Chemists based in Munich have demonstrated that the alternation in wet and dry conditions on early Earth could have been enough to kick off the prebiotic synthesis of the RNA nucleosides found in all domains of life.
While the understanding of the conditions on early Earth grows, the development of RNA and DNA around 4 billion years ago is still shrouded in mystery. What was the origin of the chemical structures that form the subunits of what we now know as hereditary molecules RNA and DNA? These molecules then went on to link into long chains that not only encoded information but reproduced and passed it on: how did all that start? The search is on to know more about the chemical evolution that preceded the first biological cells.
Research carried out at the Ludwig-Maximilians-Universitaet (LMU) in Munich, Germany, partly supported through the EU's EPiR project, has been working on this fascinating gap in our knowledge and the team's latest findings are now published in Nature. By exposing simple chemicals to the kinds of fluctuating physical conditions that would have prevailed in geothermally active areas of our planet billions of years ago, such as those caused by volcanic activity, researchers have shown that nucleosides can be formed in a continuous process.
Life-inducing cauldron of ingredients
They started with a mixture of the elements that have been shown in the past to form simple precursors in probiotic conditions: formic acid, sodium nitrite, acetic acid and a few nitrogen-containing compounds. The reaction mixture also contained iron and nickel, both of which are found in abundance in the Earth's crust. They then subjected the lot to fluctuations of temperature, pH and humidity to mimic early conditions, such as those due to strongly shifting seasonal temperatures.
The team built on work carried out last year by not only beginning with simpler precursor compounds, but choosing to replicate conditions that would be expected to prevail in a plausible geological setting, like hydrothermal springs on land.
By adding these ingredients together and subjecting them to the conditions that mimic the geology and meteorology of early Earth, the team found that a series of reactions gave rise to compounds called formamidopyrimidines – a crucial discovery as these compounds can turn into adenosine and guanosine, both of which are found in DNA. A whole series of related molecules were also synthesised.
The researchers write, "Even more strikingly, all of the modifications observed are known to occur in RNAs in all three domains of life – Eukaryota (animals and plants), Bacteria and Archaea – and are therefore essential components of functional genetic systems." From their results the researchers believe the compounds were most probably present in the last common ancestor of all life forms. This in turn, they argue, '(…) suggests that these compounds must have been available on early Earth when biological evolution began."
EU support helping to unravel the mysteries of the origin of life on Earth
The EU's advanced grant to EPiR (The Chemical Basis of RNA Epigenetics) is helping to support research into the role of chemistry in the development of early life. EPiR explains that the genetic code consists of a defined sequence of four canonical nucleosides and the sequence of these bases carries the blueprints of all life on earth. It is apparent that this sequence information alone is not sufficient to explain how a multicellular organism can establish specialised cells like the 200 known cells types of a human body.
This, EPiR explains, requires a second information layer and it has become apparent that this information layer is strongly based on chemistry. More than 150 chemical derivatives of RNA nucleosides are known and many more await discovery. Which is why EPiR is researching RNA modifications to decipher their functions.
Explore further: The chemical evolution of DNA and RNA on early Earth
Project website: cordis.europa.eu/project/rcn/210553_en.html