Science Buddies: "Ask an Expert"

Dear Expert,

My partner and I have recently completed our experiment and presentation on antioxidant effect. We were looking into the varying strengths of chosen antioxidants and whether a combination of them will help to make the antioxidant treatment for the cells even stronger.

To damage the cells in order to be able to treat them later, we used UV light. The experiment ran smooth and we had one successful treatment. However, the question of whether UV causes oxidative stress by creating free radicals and mutations arose near the completion of our project. I was looking online and found that UV, as an external agent, is classified as an exogenous damage as opposed to endogenous DNA damages such as attack by reactive oxygen species (oxidation). But I also read about how UV-A light does create mostly free radicals. We took this problem to our mentor but she reaffirmed UV as a source of oxidative stress. When we did present our project, however, one of our judges pointed out that UV is not a significant source of oxidation and that it causes thymine dimers in DNA and does not really oxidize DNA. Currently, we're confused as to the exact effect of UV light on cells, whether UV causes oxidation, if so, whether it is merely insignificant, and if not then is our experiment valid at all, since in this case we won't be measuring what we set out to measure?

Thank you for your attention,
Seriously Confused

Hi!
I myself am not quite an expert in this area, but I looked up "ultraviolet light free radicals" and from what I have read, UV radiation indirectly damages the DNA and causes free radicals and oxidative stress because the UV photon excites certain cells which damage other cells which come into contact with them. Check this website out for more information-
http://bulkactives.com/blog/index.php/t ... -radicals/
What the judge MAY have meant is that there may not necessarily be a "direct" effect, although there are definitely some indirect effects of UV radiation. Hope this helps, good luck!

Dear KeyInquisition,

I think that it depends on what type of UV light you used. Did you use UV-A or B? Here is a reason given by writers for the Scientific American for why UV-B light kills cells:

http://www.sciam.com/article.cfm?id=how ... iolet-ligh

Basically the article says that the UV light results in the creation of thymine dimers which cause DNA mutations. When there are enough mutations, the cells die. If there are some mutations but not very many, cancer cells are formed. So in relation to your project, UV-B light still damages DNA, though not because of Reactive Oxygen Species (ROS).

Here is an article that discusses the effects of UV-A light on cells and includes the creation of harmful ROS:

http://web.mit.edu/murj/www/v16/v16-Reports/v16-r1.pdf

Was your project designed to measure oxidation or the cells' damage? If, after exposure to UV-A or B light, the cells were still healthy using whatever treatment you used, you succeeded in protecting the cells from either the creation of thymine dimers or ROS. If you used UV-A light and measured the ROS like the study above, you succeeded in protecting the cells from the ROS.

I hope this helps!

Thank you all! Those were very helpful points indeed. I'll find out what type of UV we did use and then we can finally know.

Thanks again for all the information!