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DNA structure

New evidence of forces responsible for separation of DNA discovered

According to a piece of new evidence, the force which holds the DNA might also be responsible for change of shape so that its repair, gene shuffling and copying can take place. The iconic double helix structure of our DNA was discovered back in 1950. It has a structure similar to that of a twisted ladder in which the nitrogen base pairs in the middle are held by the hydrogen bonds. The findings appear in the Proceedings in the National Academy of Sciences. 

These bonds are considered as a “fundamental paradigm” because of their role in holding the DNA together. However, apart from this, one important consideration is that they are water-repelling or hydrophobic. 

Replication of DNA occurs with the help of many enzymes, in which DNA molecules are essentially unzipped by enzymes by the removal of hydrogen bonds. But this might not be the only way to do it. Scientists from the Chalmers University of Technology, Sweden have tested the DNA in an increased hydrophobic environment where they found that the water-repelling force can also be used for unraveling it. It loses its structure in a water-repelling environment when a solution of polyethylene glycol is added which is a semi-hydrophobic solution. 

Bobo Feng, lead author, and the chemical engineer said that the DNA is protected by the cells and not exposed to the hydrophobic environments that might have harmful molecules. But for its use, the DNA has to be opened up. It is kept in a water solution most of the time but the environment changes to a hydrophobic one when the DNA has to be edited, copied or repaired. 

Steven Brenner, a NASA molecular biophysicist said that although this is an important discovery of a new technique of melting the DNA for its repair, it has not been covered accurately by the media. The results do not suggest that hydrogen bonds are not important for the formation of DNA while the hydrophobic forces are. This is not a new idea as models considering hydrophobic interactions in the DNA date back to the 1990s. Researchers in 1997 tested the idea that only hydrogen bonds are sufficient to keep the double helix of DNA together. It was confirmed by a later study in 2004 that hydrogen bonding was not necessary for the stability of base pairs. A 2017 study revealed that cells are not affected by the lack of complementary hydrogen bonds as the synthetic bases are translated with the help of only hydrophobic forces. 

Floyd Romesberg, lead author of the 2017 study and a biochemist said that complementary hydrogen bonds might be considered the main definitions of DNA and RNA however there are other forces that can take part in the processes of information retrieval and storage. It often occurs that the biases of the chemist separating the molecules get reflected in the analysis of the model rather than the molecules themselves. Benner feels that self-explanations can convince us to understand what is happening if the models allow us to actually make things. 

Currently, both the concepts of hydrogen-bonding and hydrophobicity help us to make advances in human medicine besides powering NASA’s search for extraterrestrial organisms. 

Feng said that it was not surprising that this behavior was not identified to date as DNA was never placed in a hydrophobic environment. 

Journal Reference:  PNAS  (Proceedings of the National Academy of Sciences of the United States of America)