Differential adsorption of nucleic acid bases: Relevance to the origin of life

Abstract

The adsorption of organic molecules onto the surfaces of inorganic solids has long been considered a process relevant to the origin of life. We have determined the equilibrium adsorption isotherms for the nucleic acid purine and pyrimidine bases dissolved in water on the surface of crystalline graphite. The markedly different adsorption behavior of the bases describes an elutropic series: guanine > adenine > hypoxanthine > thymine > cytosine > uracil. We propose that such differential properties were relevant to the prebiotic chemistry of the bases and may have influenced the composition of the primordial genetic architecture.T he purine and pyrimidine coding elements of nucleic acids are products of putative prebiotic chemistries that invoke cyanide (1, 2) and have been synthesized in reactions that also yield amino acids (3). The prebiotic availability of these compounds supports the RNA World Hypothesis (4) for the origin of life, which presupposes that the first living system was a polymer(s) of catalytic RNA capable of self-replication that subsequently evolved the ability to encode more versatile peptide catalysts. RNA can act as both information carrier and catalyst (5) and, in the laboratory, can be coerced into different catalytic functions through directed Darwinian evolution (6).Despite these properties, there are severe difficulties with the de novo appearance of RNA, and, even in the most optimistic scenario, information-bearing molecule(s) capable of selfreplication must have first formed fortuitously from an astronomical range of possibilities (7). Although RNA-mediated catalysis and the nonenzymic polymerization of nucleotides (8,9) are well demonstrated, nucleic acid structure incorporates carbohydrate moieties. Formaldehyde, a seemingly ubiquitous compound, is regarded as the most plausible precursor of carbohydrates; however, cyanohydrin (glyconitrile) is the major highly stable product of reactions between formaldehyde and cyanide, withdrawing the latter from being a putative source of bases and amino acids (10). The recovery of nonbiogenic amino acids and bases from extraterrestrial debris (11) suggests the spatial-temporal separation of formaldehyde and cyanide. Life may have been initiated in the absence of carbohydrates, and it has been proposed that modern biology was preceded by a non-nucleic acid informational architecture (12, 13).Aperiodicity is required to convey information (14), and it has been demonstrated that aperiodic structures can self-assemble from aqueous mixtures of purine and pyrimidine bases adsorbed onto the surface of an uncharged inorganic crystalline mineral (15). The spontaneous formation of such structures suggests the existence of an organic, nonpolymeric informational architecture that may have had relevance to the origin of life.The adsorption of organic molecules onto inorganic solids has long been considered a relevant prebiotic process (16). The purine and pyrimidine bases adsorb spontaneously from aqueous media onto inorganic solids and have been observed o...

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“…Na literatura está descrita a adsorção sobre minerais de adenosina mono ou di ou tri fosfato (AMP, ADP, ATP, respectivamente), bases de ácidos nucléi-cos, cianeto, etc [15][16][17][18][19][20][21] . A formação de biopolímeros também está descrita, sendo que peptídeos e polinucleotídeos são os mais comumente estudados [22][23][24][25] .…”

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