Este blog foi feito para os alunos de Evolução do curso de Ciências Biológicas da Universidade Veiga de Almeida. O responsável é Marcelo Aguiar Costa Lima, Bacharel (UFRJ), Mestre (UFRJ) e Doutor (UFRJ) em Ciências Biológicas, na modalidade Genética.
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terça-feira, 30 de novembro de 2010
SÍNTESE DE NUCLEOTÍDEOS NA ERA PRÉ-BIÓTICA
Pois bem, haviámos comentado em sala sobre o trabalho de Powner et al. (2009) sobre a síntese de pirimidinas.
Nature. 2009 May 14;459(7244):239-42.
Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions.
Powner MW, Gerland B, Sutherland JD.
School of Chemistry, The University of Manchester, Oxford Road, ManchesterM13 9PL, UK.
·Nature. 2009 May 14;459(7244):171-2.
At some stage in the origin of life, an informational polymer must have arisen by purely chemical means. According to one version of the 'RNA world' hypothesis this polymer was RNA, but attempts to provide experimental support for this have failed. In particular, although there has been some success demonstrating that 'activated' ribonucleotides can polymerize to form RNA, it is far from obvious how such ribonucleotides could have formed from their constituent parts (ribose and nucleobases). Ribose is difficult to form selectively, and the addition of nucleobases to ribose is inefficient in the case of purines and does not occur at all in the case of the canonical pyrimidines. Here we show that activated pyrimidine ribonucleotides can be formed in a short sequence that bypasses free ribose and the nucleobases, and instead proceeds through arabinose amino-oxazoline and anhydronucleoside intermediates. The starting materials for the synthesis-cyanamide, cyanoacetylene, glycolaldehyde, glyceraldehyde and inorganic phosphate-are plausible prebiotic feedstock molecules, and the conditions of the synthesis are consistent with potential early-Earth geochemical models. Although inorganic phosphate is only incorporated into the nucleotides at a late stage of the sequence, its presence from the start is essential as it controls three reactions in the earlier stages by acting as a general acid/base catalyst, a nucleophilic catalyst, a pH buffer and a chemical buffer. For prebiotic reaction sequences, our results highlight the importance of working with mixed chemical systems in which reactants for a particular reaction step can also control other steps.
Quentinho do forno da ciência, o grupo investe na avaliação da síntese de purinas em condições plausíveis para a era pré-biótica em um artigo recém publicado!
J Am Chem Soc. 2010 Nov 24;132(46):16677-88. Epub 2010 Nov 2.
Chemoselective multicomponent one-pot assembly of purine precursors in water.
Powner MW, Sutherland JD, Szostak JW.
Howard Hughes Medical Institute and Department of Molecular Biology and Center for Computational and Integrative Biology, Massachusetts General Hospital, 185 Cambridge Street, Boston, Massachusetts 02114, United States, and MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 OQH United Kingdom.
The recent development of a sequential, high-yielding route to activated pyrimidine nucleotides, under conditions thought to be prebiotic, is an encouraging step toward the greater goal of a plausible prebiotic pathway to RNA and the potential for an RNA world. However, this synthesis has led to a disparity in the methodology available for stepwise construction of the canonical pyrimidine and purine nucleotides. To address this problem, and further explore prebiotically accessible chemical systems, we have developed a high-yielding, aqueous, one-pot, multicomponent reaction that tethers masked-sugar moieties to prebiotically plausible purine precursors. A pH-dependent three-component reaction system has been discovered that utilizes key nucleotide synthons 2-aminooxazole and 5-aminoimidazoles, which allows the first divergent purine/pyrimidine synthesis to be proposed. Due to regiospecific aminoimidazole tethering, the pathway allows N9 purination only, thus suggesting the first prebiotically plausible mechanism for regiospecific N9 purination.