The creation of life from non-living molecules is one of science's most perplexing mysteries. Now scientists at Scripps Research have found a new set of chemical reactions that can produce the basic building blocks of life out of materials previously considered to be common in the primordial sea.
The first organisms are supposed to have evolved on Earth billions of years ago, from a nutrient-rich brew known as the primordial soup. Essentially, the molecules in the mixture began reacting with one another until they formed fundamental organic chemicals, such as amino acids, which may then combine to form peptides and proteins and eventually living cells.
That is, of course, a gross oversimplification, and the precise chemical reactions that occurred throughout the process are still unknown. Scientists have tried cooking up their own versions of the primordial soup based on what was thought to be plentiful at the time, subjecting it to various conditions to see what happens and how readily life's precursorswill form.
The Scripps researchers tinkered with their own primordial soup recipe in the new research, and they found a distinct set of chemical reactions using basic components that were almost certainly widespread on early Earth. All it takes is cyanide, ammonia, carbon dioxide, and alpha-keto acids to get the soup cooking.
The sequence of events follows a certain order. The four components have specific purposes. Living cells today use alpha-keto acids as the precursors to create amino acids. Ammonia is required for the conversion process, and it serves as a source of nitrogen. Cyanide converts the ammonia to nitrogen, while carbon dioxide helps to speed things up.
“We were expecting it to be quite difficult to figure this out, and it turned out to be even simpler than we had imagined,” said Ramanarayanan Krishnamurthy, lead author of the study. “If you mix only the keto acid, cyanide and ammonia, it just sits there. As soon as you add carbon dioxide, even trace amounts, the reaction picks up speed.”
This technique is supposed to be how amino acids are generated in living cells, although instead of enzymes, cyanide is used. This simplicity and resemblance to present biological processes suggest that this is a more probable origin of early life than other ideas, which need radically different chemistry.
The chemical mixture also generates orotate as a by-product. Orotate is a precursor to DNA and RNA nucleotides, suggesting that life's essential components could have been generated in this way.
“What we want to do next is continue probing what kind of chemistry can emerge from this mixture,” said Krishnamurthy. “Can amino acids start forming small proteins? Could one of those proteins come back and begin to act as an enzyme to make more of these amino acids?”