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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Parasitology research 82 (1996), S. 468-474 
    ISSN: 1432-1955
    Schlagwort(e): Abbreviationsaa Amino acids ; BFA brefeldin A ; bp base pairs ; ER endoplasmic reticulum ; FCS fetal calf serum ; HEPES N-(2-5hydroxyethyl)piperazine-N′- (2-ethanesulfonic acid) ; mAb(s) monoclonal antibodies ; NP-40 Nonidet P-40 ; ORF open reading frame ; pSM/1.6 plasmid carrying the cDNA insert ; SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electro- phoresis ; SRP signal recognition particle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The cDNA clone pSM/1.6 encoding the 26.5-kDa precursor molecule of the 16/17-kDa microneme antigen of Sarcocystis muris cyst merozoites was expressed in a cell-free translation/translocation system to study translocation of the protein across membranes. The antigen was found to be translocated across heterologous endoplasmic reticulum membranes. Translocation was accompanied by cleavage of a signal peptide to create a 23-kDa polypeptide that was completely protected from digestion with proteinase K. Pulse-chase analysis of [35S]-methionine-labeled S. muris cyst merozoites demonstrated that the 16/17-kDa antigen derived from a 23-kDa precursor molecule and that its processing occurred at between a few minutes and 2 h after biosynthesis. This leads to the conclusion that the native microneme antigen is secreted from the parasite cell via the endoplasmic reticulum. Sorting into micronemes might occur during transition through a Golgi-like structure, involving cleavage of the hydrophilic propeptide to create the mature 16/17-kDa protein.
    Materialart: Digitale Medien
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  • 2
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    In:  Other Sources
    Publikationsdatum: 2011-08-17
    Beschreibung: The Viking biological investigation has tested four different hypotheses regarding the possible nature of Martian organisms. While significant results were obtained for each of these, tests of three of the hypotheses appear to indicate the absence of biology in the samples used, while the fourth is consistent with a biological interpretation. The original assumptions for each experiment and the experimental procedures that were utilized to test these assumptions are reviewed.
    Schlagwort(e): SPACE BIOLOGY
    Materialart: Journal of Geophysical Research; 82; Sept. 30
    Format: text
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  • 3
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    In:  Other Sources
    Publikationsdatum: 2011-08-17
    Beschreibung: The three biological experiments on board the Viking Mars Landers are discussed. The gas exchange experiment provided periodic measurements of the composition and quantity of gases from Martian surface material, either in a humid or a wet nutrient sampling mode. The labeled release experiment demonstrated that adding an aqueous solution of dilute radioactive compounds to Martian material caused a rapid release of labeled gas. The results of the pyrolytic release experiment remain difficult to interpret. Data from the first two experiments suggest that oxidants (including H2O2 and iron oxide) rather than biota may account for all the observed reactions.
    Schlagwort(e): SPACE BIOLOGY
    Materialart: Icarus; 34; June 197
    Format: text
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  • 4
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    In:  Other Sources
    Publikationsdatum: 2011-08-17
    Beschreibung: The paper discusses some of the constraints pertaining to the Viking mission for detection of life on Mars, within which the Viking experiments were conceived, designed, and developed. The most important limitation to the entire study is the complete information about the nature of Mars, such as the chemical composition of the surface material of Mars and the exact identification of the constituents of that planet. Ways in which celestial mechanics places severe limitations on the Viking biology investigation are discussed. Major engineering constraints are examined relative to the accomodation of biology instrument inside the Viking lander and to the design of the instrument itself. Other constraints discussed concern the operational aspects of the mission and the testing program.
    Schlagwort(e): SPACE BIOLOGY
    Materialart: Origins of Life; 7; Aug. 197
    Format: text
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  • 5
    Publikationsdatum: 2011-08-16
    Beschreibung: The scientific payload on the Viking Mars landers is described. Shortly after landing, two facsimile cameras capable of stereoscopic imaging will scan the landing site area in black and white, color, and infrared to reveal gross evidence of past or present living systems. A wide range mass spectrometer will record a complete mass spectrum for soil samples from mass 12 to mass 200 every 10.3 sec. Three experiments based on different assumptions on the nature of life on Mars, if it exists, will be carried out by the bio-lab. A pyrolytic release experiment is designed to measure photosynthetic or dark fixation of carbon dioxide or carbon monoxide into organic compounds. A labelled release experiment will test for metabolic activity during incubation of a surface sample moistened with a solution of radioactively labelled simple organic compounds. A gas exchange experiment will detect changes in the gaseous medium surrounding a soil sample as the result of metabolic activity. The hardware, function, and terrestrial test results of the bio-lab experiments are discussed.
    Schlagwort(e): SPACE BIOLOGY
    Materialart: Nature; 262; July 1
    Format: text
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  • 6
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    In:  Other Sources
    Publikationsdatum: 2011-08-17
    Beschreibung: In the present paper, ground-based investigations of the Viking Martian biology data, which have resulted in reasonable simulations of these data, are reviewed. These simulations, which in strong oxidants, UV-treated materials, iron-containing clays, or iron salts were used as Martian analogs, are capable of explaining the ambiguity between the GCMS (gas-chromatography mass-spectrometry) experiments, in which no organic compounds were found on Mars, and the Labeled Release experiments, in which added organics were decomposed.
    Schlagwort(e): SPACE BIOLOGY
    Materialart: Journal of Molecular Evolution; 14; Dec. 197
    Format: text
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  • 7
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    In:  Other Sources
    Publikationsdatum: 2011-08-17
    Beschreibung: The three experimental approaches incorporated into the Viking biology instrument have yielded results that are most readily explained as nonbiological phenomena. The predominant view among investigators trying to simulate the Mars results is that the surface material of Mars contains strongly oxidizing compounds which would account for many of the more intense reactions seen on Mars. Other mechanisms are also currently being proposed and studied.
    Schlagwort(e): SPACE BIOLOGY
    Materialart: Origins of Life; 9; Dec. 197
    Format: text
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  • 8
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    Publikationsdatum: 2019-04-02
    Beschreibung: Of all the other planets in the solar system, Mars remains the most promising for further elucidating concepts about chemical evolution and the origin of life. Strategies were developed to pursue three exobiological objectives for Mars exploration: determining the abundance and distribution of the biogenic elements and organic compounds, detecting evidence of an ancient biota on Mars, and determining whether indigenous organisms exist anywhere on the planet. The three strategies are quite similar and, in fact, share the same sequence of phases. In the first phase, each requires global reconnaissance and remote sensing by orbiters to select sites of interest for detailed in situ analyses. In the second phase, lander missions are conducted to characterize the chemical and physical properties of the selected sites. The third phase involves conducting 'critical' experiments at sites whose properties make them particularly attractive for exobiology. These critical experiments would include, for example, identification of organics, detection of fossils, and detection of extant life. The fourth phase is the detailed analysis of samples returned from these sites in Earth-based laboratories to confirm and extend previous discoveries. Finally, in the fifth phase, human exploration is needed to establish the geological settings for the earlier findings or to discover and explore sites that are not accessible to robotic spacecraft.
    Schlagwort(e): SPACE BIOLOGY
    Materialart: Life sciences and space research 24 (4): Planetary biology and origins of life; Topical Meeting of the COSPAR Interdisciplinary Scientific Commission F (Meeting F3) of the COSPAR Plenary Meeting, 29th (ISSN 0273-1177); 15; 3; p. 151-156
    Format: text
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  • 9
    Publikationsdatum: 2019-06-27
    Beschreibung: A preliminary progress report is presented for the Viking biological investigation through its first month. The carbon assimilation, gas exchange, and labeled release experiments are described in detail, and the chronology of the experiments is outlined. For the first experiment, it is found that a small amount of gas was converted into organic material in one sample and that heat treatment of a duplicate sample prevented such conversion. In the second experiment, a substantial amount of O2 was detected along with significant increases in CO2 and small changes in N2. In the third experiment, a significant amount of radioactive gas was evolved from one sample, but not from a duplicate heat-treated sample. Possible biological and nonbiological interpretations are considered for these results. It is concluded that while the experiments provide clear evidence for the occurrence of chemical reactions and while the results do not violate any prima facie criteria for biological processes, a definitive answer cannot yet be given to the question of whether life exists on Mars.
    Schlagwort(e): SPACE BIOLOGY
    Materialart: Science; 194; Oct. 1
    Format: text
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  • 10
    Publikationsdatum: 2019-08-27
    Beschreibung: The selection of sites on Mars that have a high priority for exobiological research is fundamental for planning future exploration. The most immediate need is to identify targets for high resolution orbital imaging during the Mars Observer and Mars '94/'96 missions that can be used to refined site priorities for surface exploration. We present an objective approach to site selection whereby individual sites are selected and scored, based on the presence of key geological features which indicate high priority environments. Prime sites are those that show evidence for the prolonged activity of liquid water and which have sedimentary deposits that are likely to have accumulated in environments favorable for life. High priority areas include fluvio-lacustrine (stream-fed lake systems), springs, and periglacial environments. Sites where mineralization may have occurred in the presence of organisms (e.g. springs) are given high priority in the search for a fossil record on Mars. A systematic review of Viking data for 83 sites in the Mars Landing Site Catalog (MLSC) resulted in the selection of 13 as being of exobiological interest. The descriptions of these sites were expanded to address exobiological concerns. An additional five sites were identified for inclusion in the second edition of the MLSC. We plan to broaden our site selection activities to include a systematic global reconnaissance of Mars using Viking data, and will continue to refine site priorities for exobiological research based on data from future missions in order to define strategies for surface exploration.
    Schlagwort(e): SPACE BIOLOGY
    Materialart: Life sciences and space research 24 (4): Planetary biology and origins of life; Topical Meeting of the COSPAR Interdisciplinary Scientific Commission F (Meeting F3) of the COSPAR Plenary Meeting, 29th (ISSN 0273-1177); 15; 3; p. 157-162
    Format: text
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