In the chemistry of the Earth, a pair of nucleic acids (DNA and RNA) is long molecules carry the genetic code, and all agencies provide a mechanism to reproduce properly, so as to generate the many proteins that are vital to living systems.
However, it is unclear how it started this “monopoly”. The DNA and RNA molecules are suitable for life and now it works. But in the chaos of the prebiotic Earth’s distant past, the chemical transition into the machinery of life must require hardware precursor, which could more easily be created by chance, maintained, and lead to the other.
One theory is that RNA could have the decisive role. This theory, the “RNA world”, proposes that life on Earth evolved from ancient forms of RNA, then going to a situation with greater role of DNA.
The team of John Chaput, a researcher at the Center for Evolutionary Medicine and Informatics at the Biodesign Institute at Arizona State University, in their search for the first piece of the machinery of life on Earth, has explored various alternatives to simple known genetic molecules. These chemicals are attractive candidates for those trying to unravel the secret of how life began, as the simplest molecular forms are those that could more easily arise during the prebiotic planet.
One approach to identify molecules that could act as precursors of RNA and DNA genetic is to examine other nucleic acids that differ slightly in their chemical composition, but still have important properties of self-assembly and replication, and the ability to fold into useful forms for biological functions.
According to Chaput, an interesting candidate for the role of primordial genetic carrier is a molecule known as ATN, whose appearance on the scene could have occurred before that of its chemical cousins known. The ATN is a nucleic acid similar to DNA and RNA-shaped, which differs in its structure a sugar, threose instead of Deoxyribose using (e.g. DNA) or ribose (as in RNA).
Chaput’s team has introduced and described the Darwinian evolution of ATN molecules from a large pool of random sequences. This is the first case in which such methods have been applied to a substance that is neither DNA nor RNA structural analogues closely related to those two. The most important finding of this research is that the ATN can be folded into complex shapes that are capable of binding to a desired target with high affinity and specificity. This feature suggests that, over time and the action of evolution, ATN enzymes could arise with the functions necessary to sustain the first forms of life.
Could a single molecule capable of replicating itself, have existed as a precursor of RNA, perhaps providing the genetic material necessary for the oldest organisms on Earth? Chaput’s experiments with the ATN presented this as a very attractive candidate. Its simple structure at key points would have allowed more easily assembled in a prebiotic world.
Although it is difficult to obtain strong evidence that the ATN act as precursor RNA in the prebiotic world, Chaput refers to the promising qualities of ATN. This nucleic acid is capable of storing information, experience natural selection processes, and fold into structures that can perform complex functions. This makes the ATN in a firm objective of research in relation to their possible role in the dawn of life on Earth.