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Biomedical subjects

Z Jericević

Publications and source records attributed to Z Jericević.

5 recordsLinked to original sources

Validation of an imaging system: steps to evaluate and validate a microscope imaging system for quantitative studies.

The processing methods described in this article are general and can be used with any computer with adequate software without reference to a specific experimental apparatus. To achieve appropriately corrected images, the operations must be performed correctly and in a specific order to extract meaningful information from digital images. The operations are subtraction of the dark current, a shading correction after low pass filtering of the shading mask, a geometric correction with a reference grid obtained at the longest wavelength of interest, and finally registration. Since the digital data sets are too large for manual evaluation, statistical criteria must be used to define the analytical capabilities and error limits of the system before the more interesting cellular studies can be undertaken.

Algorithms↗

Geometric correction of digital images using orthonormal decomposition.

We have developed an algorithm which can be used to correct the geometric distortion of digital images. The method uses an orthonormal decomposition and a two-dimensional Horner's scheme to construct and evaluate a polynomial equation of arbitrary degree in two independent variables. This numerical scheme for geometric correction combines several methods selected on the basis of their computation efficiency and numerical stability. The differences and advantages of this numerical scheme are compared with methods found in the image processing literature. The algorithm presented here has a reduced number of mathematical operations, is flexible and numerically stable. Based on the least-squares criteria, the algorithm provides corrected pixel positions with an accuracy equal to or better than the pixel size.

Algorithms↗

DNA replication past pyrimidine dimers in the absence of repair.

Post-UV DNA synthesis in Escherichia coli uvrA recA cells was studied. A low dose of UV radiation (0.07 J/m2), which caused no degradation of the dimer-containing DNA, was used. This enabled us to make a direct comparison between DNA synthesis on the normal template and DNA synthesis on the UV-damaged template. There was no change in the post-UV DNA synthesis kinetics during the first 60 min of post-irradiation incubation. A reduced rate of DNA synthesis was observed at later post-UV times when the dimers are expected to have passed through the normal replication complex. This reduced rate of DNA synthesis was associated with loss of the biological activity of the DNA. We suggest that the gaps opposite dimers rather than dimers per se interfere with normal replication, thus leading to cell death of uvrA recA bacteria.

Bacterial Proteins↗

Photochemical cleavage of phosphodiester bonds in oligoribonucleotides.

The release of inorganic phosphate from a variety of mononucleotides and the generation of new phosphomonoester end groups as a result of chain cleavage in a number of oligoribonucleotides have been studied quantitatively as a function of irradiation with 254-nm light. The reaction cross sections for adenosine 5'-phosphate, guanosine 2'(3')-phosphate, cytidine 5'-phosphate, cytidine 3'-phosphate, cytidine 2'(3')-phosphate, uridine 5'-phosphate, uridine 2'(3')-phosphate, dihydrouridine 5'-phosphate, and ribose 5-phosphate are close to 2 X 10(-7) m2/J. The value for UpU is similar. The reaction cross sections, sigma, for (Ap)n where n = 3-10 as well as for the oligonucleotides ApUpGp, m1ApCpUpCpGp, CpCpCpCpCpGp, and DpDpDpApApGp increased linearly as a function of the number of phosphodiester bonds and gave values close to 6.4 X 10(-7) m2/J per bond. The cross sections for (Up)n were also about 6.4 X 10(-7) m2/J per bond for n = 2-5 and then, unexpectedly, increased rapidly for n = 6-10. By analogy to the carefully studied release of phosphate from ethyl phosphate and several sugar phosphates by 254-nm light [Halmann, M., & Platzner, I. (1965) J. Chem. Soc., 5380-5385], we conclude that the photolysis reactions we have observed are induced by absorption of photons by the sugar phosphate groups rather than the purine or pyrimidine rings. It follows that the quantum yields for chain cleavage of both RNA and DNA have been seriously underestimated since these calculations were based on the assumption that the observed photochemistry is due to absorption of photons by the purine and pyrimidine rings, and the absorption cross section of these rings is roughly 10 000 times greater than that of the sugar phosphate group itself.

Chemical Phenomena↗