All Bases in DNA and RNA Are Present in Meteorites

All Bases in DNA and RNA Are Present in Meteorites
All Bases in DNA and RNA Are Present in Meteorites

Five bases, the sources of heredity information found in DNA and RNA, are found in space rocks that fell to Earth over the past century, according to research published April 26 in Nature Communications.

The genetic code for all life on Earth consists of these "nucleobases" (adenine, guanine, cytosine, thymine, and uracil), along with sugars and phosphates. It is still unknown whether the building blocks of life were created in space or on Earth in a hot chemistry-based soup. But the discovery adds to evidence pointing to the beginning of life in space, the researchers claim.
Since the 1960s, researchers have found fragments of adenine, guanine, and other chemical molecules in meteorites. Uracil also showed some signs, but so far cytosine and thymine have eluded researchers.

"We've run out of the whole set of bases found in DNA and RNA and life on Earth, and they're present in meteorites," says astrochemist Daniel Glavin of NASA Goddard Space Flight Center in Greenbelt, Maryland.

Geochemist Yasuhiro Oba of Hokkaido University in Sapporo, Japan, and his collaborators developed a method several years ago to precisely extract, separate, and analyze the various chemical components in liquefied meteorite dust.

Compared to other studies, “our detection method is much more sensitive,” Oba says. Three years ago, using the same method, researchers found ribose, an essential chemical for life, in three meteorites.

Researchers believe chemicals are preserved by using cold water instead of traditional acid in gentler extraction methods. According to Glavin, “we find that this extraction strategy is particularly suitable for these weak nucleobases.” “Instead of brewing hot tea, it's more like a cold brew.”

Using this method, Glavin, Oba and colleagues examined four meteorite samples that appeared decades ago in Australia, Kentucky and British Columbia to determine the abundance of bases and other chemicals important to life. Adenine, guanine, cytosine, uracil, thymine, various molecules bound to these bases, and several amino acids were found and quantified in all four.

Using the same method, the scientists also analyzed chemical abundances in the soil taken from the Australian location and then compared these results to measured meteorite levels. Meteorite values ​​for some compounds found exceed those of the surrounding soil, suggesting that these materials may have entered Earth's atmosphere through these rocks.

However, soil abundance for some chemicals, such as cytosine and uracil, is 20 times greater than for meteorites. This could indicate contamination from the earth, according to cosmochemist Michael Callahan of Boise State University in Idaho.

According to Callahan, "I believe [researchers] have positively identified these chemicals." Yet they "did not provide enough convincing data to convince me that they are indeed extraterrestrials". Callahan had previously worked for NASA, where he and Glavin and other researchers measured organic compounds in meteorites.

However, Glavin et al cite a few specific compounds that have been found to support the idea of ​​an extraterrestrial origin. According to Glavin, the researchers measured more than a dozen chemicals linked to life, including isomers of nucleobases. Isomers and the bases they are attached to have the same chemical structures, but the parts that make up them are arranged differently.
Some of these isomers were discovered by the team in meteorites, but not in soil. “If there was contamination from the soil, we should have found those isomers in the soil as well. And we couldn't find it."

Source: science-astronomy

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