Single-Molecule Mechanics of DNA - DNA Nanotechnology: From Structure to Function - page 89

Fig. 6.5 The scheme of
WLC model

l p

R

Fig. 6.6 Experimental force
curve of dsDNA ( circles )and
the fitting curves ( solid lines )
(Reprinted from Ref. [ 21 ],
Copyright 1998, with
permission from Elsevier)

l p
k B T

R
L

1
4Œ1 R.F /=L 2

1
4

F D C (6.1)

where R is the end-to-end distance (i.e., the measured length) of a polymer chain at
a given stretching force F , k B is the Boltzmann constant, T is the temperature in the
Kelvin scale, L is the contour length of the polymer chain.
The fitting process can be regarded as the process of seeking the approximate
solution of l p in a heuristic way. It was reported by Bustamante et al. that the l p of
dsDNA is 53 nm in physiological condition, which corresponds to the length of 150
base pairs; see Fig. 6.6 . This result implies that the dsDNA is rather rigid (Fig. 6.7 ).
The FJC model treats a polymer as a chain of statistically independent segments
of length l k (Kuhn segment length). The length of the segment is fixed, in other
words, the modulus of the polymer chain is infinite. The segments follow a random
walk in the 3D space. In FJC model, the elasticity of a chain purely comes from