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  • LIFE SCIENCES (GENERAL)  (9)
  • LUNAR AND PLANETARY EXPLORATION  (2)
  • 1
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    Beta structures of alternating polypeptides and their possible prebiotic significance (1975)
    In:  Other Sources
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    Publication Date: 2011-08-16
    Description: A survey of the commonest amino acids formed in prebiotic conditions suggests that the earliest form of genetic coding may have specified polypeptides with a strong tendency to form stable beta-sheet structures. Poly(Val-Lys), like other polypeptides in which hydrophobic and hydrophilic residues alternate, tends to form beta structures. It is shown that bilayers with a hydrophobic interior and a hydrophilic exterior may be present in aqueous solution.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Nature; 256; July 31
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  • 2
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    Template-directed synthesis on the pentanucleotide CpCpGpCpC (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Experiments in which CpCpGpCpC is used as a template to facilitate the co-oligomerization of 2-MeImpG and 2-MeImpC are described. It is shown that 3' to 5' prime-linked pGpGpCpGpG, whose sequence is complementary to that of the template, is substantially the most adundant pentameric product of the template-directed reaction. The yield of pGpGpCpGpG is never large (less than 20 percent), presumably becauase off-template reactions consume template-directed products. Thus pGpGpCpGpG is converted to the various isomers of G5C and G4C2 by off-template terminal addition of G or C. The 3' to 5' isomer of GpG is elongated on the template to give GpGpC, GpGpCpG, and GpGpCpGpG, while the 2' to 5' isomer does not initiate the synthesis of detectable amounts of longer oligomers.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Journal of Molecular Biology (ISSN 0022-2836); 178; 669-676
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  • 3
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    Condensation of activated diguanylates on a Poly/C/ template (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The metal-ion catalysis of the oligomerization of activated diguanylate isomers on a polycytidylic acid template is studied in an investigation of possible early prebiotic polynucleotide replication mechanisms. The 5'-imidazolides of diguanylates linked 2' to 5' or 3' to 5' were reacted with polyC in a 1-methylimidazole or a 2,6-lutidine buffer in the presence of a Zn(+2) or a Pb(+2) catalyst, and reaction products were determined by paper chromatography, paper electrophoresis and liquid chromatography. In the lutidine buffer, the presence of both the Zn(+2) catalyst and the polyC template is found to result in the production of 3'-5' linked oligomers with up to 10 diguanylate units, and from diguanylates in the presence of the monomer. In the reactions conducted in the 1-methylimidazole buffer, the addition of Pb(+2) is found to lead to less marked increases in oligomerization in the presence of template, with approximately equal proportions of 2'-5' and 3'-5' oligomers formed from the 2'-5' substrate and mainly 3'-5' bonds from the 3'-5' linked dimer.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Journal of Molecular Evolution; 17; Aug. 198
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  • 4
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    Synthesis of oligoguanylates on oligocytidylate templates (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The influence of template length in the self-condensation of guanosine 5'-phosphorimidazole in the presence of oligocytidylate templates is investigated. Reactions were carried out with cyclic cytidine 2',3'-phosphate, oligo- or polyC, and radioactively labeled guanosine 5'-phosphorimidazolide in the presence of Zn(+2) or Pb(+2) catalyst; product yields were determined by paper chromatography, thin-layer chromatography, and high-performance liquid chromatography. In the absence of a catalytic metal or in the presence of Pb(+2), a significant template effect is observed starting with the cytidine dimer and increasing in yield up to the hexamer template. Oligomers longer than the template are observed, and are predominantly 2'-5' linked in the presence of Pb(+2) and of mixed linkages in the uncatalyzed reaction. With the zinc ion as the catalyst, the template effect is first observed with the pentamer and is maximal with the heptamer. Products are predominantly 3'-5', and only a small proportion of them are longer than the template. The importance of the demonstrated formation of molecules with up to 10 guanosine units from oligocytidines as short as the dimer on the primitive earth is noted.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Journal of Molecular Evolution; 17; Aug. 198
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  • 5
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    Self-condensation of activated dinucleotides on polynucleotide templates with alternating sequences (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Substantial quantities of the alternating polymers poly(U-G) and poly(C-A) have been prepared and used as templates for the self-condensation of ImpApC, ImpCpA, ImpGpU and ImpUpG. It is found that the condensation of ImpGpu and ImpUpG on poly(C-A) is efficient, the condensation of ImpCpA on poly(U-G) is moderately efficient, while the condensation of ImpApC on poly(U-C) proceeds poorly. In many cases, the product is predominantly 3'-5'-linked. These reactions demonstrate unequivocally, for the first time, that template-directed reactions occur in double-helical structures. Furthermore, they describe for the first time a pair of reactions in which each of two complementary polymers facilitates the synthesis of the other. The prebiotic significance of these findings is discussed.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Journal of Molecular Evolution; 14; Dec. 197
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  • 6
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    Non-enzymatic template-directed synthesis on RNA random copolymers - Poly(C, U) templates (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Random copolymer templates containing cytosine and uracil in ratios of 3:1 and 1:1 are used to explore the optimum conditions for efficient synthesis of guanine and adenine-containing oligonucleotides. The experimental procedure is described, including the preparation of mononucleoside 5'-phospho-2-methylimidazolides and random copolymers, the template-directed oligomerization, the removal and reintroduction of mononucleotides in interrupted reactions, the determination of oligomerization efficiency, the alkaline and enzymatic hydrolysis of reaction products, and the column chromatography. Results are presented and discussed for the dependence of adenine incorporation on the formation of short oligo(G)s, optimization of incorporation efficiencies by adjusting monomer concentrations, the characterization of oligomeric product distribution, and the regiospecificity of adenine incorporation. The prebiotic significance of the results is assessed.
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Journal of Molecular Biology (ISSN 0022-2836); 176; 279-306
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  • 7
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    The search for organic substances and inorganic volatile compounds in the surface of Mars (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A total of four Martian samples, one surface and one subsurface sample at each of the two Viking landing sites, Chryse Planitia and Utopia Planitia, have been analyzed for organic compounds by a gas chromatograph-mass spectrometer. In none of these experiments could organic material of Martian origin be detected at detection limits generally of the order of parts per billion and for a few substances closer to parts per million. The evolution of water and carbon dioxide, but not of other inorganic gases, was observed upon heating the sample to temperatures of up to 500 C. The absence of organic compounds seems to preclude their production on the planet at rates that exceed the rate of their destruction. It also makes it unlikely that living systems that behave in a manner similar to terrestrial biota exist, at least at the two Viking landing sites.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research; 82; Sept. 30
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  • 8
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    Search for organic and volatile inorganic compounds in two surface samples from the Chryse Planitia region of Mars (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Two surface samples collected from the Chryse Planitia region of Mars were heated to temperatures up to 500 C, and the volatiles that they evolved were analyzed with a gas chromatograph-mass spectrometer. Only water and carbon dioxide were detected. This implies that organic compounds have not accumulated to the extent that individual components could be detected at levels of a few parts per billion by weight in the samples. Proposed mechanisms for the accumulation and destruction of organic compounds are discussed in the light of this limit.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 194; Oct. 1
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  • 9
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    Prebiotic peptide-formation in the solid state. III - Condensation reactions of glycine in solid state mixtures containing inorganic polyphosphates (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Journal of Molecular Evolution; 6; Nov. 4
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  • 10
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    Prebiotic peptide-formation in the solid state. II - Reaction of glycine with adenosine 5 prime-triphosphate and P1, P2-diadenosine-pyrophosphate (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Keywords: LIFE SCIENCES (GENERAL)
    Type: Journal of Molecular Evolution; 6; Nov. 4
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