CDR: Re: DNA

[David Marshall]

Michael Motyka <mmotyka at 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.