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Thermodynamic stability theory for DNA doughnut shapes induced by charge neutralization
Author(s) -
Manning Gerald S.
Publication year - 1980
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1980.360190104
Subject(s) - chemistry , ionic strength , curvature , neutralization , bending , ionic bonding , persistence length , charge (physics) , chemical physics , electrostatics , radius , aqueous solution , crystallography , thermodynamics , molecular physics , atomic physics , ion , molecule , physics , quantum mechanics , organic chemistry , geometry , mathematics , computer security , computer science , antibody , immunology , biology
Abstract A thermodynamic analysis of the bending free energy of DNA, initiated previously, is extended. It was demonstrated that the ionic‐strength dependence of the persistence length of DNA in aqueous NaCl can be understood by postulating (1) a rigid‐rod 60 base‐pair unit and (2) a negative contribution from nonelectrostatic sources to the bending free energy of this unit. On electrostatic neutralization of the phosphate charge, the latter term alone survives, and bending becomes a spontaneous process. In this paper it is demonstrated from a theoretical analysis of the ionic‐strength dependence of the rate of denaturation of DNA that the above statements are restricted in their validity to radii of curvature greater than 170 Å; beyond this limit, the steeply rising repulsive energy of tightly packed atoms dominates the bending free energy. Therefore, spontaneous bending on charge neutralization proceeds up to, but not beyond, this barrier to curvature. It is noted that doughnut forms of DNA induced by binding of cationic spermidine, or mixtures of Mg 2+ and polyamines are observed to possess maximum curvatures, corresponding to the radius of the “hole in the middle,” in the range 1/150–1/200 Å.