The life-giving sun can be quite rough on genetic material. Most organisms, including plants and many animals, are equipped with a special enzyme in their cells that is quick to repair DNA damage wrought by the sun's ultraviolet (UV) rays. Humans, however, have less effective repair strategies and as a result are prone to painful sunburns and deadly skin cancer.

Until now, scientists had never seen this enzyme (known as photolyase) at work. But a new study describes the way—and the speed at which—this molecular actor gets to work, harnessing photons to fix a damaged double helix.

Ultraviolet light can penetrate cells and mess up bonds in a stretch of DNA, making the genetic code copy incorrectly or uncontrollably, or unable to copy at all. Such errors can sometimes cause cell death or cancer when they are not properly repaired.

"People have been working on this for years," Dongping Zhong, an associate professor of physics, chemistry and biochemistry at Ohio State University and coauthor of the new paper, said in a prepared statement. "But now that we've seen it, I don't think anyone could have guessed exactly what was happening." The work was published online July 25 in Nature (Scientific American is part of Nature Publishing Group).

To peer into the processes, the researchers used ultrafast stereoscopy, which flashed light quick enough to catch changes on the scale of picoseconds.

Zhong and his team observed that the photolyase enzyme was able to convert visible light into a healing energy by discharging a proton and an electron into the damaged DNA segment. "It sounds simple, but those two atomic particles actually initiated a very complex series of chemical reactions," Zhong said. After the proton and electron did their work—a process that took mere nanoseconds—they popped back out of the double helix to rejoin the photolyase enzyme, likely making it ready to fix the next damaged area.

The enzyme might be one way to shore-up sunscreen, providing a fix for damage from UV rays that make it through your SPF.

Image courtesy of Wikimedia Commons/NASA/David Herring