A three-state model with loop entropy for the overstretching transition of DNA.
We introduce a three-state model for a single DNA chain under tension that distinguishes among B-DNA, S-DNA, and M (molten or denatured) segments and at the same time correctly accounts for the entropy of molten loops, characterized by the exponent c in the asymptotic expression S approximately -c ln n for the entropy of a loop of length n. Force extension curves are derived exactly by employing a generalized Poland-Scheraga approach and then compared to experimental data. Simultaneous fitting to force-extension data at room temperature and to the denaturation phase transition at zero force is possible and allows us to establish a global phase diagram in the force-temperature plane. Under a stretching force, the effects of the stacking energy (entering as a domain-wall energy between paired and unpaired bases) and the loop entropy are separated. Therefore, we can estimate the loop exponent c independently from the precise value of the stacking energy. The fitted value for c is small, suggesting that nicks dominate the experimental force extension traces of natural DNA.
Einert
Thomas R
TR
Physik Department, Technische Universität München, Garching, Germany. einert@ph.tum.de
Staple
Douglas B
DB
Kreuzer
Hans-Jürgen
HJ
Netz
Roland R
RR
D004247:DNA / Q000737:chemistry*; D019277:Entropy; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D013696:Temperature
D004247:DNA