Fostering Basic Problem-Solving Skills in Chemistry

A triangle divided in three parts was used to relate three variables, or two variables and a constant. Students learned to manipulate a given equation so that one of the variables is a product of the other two variables. Problems relating density, mass, and volume; speed of light, frequency and wavelength; gram, mole, and molar mass, molarity, moles and liters; and number of particles, Avogadro’s number, and mole were attempted using triangles. In addition, a special triangle was constructed to relate the variables and a constant of the ideal gas law equation, and was used to solve ideal gas law problems. This visual representation of the problem helped students to understand the factors that need to be considered and the operations that needed to be performed in the problem-solving process. Over the course of two years, the method was used in four different introductory chemistry classes that had a total of 87 students. More than 80% of the students who use triangles were able to arrive at the correct answers. A big percentage of students also liked using triangles to solve simple problems

Saccharomyces cerevisiae chitin biosynthesis activation by N-acetylchitooses depends on size and structure of chito-oligosaccharides

<p>Abstract</p> <p>Background</p> <p>To explore chitin synthesis initiation, the effect of addition of exogenous oligosaccharides on <it>in vitro </it>chitin synthesis was studied. Oligosaccharides of various natures and lengths were added to a chitin synthase assay performed on a <it>Saccharomyces cerevisiae </it>membrane fraction.</p> <p>Findings</p> <p><it>N</it>-acetylchito-tetra, -penta and -octaoses resulted in 11 to 25% [¹⁴C]-GlcNAc incorporation into [¹⁴C]-chitin, corresponding to an increase in the initial velocity. The activation appeared specific to <it>N</it>-acetylchitooses as it was not observed with oligosaccharides in other series, such as beta-(1,4), beta-(1,3) or alpha-(1,6) glucooligosaccharides.</p> <p>Conclusions</p> <p>The effect induced by the <it>N</it>-acetylchitooses was a saturable phenomenon and did not interfere with free GlcNAc and trypsin which are two known activators of yeast chitin synthase activity <it>in vitro</it>. The magnitude of the activation was dependent on both oligosaccharide concentration and oligosaccharide size.</p

A novel use of TAT-EGFP to validate techniques to alter osteosarcoma cell surface glycosaminoglycan expression

Several methods to alter cell surface glycosaminoglycan (GAG) expression have previously been described, including treatments with chlorate to reduce the addition of charged sulfate groups, xyloside compounds to displace GAGs from their core proteins, and GAG lyases, such as heparinase and chondroitinase, to release GAG fragments from the cell layer. While these methods are useful in identifying cellular mechanisms which are dependent on GAGs, they must be stringently validated to assess results in the appropriate context. To determine the most useful technique for the evaluation of GAG function in osteogenesis, MG-63 osteosarcoma cells were systematically treated with these agents and evaluated for changes in cell surface GAGs using a TAT-EGFP fusion protein. TAT, a protein transduction domain from the HIV-1 virus, requires cell surface GAGs to traverse cell membranes. The EGFP component provides a method to assess protein entry into cells in both qualitative and quantitative tests. Here, TAT-EGFP transduction analysis confirmed radiochemical and physiological data that chlorate effectively disrupts GAG expression. TAT-EGFP entry into cells was also inhibited by the exogenous application of commercial heparin and GAGs extracted from MG-63 cells as well as by the pre-treatment of cells with chondroitinase ABC. However, neither heparinase III treatment nor the addition of exogenous chondroitin-6-sulfate affected TAT-EGFP entry into cells. In addition, xyloside-beta-D-naphthol and xyloside-beta-D-cis/trans-decahydro-2-naphthol treatment could not induce significant phenotypic change in these cells, and the unaffected TAT-EGFP transduction confirmed that this was due to an inability to efficiently prime GAG synthesis. The use of TAT-EGFP is thus a useful technique to specifically evaluate cell surface GAG expression in a simple, quantifiable manner, and avoids the complications involved with conventional radiochemical assays or analytical chromatography