According to a new study, the building blocks of life; DNA and RNA may have appeared together before life on Earth began.
For the first time, scientists have discovered conclusive evidence that both RNA and DNA may have come into existence from the very same group of precursor molecules, even before primitive life appeared on Earth, some four billion years ago.
The new study, published in the journal Nature Chemistry tells us that the first living beings on the planet may have used both RNA and DNA, just as cell-based organisms do now.
Previous scientific theory suggests that early life forms on Earth were solely based on RNA and that they eventually evolved to make and use DNA.
“These new findings suggest that it may not be reasonable for chemists to be so heavily guided by the RNA World hypothesis in investigating the origins of life on Earth,” explained co-principal investigator Ramanarayanan Krishnamurthy, Ph.D., associate professor of chemistry at Scripps Research.
As part of Simons Foundation’s Collaboration on the Origins of Life, Krishnamurthy and his colleagues worked side by side with John Sutherland, DPhil, of the UK Medical Research Council’s Laboratory of Molecular Biology at Cambridge.
Even though RNA and DNA are very similar in chemical terms, scientists were unable to demonstrate how one could have been converted into the other on ancient Earth, around four billion years ago, except with the help of enzymes produced by early organisms.
Since scientists were unable to demonstrate how this was possible, the long-standing theory suggested that the simple, and more versatile RNA was the basis for early life forms, or at least played a part in an early stage of life before the appearance of DNA.
But despite the long-standing, and generally accepted theory based on RNA, Sutherland, Krishnamurthy, Harvard’s Jack Szostak and others have discovered conclusive evidence that indicates how RNA and DNA may have come into existence more or less all at once in the first life forms on an early Earth.
In the new study, scientists combined data from a study published in 2017 (which found a compound that may have been present on the prebiotic Earth, and may have helped perform the task of linking RNA building blocks into RNA strands), with a recent discovery made by Sutherland, on a compound called thiouridine.
Thiouridine is thought to have been present on the planet before life came into existence and may have been the chemical precursor of the nucleoside building blocks of early RNAs.
Scientists successfully demonstrated that with fewer chemical-reaction steps, they were able to convert the precursor of an RNA building block into a DNA building block: deoxyadenosine.
This discovery should make it much easier for other scientists to accept the idea that both DNA and RNA came into existence and were included in the very first life forms on Earth, some four billion years ago.
Southland, as well as other experts, have even proposed that RNA and DNA may have been mixed together to create the very first genes.
“There is the beginning of a realization in the field that RNA and DNA could have been mixed together initially but later separated according to the things they do best,” Krishnamurthy explained.