There and (slowly) back again: entropy-driven hysteresis in a model of DNA overstretching
2008 (English)In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 94, no 7, 2452-2469 p.Article in journal (Refereed) Published
When pulled along its axis, double-stranded DNA elongates abruptly at a force of similar to 65 pN. Two physical pictures have been developed to describe this overstretched state. The first proposes that strong forces induce a phase transition to a molten state consisting of unhybridized single strands. The second picture introduces an elongated hybridized phase called S-DNA. Little thermodynamic evidence exists to discriminate directly between these competing pictures. Here we show that within a microscopic model of DNA we can distinguish between the dynamics associated with each. In experiment, considerable hysteresis in a cycle of stretching and shortening develops as temperature is increased. Since there are few possible causes of hysteresis in a system whose extent is appreciable in only one dimension, such behavior offers a discriminating test of the two pictures of overstretching. Most experiments are performed upon nicked DNA, permitting the detachment (unpeeling) of strands. We show that the long-wavelength progression of the unpeeled front generates hysteresis, the character of which agrees with experiment only if we assume the existence of S-DNA. We also show that internal melting can generate hysteresis, the degree of which depends upon the nonextensive loop entropy of single-stranded DNA.
Place, publisher, year, edition, pages
2008. Vol. 94, no 7, 2452-2469 p.
IdentifiersURN: urn:nbn:se:kth:diva-79153DOI: 10.1529/biophysj.107.117036ISI: 000254076300007OAI: oai:DiVA.org:kth-79153DiVA: diva2:495170
QC 201202092012-02-082012-02-082012-02-09Bibliographically approved