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pen
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Hello!
From a data set of F-x measurements of a single dsDNA molecule I want to calculate the persistence length [itex] P [/itex]. So I plotted [itex] \frac {1} {\sqrt{(F)}}[/itex] vs. [itex]x[/itex] and fitted these data points (linear).
According to an interpolation formula the extension [itex]x[/itex] of a worm like chain with contour length [itex]L_0 [/itex] (Bustamante et al.,1994) is:
[itex] \frac{FP}{k_BT}= \frac{1}{4} \Big( 1-\frac{x}{L_0}\Big)^{-2} -\frac{1}{4} + \frac{x}{L_0}[/itex], applicable for extensions [itex]\frac{x}{L_0}<0.97[/itex]
Thus the y-intercept of the straight line fitted to the data as described above is [itex] 2\sqrt{\frac{P}{k_BT}}[/itex].
When I calculate [itex] P [/itex] this way, I get values between ~2.7 nm (when I choose a force range beween ~6-17pN, which is roughly linear, and the dsDNA molecule behaves as a Hookean spring). However these values are far below the expected value for the persistence length of dsDNA (50nm).
Does anyone see what' s wrong with my approach ?
Thanks a lot for help
Pen
P.S. please find attached the F-x-graph and the 1/sqrt(F)-x-graph
From a data set of F-x measurements of a single dsDNA molecule I want to calculate the persistence length [itex] P [/itex]. So I plotted [itex] \frac {1} {\sqrt{(F)}}[/itex] vs. [itex]x[/itex] and fitted these data points (linear).
According to an interpolation formula the extension [itex]x[/itex] of a worm like chain with contour length [itex]L_0 [/itex] (Bustamante et al.,1994) is:
[itex] \frac{FP}{k_BT}= \frac{1}{4} \Big( 1-\frac{x}{L_0}\Big)^{-2} -\frac{1}{4} + \frac{x}{L_0}[/itex], applicable for extensions [itex]\frac{x}{L_0}<0.97[/itex]
Thus the y-intercept of the straight line fitted to the data as described above is [itex] 2\sqrt{\frac{P}{k_BT}}[/itex].
When I calculate [itex] P [/itex] this way, I get values between ~2.7 nm (when I choose a force range beween ~6-17pN, which is roughly linear, and the dsDNA molecule behaves as a Hookean spring). However these values are far below the expected value for the persistence length of dsDNA (50nm).
Does anyone see what' s wrong with my approach ?
Thanks a lot for help
Pen
P.S. please find attached the F-x-graph and the 1/sqrt(F)-x-graph
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