UV Forces DNA Film To Filter More Light

Cancer seems to be almost ever present in today’s society. Everyday more things are announced that might cause cancer and various chemicals that are potential cures are discovered. But to this day, the most common thing that can cancer, that run into every single day, is ultraviolet light. Ultraviolet light has a direct photochemical effect on the DNA of humans; catalysing the bonding of two thymine bases (pyrimidines) into either a cyclobutane pyrimidine dimer or a 6-4 photoproduct:

Figure 3
Thank you to Photobiolgical Sciences Online for this diagram.

These conversions result in the DNA becoming bent out of shape and hampers the correct reproduction and duplication. Now although the smaller wavelengths of ultraviolet light have greater energy, they are actually completely removed by the Earth’s atmosphere. It is the range of 280 to 400 nanometres that offers the most tangible risk.

DNA has also been used recently in creating self assembling three dimensional structures. Thin films of DNA have been shown to have the unique optical properties as well as hiving possible applications in sensing technology. Now when the solutions of DNA are denatured by heat of acidic conditions it has been shown that these liquids gain optical density significantly. This sudden drop in transparency (and therefore rise in absorbance) is called hyperchromicity. The effect of ultraviolet radiation on the properties of long DNA molecules has not yet been studied in great detail.

By using spectrophotometry (shining a beam of monochromatic light through a solution to determine the absorbence of the solution to that frequency), except for a film rather than a solution, the changes in transmittance of light were observed after irradiation with UV light. It was found, that like in a liquid, the result was an increase in attenuation of light passing through. There are many theories about what could cause this such as the previously mentions deformations induced being able to absorb light or perhaps changes to the crystalline polymer structure result in more cross links and greater light scattering. Whether its one or the other or possibly both of these effects still needs to be determined and further research is required in order to find out the answer.

Paper links: Non-ionising UV light increases the optical density of hygroscopic self assembled DNA crystal films

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