X-Rays Reveal How DNA Survives UV Light Exposure


X-Rays Reveal How DNA Survives UV Light Exposure

26 June 2014
 
Using a powerful X-ray laser, scientists have been able to observe how strains of DNA successfully absorb ultraviolet (UV) light that should deactivate them, according to research published in the Nature Communications journal.
 
In the experiment, which was carried out in a US Department of Energy laboratory, scientists used an ultra-short X-ray laser pulse capable of detecting changes in molecular structure that occur in individual atoms in quadrillionths of a second. Thymine, a DNA building block, was turned into gas and hit with two such laser pulses. The first one was a UV pulse to trigger the molecule's reaction and the second was an X-ray to measure the response.
 
What the scientists observed was that within 200 quadrillionths of a second a single chemical bond stretched and snapped back, causing in turn a wave of vibrations along the strain. All the absorbed light energy was instantly turned into heat instead of being used by the molecule to make or break chemical bonds. This relaxation response, which the scientists describe as resembling a spring, dissipated the otherwise deadly UV energy.
 
The researchers were able to measure thymine response with X-rays using a process known as Auger decay. During this process, after some of the atoms' innermost electrons were stripped away, a wave of other electrons was ejected out of the molecule and into a detector, carrying information about the state of the atom.
 
The experiment revealed for the first time why thymine is resistant to damage from UV rays, which cause sunburn and skin cancer.