DNA and RNA are two very similar molecules, but they behave quite differently when a force is applied to them. As one would expect, by stretching a double ribonucleic acid (RNA) helix, the molecule winds off and lengthens. However, the behavior of the double helix of deoxyribonucleic acid (DNA) is contrary to what the intuition would dictate: when it is stretched, it winds even more. Why do they behave so differently despite sharing such a similar structure?

“Neither DNA nor RNA are those perfect linear structures that the books show us. To correctly perform their biological function they need to be subjected to twists, torsions, stretching and other very specific physical forces,” explains Alberto Marín, author of the paper and researcher at the National Center for Biotechnology (CNB) which forms part of the Spanish National Research Council (CSIC). As a result of these forces, local changes occur in the structure of the molecule to facilitate or prevent the binding of certain proteins to specific points of the nucleic acid. In this, many of the processes essential to the cell’s life can be regulated.

Previous studies have already shown that these two molecules so structurally similar behave differently by applying a force on them. But this work has allowed, for the first time, to see how atoms of nucleic acids change position when they are stretched. When the DNA is stretched, the distance between the two strands within its double helix decreases, which makes the molecule narrower. In the case of a double RNA helix (present in some virus types, whereas in most organisms the RNA is formed by a single nucleotide chain), the distance hardly varies. Then, if the distance between the DNA strands is reduced, an over-winding occurs when stretched. But if the separation between two strands of RNA is kept fixed, the molecule unwinds by stretching it.

The results of the study suggest that, ultimately, the counterintuitive behavior of DNA (over-winding when stretched) is related to the small but fundamental difference that distinguishes it from RNA: the absence of a hydroxyl group. “These computer simulations can be a very powerful tool for uncovering changes in biological functionality associated with structural changes,” the authors conclude.

 

Source: Agencia ID