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Living building blocks may not have originated on this planet



  Ultra-high vacuum reaction chamber

An interior of an ultra-high vacuum reaction chamber that simulates chemical reactions in an interstellar cloud environment. Credit: Hokkaido University

Experiment shows that one of the basic units of life – nucleobases – could occur in giant gas clouds crossed between stars.

Basic building blocks of DNA – compounds called nucleobases – were first discovered in a simulated environment, imitating gaseous clouds, which were crossed by stars. The finding published in the journal Nature Communications brings us closer to understanding the origin of life on Earth.

"This result could be key to unraveling fundamental questions about humanity, such as what organic compounds exist during the formation of the solar system and how they contributed to the birth of life on Earth," says Yasuhiro Oba of the Institute

Scientists have already discovered some of the major organic molecules needed to get started in comets, asteroids and interstellar molecular clouds: giant gaseous clouds scattered between the stars. These molecules are thought to have been able to reach the Earth through meteoric effects about four billion years ago, providing key ingredients for a life-giving chemical cocktail. Learning how these molecules form is vital to understanding the origin of life. [19659005] The basic structural unit of DNA and RNA is called nucleotide and consists of a nucleobase, a sugar and a phosphate group. Previous studies simulating the expected conditions in interstellar molecular clouds have found the presence of sugar and phosphates, not the nucleobases.

  Nucleobases found in a simulated interstellar cloud environment

The major nucleobases found in a simulated interstellar cloud environment. Credit: Hokkaido University

Now, Yasuhiro Oba and his colleagues at Hokkaido University, Kyushu University, and Japan's Maritime Science and Technology Agency (JAMSTEC) have used modern analytical methods to detect major nucleobases in a 1965 simulated environment5 ] The team conducts their experiments in an ultra-high vacuum reaction chamber. A gaseous mixture of water, carbon monoxide, ammonia and methanol is continuously fed to the space-powder analogue at -263 ° C. Two deuterium lamps attached to the camera provided vacuum ultraviolet light to cause chemical reactions. The process led to the formation of an ice film on the powder analogue inside the chamber.

  Akira Kuchi, Yasuhiro Oba and Naoki Watanabe

Akira Kuchi (left), Yasuhiro Oba (center) and Naoki Watanabe (right) from the research team at the Institute of Low Temperatures at Hokkaido University. Credit: Hokkaido University

The team uses a high resolution mass spectrometer and a high performance liquid chromatograph to analyze the product formed on the substrate after warming it to room temperature. Recent advances in these technological tools have enabled them to detect the presence of nucleobases cytosine, uracil, thymine, adenine, xanthine and hypoxanthin. They also discovered amino acids, which are the building blocks of proteins and several types of dipeptide, or dimer of amino acid in the same product.

The team suspects that past experiments simulating an interstellar cloud molecule would create nucleobases, but the analytical tools used are not sensitive enough to detect them in complex mixtures.

"Our findings show that the processes we reproduce could lead to the formation of molecular precursors to life," says Yasuhiro Oba. "The results could improve our understanding of the early stages of chemical evolution in space." Nature Communications .
doi: 10.1038 / s41467-019-12404-1


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