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  • 1
    ISSN: 1432-1424
    Keywords: cardiac sarcoplasmic reticulum ; monovalent cation channel ; succinyl choline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have investigated the effect of the skeletal muscle relaxant succinyl choline (SC) on the conduction of potassium ions through a monovalent cation-selective channel present in the cardiac muscle sarcoplasmic reticulum membrane (CSR). This channel has been studied under voltage-clamp conditions following the fusion of purified CSR membrane vesicles with preformed planar phospholipid bilayers. The channel assumes a fixed orientation in the bilayer and displays two conducting states (B. Tomlins, A.J. Williams & R.A.P. Montgomery, 1984,J. Membrane Biol. 80: 191–199). SC blocks potassium conductance through the channel in a voltage-dependent manner. Block occurs from both sides of the channel, in both conducting states and is resolved as discrete “flickering” events. Although SC is capable of blocking potassium conductance from both sides of the membrane, block is asymmetric. The zero-voltage dissociation constant for block from the cis side of the membrane is approximately threefold lower than that from thetrans side. Block from thecis side displays a linear dependence on SC concentration for both open states and is competitive with potassium ions at saturating potassium activities, consistent with a singlesite blocking model. The degree of SC-induced block is also influenced by membrane surface charge. SC block differs from that previously described for bis quaternary ammonium (bis Qn) compounds such as decamethonium in that SC blocks preferentially from thecis side of the channel.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 28 (1988), S. 98-112 
    ISSN: 1432-1432
    Keywords: rRNA ; Evolution ; Sequence comparison ; Parsimony ; Bootstrap
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Sequences of small subunit (SSU) and large subunit (LSU) ribosomal RNA genes from archaebacteria, eubacteria, and the nucleus, chloroplasts, and mitochondria of eukaryotes have been compared in order to identify the most conservative positions. Aligned sets of these positions for both SSU and LSU rRNA have been used to generate tree diagrams relating the source organisms/organelles. Branching patterns were evaluated using the statistical bootstrapping technique. The resulting SSU and LSU trees are remarkably congruent and show a high degree of similarity with those based on alternative data sets and/or generated by different techniques. In addition to providing insights into the evolution of prokaryotic and eukaryotic (nuclear) lineages, the analysis reported here provides, for the first time, an extensive phylogeny of the mitochondrial lineage.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1432
    Keywords: Key words: RNA polymerase — Evolution — Mitochondria — Bacteriophage — Linear plasmid — Phylogenetic tree
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Many eukaryotic nuclear genomes as well as mitochondrial plasmids contain genes displaying evident sequence similarity to those encoding the single-subunit RNA polymerase (ssRNAP) of bacteriophage T7 and its relatives. We have collected and aligned these ssRNAP sequences and have constructed unrooted phylogenetic trees that demonstrate the separation of ssRNAPs into three well-defined and nonoverlapping clusters (phage-encoded, nucleus-encoded, and plasmid-encoded). Our analyses indicate that these three subfamiles of T7-like RNAPs shared a common ancestor; however, the order in which the groups diverged cannot be inferred from available data. On the basis of structural similarities and mutational data, we suggest that the ancestral ssRNAP gene may have arisen via duplication and divergence of a DNA polymerase or reverse transcriptase gene. Considering the current phylogenetic distribution of ssRNAP sequences, we further suggest that the origin of the ancestral ssRNAP gene closely paralleled in time the introduction of mitochondria into eukaryotic cells through a eubacterial endosymbiosis.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 443 (2006), S. 863-866 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The minor spliceosome is a ribonucleoprotein complex that catalyses the removal of an atypical class of spliceosomal introns (U12-type) from eukaryotic messenger RNAs. It was first identified and characterized in animals, where it was found to contain several unique RNA constituents that ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 434 (2005), S. 29-31 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Hydrogenosomes are double-membraned subcellular structures that generate hydrogen while making the energy-storage compound ATP. They are found in certain eukaryotic (nucleus-containing) microbes that inhabit oxygen-deficient environments. The evolution of the hydrogenosome has remained obscure, ...
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 408 (2000), S. 302-305 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Mitochondria, the cell's energy-generating organelles, have their own genome, known as mitochondrial (mt) DNA. This genome is, however, minuscule compared with that of the free-living bacterium from which mitochondria originated in eukaryotes — organisms whose cells have a defined nucleus. ...
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Genetics 33 (1999), S. 351-397 
    ISSN: 0066-4197
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Recent results from ancestral (minimally derived) protists testify to the tremendous diversity of the mitochondrial genome in various eukaryotic lineages, but also reinforce the view that mitochondria, descendants of an endosymbiotic alpha-Proteobacterium, arose only once in evolution. The serial endosymbiosis theory, currently the most popular hypothesis to explain the origin of mitochondria, postulates the capture of an alpha-proteobacterial endosymbiont by a nucleus-containing eukaryotic host resembling extant amitochondriate protists. New sequence data have challenged this scenario, instead raising the possibility that the origin of the mitochondrion was coincident with, and contributed substantially to, the origin of the nuclear genome of the eukaryotic cell. Defining more precisely the alpha-proteobacterial ancestry of the mitochondrial genome, and the contribution of the endosymbiotic event to the nuclear genome, will be essential for a full understanding of the origin and evolution of the eukaryotic cell as a whole.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Genetics 38 (2004), S. 477-524 
    ISSN: 0066-4197
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Over the past several decades, our knowledge of the origin and evolution of mitochondria has been greatly advanced by determination of complete mitochondrial genome sequences. Among the most informative mitochondrial genomes have been those of protists (primarily unicellular eukaryotes), some of which harbor the most gene-rich and most eubacteria-like mitochondrial DNAs (mtDNAs) known. Comparison of mtDNA sequence data has provided insights into the radically diverse trends in mitochondrial genome evolution exhibited by different phylogenetically coherent groupings of eukaryotes, and has allowed us to pinpoint specific protist relatives of the multicellular eukaryotic lineages (animals, plants, and fungi). This comparative genomics approach has also revealed unique and fascinating aspects of mitochondrial gene expression, highlighting the mitochondrion as an evolutionary playground par excellence.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1539-6924
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Over the last 10 years, a number of researchers have used Monte Carlo analysts to investigate the variation in long-term average dose rates in exposed populations and the uncertainty in estimates of long-term average dose rates for specific individuals. In general, these researchers have modeled long-term exposures using simple dose rate equations which assume that individuals are exposed to a single environmental concentration at a constant rate over a specified exposure duration. This paper presents an alternative approach for modeling long-term average exposures called microexposure event modeling which addresses a number of shortcomings in traditional dose rate equations. The paper discusses the limitations of the traditional dose rate equation, presents a description of the methodology, and illustrates advantages of the approach with a case study.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 46 (1999), S. 0 
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The Organelle Genome Megasequencing Program (OGMP) investigates mitochondrial genome diversity and evolution by systematically determining the complete mitochondrial DNA (mtDNA) sequences of a phylogenetically broad selection of protists. The mtDNAs of lower fungi and choanoflagellates are being analyzed by the Fungal Mitochondrial Genome Project (FMGP), a sister project to the OGMP. Some of the most interesting protists include the jakobid flagellates Reclinomonas americana, Malawimonas jakobiformis, and Jakoba libera, which share ultrastructural similarities with amitochondriate retortamonads, and harbor mitochondrial genes not seen before in mtDNAs of other organisms. In R. americana and J. libera, gene clusters are found that resemble, to an unprecedented degree, the contiguous ribosomal protein operons str, S10, spc, and alpha of eubacteria. In addition, their mtDNAs code for an RNase P RNA that displays all the elements of a bacterial minimum consensus structure. This structure has been instrumental in detecting the rnpB gene in additional protists. Gene repertoire and gene order comparisons as well as multiple-gene phylogenies support the view of a single endosymbiotic origin of mitochondria, whose closest extant relatives are Rickettsia-type α-Proteobacteria.
    Type of Medium: Electronic Resource
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