Scripps Research scientists have discovered a new set of chemical reactions that use cyanide, ammonia, and carbon dioxide, all of which were thought to be common on the early Earth, to produce amino acids and nucleic acids, the building blocks of proteins and DNA.
New Chemical Reaction Yields Protein Through the Aid of Cyanide
Ramanarayanan Krishnamurthy, the study's lead author, said they had come up with a new paradigm to explain the shift from prebiotic to biotic chemistry. He said that they thought the kinds of reactions they described were probably what could have happened early on Earth. The newly discovered chemical reactions are useful in certain manufacturing processes, such as generating custom labeled biomolecules from inexpensive starting materials.
Krishnamurthy's group showed in research published in Nature Chemistry earlier this year how cyanide could facilitate the chemical reactions that convert prebiotic molecules and water into the basic organic compounds required for life. This reaction, unlike previous ones, worked at room temperature and across a wide pH range. The researchers wondered if there was a way to generate amino acids, more complex molecules that makeup proteins in all known living cells, under the same conditions.
Today, amino acids are synthesized in cells from α-keto acids using both nitrogen and specialized proteins are known as enzymes. Researchers discovered evidence that α-keto acids existed very early in Earth's history. Many have speculated that before the emergence of cellular life, amino acids must have been produced from completely different precursors, such as aldehydes, rather than α-keto acids because enzymes to carry out the conversion did not yet exist.
However, this idea sparked debate about how and when the key ingredient for amino acid production shifted from aldehydes to α-keto acids. Following their success in driving other chemical reactions with cyanide, Krishnamurthy and his colleagues suspected that cyanide, even in the absence of enzymes, could aid in converting α-keto acids to amino acids. They added ammonia, a form of nitrogen that would have been present on the early Earth because they knew nitrogen would be required in some form. Through trial and error, they then discovered that the third key ingredient is carbon dioxide. They saw amino acids form quickly with this mixture.
"We were expecting it to be quite difficult to figure this out, and it turned out to be even simpler than we had imagined," Krishnamurthy said.
New Study Shows the Importance of Carbon Dioxide in the Origin of Life
The new reaction is more likely to be the origin of early life than vastly different reactions, the researchers say, because it is relatively similar to what happens inside cells today-with the exception that cyanide instead of a protein drives it.
The study also helps to reconcile two opposing viewpoints on the importance of carbon dioxide in early life, concluding that carbon dioxide was important, but only in conjunction with other molecules.
The team discovered orotate, a precursor to nucleotides that make up DNA and RNA, as a byproduct of the same reaction while studying their chemical soup. This implies that, under the right conditions, the same primordial soup could have given rise to many of the molecules required for the key elements of life.
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