Scientists have taken a major step towards solving one of biology’s deepest mysteries: how two pieces of life’s essential molecules first came together more than four billion years ago.
Proteins, constructed from chains of amino acids, are the workhorses of life, comprising tissues and performing numerous functions throughout organisms. But they can’t pass on the instructions for making themselves.
That job falls to RNA, which acts as the messenger and translator of genetic information in all living cells today.
The mystery lies in how these two very different kinds of molecules first became linked, setting in motion the chain of events that led to the genetic code and, eventually, to us.
“RNA molecules communicate information between themselves in a highly predictable and extremely effective way, but RNAs do not inherently communicate with the amino acids that they need to control in protein synthesis,” senior author of the new study detailing the findings, Prof Matthew Powner, told BBC Science Focus.
“So how and why these two molecules first came to be linked has been an open and unresolved question for decades.”
Previous attempts to recreate this chemistry in the lab ran into roadblocks. Amino acids tended to react with each other rather than RNA, and unstable conditions in water led to the reactions breaking down.
Powner’s team took a different approach. By attaching amino acids to a sulphur-bearing chemical group called a thioester – a high-energy link that cells still use today – the team found the molecules reacted spontaneously and selectively with RNA.
Remarkably, the natural structure of RNA helped guide the amino acids to the correct location at the end of the RNA strand, exactly where they need to be attached for protein synthesis.
This offers a plausible chemical route for one of life’s most fundamental processes to have started without first developing more complex catalysts, like enzymes.
“These molecules are all very simple and all likely to have existed on the early Earth,” Powner said.
While conditions would have been too dilute in the oceans for these early reactions to get going, nutrient-rich pools, ponds, and lakes could have provided a perfect melting pot.
The work also bridges two long-standing hypotheses for life’s beginnings: the ‘RNA world’, which sees RNA as the key driver, and the ‘thioester world’, in which high-energy thioesters powered early metabolism.
For Powner, the next challenge is clear: he wants to “elucidate the origins of life’s universal genetic code”. From there, scientists can begin to figure out exactly how and where life began on our planet.
“Scientists will build an experimentally validated set of reactions which can build a ‘cell’,” Powner said.
These cells will be able not only to evolve, but reveal the origin of life's universal structures and how they're organised.
“These reactions will provide the information that is required to rationally evaluate how and where life began on Earth.”
Read more:
- Here’s why scientists don’t know how life on Earth began
- Strange microscopic lightning may have kickstarted life on Earth
- Here's how scientists are rewriting the origin story of Earth & life itself
About our expert
Matthew Powner is a professor of organic chemistry at University College London. His research centres on chemistry associated with the origin of life, and, along with his research group, Powner has made contributions in the areas of nucleic acid and amino acid chemistry, protometabolic networks, ribozymes, lipids, crystal engineering, green chemistry, catalysis and photochemistry.