Michael Motyka <mmotyka@lsil.com> writes:

Does UV light destroy DNA? I know it is a reasonable way to sterilize water ( with some caveats ) which it does by denaturing proteins.

UV light tends to totally hose up the DNA. The main problem, at least in bacteria, is caused by the creation of a bunch of cyclobutane-pyrimidine dimers and pyrimidine dimers. An enzyme called photolyase cuts pyramidine dimers to get the original _two_ pyramidines back. (Photolyase uses visible light for activation, if anyone cares.) This is a repair mechanism, but doesn't work 100% of the time and has the occasional error. The short answer is that UV light screws the DNA up. Sometimes the cell can fix it, and sometimes it can't. But it probably wouldn't throw off gel electrophoresis too much. (In forensics, the DNA is subjected to a bunch of restriction enzymes which cut it at specific sequences. Different DNA gets cut at different places, meaning that the fragments have different lengths, meaning that they're of substantially different weight. These are put on a gel and pulled through it by an electrical field. If a fragment is heavier, it doesn't go as far.) DNA isn't a protein, though, and, strangely enough, isn't anywhere near as dependent on secondary, tertiary, and quartenary structure as proteins tend to be. Proteins have to be in a specific confirmation to get the desired functionality. DNA just kind of needs to be there. (It's more complicated than this, of course, because of things that happen in cell division, but I could sit here and write a book-sized posting which nobody, including me, wants.) IIRC, DNA also tends to renature, either by itself or with the help of other mechanisms. (cf. histones, etc.)

If DNA is also destroyed would not a baseball eventually become invalidated just by sitting on a shelf?

Yes, but not so much by UV light as by the occasional bacterium which secretes something to break it, and by probably hundreds of other processes.

As someone wears and handles clothing, washes it along with clothing worn by others wouldn't the DNA become damaged or contaminated?

One would think.

Sounds trendy but I'd bet it has problems.

Oh yeah.