7. The nucleus. (a) Section through an intact nucleus, (b) surface view,
with the internal chromatin exposed by removal of part of the pore covered nuclear envelope, and (c) the nucleolus (nuc) and nucleoskeleton after DNA removal, (d), (e) nuclear pores viewed from the outside and inside of the nucleus, (f) leukaemia cells containing distorted nuclei
A scaled-up analogy of pore traffic activity would involve a short length of drainpipe (as the pore channel) through which a mixture of tennis balls, golf balls, and marbles would pass in both directions at a rate of 1000 journeys per second. The flow is controlled by nucleoporin proteins which project into the channel, sorting and propelling the various molecules in the correct direction.