Life on Earth originated in an intimate partnership between the nucleic acids (genetic instructions for all organisms) and small proteins called peptides, according to two new articles from biochemists and biologists. Their ‘peptide-RNA’ hypothesis contradicts the widely-held ‘RNA-world’ hypothesis, which states that life originated from nucleic acids and only later evolved to include proteins.
Co-author Peter Wills, PhD, professor of physics at the University of Auckland, said, “Compared to the RNA-world hypothesis, what we’ve outlined is simply a much more probable scenario for the origin of life. We hope our data and the theory we’ve outlined in these papers will stimulate discussion and further research on questions relevant to the origins of life.”
The two scientists are fully aware that the RNA-world hypothesis still dominates the origin-of-life research field. “That theory is so alluring and expedient that most people just don’t think there’s any alternative,” Carter said. “But we are very confident there is.”
But if RNA world works as well as pop science writers claim, why does there need to be an alternative? Ah, we find out:
Carter and Wills argue that RNA could not kick-start this process alone because it lacks a property they call “reflexivity.” It cannot enforce the rules by which it is made. RNA needed peptides to form the reflexive feedback loop necessary to lead eventually to life forms.
We don’t hear that often about RNA world, the five-star origin of life theory. We hear it because Wills and Carter are promoting a new, untested theory.
At the heart of the peptide-RNA theory are enzymes so ancient and important that their remnants are still found in all living cells and even in some sub-cellular structures, including mitochondria and viruses. There are 20 of these ancient enzymes called aminoacyl-tRNA synthetases (aaRSs).
The text in support of RNA-peptide world is littered with the familiar, suspicious “would have”’s but hey, meanwhile,
Carter and Wills developed two additional reasons why a pure RNA biology of any significance was unlikely to have predated a peptide-RNA biology. One reason is catalysis — the acceleration of chemical reactions involving other molecules.
Catalysis is a key feature of biology that RNA cannot perform with much versatility. In particular, RNA enzymes cannot readily adjust their activities to temperature changes likely to have happened as the earth cooled, and so cannot perform the very broad range of catalytic accelerations that would have been necessary to synchronize the biochemistry of early cell-based life forms. Only peptide or protein enzymes have that kind of catalytic versatility, Carter said.
Secondly, Wills has shown that impossible obstacles would have blocked any transition from a pure-RNA world to a protein-RNA world and onward toward life.
“Such a rise from RNA to cell-based life would have required an out-of-the-blue appearance of an aaRS-like protein that worked even better than its adapted RNA counterpart,” Carter said. “That extremely unlikely event would have needed to happen not just once but multiple times — once for every amino acid in the existing gene-protein code. It just doesn’t make sense.” Paper 1. (paywall) – Charles W Carter, Peter R Wills. Interdependence, Reflexivity, Fidelity, Impedance Matching, and the Evolution of Genetic Coding. Paper 2. (paywall) Peter R. Wills, Charles W. Carter. Insuperable problems of the genetic code initially emerging in an RNA world. Biosystems, 2017; DOI: 10.1016/j.biosystems.2017.09.006 More.
“It just doesn’t make sense?” RNA world was not marketed so widely because it made sense but because it was easy to explain to an educated public. And RNA-peptide world may be fronted in pop science literature on the same basis. It’s somewhat like an authoritarian dictatorship where the People’s Hero disappears overnight, is denounced as a Traitor in the morning, and a new Hero put in place.
So are Wills and Carter proponents of self-organization, like James Shapiro? A friend draws our attention to the Biosystems abstract:
Abstract: Differential equations for error-prone information transfer (template replication, transcription or translation) are developed in order to consider, within the theory of autocatalysis, the advent of coded protein synthesis. Variations of these equations furnish a basis for comparing the plausibility of contrasting scenarios for the emergence of specific tRNA aminoacylation, ultimately by enzymes, and the relationship of this process with the origin of the universal system of molecular biological information processing embodied in the Central Dogma. The hypothetical RNA World does not furnish an adequate basis for explaining how this system came into being, but principles of self-organisation that transcend Darwinian natural selection furnish an unexpectedly robust basis for a rapid, concerted transition to genetic coding from a peptide·RNA world.
Self-organization does not have wheels because we don’t know why cells self-organize and rocks don’t. But its proponents at least recognize the problem. And we certainly don’t need mre Darwinblather.
See also: Welcome to “RNA world,” the five-star hotel of origin-of-life theories
Self-organization: Can we wring information from matter — shake the bit out of the it?
Natural genetic engineering? Natural popcorn? Or something more important?