An actin filament fragment observed by fluorescence microscopy has contour length

PHYSICS · Subjective · Fermi University Physics · Condensed Matter, Materials & Soft Matter · Soft condensed matter · Soft condensed matter

Soft Matter at the Thermal Scale, Ch The size and shape of a polymer chain

Problem

An actin filament fragment observed by fluorescence microscopy has contour length L=3.0 μmL = 3.0\,\mu\mathrm{m}. Its mean-square end-to-end distance, averaged over many images, is measured to be ⟨R2⟩=8.4 μm2\langle R^2\rangle = 8.4\,\mu\mathrm{m}^2. Because LL is much shorter than the persistence length reported for actin filaments (of order 10 μm10\,\mu\mathrm{m}), use the short-contour-length limit of the worm-like chain, ⟨R2⟩≈L2(1−L3lp),\langle R^2\rangle \approx L^2\left(1-\frac{L}{3l_p}\right), to estimate the persistence length lpl_p of this filament.

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