Single-Molecule Mechanics of DNA - DNA Nanotechnology: From Structure to Function - page 88

Fig. 6.4 Scheme of
AFM-based single-molecule
force spectroscopy

Extension

converted into a force-extension curve, which is often called force curve in brief.
Currently, the AFM-based SMFS is one of the most widely used methods in the
field of single-molecule mechanics [ 13 - 17 ](Fig. 6.4 ).

6.2 Single-Molecule Mechanics of dsDNA

6.2.1 Single-Molecule Elasticity of dsDNA

6.2.1.1 Single-Molecule Entropic Elasticity of dsDNA

In 1992, by utilizing the magnetic tweezers, Bustamante et al. first measured the
stretching elasticity of single molecules of dsDNA in the buffer solution. The worm-
like chain (WLC) model and freely jointed chain (FJC) model are two popular
models to describe the single polymer chain. To understand single molecule dsDNA,
the biomacromolecule was treated by the two models, respectively [ 2 , 18 ].
The WLC model describes a polymer as a homogenous string of constant
bending elasticity, see Fig. 6.5 . The conformation of the molecule can be described
as a smooth curve, a worm-like chain. The persistence length, l p , is an important
parameter in the WLC model, which quantifies the stiffness of a polymer. In general,
alarger l p corresponds to a more rigid polymer chain. An approximate relation
between the end-to-end distance of the WLC chain and stretching force can be
written as Eq. 6.1 ,[ 13 , 15 ]