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Re: natural and un-natural radiation



 
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On Thu, 4 May 2000 10:21:12    Jim Muckerheide wrote:
>Group,
>
>Re the discussion of "DNA damage" as a thesis for adverse health effects due
>to radiation exposure.  Additional comments on the substance of the analysis,


Here's some food for thought.

1. It is difficult to compare the various protective mechanisms of the cell - apples and oranges. The action of super oxide dismutase being a first line defense against free radicals (and being most efficient at that) and DNA repair enzymes which can be considered a second line of defense.

2. There are different ways and types the DNA of a cell can be damaged ie., the polysaccharide DNA backbone, Nucleotide dimerization, crosslinkage between the two separate DNA strands (watson and crick), individual base alterations, etc...

3. There are numerous ways the DNA is repaired: excision repair, both nucleotide and base etc. There are also numerous different DNA repair enzymes.  These enzymes work by themselves or as a team with different repair mechanisms having various components.  These repair reactions occur at varying rates, thus the 30 - 40 minutes is not meaningful.  The point being the rate of repair, depends upon the type of damage the system has to repair, and the type of damage is related to the energy of the insult (type and strength of ionizing radiation).  R. Setlow (PNAS 1969)performed experiments utilizing UV irradiation on tissue culture cells.  This type of radiation induced dimerization of thymidines which were located next to each other. For 50% DNA repair it took 12 hrs.

My question is how did they measure 100,000 vs 30,000?
I am just offering some food for thought - I have not read these studies.  I hope the above contributes to this discussion.

                             Tom


>> shorter than 30-40 minutes. 
>
>


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