Life may have sprung up spontaneously from self-organising fragments of DNA-like molecules four billion years ago, a study suggests.
While experts have evidence of single-celled organisms dating back 3.5 to 3.8 billion years, what preceded their evolution remains a mystery.
The research highlights a novel mechanism behind the non-biological origins of nucleic acids, the building blocks of living things.
In the 1980s, scientists discovered that RNA − DNA’s close nucleic acid cousin − was able to alter its own structure. This led to the concept of an ‘RNA world’ in which primordial life consisted of RNA chains capable of duplicating themselves from simpler molecules.
Since then, most origin-of-life experts have come to the conclusion that such RNA chains are too specialised to have been created from random chemical reactions.
Our observations are suggestive of what may have happened on the early earth
Now researchers have demonstrated an alternative scenario. Writing in the journal Nature Communications, they show how the spontaneous self-assembly of tiny DNA fragments into a liquid crystal form can drive the formation of bonds that link short chains of the molecule to form longer ones. This occurs without the aid of any biological mechanism.
Liquid crystals have properties between those of conventional liquids and solid crystal. They may flow like a liquid, but have molecules arranged in an ordered crystalline way. And order is the essence of life.
Noel Clark, from the University of Colorado at Boulder, US, said: “Our observations are suggestive of what may have happened on the early earth when the first DNA-like molecular fragments appeared.
“The new findings show that in the presence of appropriate chemical conditions, the spontaneous self assembly of small DNA fragments into stacks of short duplexes greatly favours their binding into longer polymers, thereby providing a pre-RNA route to the RNA world.”
In higher organisms, DNA acts as a template for assembling RNA, which carries the protein-making ‘instructions’ of the genetic code.