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Fwd: Single and double strand DNA breaks -Reply

Actually, I was thinking the same thing at first but then I went along with
Andy's train of thought and an interesting idea came to mind.  Maybe, if
our ancestors of the ameboid type had had to compensate for alpha
radiation they would have developed a system for deaing with double
strand breaks.  Like, how about, triple stranded DNA?  Or each cell
having two copies of all DNA and a process to confirm that both sets
agree before the cell is allowed to reproduce.  I know this is a little sci-fi
but as an intellectual exercise I find it facinating.

Joelle Key

This is way beyond my educational background let alone my professional
niche, so just take it for what it is worth.  :-)

>>> "Thatcher, Drew" <dht0303@hub.doh.wa.gov> 04/03/98 02:43pm

Perhaps you may be looking too deep for other answers or perhaps I'm
understanding the question.  If the two breaks are in close proximity the 
strands can no longer use the other as a template - without a map, errors

are bound to occur.  So are you thinking that, if evolution had more time 
that perhaps repair mechanisms would have found a way to error check 
themselves and correct the misrepair?

Andrew H. Thatcher, MSHP, CHP
Washington Department of Health
360-236-3255 voice*
360-236-2255 fax*
*new number                  

                  ***** Original Message Follows *****


One topic about which I am curious is that repair of double-strand DNA
breaks is so much more "iffy" than repair of single-strand breaks.  I
realize that SSBs are inherently easier to repair than are DSBs, but I am
wondering if there might be any additional factors.

For instance, it occurred to me that, until lungs and gills evolved (well
into the history of life) life would only have been exposed to
alpha-emitting atoms that happened to be within about a micron of the 
(or algal mat or whatever).  This was the state of things for the first 3
billion years life existed.  After the evolution of gills and lungs, of
course, animals could pump large volumes of water or air past tender
internal tissues, increasing alpha exposure.  Could it be that alpha
radiation is so damaging simply because life didn't have to worry about
DSBs until relatively recently?

This is all speculation, of course; I would welcome any comments from 
of you who know more about this than I.



The opinions expressed above are well-reasoned and insightful. 
say, they are not those of my employer. (with apologies to Michael 

Andrew Karam, MS, CHP					(614)
292-1284 (phone)
The Ohio State University 					(614)
292-7002 (fax)
Office of Radiation Safety					"The mind is
not a vessel to
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fire to be
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