nucleus 整理.doc

Chapter 1: the cell nucleus the structure and regulate of nuclear envelope. structure: The nuclear lamina supports the nuclear envelope. The nuclear lamina is a meshwork of interconnected protein subunits called nuclear lamins. The lamins are a special class of intermediate filament proteins that polymerize into a two-dimensional lattice . disassembled: When a nucleus disassembles during mitosis, the nuclear lamina depolymerizes. The disassembly is at least partly a consequence of direct phosphorylation of the nuclear lamins by the cyclin-dependent kinase (M-cdk) activated at the onset of mitosis. At the same time, proteins of the inner nuclear membrane are phosphorylated, and the nuclera pore complexes disassemble and disperse in the cytosol. assembled: Later in the anaphase, the nuclear envelope reassembles on the surface of the chromosomes, as inner nuclear membrane proteins and dephosphoylated lamins rebind to chromatin. ER menmbranes wrap around groups of chromosomes and continue fising until a sealed nuclear envelope is reformed. During this process, the nuclear pole complexes also reassemble and start actively reimporting proteins that contain nuvlear localiation signals. Because the envelope is closely applied to the surface of the chromosomes, all other large proteins are kept out of the newly assembled nucleus. the consists, structure of the Nuclear Pore Complexes(NPC) In cross section, a nuclear pore complex seems to have four structural building blocks: column subunits, which form the bulk of the pore wall; annular subunits, which extend spokes toward the center of the pore; lumenal subunits, which contain transmembrane proteins that anchor the complex to the nuclear membrane; ring subunits, which form the cytosolic and nuclear faces of the complex. In addition, fibrils protrude from both the cytosolic and the nuclear sides of the complex. On the nuclear side, the fibrils converge to form basketlike structures. This is in contrast to proteins that make