2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/29015A unified model is constructed to study the recently observed DNA entropic elasticity, cooperative extensibility, and supercoiling property. With the introduction of a new structural parameter (the folding angle $ϕ$), bending deformations of sugar-phosphate backbones, steric effects of nucleotide basepairs, and short-range basestacking interactions are considered. The comprehensive agreement of theoretical results with experimental observations on both torsionally relaxed and negatively supercoiled DNAs strongly indicates that, basestacking interactions, although short-ranged in nature, dominate the elasticity of DNA and hence are of vital biological significance.4 pages in Latex format, with 3 EPS figures included. A typographic mistake in Eq. (7) is corrected in this version. A slightly different version of this paper will appear in PRLSoft Condensed MatterDisordered Systems and Neural NetworksBiological PhysicsQuantitative Biologytext