A globular protein of molecular mass and effective radius diffuses in water of…

PHYSICS · Subjective · Fermi University Physics · Thermal, Statistical & Complex Systems · Biophysics & Medical Physics · Physical foundations of the living cell

Forces, Machines and Signals, Ch Diffusion: friction, capture and the crowded cytoplasm

Problem

A globular protein of molecular mass 100 kDa100\,\mathrm{kDa} and effective radius 3.0 nm3.0\,\mathrm{nm} diffuses in water of viscosity η=1.0 mPa s\eta = 1.0\,\mathrm{mPa\,s} at 293 K293\,\mathrm{K}. Take ζ=6πηa\zeta = 6\pi\eta a as quoted for a sphere, and use the Avogadro constant NA=6.022×1023 mol−1N_A = 6.022\times10^{23}\,\mathrm{mol^{-1}} to convert its molar mass to a single-molecule mass. Find the Langevin crossover time τm=m/ζ\tau_m = m/\zeta.

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