New details of how DNA protects itself from harmful Ultraviolet (UV) radiation show a hidden network of ultrafast molecular reactions that help prevent damage before it can trigger mutations that might lead to cancer, according to a study led by the University of Surrey.

Working with researchers from Aix Marseille University, the French National Centre for Scientific Research (CNRS) and Université Claude Bernard Lyon 1, the team used advanced computer simulations to watch what happens to DNA in real time at the atomic scale.

DNA constantly absorbs UV light from the Sun, which can potentially trigger harmful chemical reactions. However, DNA is remarkably photostable – meaning it can rapidly deactivate excited energy states before lasting damage occurs.

In the study, published in The Journal of Physical Chemistry Letters, researchers focused on guanine and cytosine base pairs – two of the fundamental building blocks of genetic material. Using high-level quantum chemistry simulations, the researchers found that, after absorbing UV light, the excited energy is funnelled through a series of molecular processes that safely return it to its stable state. The simulations showed that DNA does not rely on a single protective mechanism but instead accesses a complex network of competing ultrafast relaxation pathways.

These pathways are far more diverse and dynamic than previously thought. Rather than following a single route, DNA appears to use multiple ultrafast reactions involving moving electrons and protons that dissipate the energy within femtoseconds – a femtosecond being one quadrillionth of a second.

Dr Marco Sacchi, Associate Professor of Physical and Computational Chemistry at the University of Surrey and senior author of the study, said:

“DNA has evolved under constant exposure to UV radiation, yet it is extraordinarily resilient. What’s exciting about this research is that we can now see the incredibly fast molecular processes that safely drain away the energy before damage has a chance to spread. Understanding how Nature has developed these built-in defence mechanisms could help us better understand

everything from mutation and ageing to the ways radiation affects living cells.”

Juliana Gonçalves de Abrantes, Postgraduate Researcher at the University of Surrey and lead author, added:

“What surprised us most was the diversity of the relaxation pathways – the different ways DNA can safely get rid of harmful UV energy. The electron and proton motions are strongly coupled, meaning they closely influence each other, but they are not rigidly locked together. This creates a rich network of possible decay routes that collectively enhance DNA photostability.”

The findings could improve understanding of how radiation damages DNA and how cells naturally protect themselves, with potential long-term implications for fields including cancer biology, ageing research, biotechnology and astrobiology.

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