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Four billion years ago, the Earth looked very different from today, lifeless and covered by a vast ocean. Over millions of years, in that primordial soup, life emerged. Researchers have long theorized how the molecules came together to cause this transition. Now, Scripps Research scientists have discovered a new set of chemical reactions that use cyanide, ammonia and carbon dioxide, which are thought to be common on early Earth, to generate amino acids and nucleic acids, the building blocks of proteins and DNA .
“We’ve created a new paradigm to explain this shift from prebiotic to biotic chemistry,” says Ramanarayanan Krishnamurthy, Ph.D., associate professor of chemistry at Scripps Research and lead author of the new paper, published July 28. , 2022 in the newspaper Chemistry of nature. “We think the kind of reactions we’ve described are probably what could have happened on the early Earth.”
In addition to giving researchers insight into the chemistry of early Earth, the newly discovered chemical reactions are also useful in certain manufacturing processes, such as generating custom-labeled biomolecules from inexpensive starting materials.
Earlier this year, Krishnamurthy’s group showed how cyanide can enable the chemical reactions that convert prebiotic molecules and water into basic organic compounds necessary for life. Unlike the previously proposed reactions, this one worked at room temperature and in a wide pH range. The researchers wondered if, under the same conditions, there was a way to generate amino acids, the more complex molecules that make up proteins in all known living cells.
In today’s cells, amino acids are generated from precursors called α-keto acids using both nitrogen and specialized proteins called enzymes. Researchers have found evidence that α-keto acids probably existed early in Earth’s history. However, many have hypothesized that before the advent of cellular life, amino acids must have been generated from completely different precursors, aldehydes, rather than α-keto acids, since the enzymes to carry out the conversion did not yet exist. But this idea has led to a debate about how and when the shift from aldehydes to α-keto acids as the key ingredient for making amino acids occurred.
After their success using cyanide to drive other chemical reactions, Krishnamurthy and his colleagues suspected that cyanide, even without enzymes, could also help convert α-keto acids to amino acids. Knowing that nitrogen would be required in some form, they added ammonia, a form of nitrogen that would have been present on early earth. Then, through trial and error, they discovered a third key ingredient: carbon dioxide. With this mixture, they quickly began to see the formation of amino acids.
“We expected it to be quite difficult to figure out, and it turned out to be even simpler than we imagined,” says Krishnamurthy. “If you mix just the keto acid, the cyanide, and the ammonia, it just sits there. As soon as you add carbon dioxide, even in small amounts, the reaction speeds up.”
Because the new reaction is relatively similar to what happens inside cells today, except that it is driven by cyanide instead of a protein, it seems more likely that it was the source of early life, rather than of dramatically different reactions, the researchers say. The research also helps bring together two sides of a long-standing debate about the importance of carbon dioxide to early life, concluding that carbon dioxide was key, but only in combination with other molecules.
In the process of studying their chemical soup, Krishnamurthy’s group discovered that a byproduct of the same reaction is orotate, a precursor to the nucleotides that make up DNA and RNA. This suggests that the same primordial soup, under the right conditions, could have given rise to a large number of molecules necessary for the key elements of life.
“What we want to do next is to continue to investigate what kind of chemistry can emerge from this mixture,” says Krishnamurthy. “Can amino acids start to form small proteins? Could one of these proteins come back and start acting as an enzyme to make more of these amino acids?”
In addition to Krishnamurthy, the authors of the study, “Prebiotic Synthesis of α-Amino Acids and Orotate from α-Keto Acids Enhances Transition to Existing Metabolic Pathways,” are Sunil Pulletikurti, Mahipal Yadav and Greg Springsteen.
Novel role of cyanide in early Earth and the search for extraterrestrial life More information: Ramanarayanan Krishnamurthy, Prebiotic synthesis of α-amino acids and orotate from α-ketoacids enhances transition to existing metabolic pathways, Chemistry of nature (2022). DOI: 10.1038/s41557-022-00999-w. www.nature.com/articles/s41557-022-00999-w Provided by The Scripps Research Institute
Citation: Scientists discover new chemical reactions ‘origins of life’ (2022, July 28) Retrieved July 28, 2022 from
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