Nucleo-Cytoplasmic Exchange

ID #1224

My question pertains to the passive diffusion of molecules into and out of the Nuclear Pore Complex. I have written down that the passive diameter is from 9-40 kDa; however, in the lecture notes it says that passive diffusion occurs with molecules less than 20 kDa. If this is the case why is it necessary for the passive diameter to extend out to 40 kDa for the Nuclear Pore Complex cause wouldn't a molecule that is 40 kDa have to be actively transported into Nucleus through the pore complex?

The size exclusion for proteins is given in molecular weight (kilodaltons), but the diameter is given in nanometers. 40 nanometers is as wide as the central channel can get, but that's big enough to pass even a large ribosomal subunit!

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