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Physics 850: Soft Condensed Matter Physics, Fall04 A.D. Dinsmore

Lecture 6: the Worm-like Chain (‘Kratky-Porod’) Model

(see next page for definition of u)

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all of the molecular detail is in this one parameter

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DNA experiment: 97,000-base DNA force-vs.-extension curve measured with laser trap and microscopy. (from R.H. Austin et al, Physics Today Feb., 1997 p32).

Solid curve: WLC model, lp = 50 nm. Dashed curve: FJC model.

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Model works for all extensions (for DNA, at least) until full extension (L ~ L0), when bond stretching plays a role.