Conceptual image of meteoroids delivering nucleobases to ancient Earth. The nucleobases are represented by structural diagrams with hydrogen atoms as white spheres, carbon as black, nitrogen as blue and oxygen as red. Credit: NASA Goddard/CI Lab/Dan Gallagher
Using new analyses, scientists have just found the last two of the five informational units of DNADNA, or deoxyribonucleic acid, is a molecule composed of two long strands of nucleotides that coil around each other to form a double helix. It is the hereditary material in humans and almost all other organisms that carries genetic instructions for development, functioning, growth, and reproduction. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>DNA and RNARibonucleic acid (RNA) is a polymeric molecule similar to DNA that is essential in various biological roles in coding, decoding, regulation and expression of genes. Both are nucleic acids, but unlike DNA, RNA is single-stranded. An RNA strand has a backbone made of alternating sugar (ribose) and phosphate groups. Attached to each sugar is one of four bases—adenine (A), uracil (U), cytosine (C), or guanine (G). Different types of RNA exist in the cell: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>RNA that had yet to be discovered in samples from meteorites. While DNA formation in a meteorite is unlikely, this discovery demonstrates that these genetic pieces are available for delivery and could have contributed to the development of the instructional molecules on early Earth. The discovery, made by an international team with NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. It's vision is "To discover and expand knowledge for the benefit of humanity."” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>NASA researchers, adds to evidence that chemical reactions in asteroids can produce some of the building blocks of life, which could have been delivered to ancient Earth by meteorite impacts or perhaps the infall of dust.
All DNA and RNA, which contains the instructions to build and operate every living being on Earth, contains five informational components, called nucleobases. Until now, scientists scouring extraterrestrial samples had only found three of the five. However, a recent analysis by a team of scientists led by Associate Professor Yasuhiro Oba of Hokkaido UniversityFounded in 1876 as Sapporo Agricultural College, Hokkaido University (Hokkaidō daigaku or Hokudai) is a Japanese national university in Sapporo, Hokkaido. It was selected as a Top Type university of Top Global University Project by the Japanese government.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Hokkaido University, Hokkaido, Japan, identified the final two nucleobases that had eluded scientists before.
Nucleobases belong to classes of organic molecules called purines and pyrimidines, which have a wide variety. However, it remains a mystery why more types haven’t been discovered in meteorites so far.
“I wonder why purines and pyrimidines are exceptional in that they do not show structural diversity in carbonaceous meteorites unlike other classes of organic compounds such as amino acids<div class="cell text-container large-6 small-order-0 large-order-1">
<div class="text-wrapper"><br />Amino acids are a set of organic compounds used to build proteins. There are about 500 naturally occurring known amino acids, though only 20 appear in the genetic code. Proteins consist of one or more chains of amino acids called polypeptides. The sequence of the amino acid chain causes the polypeptide to fold into a shape that is biologically active. The amino acid sequences of proteins are encoded in the genes. Nine proteinogenic amino acids are called "essential" for humans because they cannot be produced from other compounds by the human body and so must be taken in as food.<br /></div>
</div>” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>amino acids and hydrocarbons,” said Oba, lead author of a paper about the research that was published today (April 26, 2022) in the journal Nature Communications. “Since purines and pyrimidines can be synthesized in extraterrestrial environments, as has been demonstrated by our own study, one would expect to find a wide diversity of these organic molecules in meteorites.”
“We now have evidence that the complete set of nucleobases used in life today could have been available on Earth when life emerged,” said Danny Glavin, a co-author of the paper at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
This newly discovered pair of nucleobases, cytosine, and thymine, have been elusive in previous analyses likely because of their more delicate structure, which may have degraded when scientists previously extracted samples. In the earlier experiments, scientists created something of a “meteorite tea,” placing grains of meteorite in a hot bath to let the molecules on the sample extract into the solution and then analyzed the molecular makeup of the extraterrestrial broth.
“We study these water extracts since they contain the good stuff, ancient organic molecules that could have been key building blocks for the origin of life on Earth,” said Glavin.
Because of how delicate these two nucleobases are, the team was initially skeptical to see them in the samples. But two factors may have contributed to the new discovery: first, the team used cool water to extract the compounds instead of hot formic acidAny substance that when dissolved in water, gives a pH less than 7.0, or donates a hydrogen ion.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>acid — which is very reactive and could have destroyed these fragile molecules in previous samples. Second, more sensitive analytics were employed that could pick up on smaller amounts of these molecules.
“This group has managed a technique that is more like cold brew than hot tea and is able to pull out more delicate compounds,” said Jason Dworkin, a co-author of the paper at NASA Goddard. “I was amazed that they had seen cytosine, which is very fragile.”
The finding doesn’t provide a smoking gun as to whether life on Earth got an assist from space or came about exclusively in the prebiotic soup in the planet’s infancy. But completing the set of nucleobases that make up life today, in addition to other molecules found in the sample, gives scientists who are trying to understand the beginning of life more compounds to experiment with in the lab.
“This is adding more and more pieces; meteorites have been found to have sugars and bases now,” Dworkin said. “It’s exciting to see progress in the making of the fundamental molecules of biology from space.”
Not only did this analysis add to the kit for those modeling the inception of life on Earth, it also provides a proof of concept for a more effective technique to extract information from asteroids in the future, especially from the samples of Bennu making their way to Earth in the next year via NASA’s OSIRIS-REx mission.
Reference: “Identifying the wide diversity of extraterrestrial purine and pyrimidine nucleobases in carbonaceous meteorites” by Yasuhiro Oba, Yoshinori Takano, Yoshihiro Furukawa, Toshiki Koga, Daniel P. Glavin, Jason P. Dworkin and Hiroshi Naraoka, 26 April 2022, Nature Communications.
DOI: 10.1038/s41467-022-29612-x
The research was supported by JSPS KAKENHI Grant Numbers JP21H04501, JP21H05414, JP20H02019, 21KK0062, 21J00504, JP20H00202 and JP20H05846; NASA Astrobiology Institute through award 13-13NAI7-0032 to the Goddard Center for Astrobiology, NASA’s Planetary Science Division Internal Scientist Funding Program through the Fundamental Laboratory Research (FLaRe) work package at NASA Goddard, and a grant from the Simons Foundation (SCOL award 302497). This study was conducted in accordance with the Joint Research Promotion Project at the Institute of Low Temperature Science, Hokkaido University (21G008).
Source: SciTechDaily
