Researchers at the Chalmers University of Technology, Sweden, refute the prevailing theory of how DNA binds itself. It is not, as is generally believed, hydrogen bonds that connect the two sides of the DNA structure. Instead, water is the key. The discovery opens doors to new insights in research in medicine and life sciences. Results of researchers are presented in the magazine PNAS .
DNA consists of two strands consisting of sugar molecules and phosphate groups. Between these two strands are nitrogen bases, the compounds that make up the genes of the organisms and between which there are hydrogen bonds. So far it has been commonly assumed that these hydrogen bonds hold the two strands together.
Chalmers University of Technology researchers, however, show that the secret of the helical structure of DNA is that the molecules have a hydrophobic interior that is primarily water. The environment is therefore hydrophilic, while the nitrogenous bases of the DNA molecules are hydrophobic and push away the surrounding water. When hydrophobic moieties are in a hydrophilic environment, they group together to minimize exposure to water.
The role of hydrogen bonds, previously thought to be critical for holding together DNA helixes, seems more likely to involve sorting the base pairs so that they combine in the correct order.
The discovery is critical to understanding the relationship of DNA to its environment.
"Cells want to protect their DNA and not expose it to hydrophobic environments that can sometimes contain harmful molecules," says Bobo Feng, one of the researchers behind the study. "At the same time, the cells' DNA has to open up to be used."
"We believe the cell stores its DNA in a water solution most of the time, but as soon as a cell desires to do something with its DNA, As she reads, copies or repairs, she exposes the DNA to a hydrophobic environment. "
During reproduction, for example, the base pairs separate from each other and open. Enzymes then copy both sides of the helix to generate new DNA. When repairing damaged DNA, the damaged areas are exposed to a hydrophobic environment to be replaced. A catalytic protein creates the hydrophobic environment. This type of protein is central to all DNA repair, which means it could be the key to fighting many serious diseases.
Understanding these proteins could provide many new insights into how we can, for example, fight or even cure resistant bacteria. Bacteria use a protein called RecA to repair their DNA, and the researchers believe that their findings could provide new insights into how this process works – possibly ways to stop it and kill off the bacteria.
In human cells, the protein repairs Rad51 DNA and fixes mutated DNA sequences that could otherwise cause cancer.
"To understand cancer, we need to understand how DNA repairs. To understand that, we first have to understand the DNA itself, "says Bobo Feng. "So far, we did not do that because we thought that hydrogen bonds hold it together. Now we have shown that instead the hydrophobic forces are behind it. We also showed that DNA behaves completely differently in a hydrophobic environment. This could help us to understand the DNA and its repair. So far, no one has brought DNA into a hydrophobic environment like this and studied its behavior. It is therefore not surprising that nobody has discovered this yet.
For more information on the methods that researchers used to demonstrate how DNA holds together:  The researchers looked at how DNA behaves in an environment that is more hydrophobic than normal, a method it first experimented with to have.
They used the hydrophobic solution polyethylene glycol and gradually changed the environment of the DNA from the naturally hydrophilic environment to a hydrophobic one. They wanted to find out if there is a limit to how DNA starts to lose its structure if DNA has no reason to bind because the environment is no longer hydrophilic. The researchers found that the characteristic spiral shape of the DNA molecules dissolves when the solution reaches the boundary between hydrophilic and hydrophobic.
On closer inspection, they found that the base pairs split (due to external influences). or simply by accidental movements), holes are formed in the structure that allow the ingress of water. As the DNA tries to keep its interior dry, it contracts, bringing the base pairs back together to squeeze out the water. In a hydrophobic environment, this water is missing, leaving the holes in place.
Reference: "Hydrophobic catalysis and a possible biological role of DNA unstacking caused by environmental influences" by
Anna KF Mårtenssonand