DNA's double helix is twisty because of water — not hydrogen

• A new study in PNAS disproves the theory that hydrogen bonds hold DNA strands together.
  
• Researchers at the Chambers University of Technology have discovered that water is why DNA strands are wrapped around each other and have a helix shape.
  
• Understanding how DNA repairs itself could lead to new insights on how fight resistant bacteria or prevent cancer.
  

The signature imagery of two DNA strands locked around each other is one that everyone has seen in school. And, everyone was also taught that the double helix shape with the strands are bound by hydrogen bonds — but that might no longer be true.

According to a new study published in PNAS, the key might be water.

It's not hydrogen bonds don't have a role to play. They're still the ones responsible for sorting base pairs and making sure they're all in the right sequence. But, it's water that holding the DNA helixes together.

In fact, the entire helical structure of the DNA might be because of its hydrophobic interior in an environment that consists mainly of water.

How DNA gets its shape

Researchers at the Chambers University of Technology in Sweden may have disproved the old theory around hydrogen bonds, but they have also opened up new avenues of research with their discovery.

DNA has two strands — one is made of sugar molecules and the other of phosphate groups. Between these two strands are nitrogen bases that hold all the genes.


Then come the hydrogen bonds, which no longer hold the strands together but still serve the function of making sure the genes are in the right order.

Nitrogen bases are hydrophobic, so they are pushing away the surrounding water — a hydrophilic environment. The helix forms since hydrophobic elements in hydrophilic environments group together in order to minimise their exposure.

"We believe that the cell keeps its DNA in a water solution most of the time, but as soon as a cell wants to do something with its DNA, like read, copy or repair it, it exposes the DNA to a hydrophobic environment," said Bobo Feng, one of the authors of the study, in a statement.

The hydrophobic environment is created by a catalytic protein that is central to all DNA repair, which could mean it holds the key to curing a lot of serious illnesses in the future.