The newly proposed mechanism for the formation of adenine gives a
clear picture of how it could have become one of the building blocks
essential for the formation of DNA. The research was published today
in the print version of the Proceedings of the National Academies of
Science. Schleyer�s coworkers were Ph. D. candidate Debjani Roy, the
first author of the paper, and Katayoun Najafian, his former student
from Iran.
DNA is the nucleic acid blueprint of life that is passed on from
generation to generation. First isolated in 1869 from the pus of
discarded surgical bandages by Friedrich Miescher, a Swiss doctor,
DNA�s double helix structure was solved by Watson and Crick in 1953.
DNA is shaped somewhat like a twisted ladder with the rungs anchored
by matching pairs of only four bases: adenine, guanine, cytosine and
thymine.
The UGA chemists focused on adenine because of its relative prevalence
on Earth and its formation in the dark in from simple components.
Along with other fundamental building blocks, adenine has even been
detected extraterrestrially. Still, the vast distance between the
smaller molecules required to form adenine in outer space precludes
its formation, unless some nucleation centers, like specks of
interstellar dust, are present.
�Numerous experiments have demonstrated that amino acids, nucleotides,
carbohydrates and other essential compounds form under simulated
primitive Earth conditions,� the authors write in their paper.
Remarkably, a solution of highly poisonous cyanide in ammonia, frozen
solid in a refrigerator for 25 years, produced adenine, a necessary
component of life. A substantial amount of adenine also was formed in
a high-temperature experiment designed to simulate early volcano-like
environments. But the question is how.
The Georgia researchers arrived at an answer by solving a series of
key riddles. They worked out the processes in which five cyanide
molecules might combine to form adenine under terrestrial conditions.
Their predictions are based on extensive computations of sequences of
reaction steps along possible mechanistic routes.
�Finding a viable, thermodynamically feasible, step-by-step mechanism
that can account for the formation of adenine was far from
straightforward,� the authors said. �Our report provides a more
detailed understanding of some of the chemical process involved in
chemical evolution, and a partial answer to the fundamental question
of molecular biogenesis. Our investigation should trigger similar
investigations of the abiotic formation of the remaining nucleic acid
bases as well as other biologically relevant molecules.�
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