Four billion years ago, the Earth looked completely different than it does today, devoid of life and covered by a huge ocean. Over millions of years, in that primordial soup, life arose. Scientists have long theorized how molecules came together to trigger this transition. Now scientists at Scripps Research have discovered a new set of chemical reactions that use cyanide, ammonia and carbon dioxide – all thought to be common on the early Earth – to generate amino acids and nucleic acids, the building blocks of proteins and DNA.
“We’ve come up with a new paradigm to explain this shift from prebiotic to biotic chemistry,” says Ramanarayanan Krishnamurthy, Ph.D., an associate professor of chemistry at Scripps Research, and lead author of the new paper, published July 28. 2022 in the journal Natural chemistry. “We think the kind of reactions we’ve described are probably what could have happened on early Earth.”
In addition to giving researchers insight into the chemistry of the early Earth, the newly discovered chemical reactions are also useful in certain manufacturing processes, such as the generation of specially labeled biomolecules from inexpensive starting materials.
Earlier this year, Krishnamurthy’s group showed how cyanide can activate the chemical reactions that turn prebiotic molecules and water into basic organic compounds required for life. In contrast to 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, more complex molecules that make up proteins in all known living cells.
In cells today, amino acids are generated from precursors called α-keto acids using both nitrogen and specialized proteins called enzymes. Scientists have found evidence that α-keto acids probably existed early in Earth’s history. However, many have assumed that before the advent of cellular life, amino acids must have been generated from completely different precursors, aldehydes, rather than α-keto acids, since enzymes to carry out the conversion did not yet exist. But that idea has led to debate about how and when the transition occurred from aldehydes to α-keto acids as the key ingredient for making amino acids.
After the success of using cyanide to drive other chemical reactions, Krishnamurthy and his colleagues suspected that cyanide, even without enzymes, could also help turn α-keto acids into amino acids. Knowing that nitrogen would be needed in some form, they added ammonia—a form of nitrogen that would have been present on the early Earth. Then, through trial and error, they discovered a third key ingredient: carbon dioxide. With this mixture, they quickly began to see amino acids being formed.
“We expected this to be quite difficult to figure out, and it turned out to be even easier than we imagined,” says Krishnamurthy. “If you just mix the keto acid, cyanide and ammonia, it just sits there. As soon as you add carbon dioxide, even trace amounts, the reaction speeds up.”
Because the new reaction is relatively similar to what happens in cells today — except that it is powered by cyanide instead of a protein — it seems more likely to be the source of early life, rather than drastically different reactions, the researchers say. The research also helps bring together two sides of a long-running debate about the importance of carbon dioxide for 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 the molecules required for the key elements of life.
“What we want to do next is continue to investigate what kind of chemistry might emerge from this mixture,” says Krishnamurthy. “Can amino acids start to form small proteins? Can one of these proteins come back and start acting as an enzyme to make more of these amino acids?”
In addition to Krishnamurthy, authors of the study, “Prebiotic Synthesis of α-Amino Acids and Orotate from α-Ketoacids Potentiates Transition to Extant Metabolic Pathways,” are Sunil Pulletikurti, Mahipal Yadav and Greg Springsteen.
New role for cyanide in early Earth and the search for extraterrestrial life
Ramanarayanan Krishnamurthy, Prebiotic synthesis of α-amino acids and orotate from α-ketoacids potentiates switch to existing metabolic pathways, Natural chemistry (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 ‘origin of life’ chemical reactions (2022, July 28) Retrieved July 28, 2022, from https://phys.org/news/2022-07-scientists-life-chemical-reactions.html
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