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  • 2000-2004  (3)
  • 1975-1979  (4)
  • 1
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The effect of recombination on genotypes can be represented in the form of P-structures, i.e., a map from the set of pairs of genotypes to the power set of genotypes. The interpretation is that the P-structure maps the pair of parental genotypes to the set of recombinant genotypes which result from the recombination of the parental genotypes. A recombination fitness landscape is then a function from the genotypes in a P-structure to the real numbers. In previous papers we have shown that the eigenfunctions of (a matrix associated with) the P-structure provide a basis for the Fourier decomposition of arbitrary recombination landscapes. Here we generalize this framework to include the effect of genotype frequencies, assuming linkage equilibrium. We find that the autocorrelation of the eigenfunctions of the population-weighted P-structure is independent of the population composition. As a consequence we can directly compare the performance of mutation and recombination operators by comparing the autocorrelations on the finite set of elementary landscapes. This comparison suggests that point mutation is a superior search strategy on landscapes with a low order and a moderate order of interaction p 〈 n/3 (n is the number of loci). For more complex landscapes 1-point recombination is superior to both mutation and uniform recombination, but only if the distance among the interacting loci (defining length) is minimal. Furthermore we find that the autocorrelation on any landscape is increasing as the distribution of genotypes becomes more extreme, i.e., if the population occupies a location close to the boundary of the frequency simplex. Landscapes are smoother the more biased the distribution of genotype frequencies is. We suggest that this result explains the paradox that there is little epistatic interaction for quantitative traits detected in natural populations if one uses variance decomposition methods while there is evidence for strong interactions in molecular mapping studies for quantitative trait loci.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of mathematical biology 62 (2000), S. 1061-1086 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A class of autocatalytic reaction networks based on template-dependent ligation and higher-order catalysis is analysed. Apart from an irreversible ligation reaction we consider only reversible aggregation steps that provide a realistic description of molecular recognition. The overall dynamics can be understood by means of replicator equations with highly non-linear interaction functions. The dynamics depends crucially on the total concentration c 0 of replicating material. For small c 0, in the hyperbolic growth regime, we recover the familiar dynamics of second-order replicator equations with its wealth of complex dynamics ranging from multi-stability to periodic and strange attractors as well as to heteroclinic orbits. For large c 0, in the parabolic growth regime, product inhibition becomes dominating and we observe a single globally stable equilibrium tantamount to permanent coexistence. In an intermediate parameter range we sometimes observe a behavior that is reminiscent of ’survival of the fittest’. Independently replicating species (Schlögl’s model) and the hypercycle are discussed in detail.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1439-099X
    Keywords: Schlüsselwörter: p53-Überexpression ; Hypoxie ; Kopf-Hals-Karzinome ; Key Words: p53 ; Hypoxia ; Head and neck carcinomas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Purpose: Clinical investigation of a potential relationship between the polarographically measured tumor oxygenation and the p53 status in patients with squamous cell carcinoma of the head and neck. Patients and Methods: In 99 patients with mostly advanced, histologically proven squamous cell carcinoma of the head and neck were estimated the classical tumor parameters (TNM stage, histological grading) the immunohistochemical p53-overexpression (DO-7) and the tumor oxygenation status (Eppendorf pO2 Histograph). The tumor volume and the hemoglobin concentration were evaluated simultaneously. Results: No statistically significant difference could be detected between immunohistological p53-positive (p53 ≥ 10% stained cells) and p53-negative tumors (p53 〈 10% stained cells) regarding both the median pO2 and the relative frequency of values ≤ 5 mm Hg. Moreover, no statistically relevant differences could be seen between both p53-groups considering the hemoglobin concentration, the TNM stag, the histological grading and the tumor volume. Conclusion: Our data imply that there is no association between p53-overexpression and tumor hypoxia in head and neck carcinomas. However, this is not necessarily in contradiction to experimental or clinical data that confirmed a relationship between hypoxia and p53-mediated increased malignancy of tumor cells in other tumor entities. The comparable oxygenation status of p53-positive and p53-negative tumors in our study is associated with an analogous clinical tumor aggressiveness of both groups. That could be caused by hypoxia related but p53-independent selection of tumor cells with a more malignant phenotype in head and neck carcinomas. However, further research is needed to prove this possible relationship.
    Notes: Ziel: Klinische Prüfung einer potentiellen Beziehung zwischen polarographisch gemesener Tumoroxygenierung und p53-Status bei Patienten mit Plattenepithelkarzinomen der Kopf-Hals-Region. Patienten und Methode: Bei 99 Patienten mit überwiegend fortgeschrittenen, histologisch gesicherten Plattenepithelkarzinomen der Kopf-Hals-Region wurden neben den klassischen Tumorparametern (TNM-Stadium, histologisches Grading) die immunhistochemische p53-Überexpression (DO-7) und der Tumoroxygenierungsstatus ermittelt (Eppendorf-pO2-Histograph). Simultan erfolgte die Bestimmung des Tumorvolumens und der Hämoglobinkonzentration. Ergebnisse: Zwischen immunhistochemisch p53-positiven (≥ 10% angefärbte Zellen) und p53-negativen (〈 10% angefärbte Zellen) Tumoren fand sich weder für den pO2-Median noch für die relative Anzahl von Werten ≤ 5 mm Hg ein statistisch signifikanter Unterschied. Auch bei der Betrachtung der Hämoglobinkonzentration, der TNM-Klassifikation, des histologischen Gradings und des Tumorvolumens fanden sich zwischen beiden p53-Gruppen keine statistisch relevanten Differenzen. Schlussfolgerung: Unsere Daten sprechen gegen eine Assoziation von p53-Überexpression und Tumorhypoxie bei Kopf-Hals-Karzinomen. Zu experimentellen und klinischen Ergebnissen, die bei anderen Tumorentitäten zeigen, dass Hypoxie zu einer p53-vermittelten Steigerung der Malignität führt, ergibt sich trotzdem kein prinzipieller Widerspruch. Die in unserer Studie adäquate Oxygenierung von p53-positiven und p53-negativen Tumoren reflektiert sich in einer vergleichbaren klinischen Tumoraggressivität beider Gruppen. Dies könnte dadurch bedingt sein, dass bei Kopf-Hals-Karzinomen hypoxieassoziierte, aber p53-unabhängiger Formen der Selektion von Tumorzellen mit malignerem Phänotyp zum Tragen kommen. Es bedarf jedoch weiterführender Untersuchungen, um einen solchen möglichen Zusammenhang zu belegen.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 110 (1977), S. 1896-1907 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Branched-chain Sugars, XV. Glycoside Syntheses with L-StreptoseThe halogeno derivatives of the cyclic carbonates 11 a and 11 b are most suitably used in the synthesis of L-streptose β-glycosides. α-Glycosides are obtained from the benzylidene compound 20. The benzylidene group can be subsequently removed by catalytic hydrogenation. Using the glycosyl halide 16 a also α-glycosides are formed in high yields. However, it is difficult to cleave the isopropylidene group under acidic conditions. Acetylated halides of type 4 are very labile and therefore not useful in glycoside synthesis.
    Notes: Zur Herstellung β-L-glycosidischer Verknüpfungen der L-Streptose sind die Halogenide des cyclischen Carbonats 11 a und 11 b am besten geeignet. α-L-Glycosidische Verknüpfungen der L-Streptose werden am günstigsten mit der Benzylidenverbindung 20 erhalten. Die Benzylidengruppe ist anschließend hydrogenolytisch abspaltbar. Auch das Halogenid 16 a liefert hohe Anteile an α-Glycosid. Die Isopropylidengruppe ist aber schwierig sauer abspaltbar. Acetylierte Halogenide wie 4 sind wegen ihrer Empfindlichkeit zur Glycosidsynthese weniger geeignet.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 110 (1977), S. 1925-1930 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Building Units for Oligosaccharides, VI. Synthesis of StreptobiosamineA synthesis of 5-deoxy-2-O-(2-deoxy-2-methylamino-α-D-glucopyranosyl)-3-C-formyl-D-lyxofuranose (11) (D-streptobiosamine) is described. The same synthesis was repeated with the corresponding L-sugars. It leads to 5-deoxy-2-O-(2-deoxy-2-methylamino-α-L-glucopyranosyl)-3-C-formyl-L-lyxofuranose (1) (L-streptobiosamine), the disaccharide portion of streptomycin.
    Notes: Eine Synthese der 5-Desoxy-2-O-(2-desoxy-2-methylamino-α-D-glucopyranosyl)-3-C-formyl-D-lyxofuranose (11) (D-Streptobiosamin) wird beschrieben. Die gleiche Synthese wurde auch mit den entsprechenden L-Zuckern durchgeführt. Sie lieferte 5-Desoxy-2-O-(2-desoxy-2-methylamino-α-L-glucopyranosyl)-3-C-formyl-L-lyxofuranose (1) (L-Streptobiosamin), das den Disaccharidbaustein des Streptomycins darstellt.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 110 (1977), S. 1916-1924 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Building Units for Oligosaccharides, V. Synthesis of Dihydrostreptosyl-deoxystreptamineReaction of the streptosyl chloride 1 and the streptosyl bromide 6 with the racemie mixture of the 2-deoxystreptamine derivative 2 leads to diastereoisomeric mixtures of the α-glycosidic bonded pscudo-disaccharides, which can be separated by column chromatography. Complete deblocking, affording the pseudo-disaccharides of 4-O- and 6-O-linked dihydrostreptosyl-2-deoxystreptamines 10 a and 10 b, is possible in the case of compounds 8 a and 8 b, which are protected by the benzylidene group in the streptose moiety.
    Notes: Das Streptosylchlorid 1 und das Streptosylbromid 6 reagieren mit dem racemischen 2-Desoxy-streptamin-Derivat 2 zu trennbaren Diastereomerengemischen der α-glycosidisch verknüpften Pseudodisaccharide. Im Falle der mit der Benzylidengruppe im Streptose-Teil geschützten Produkte 8 a und 8 b ist eine vollständige Entblockierung zu den Pseudodisacchariden des 4-O- und 6-O-verknüpften Dihydrostreptosyl-2-desoxystreptamins 10 a und 10 b gelungen.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 110 (1977), S. 1908-1915 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Building Units for Oligosaccharides, IV. Synthesis of DihydrostreptosylstreptidineReaction of the streptosyl chloride 1 with the optically active heptaacetylstreptidine 2 gives the pseudo-disaccharide 3, which can be transformed into the 2,3-O-isopropylidene derivative of streptosylstreptidine (5). Condensation of the chloride 6 with 2 leads to the glycoside 7. Deblocking and hydrogenation of 7 yields the free dihydrostreptosylstreptidine 10.
    Notes: Das Streptosylchlorid 1 reagiert mit chiralem Heptaacetylstreptidin 2 zum Pseudodisaccharid 3, das in das 2,3-O-Isopropyliden-Derivat des Streptosylstreptidins (5) überführbar ist. Das Chlorid 6 kann mit 2 zum Glycosid 7 umgesetzt werden. Hieraus gelingt es, durch Deblockierungs- und Hydrierungsschritte das freie Dihydrostreptosylstreptidin 10 zu gewinnen.
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