Abstract
In this article, we investigate the principal structural features of the DNA double helix and their effects on its elastic mechanical properties. We develop, in the pursuit of this purpose, a helical continuum model consisting of a soft helical core and two stiff ribbons wrapping around it. The proposed model can reproduce the negative twist-stretch coupling of the helix successfully as well as its global stretching, bending, and torsional rigidities measured experimentally. Our parametric study of the model using the finite element method further reveals that the stiffness of phosphate backbones is a crucial factor for the counterintuitive overwinding behavior of the duplex and its extraordinarily high torsional rigidity, the major-minor grooves augment the twist-stretch coupling, and the change of the helicity might be responsible for the transition from a negative to a positive twist-stretching coupling when a tensile force is applied to the duplex.
Highlights
Recent advances in single-molecule experiments have thrown new light on the mechanics of the DNA double helix through direct manipulation of individual DNA molecules and characterization of their structural properties [1,2,3]
In-plane shear stresses under torsion, on the other hand, are concentrated on the edges due to the cross-sectional warping, but the level of concentration decreases with the helicity (Fig 2d)
Both S/B and C/B show a similar dependency on aspect ratio (AR), C/B is almost independent of D while S/B decreases with D (Fig 3a and 3b) that can be inferred from the rigidities of rectangular prism structures whose S/B and C/B are proportional to (1+AR2)/D2 and 1+AR2, respectively
Summary
Recent advances in single-molecule experiments have thrown new light on the mechanics of the DNA double helix through direct manipulation of individual DNA molecules and characterization of their structural properties [1,2,3]. The elastic response of DNA double strands has been extensively studied, revealing their unique mechanical properties including the extraordinarily high torsional rigidity (approximately twice the bending rigidity) [4] and the counterintuitive overwinding behavior under tension [4,5,6]. We study the principal structural features of the duplex and their plausible role on its elastic mechanical properties using a helical continuum model where DNA double helices are treated as elastic helical solids with a polygonal cross-section. It is noteworthy that a PLOS ONE | DOI:10.1371/journal.pone.0153228 April 7, 2016
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