Nuclear pore

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Overview of the cell and its contents.

Nuclear pores are small specialized channels that perforate the nuclear envelope of a cell nucleus. Each pore has an outer diameter of about 130 nm and an inner pore diameter measuring about 9 nm. There are approximately 4000 nuclear pores present in the entire nuclear envelope of an active cell.

Each nuclear pore contains a cylinder-like structure, the nuclear pore complex, which is composed of over 50 core proteins called nucleoporins. The pores span the inner and outer nuclear membranes and allow for the movement of various molecules between the cytoplasm and nucleoplasm. 

Ions and small molecules pass freely across the pores by simple diffusion, while larger macromolecules such as ribonucleic acid, ribosomal subunits, proteins, transcription factors and enzymes, use an energy-dependent transport process. 

In addition to regulating the transport of molecules and creating a selectively permeable nuclear membrane, the nuclear pores play a role in the structural integrity of the nuclear membrane by holding the two lipid bilayers of the nuclear envelope together.