Before DNA, before RNA: Life in the hodge-podge world
Because RNA can do many things at once, those studying the origins of life have long thought that it was the first genetic material. But the discovery that a chemical relative called TNA can perform one of RNA’s defining functions calls this into question. Instead, the very first forms of life may have used a mix of genetic materials.
RNA, DNA… TNA
Today, most life bar some viruses uses DNA to store information, and RNA to execute the instructions encoded by that DNA. However, many biologists think that the earliest forms of life used RNA for everything, with little or no help from DNA.
A key piece of evidence for this “RNA world” hypothesis is that RNA is a jack of all trades. It can both store genetic information and act as an enzyme, seemingly making it the ideal molecule to start life from scratch.
Now it seems TNA might have been just as capable, although it is not found in nature today.
It differs from RNA and DNA in its sugar backbone: TNA uses threose where RNA uses ribose and DNA deoxyribose. That gives TNA a key advantage, says John Chaput of Arizona State University in Tempe: it is a smaller molecule than ribose or deoxyribose, possibly making TNA easier to form.
Chaput and his colleagues have now created a TNA molecule that folds into a three-dimensional shape and clamps onto a specific protein. These are key steps towards creating a TNA enzyme that can control a chemical reaction, just like RNA.
The team took a library of TNAs and evolved them in the presence of a protein. After three generations, a TNA turned up that had a complex folded shape like an enzyme and could bind to the protein……….
Read more: www.newscientist.com