The answer, according to their new work, is likely yes.
"We now have a pathway that goes more or less from the very simple starting materials available in the early Earth to the complex prebiotic molecules you need for the origin of life," said Ramanarayanan Krishnamurthy, a TSRI professor and member of the Skaggs Institute for Chemical Biology.
For decades, scientists have been trying to understand how the first cell originated from inanimate matter—a concept often referred to as the "origin of life." Many biologists believe that the RNA molecule—which has both information storage (like DNA) and activity-performing (like proteins)—may have been the original molecular ancestor that ultimately led to the first living organism. RNA, however, is made of building blocks that are rather hard to come by.
But in a report in the journal Nature Chemistry, Krishnamurthy's team presents new insights that could change the view on how first replicator molecule came about.
Krishnamurthy's lab, along with that of TSRI Professor Matthew Disney and former TSRI postdoc and current University of South Carolina professor Andrew Ellington, has studied the concept that the genetic code could have emerged naturally from a very complex mixture of building blocks. But what they really needed was a simple, realistic explanation of how those original building blocks could have formed in the first place.
"You can't start talking about the origin of life without first considering the origin of the right building blocks," said first author and TSRI graduate student Yunwei Mao. "Fortunately, we have a couple of decades of work telling us what simple building blocks are required to make RNA strands."
One such simple building block is the molecule isocytosine, which in previous research TSRI scientists have shown can assemble spontaneously to form the essential building blocks of genetic molecules, known as nucleotides.
Working closely with Krishnamurthy, Disney and Ellington, Mao and her colleagues have now identified a very plausible explanation of how isocytosine could have arisen on the early Earth. They began by identifying the simplest set of conditions that would allow isocytosine to form by mixing simple components such as hydrogen cyanide in water and subjecting it to ultraviolet (UV) light. Through a series of experiments, they were able show that the key reaction is catalyzed naturally: in essence, the reaction triggers itself after the initial UV light exposure and can go on to generate isocytosine relatively rapidly.
The implications of this finding, Krishnamurthy said, are profound: "It means the building blocks necessary to kick-start a genetic system can, indeed, arise under quite simple and realistic conditions on the early Earth. Now we can envision a scenario where the very simple chemistry that we see in interstellar clouds gives rise to the complexity we see in biology on the Earth."
The researchers note, however, that additional steps must be worked out before their theory could be considered complete. For example, they need to find out how the molecules of isocytosine they generated can be transformed into the ribonucleotides—the building blocks of RNA. Additionally, they want to understand the detailed molecular mechanism that allows the spontaneous formation of genetic information from a complex mixture or organic molecules.
This work was supported by Defense Advanced Research Projects Agency (DARPA) grant W911NF-13-C-0043 and National Institutes of Health grant R01GM078401.
