title: Degradation of nucleic acid in aqueous solution by ionizing radiation. III. The correlation of radiation damage with change in melting transition--model experiments.
abstract: The melting behavior of polydeoxynucleotide double helices of known structure is analyzed in terms of the thermodynamics of helix stability, taking into account separately those contributions to the transition free energy that are proportional to the numbers of polymer molecules and those that are proportional to the numbers of base pairs formed. From the analysis of the melting transitions of helices having an alternating (d-)A.T, G.C base-pair sequence and containing either single-strand nicks or both nicks and damaged thymine bases, the effects of these structural lesions are assessed; it is concluded that, in a moderately long helix of this sequence (400 base pairs), the initial introduction of one mid-chain double-strand break or single-strand break produces respectively some 3.5 or 4 times as much depression in the transition temperature (Tm) as does the destruction of a single internal A.T base pair.
mesh_terms: D004277:DNA, Single-Stranded; D009691:Nucleic Acid Denaturation; D009838:Oligodeoxyribonucleotides; D011089:Polydeoxyribonucleotides / Q000528:radiation effects*; D012996:Solutions; D013329:Structure-Activity Relationship; D013696:Temperature; D013816:Thermodynamics
chemical_list: D004277:DNA, Single-Stranded; D009838:Oligodeoxyribonucleotides; D011089:Polydeoxyribonucleotides; D012996:Solutions