Three of the five nucleobases — molecular subcomponents of information-bearing nucleotides which make up our genetic code — likely came from space. But the origins of two key components of RNA and DNA remain a mystery, say two McMaster University astrobiologists.
In a paper just published in the journal Astrobiology, co-authors Ben K.D. Pearce and Ralph Pudritz report that they are able to account for the meteoritic origins of the genetic nucleobases adenine, guanine, and uracil. But after painstaking models to simulate the creation of the five nucleobase building blocks of RNA and DNA — the molecular data-storing templates for life as we know it — they remain puzzled over the origins of cytosine and thymine.
“Imagine an asteroid collision occurs, fragmenting the asteroid and sending fragments on trajectories that will intercept early Earth,” said Pearce. “These nucleobases would fall to the surface as meteorites, and thaw.”
If a meteorite fell into, say, a pond, he explains, the nucleobases could seep from the pores of the meteorite into the pond water, and possibly react with other chemicals to form nucleotides, and then RNA.
However, no nucleobases have yet been detected on the surfaces of ices in space, the authors note.
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