  In this paper a lattice model for diffusional transport of particles in the
interphase cell nucleus is proposed. Dense networks of chromatin fibers are
created by three different methods: randomly distributed, non-interconnected
obstacles, a random walk chain model, and a self avoiding random walk chain
model with persistence length. By comparing a discrete and a continuous version
of the random walk chain model, we demonstrate that lattice discretization does
not alter particle diffusion. The influence of the 3D geometry of the fiber
network on the particle diffusion is investigated in detail, while varying
occupation volume, chain length, persistence length and walker size. It is
shown that adjacency of the monomers, the excluded volume effect incorporated
in the self avoiding random walk model, and, to a lesser extent, the
persistence length, affect particle diffusion. It is demonstrated how the
introduction of the effective chain occupancy, which is a convolution of the
geometric chain volume with the walker size, eliminates the conformational
effects of the network on the diffusion, i.e., when plotting the diffusion
coefficient as a function of the effective chain volume, the data fall onto a
master curve.
