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An international team of scientists from Japan and the United States has found ribose and other bioessential sugars in two primitive meteorites, NWA 801 and Murchison.
A model of the molecular structure of ribose and an image of the Murchison meteorite. Image credit: Yoshihiro Furukawa.
Sugars are indispensable molecules for life, working along essential metabolic pathways and as constituents of sugar phosphate backbone of genetic molecules.
Ribose is particularly essential as a building block of RNA, which could have both stored information and catalyzed reactions in primitive life on Earth.
“Other important building blocks of life have been found in meteorites previously, including amino acids (components of proteins) and nucleobases (components of DNA and RNA), but sugars have been a missing piece among the major building blocks of life,” said Dr. Yoshihiro Furukawa, a researcher in the Department of Earth Science at Tohoku University.
“The research provides the first direct evidence of ribose in space and the delivery of the sugar to Earth. The extraterrestrial sugar might have contributed to the formation of RNA on the prebiotic Earth which possibly led to the origin of life.”
“It is remarkable that a molecule as fragile as ribose could be detected in such ancient material,” said Dr. Jason Dworkin, a scientist in the Solar System Exploration Division at NASA’s Goddard Space Flight Center.
“These results will help guide our analyses of pristine samples from primitive asteroids Ryugu and Bennu, to be returned by JAXA’s Hayabusa 2 and NASA’s OSIRIS-REx spacecraft.”
“The sugar in DNA (2-deoxyribose) was not detected in any of the meteorites analyzed in this study,” said Dr. Danny Glavin, also from the Solar System Exploration Division at NASA’s Goddard Space Flight Center.
“This is important since there could have been a delivery bias of extraterrestrial ribose to the early Earth which is consistent with the hypothesis that RNA evolved first.”
The study authors analyzed powdered samples of three carbonaceous chondrites — NWA 801, Murchison and NWA 7020 — using gas chromatography mass spectrometry, which sorts and identifies molecules by their mass and electric charge.
They found that the abundances of ribose, arabinose, xylose, and lyxose ranged from 2.3 to 11 parts per billion in NWA 801 and from 6.7 to 180 parts per billion in Murchison.
Since Earth is awash with life, they had to consider the possibility that these sugars simply came from contamination by terrestrial life.
Multiple lines of evidence indicate contamination is unlikely, including isotope analysis.
Isotopes are versions of an element with different mass due to the number of neutrons in the atomic nucleus. For example, life on Earth prefers to use the lighter variety of carbon (12C) over the heavier version (13C). However, the carbon in the meteorite sugars was significantly enriched in the heavy 13C, beyond the amount seen in terrestrial biology, supporting the conclusion that it came from space.
The researchers now plan to analyze more meteorites to get a better idea of the abundance of the extraterrestrial sugars.
They also plan to see if the extraterrestrial sugar molecules have a left-handed or right-handed bias.
The findings were published in the Proceedings of the National Academy of Sciences.
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Yoshihiro Furukawa et al. Extraterrestrial ribose and other sugars in primitive meteorites. PNAS, published online November 18, 2019; doi: 10.1073/pnas.1907169116
