Conceptual image of meteoroids delivering nuclear bases to ancient Earth. Nucleobases are represented by structural diagrams with hydrogen atoms such as white spheres, carbon as black, nitrogen as blue, and oxygen as red. Credit: NASA Goddard / CI Lab / Dan Gallagher
Using new analysis, scientists have just discovered the last two of the five DNA and RNA information units that have not yet been found in meteorite samples. While the formation of DNA in a meteorite is unlikely, this finding indicates that these genetic parts are available for delivery and could contribute to the development of training molecules on early Earth. The discovery, made by an international team of NASA researchers, adds to the evidence that chemical reactions in asteroids can produce some of the building blocks of life that could be delivered to ancient Earth by meteorites or perhaps falling dust.
All DNA and RNA, which contains instructions for building and managing every living thing on Earth, contains five information components called nucleobases. So far, scientists searching for alien samples have found only three of the five. However, a recent analysis by a team of scientists led by Associate Professor Yasuhiro Oba of Hokkaido University in Hokkaido, Japan, has identified the last two nucleobases that have escaped scientists before.
Nucleosides belong to classes of organic molecules called purines and pyrimidines, which have a great variety. However, it remains a mystery why no more species have been found in meteorites so far.
“I wonder why purines and pyrimidines are exceptional in that they don’t show structural diversity in carbon meteorites, unlike other classes of organic compounds such as amino acids and hydrocarbons,” said Oba, lead author of an article for the study published today (April 26, 2022). .) in the journal Nature Communications. “Because purines and pyrimidines can be synthesized in an alien environment, as shown by our own study, a wide variety of these organic molecules can be expected to be found in meteorites.
“We now have evidence that the full range of nucleobases used in life today may have been available on Earth when life came into being,” said Danny Glavin, co-author of the article at NASA’s Space Flight Center in Greenbelt, Maryland.
This newly discovered pair of nucleobases, cytosine and thymine, were elusive in previous analyzes, probably due to their more delicate structure, which may have degraded when scientists had previously extracted samples. In earlier experiments, scientists created something like “meteorite tea” by placing meteorite beads in a hot bath to leave the sample extract molecules in solution and then analyzing the molecular composition of the alien broth.
“We are studying these aqueous extracts because they contain good things, ancient organic molecules that could be key building blocks to the origin of life on Earth,” Glavin said.
Because of how delicate these two nucleobases are, the team was initially skeptical of seeing them in the samples. But two factors may have contributed to the new discovery: first, the team used cold water to extract the compounds instead of hot formic acid – which is very reactive and could destroy these fragile molecules in previous samples. Second, more sensitive assays have been used that can capture smaller amounts of these molecules.
“This group has driven a technique that looks more like cold brewing than hot tea and is able to extract more delicate compounds,” said Jason Dworkin, co-author of the NASA Goddard article. “I was amazed to see cytosine, which is very fragile.”
The discovery does not provide a smoking gun about whether life on Earth received help from space or originated exclusively in prebiotic soup in early childhood on the planet. But completing the set of nucleobases that make up life today, in addition to other molecules found in the sample, gives scientists trying to understand the beginnings of life more compounds to experiment with in the lab.
“This adds more and more pieces; “Meteorites have been found to have sugars and bases,” Dworkin said. “It is exciting to see progress in the creation of the fundamental molecules of biology from space.”
This analysis not only adds to the kit for those who model the beginning of life on Earth, but also provides evidence of a concept for a more efficient technique for extracting information from asteroids in the future, especially from Benu’s samples, which are making their way to Earth next year through NASA’s OSIRIS-REx mission.
Reference: “Identification of the Great Diversity of Extraterrestrial Purine and Pyrimidine Nucleobases in Carbon Meteorites” by Yasuhiro Oba, Yoshinori Takano, Yoshihiro Furukawa, Toshiki Koga, Daniel P. Glavin, Jason P. Dworkin and Hiroshi Naralka. s41467-022-29612-x
The study was supported by JSPS KAKENHI Grant Numbers JP21H04501, JP21H05414, JP20H02019, 21KK0062, 21J00504, JP20H00202 and JP20H05846; NASA Institute of Astrobiology Award 13-13NAI7-0032 from the Goddard Center for Astrobiology, NASA’s Godardard Foundation’s Fundamental Laboratory Research Work (FLaRe) Internal Funding Program for Scientists, and a grant from the Goddard Foundation Simmons (SCOL7 Award 3024). This study was conducted in accordance with a joint project to promote research at the Institute of Low Temperature Science, University of Hokkaido (21G008).
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