Nuclear pore is a pore on the boundary membrane between the nucleus and the cytoplasm, but the nuclear membrane is not connected, and there are many small holes on it. This is called a nuclear pore.
Figure 1. Diagram of human cell nucleus.
Definition: Channels with a complex ring structure on the nuclear membrane of the nucleus have a certain regulatory effect on the material exchange between the nucleus and the cytoplasm. Also known as nuclear membrane pore or nuclear pore. Structurally, the nuclear pore complex is mainly composed of proteins; functionally, the nuclear pore complex can be regarded as a special transmembrane transport protein complex, and it is a bifunctional and bidirectional hydrophilic nucleoplasm exchange channel. The nuclear membrane pores of different organisms have the same structure and exist in the form of nuclear pore complexes. Its internal and external caliber is about 70-80 nm, and the diameter of the channel is about 9 nm. There are 8 spherical particles arranged symmetrically around the inner and outer mouths of the nuclear membrane pores, with a diameter of about 15 nm; there is still a central particle in the center, with a diameter of about 30 nm. There are filaments between the central particles and the spherical particles. These filaments have the properties of ribonucleoproteins. There are also some amorphous substances in the nuclear membrane pore channels. The number, distribution and density of nuclear membrane pores are related to the metabolic activity of the cells, and the number of nuclear membrane pores is high in the place where the material exchange between nuclear and cytoplasm is strong. It can be seen that nuclear membrane pores have a certain role in regulating the nuclear and cytoplasmic material exchange.
What substances can pass through the pores? What substances can pass through the nuclear membrane?
Those that can pass through the pores are:
mRNA, tRNA, protein, enzyme. Because mRNA is formed in the nucleus, and proteins are synthesized in the cytoplasm, mRNAs need to come out, as do tRNAs.
Those that can pass through the nuclear membrane are:
Ions and smaller molecules, such as amino acids, sugars, protamines, histones, RNases and DNases.
Nuclear and cytoplasmic transport occurs in two directions. Since all proteins are synthesized in the cytoplasm, the proteins needed in the nucleus must be transported from the cytoplasm. Because all RNA is synthesized in the nucleus, all cytoplasmic RNA (mRNA, rRNA, tRNA, and other small RNAs) must be transported out of the nucleus.
Figure 2. Nuclear pore. Side view.
Nuclear pore complex
Nuclear pore complex, there are many holes in the nuclear envelope, called nuclear pores, which are the openings in the nuclear membrane of the cell that communicate the cytoplasm and cytoplasm. They are formed by the local fusion of the inner and outer membranes. 80 ~ 120nm. A typical mammal has 3,000 to 4,000 nuclear pores on its nuclear membrane. The number of nuclear pores is large when cells with strong functions are synthesized. A nuclear pore is a structure in which a group of protein particles are arranged in a specific way. It can be separated from the nuclear membrane and is called a nuclear pore complex. NPC is a round structure with an outer diameter of 120 nm and an 8-plane symmetry. The hub is a cylindrical plug, called the central transporter. Eight spokes are extended outward from the central transport protein and connected to the nucleoplamic ring on the nucleus surface of the nuclear pore complex and the cytoplasmic ring on the cytoplasmic surface. On the surface of the cytoplasmic ring, there are often 8 cytoplasmic particles on it, and the filaments on the nucleus ring extend to the nucleus to form a cage structure, called a basket. In some organisms, NPC baskets are often connected to a layer of interwoven fibers, called a nuclear envelope lattice.
Figure 3. Cell nucleus with pores.