Meteorites could have brought all 5 DNA genetic elements to the early Earth

(ORDO NEWS) — Key building blocks of DNA that previous studies have mysteriously failed to detect in meteorites have now been found in space rocks, suggesting that cosmic impacts could have once helped deliver these vital components of life to ancient Earth.

DNA consists of four main building blocks – nucleobases: adenine (A), thymine (T), cytosine (C) and guanine (G). A related DNA molecule, RNA, also uses A, C, and G, but swaps thymine for uracil (U).

Scientists wondering if they could help bring these compounds to Earth have previously searched for nucleobases in space rocks, but so far scientists have only found A and G in space rocks, not T, C or U.

Nucleobases are of two types, known as purines and pyramidins. The nucleobases previously found in meteorites are purines, each consisting of a hexagonal molecule connected to a pentagonal molecule. So far, space rocks lacked pyramidins, which are smaller structures made up of only a hexagonal molecule.

For a long time it remained a mystery why only purines and not pyramidines are found in meteorites. Preliminary laboratory experiments simulating conditions in outer space suggested that purines and pyramidins could be formed during chemical reactions under the influence of light in interstellar molecular clouds, and then these compounds could be released into asteroids and meteorites during the formation of the solar system. Such chemical reactions could also take place directly in space rocks.

Now, scientists have finally found all the pyramidins and purines found in DNA and RNA in meteorites that hit Earth.

“The presence of the five major nucleobases in meteorites could contribute to the emergence of genetic functions even before the emergence of life on the early Earth,” said lead author Yasuhiro Oba, an astrochemist at Hokkaido University in Japan.

The researchers used state-of-the-art analytical techniques, originally developed for use in genetic and pharmaceutical research, to detect tiny amounts of nucleobases, down to parts per trillion. This is at least 10 to 100 times more sensitive than previous methods that have tried to detect pyramidins in meteorites, Ohba said.

The scientists analyzed samples of three carbon-rich, or carbonaceous, meteorites in which, according to previous work, chemical reactions could occur that lead to the formation of nucleobases – the Murchison, Murray and Tagish Lake meteorites.

Scientists have found T, C and U at levels up to several parts per billion in meteorites. These compounds were present at concentrations similar to those predicted by experiments reproducing conditions that existed before the formation of the solar system.

In addition to the crucial compounds T, C, and U, the scientists also found other pyramidins not used in DNA or RNA, further proving the ability of meteorites to carry these compounds.

“Thanks to our results, we can say that nucleobases also show a wide variety in carbonaceous meteorites,” Ohba said.

It remains unclear why there were much fewer pyramidins in these meteorites than purines. Ohba suggested that the clue might be that purines include a pentagonal ring known as imidazole, while pyramidins do not.

Imidazole and similar molecules were found to be much more abundant than pyramidins in these meteorites, suggesting that they could be more easily synthesized through natural chemical reactions. In addition, imidazole can act as a primitive catalyst to drive chemical reactions, such as the formation of purines instead of pyramidines.

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