| Method |
According to hydrodynamics, the coefficient of diffusion of spherically shaped
particles in water is given by D=KBT/6/p/?/R , where R is the
particle radius, and ? is the viscosity. For miRNA (or folded
proteins), R is about 2×10^-9m. Using this value and ?=0.01g/cm/sec=0.001kg/m/sec, (1.380?6504(24)×10^-23Kg× m^2×sec^-2×K^-1×300K)/ (6×3.14×0.001Kg×m^-1sec^-1×2×10^-9m)=1.1×10^-10m^2/sec =110µm^2/sec˜100µm^2/sec. Inside cells, the
diffusion coefficient is, however, lower by about one order of
magnitude (Misteli 2008 PMID 17994245) due to macromolecular crowding resulting in
steric constraints on diffusion and influencing diffusion via
weak intermolecular interactions, i.e., D=10µm^2/sec. |