TNA WORLD . . . . . . . . Is TNA is the proginator of DNA? By: Desh Bandhu Gangwar M.Tech Biotech (2 year) 10/pbt/006 DNA is building block for life on earth. But it is highly complex molecule and could not be arranged itself spontaneously. What did it develop from? Astrobiologist examine possible ancestor of DNA: nucleic acid called TNA. (3’-2’)-alfa-L-Threose nucleic acid (TNA) is an unnatural polymer that posses the rare ability to base pair with RNA, DNA and itself. This feature coupled with its chemical simplicity, makes TNA of interest as a possible proginator of DNA during the early history of life. Scientist have put forth the theory that RNA was the predecessor of DNA and evolved into that more complex molecule. But while RNA is slightly simpler then DNA, it too is very complex. So what is the ancestor of RNA? One recent report suggested that it may have been yet another nucleic acid called (3’-2’)- alfa-L-Threose nucleic acid also known as TNA. Dr. Albert Eschenmoser and his colleagues at the scripps research institute in La Jolla, California, and the federal institute of technology in zurich, Switzerland, chemically synthesized TNA in a number of steps. They found that complementary TNA strands can form stable double helix. The TNA strand can also pair up with complementary strand of RNA and DNA. This ability is though to be one of the requirement of any system that would be considered a possible ancestor of RNA. A second requirement is that it should be a simpler molecule than RNA. The backbone of DNA and RNA composed of sugar molecule-ribose for RNA and deoxyribose for DNA- that contain five carbon atom. In TNA that backbone composed of sugar molecules threose that contain only four carbon atom. under nonbiological conditions, threose form easily than ribose.
But it is not only the number of the carbon atoms that threose an intrisicallysimpler molecule than ribose. it is also the fact that, unlike ribose, the simplestformation of threose requires only a single type of starting material.TNA does not occur naturally today. Scientists have to create it in the lab inorder to study it. Since we can’t go back in time to witness the evolution ofnucleic acid, we will never to prove whether natural TNA made an appearanceon earth.But scientist can examine the basic property of TNA and determine whetherthey could have formed in a prebiotic earth environment. The reason forsynthesizing and studying it to screen the structural nighborhood of RNA forpotential nucleic acid alternative that could also have fulfilled the function ofgenetic system. The origin of DNA are confronted with a paradox. DNA needscertain proteins to replicate. But in order to make the correct proteins for thisfunction, modern cells need to have DNA. Since DNA and the proteins aredependent on each other. It is hard to see how either of them could havecome first. One answer to this riddle is the RNA world theory, which suggestedthat both DNA and protein could descendents of RNA. But where did RNAcome from? To date no one has been able to form RNA under in the laboratoryunder condition that mimic those believed to have existed on primitive earth.Some scientist also question whether nucleic acid with a backbone of ribose, orany other sugar molecule, would be stable enough to survive the harshcondition of early earth.So it is generally agreed that RNA must have evolved from an earlier form,while TNA is a good candidate other polymer that exhibit self replication andbase pairing could have evolved into RNA. TNA is the best bet so far.