The Half Life of DNA

521 years- The Half-life of DNAby Maria Atia

For quite some time scientists have come across various proofs of intact dinosaur DNA even after the passage of thousands of years. But the main question arising from this is that how much more time does the DNA has left before it starts to degrade and the DNA information lost forever. A new study on the fossils found in New Zealand is bringing many aspects to light. Hopes are that through that information the cloning of a dinosaur named Tyrannosaurus rex would become possible.

DNA backbone remains in one piece as long as the cell is alive. Once cell death occurs certain enzymes are released which attack the DNA backbone and breaks it into smaller nucleotide fragments by breaking the bonds binding two nucleotides together. Action of micro-organisms on the fossils is found to increase the decaying process. Water although important for life but also breaks bonds between the nucleotides upon reaction. Water is in abundance so it can be deduced that the fossil DNA will break or degrade at a set rate.

The problem which comes next is that at what rate the degradation process occurs. The main hurdle for this kind of study is that a large number of fossils having DNA are not available. Thus comparisons cannot be done among them to make a useful deduction. Not only this but temperature, amount of microbial attack and the rate of oxygenation process and other environment related factors also affect the degradation process.

Morten Allentoft, University of Copenhagen, and Michael Bunce, Murdoch University in Perth, along with their team of palaeogeneticists studied the DNA samples collected from 158 DNA containing leg bones. The legs were identified to be of three different species of large giant birds called moa which are now extinct in the present day. The bone samples were collected from three different locations, all within a 5 kilometer distance from each other. The preservation conditions for all three locations were also the same along with the temperature of 13.1° C. The life of the bones is found to be between 600 and 8000 years old. All these discoveries and results were published in the Proceedings of the Royal Society B today.

By performing some testing on the DNA-carrying bones scientists have managed to tell about the age of those bones. Based on this information and on the rate of degradation, the DNA half-life has been found to be of 521 years. After 521 years half of the DNA binding bonds will break resulting in the breakage of all the bonds after another 521 years.

Allentoft and Bunce along with their colleagues have made an assumption that if a bone is kept at ideal preservation conditions, for example -5°C, even then all the DNA bonds will break down but may be in this case after the time span of 6.8 million years. But after only 1.5 million years the DNA starts to get degraded in smaller fragments making it impossible to be read.

Simon Ho, a computational evolutionary biologist at University of Sydney in Australia said that from this study it can be said that all the previous work done on the identification of dinosaurs and insects is absolutely correct.  With dinosaurs being 65 million years old, this study will only help in setting the record right for the oldest authentic DNA sequence till now.

 Michael Knapp, a palaeogeneticist at the University of Otago in Dunedin, New Zealand while giving his comments on this research said that it will be another very important field of study to find the effect of other different environments such as permafrost and caves, on the bacteria.

38.6% variation in DNA decay caused by the age differences of the samples after the degradation has identified in the moa-bone study. According to Bruce, they are trying to identify what other factors may influence the DNA degradation. He said that so far storage preceding excavation, soil chemistry and the time of the year when the organism died is also very important for DNA degradation studies.

-Maria

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