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Biomedical subjects

G F Bahr

Publications and source records attributed to G F Bahr.

11 recordsLinked to original sources
PubMed1979

Reconstruction of a chromosome model from its projections.

As a pilot experiment towards the reconstruction of human chromosomes from their electron microscopic projections, a chromosome model was photographed and several cross-sectional planes successfully reconstructed. Some practical constraints and conditions for this type of work are defined.

Chromatin↗
PubMed1976

Determination of the mass of viruses by quantitative electron microscopy.

The photometric method of quantitative determination of dry mass by electron microscopy has been applied to the study of various types of viruses: animal, plant, insect, and bacterial. The method is applicable to all viruses having a mass of 1 x 10-18g or greater. The molecular weight of viruses can be calculated from the mass value by multiplying it by Avogadro's number. In comparison to other methods of determining the molecular weight of viruses, sedimentation and diffusion, sedimentation equilibrium, light scattering, and electron microscopy counting, the method of quantitative electron microscopy is competitive. In some ways quantitative electron microscopy is superior to other methods for the determination of molecular weight: There is no limitation to the size of the virus, no experimental time involved and no concentration and purity of virus preparations required, and finally it is independent of the geometry of the virion. In one important aspect it is unique when compared to other methods; namely, it affords one the capacity to analyse individual virus particles.

Biophysical Phenomena↗
PubMed1975

Comparison of G-, Q- and EM-banding patterns exhibited by the chromosome complement of the Indian muntjac, Muntiacus muntjak, with reference to nuclear DNA content and chromatin ultrastructure.

When the chromosomes of the Indian muntjac, Muntiacus muntjak, were compared following treatment with two presently used banding methods, trypsin-Giemsa (G) and quinacrine-hydrochloride (Q) with structural bands as seen in the electron microscope, definite correlations were observed with respect to the numbers and positions of individual bands. - Weights obtained for the individual chromosomes were: No. 1, 9.98 pg; No. 2, 4.10 pg; No. 3, 4.43 pg; No. 3-X, 5.05 pg; and Y, 0.55 pg. Average diameters and weights for individual fibers were 193 A and 8.74 times 10-16 g/micron, respectively, for stimulated metaphase chromosomes and 185 A and 8.73 times 10-16 g/micron, respectively, for unstimulated chromosomes. Fibers of interphase nuclei exhibited an average diameter of 191 A and a weight of 5.87 times 10-16 g/micron. - The total amound of nuclear DNA present in interphase nuclei was 3.88 pg.

Animals↗
PubMed1975

Localization and quantitation of EBV-associated nuclear antigen (EBNA) in Raji cells.

Epstein-Barr virus (EBV)-associated nuclear antigen (EBNA) was localized to chromatin fibers of Raji cells. When EBNA was labeled with the horseradish-peroxidase technique of Sternberger a strong reaction covered most fiber surfaces as observed by electron microscopy. The dry mass of Raji chromatin increased after exposure to both EBV-positive and -negative serum, but the increase was significantly larger in the material treated with positive serum.

Antigens, Viral↗
PubMed1975

The fibrous structure of human chromosomes in relation to rearrangements and aberrations; a theoretical consideration.

Human chromosomes as a type-sample for mammalian chromosomes consist of 200-A fibers, folded to chromomeres, which are interconnected by about a dozen longitudinal fibers. The average fiber at both interphase and metaphase contains 28.3 lengths of one double helix of DNA per length of fiber. The orientation of DNA imparts polarity to the fiber and thus to the chromosome and is an important constraint in concepts of chromosomal aberrations and rearrangements, some of which are being interpreted on the basis of fiber-fiber exchanges. Chromosomal rearrangements discernible by light microscopy are not likely to be fully synonymous with change in gene sequence. Chromosomes are considered to possess a plane of symmetry originating from semiconservative replication. Implications for chromosomal structure, centromeric function, and chromatid cohesion are discussed. Fibers connecting one chromosome to others are discussed in light of the proposal that fiber regions of repeated nucleotide sequences exist that facilitate fiber-fiber exchanges. No free fiber or DNA ends are thought to occur at any time in the nucleus.

Chromatids↗
PubMedDate not supplied

An automated device for the production of cell preparations suitable for automatic assessment.

A set of preparatory steps has been developed for the processing of clinical samples from the female genital tract onto microscopic slides suitable both for machine assessment and for regular microscopic evaluation. These steps involve the depositing of the cell sample in a collection fluid, the semi-automatic adjustment of cell concentration to about 30,000 cells per milliliter through a combination of transmittance and light scatter measurements, the dispersion of the sample by syringing, and the deposition of the cellular content onto microscope slides by centrifugation. These steps were designed so as not to allow loss of cells--except the lysis of erythrocytes--with the understanding that this condition entails the presence of 4--10 per cent cell aggregates in the final preparation.

Autoanalysis↗