Assumptions about Origins of Life Challenged
New research from the UNC School of Medicine has raised important questions about exactly how primitive molecule systems managed to replicate themselves and create life, and offers an intriguing view on how life began.
According to current thought, before life on Earth there was a ‘primordial soup’, a mixture of molecules that began self-replicating and beginning a biochemical process that would lead to the first organisms. How and why this process occurred has been one of science’s enduring mysteries.
Biochemist Charles Carter conducted experiments in which he recreated ancient protein enzymes (Ribonucleic Acid [RNA]) that are assumed to have played a vital role in helping create life on Earth. But his findings challenge the widely-held theory that RNA self-replicated on their own without the aid of proteins and led to life as we know it.
In the early 1980s, researchers developed the “RNA World” hypothesis which maintained that RNA can act as both the blueprints and the chemical catalysts that put those blueprints into action. The implication is that RNA alone triggered the rise of life from a sea of molecules. However, subsequent research found that it would have taken much longer than the age of the universe for RNA molecules to evolve sufficiently to give rise to the vast biological complexity on Earth today. Moreover, there is no proof that such RNA even existed billions of years ago.
Carter, who has been an expert in ancient biochemistry for four decades, took a different approach. Since our genetic code is translated by two super-families of modern-day enzymes, Carter's research team created and superimposed digital three-dimensional versions of the two super-families to see how their structures aligned. Carter found that all the enzymes have virtually identical cores that can be extracted to produce "molecular fossils" he calls Urzymes. The other parts, he said, are variations that were introduced later, as evolution unfolded.
These two Urzymes are as close as scientists have gotten to the actual ancient enzymes that would have populated Earth billions of years ago, and the experiment showed that they were very good at accelerating reactions necessary to translate the genetic code.
"Our results suggest that there were very active protein enzymes very early in the generation of life, before there were organisms," Carter said. "And those enzymes were very much like the Urzymes we've made."
This theory, called the “Peptide-RNA World” scenario maintains that RNA would have contained the instructions for life while peptides would have accelerated key chemical reactions to carry out those instructions.
However, the study leaves open the question of exactly how those primitive systems managed to replicate themselves, something neither the RNA World hypothesis nor the Peptide-RNA World theory can yet explain. So for now, the biological origin of life remains one big mystery still to be solved.