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Biomedical subjects

T Schmidt

Publications and source records attributed to T Schmidt.

At least 343 records · Page 19Linked to original sources
PubMed1982

[The integral dose in computerized tomography of the skull (author's transl)].

A comparison of the exposure to radiation based on the surface dose - as has been frequently done in conventional x-ray diagnosis - becomes entirely questionable if computerized tomography is included. A better comparative measure - also with regard to the hazard associated with the exposure - is represented by the amount of absorbed energy (integral dose). In this article, the amount of absorbed energy is determined for a CT examination of the skull. The absorbed energy is determined from a great number of dosage measurements using a suitable phantom. Under the conditions obtaining in this case, the absorbed energy is about 6 mJ for a single scan. The errors associated with this method are discussed in detail. It is also stated in the course of the discussion that the amount of absorbed energy can serve as a comparative measure and as a basis for assessing the involved hazard.

Computers↗
PubMed1982

Studies on the role of exogenous calcium in fertilization, activation and development of the sea urchin egg.

Both isotopic and microelectrode studies reveal a significant Ca2+ influx at fertilization. The role, if any, of this influx is disputed. An attempt to reevaluate contradictory findings by others on this role was made and the results with S. purpuratus and L. pictus eggs, using acrosome reacted sperm and EGTA- buffered media (free [Ca2+] less than 10(-11M), indicate that exogenous Ca2+, and hence the Ca2+ influx, is not required for fertilization, activation and subsequent cleavage. Blastomere adhesion, however, is affected. The contradictory findings by others may have resulted from reduced fertilizability in Ca2+-free seawater, which can be circumvented by higher sperm concentration and by a sensitivity to temperature in Ca2+-free medium, which can be bypassed by carrying out fertilization at lower temperatures. Under the assay conditions, there is also no effect of Ca2+-free media on the kinetics of the cortical reaction or polyspermy. The data support the hypothesis that sperm induce release of Ca2+ from intracellular stores, perhaps by affecting an equilibrium between Ca2+ sequestration and Ca2+ release.

Acrosome↗
PubMed1981

The initiator tRNA genes of Drosophila melanogaster: evidence for a tRNA pseudogene.

We have isolated four segments of Drosophila melanogaster DNA that hybridize to homologous initiator tRNAMet. Three of the cloned fragments contain initiator tRNA genes, each of which can be transcribed in vitro. The fourth clone, pPW568, contains an initiator tRNA pseudogene which is not transcribed in vitro by RNA polymerase III. The pseudogene is contained in a 1.15 kb DNA fragment. This fragment has the characteristics of dispersed repetitive DNA and hybridizes in situ to at least 30 sites in the Drosophila genome. The arrangement of the initiator tRNA genes we have isolated, is different to that of other Drosophila tRNA gene families. The initiator tRNA genes are not clustered nor intermingled with other tRNA genes. They occur as single copies within an approximately 415-bp repeat segment, which is separated from other initiator tRNA genes by a mean distance of 17 kb. In situ hybridization to polytene chromosomes localizes these genes to the 61D region of the Drosophila genome. Hybridization analysis of genomic DNA indicates the presence of 8-9 non-allelic initiator tRNA genes in Drosophila melanogaster.

Animals↗
PubMed1981

The genes coding for tRNA Tyr of Drosophila melanogaster: localization of determination of the gene numbers.

Transfer RNA(Tyr) (anticodon G psi A) was isolated from Drosophila melanogaster by means of Sepharose 4B, RPC-5, and polyacrylamide gel electrophoresis. The rRNA was iodinated in vitro with Na125 I and hybridized in situ to salivary gland chromosomes from Drosophila. The genes of rRNA(Tyr) were localized in eight regions of the genome by autoradiography. Restriction enzyme analysis of genomic DNA indicated that the haploid Drosophila genome codes for about 23 tRNA(Tyr) genes. The regions 22F and 85A each contain four to five tRNA(Tyr) genes, whereas the regions 28C, 41AB, 42A, 42E, and 56D each contain two to three tRNA(Tyr) genes.

Animals↗
PubMed1980

The localization of tRNA5Asn, tRNAHis, and tRNAAla genes from drosophila melanogaster by in situ hybridization to polytene salivary gland chromosomes.

Transfer RNA5 gammaAsn, tRNA gamma His, and tRNAAla were isolated from Drosophila melanogaster by means of Sepharose 4B chromatography and 2-dimensional polyacrylamide gel electrophoresis. The tRNAs were iodinated in vitro with Na125I and hybridized in situ salivary gland chromosomes from Drosophila. Subsequent autoradiography allowed the localization of the genes for tRNA 5 gammaAsn in the regions 42A, 59F, 60C, and 84F; for tRNAHis in the regions 48F and 56E; and for tRNAAla in the regions 63A and 90C. From these and our previous results it can be concluded that the genes for the Q-base containing tRNAs (tRNAAsn, tRNAAsp, and tRNAHis, are not clustered in the Drosophila melanogaster genome.

Alanine↗
PubMed1980

[Tumour induction by methylnitrosourea in clawed frogs (Xenopus laevis) (author's transl)].

15 clawed frogs were bathed 12 to 17 times in solutions of 2 mg methylnitrosourea, dissolved in 1000 ml destilled water. 7 frogs developed tumours 8 to 22 months after starting the experiments. Another frog died of polycystic kidneys. The tumours were adenocarcinomas of the kidneys, sarcomas and a benign papilloma of the pelvis of the left kidney. A sarcoma of the soft tissues of the head showed an excessive granular storage of acid mucopolysaccharides in the cytoplasma of many tumour cells. Tumours of the nervous system did not occur.

Adenocarcinoma↗
PubMed1978

The localization of tRNAAsp2 genes from Drosophila melanogaster by "in situ" hybridization.

Transfer RNAAsp2delta was isolated from Drosophila melanogaster by affinity chromatography on concanavalin A-Sepharose. The tRNA was iodinated "in vitro" with Na [125I] and hybridized "in situ" to salivary gland chromosomes from Drosophila. Subsequent autoradiography allowed the localization of the genes for tRNAAsp2 to the left arm of the second chromosome in the regions 29 D and E.

Animals↗
PubMed1978

The localization of tRNA4Glu genes from Drosophila melanogaster by "in situ" hybridization.

Transfer RNAGlu4 was isolated from Drosophila melanogaster by affinity chromatography. The tRNA was iodinated "in vitro" with Na[25I] and hybridized "in situ" to salivary gland chromosomes from Drosophila. Subsequent autoradiography allowed the localization of the genes for tRNAGlu4 to the right arm of the second chromosome and to the left arm of the third chromosome in the regions 52 F, 56 EF and 62 A.

Amino Acyl-tRNA Synthetases↗