The chemical complexity of DNA has convinced most biologists that it almost certainly did not arise spontaneously from the prebiotic soup existing early in earth's history. According to one hypothesis, the simpler RNA molecule may at one time have held dominion as the sole transmitter of the genetic code. RNA is also capable of acting as an enzyme and may have catalyzed important chemical reactions leading eventually to the first cellular life.
But RNA is still a complex molecule and the search for a simpler precursor that may have acted as a stepping-stone to the RNA, DNA and protein system that exists today has been intense.
A variety of xenonucleic acids are being explored as candidates for the role of transitional molecule. In the current study, threose nucleic acid or TNA is investigated. Chaput says that establishing TNA as a progenitor of RNA would require demonstrating that TNA can perform functions that would help support a pre-RNA world. Of particular importance, would have been the ability replicate itself in the absence of protein enzymes.
Like DNA, TNA can form double-helicesspiral staircase structures consisting of the 4 nucleotide bases, which make up the ladder-like rungs, and a sugar and phosphorus backbone, which forms the ladder's railing. The sugar portion of this backbone is a defining component of the nucleic acid. DNA uses deoxyribose, RNA uses ribose and TNA uses threose.
Both DNA and RNA have sugars containing five carbon atoms, but TNA's threose sugar contains only four. This enables TNA to assemble from just two identical carbon units, making it far easier to form under the non-biological conditions than RNA or
|Contact: Joseph Caspermeyer|
Arizona State University