Nuclear pore

Nuclear pores (abbreviated NPC, of Engl. Nuclear pore complex ) are protein complexes in the nuclear envelope of the cell nuclei of eukaryotic cells. The core sleeve consists of a double membrane. Nuclear pores go through both membranes, thus they act as "gates" and allow the transport of certain molecules in and out of the nucleus.

In the nuclear envelope of a vertebrate cell, there are about 2,000 pores.

Structure

The edge of the pore is both outside and inside of eight protein complexes. Spoke -like extensions extend to the center of the pore, where a Zentralgranulum sitting, which also constitutes a ribonucleoprotein complex.

The pore comprises a channel that is constructed by a 3-D network of braid FG repeats ( F = phenylalanine, G = glycine) can diffuse freely through the water.

Function

Nuclear pore catalyze the passive or active transport of proteins, RNA, ribonucleotide protein complexes and small molecules through the nuclear membrane.

Passive transport

Small molecules up to 5,000 Da (Daltons ) can diffuse freely through the nuclear pore. Molecules of about 17,000 Da already need 2 minutes for passage. Larger particles with a diameter of up to two nm or 40,000 Da can not pass independently through the nuclear pores.

Transport of mRNA out of the nucleus

At an increased rate of transcription, for example, in cells which produce a lot of proteins, the number of nuclear pores is increased, however, because the transcription, although the nucleus, translation is carried out of the cell nucleus and each final mRNA molecule must therefore leave the cell nucleus.

First, the protein binds nuclear RNA export factor 1 to the exon junction RNA complex ( EJC ). This unit is now on the other hand binds to the export receptor of the NPC. Everything together is called an export- competent complex. The movement of this complex through the pore requires energy, which is provided in the form of GTP. At the other end of the said complexes dissociate into their component complexes.

Import of proteins

The reverse transport of proteins into the nucleus is performed only when the protein has a nuclear localization sequence. This is a made ​​up of a few amino acids peptide sequence. Also required certain transport molecules ( importins ) that initiate transport.