ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The degradation of deoxyribonucleic acid (DNA) by irradiation of its aqueous solutions with ionizing radiations in the presence of oxygen has been discussed in terms of the reactions of free radicals (produced by the radiolytic decomposition of the water) with the different molecular entities of the macromolecule. It has been found that attack of the radicals on the purine and pyrimidine bases is a major effect of the irradiation, and it has been estimated that about 80% of the OH radicals attack the base components. In the presence of oxygen an important radiation-induced reaction is the formation of peroxidic compounds from the pyrimidines. Breakage of the strands in the DNA helix is apparently due mainly to an attack of the radiation-produced radicals on the sugar moieties which leads to a splitting of the phosphate ester linkages along the chains. The extent of attack which leads to breakage of internucleotide bonds, leading to the production of phosphomonoester groups, has been determined directly: the number of endgroups formed on irradiation with 200 k.v. x-rays corresponds to a yield of G ⋍ 0.5 (endgroups/100 e.v.). Rupture of hydrogen bonds within the helix is a consequence of chemical changes in the polynucleotide chains; several hydrogen bonds can be broken following a single chemical event. The hyperchromic effect which is observed in the action of the radiations on nucleic acids in solutions has been investigated in some detail. It has been concluded that this effect is caused, in general, by environmental changes of the chromophoric groups of the purine and pyrimidine bases of the DNA, and is due to the change of the nature of the hydrogen bonding of the bases within the intact helix, where the bases of one strand are bonded to the bases of the complementary strand, to hydrogen bonding with water molecules when the latter have penetrated between the strands of the helix.
Additional Material:
2 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1960.1204815028
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