DNA protects itself from UV light

DNA makes use of a 'molecular sunscreen' to protect itself from the harmful Ultraviolet (UV) light, according to a new research.
The molecular building blocks that make up DNA absorb ultraviolet light so strongly that sunlight should deactivate them - yet it does not.
Now scientists have made detailed observations of a "relaxation response" that protects these molecules, and the genetic information they encode, from UV damage.
The experiment at the US Department of Energy's SLAC National Accelerator Laboratory focused on thymine, one of four DNA building blocks.
Researchers hit thymine with a short pulse of ultraviolet light and used a powerful X-ray laser to watch the molecule's response.

They found that a single chemical bond stretched and snapped back into place within 200 quadrillionths of a second, setting off a wave of vibrations that harmlessly dissipated the destructive UV energy.

While protecting the genetic information encoded in DNA is vitally important, the significance of this result goes far beyond DNA chemistry, said Philip Bucksbaum, director of the Stanford PULSE Institute and a co-author of the report.
Scientists turned thymine into a gas and hit it with two pulses of light in rapid succession: first UV, to trigger the protective relaxation response, and then X-rays, to detect and measure the response.

"As soon as the thymine swallows the light, the energy is funnelled as quickly as possible into heat, rather than into making or breaking chemical bonds," said Markus Guehr, senior staff scientist at PULSE who led the study.
"It's like a system of balls connected by springs; when you elongate that one bond between two atoms and let it loose, the whole molecule starts to tremble," said Guehr.
The research was published in the journal Nature Communications.