the teacher candidates remained committed to implementing their tutoring strategies in future teaching positions. This document highlights the need for teacher candidates with instructional experience prior to teacher education, to engage in cognitive negotiations to assimilate newly acquired pedagogies into existing pedagogies.