Practice question

Nuclear pore complexes are massive one hundred ten to one hundred twenty megadalton assemblies spanning two lipid bilayers with eightfold rotational symmetry, comprised of about thirty distinct proteins called nucleoporins organized into scaffold and barrier layers. Y-complex Nup107-Nup160 forms outer rings, Nup93-Nup205 inner ring, and intrinsically disordered FG-repeat nucleoporins such as Nup62 complex, Nup98, Nup214 line central channel forming selective hydrogel that blocks nonspecific diffusion above forty kDa while allowing receptor-mediated transport. Importin beta family receptors bind nuclear localization signals and traverse FG mesh by transient hydrophobic interactions, exportins bind nuclear export signals in Ran-GTP dependent manner. Cytoplasmic filaments contain Nup358, nuclear basket contains Tpr. Actin filaments, spectrin network and dynein motors are cytoplasmic cytoskeletal components not part of pore scaffold. Knockdown of scaffold nucleoporins causes nuclear export defects and developmental arrest, while FG nucleoporin mutations linked to leukemia illustrate essential role in nucleocytoplasmic exchange maintaining compartment identity. Integration with cell cycle kinases, calcium signaling and mechanical cues ensures coordinated remodeling during growth, migration and differentiation.