UV Tanning[a small addition]

["EMIL KERREMBAEV" <EKERREMBAEV@r06.tdh.state.tx.us>]

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 know that this could sound like a speculation and RADSAFE is not 
the place. But.... 
There is a probability of two UV photons simultaneous strike to two
strands of the same DNA, in certain geometic conditions, to produce 
DSB.  I would speculate that it could cause a mutation=>...=>melanoma

About North European's susceptibility to melanoma, I don't speculate,
I heard about that and probably it is the result of a different 
pigmentation process within the skin which leads to a different UV 
adsorbtion (shielding)in the top layer of the skin (or dead layer?), 
where no stems cells (targets- sources of mutations). 
Just some thoughts during . 
Any comments?

Thanks for your time.

Emil M. Kerrembaev.
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