Scientists have found a piece of strong evidence that both DNA and RNA might have been formed from the same precursor molecules even before the evolution of life on Earth. The research published in Nature Chemistry shows that the first living beings on our planet might have had both RNA and DNA like all other cellular-based life forms. This is in contrast to the current understanding that the earliest life forms only possessed RNA and DNA was formed with the evolution of life. This is commonly known as the RNA World Hypothesis. After this new finding, scientists should not fully rely on the RNA World Hypothesis for carrying out investigations on the origin of life on Earth.
RNA and DNA are chemically quite similar but chemists have not been able to show how one could have been converted to the other in earliest stages of our planet without the help of enzymes which are produced by the organisms. Because of this reason, researchers have always concluded that RNA is the basic component of the earliest life forms. RNA can store genetic information like DNA and also store catalyse biochemical reactions like protein enzymes. Hence it could have performed the basic biological functions in the earliest forms of life.
Ramanarayanan Krishnamurthy, a chemistry professor at Scripps Research along with his colleagues found a compound which was present in pre-biotic Earth and performed the essential task of linking RNA blocks to larger RNA strands and could have done the same for proteins and DNA.
Scientists have identified a compound named thiouridine which was likely to be present on Earth before the formation of life and it could have been a chemical precursor to the nucleoside blocks of the early RNA. It was found that by means of few chemical reactions this compound could be transformed to deoxyadenosine, a basic building block of DNA. They could also convert thiouridine to deoxyribose which is very closely related to deoxyadenosine.
These findings are a strong indicator that both RNA and DNA developed together and were present in the earliest life forms. Scientists have also suggested that both RNA and DNA might have been combined to form the first genes. Although no such organism has occurred naturally but a paper by Scripps Research described an engineered bacteria which can survive with genes formed by a combination of RNA and DNA.
Irrespective of the ways in which life formed, both RNA and DNA with their respective strengths and weaknesses would have arranged themselves into a proper division of labour as evident in the cells today.