Re: UV Tanning[a small addition]

[paul charp <pcharp@ix.netcom.com>]

At 05:06 PM 2/29/96 -0600, you wrote:
>Hello Radsafers,
>During my time at school I was interested about this subject.
>A something from the memory.
>As I remember from Radiation Biology, UV photons can make only a 
>Single Strand Break (SSB) in DNA structure, which is repairable 
>without following aberrations in the structure. This is a result of 
>the DNA evolution process and DNA have "learnt" how to repair SSB 
>during its evolution; another thing with Double Stand Break(DSB), 
>ionizing radiation can cause DSB, which leads to a some probability 
>of a mutation=>...=>cancer. A one UV photon physically 
>(energetically) can not produce DSB. 
>
>Why? DNA did not learn how to repair DSB, it is hard to explain.  
>Might be the amount of damage to DNA is so big that for DNA "easier" 
>to go to Aposiopesis (cell suicide). However the Aposiopesis works 
>not always because of protein (P-53) mutation. The mutation of P-53
>leads ,NOT DIRECTLY, to (I do not remeber the exact number) 60 -..% of 
>all types of cancers.....
>      

I remember a few details of DNA repair resulting from UV exposure from my
time as a radiation
biologist.  The photo products produced by UV essentially deform the DNA.
This  "bump" is
recognized by the repair enzymes which then excise the photoproducts -
sometimes as much
 as a 100 base pairs or more.  The resulting repair or SSB is much different
from the DSB.  
With a SSB, the remaining undamaged
DNA can serve as a template for the repair; whereas, in the DSB, that
capability may be lost.  Also,
with ionizing radiation, the excised bases may number around 4 or so bases.
        Of course in the 10 years since I last reviewed the UV literature,
things may have changed.

paul charp (pcharp@ix.netcom.com)
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paul charp (pcharp@ix.netcom.com)

a clean desk is a sign of a sick mind
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