Exactly how life sprung out of non-living matter is one of biology's biggest mysteries. But with continued research into our own origin story, it's starting to seem like life on early Earth was just itching to be born. In new research from Georgia Tech and the Scripps Research Institute, scientists cooked up a "primordial soup" and found that some of the crucial building blocks of life spontaneously stacked themselves in a surprisingly efficient way.
Currently, our best theory for how life arose revolves around the primordial soup, a nutrient-rich fluid full of chemicals that reacted with each other to create molecules like RNA and amino acids. These in turn go on to form proteins, cells, and other important pieces of life.
For this study, the researchers recreated this primordial soup with ingredients that could have reasonably been around on Earth at the time. That included some amino acids that life uses – lysine, arginine and histidine – as well as three others that life doesn't use. Then, this was placed into water containing hydroxy acids, which help amino acid reactions occur. Finally, the mixture was heated to 85° C (185° F) to mimic mild conditions of the era, and trigger chemical reactions.
The team was testing just how readily amino acids link together under these conditions, particularly how well the biological ones formed fragments that look like early proteins. They anticipated that the non-biological amino acids would get in the way of this process, expecting that they would give lysine in particular a hard time.
But surprisingly, they were wrong. The biological amino acids linked up readily, almost actively excluding the non-biological ones. Even lysine fit in well, in much the same way as it does today. This was unexpected because they linked through the α-amine, in the core of an amino acid, which is usually less reactive than others.
"We found this high preference for the inclusion of these biological amino acids and the linkage via the α-amine," says Moran Frenkel-Pinter, first author of the study. "It surprised us that this chemistry favored the α-amine connection found in proteins, even though chemical principles might have led us to believe that the non-protein connection would be favored. The preference for the protein-like linkage over non-protein was about seven to one."
This, the team says, could help explain why life uses only 20 of the 500 or so amino acids that were naturally present on early Earth. These are the ones that link up most readily, forming protein fragments that life could then start working with to get more creative.
"Our idea is that life started with the many building blocks that were there and selected a subset of them, but we don't know how much was selected on the basis of pure chemistry or how much biological processes did the selecting," says Loren Williams, a principal investigator on the study. "Looking at this study, it appears today's biology may reflect these early prebiotic chemical reactions more than we had thought."
The general consensus for the origins of life says that there was probably some kind of energetic catalyst to kick all this off – possibly from volcanic activity or lightning strikes. But this team says that this recipe for life doesn't need that, and could have gotten by with much more gentle conditions. In previous work, the researchers showed how repeated drying and rewetting of the primordial soup could have aided the evolution of life.
The research was published in the journal Proceedings of the National Academy of Sciences.
Source: Georgia Tech