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Proteins, transfer RNA, and assembled ribosomal subunits are exported from the nucleus due to association with exportins, which bind signaling sequences called nuclear export signals (NES). The ability of both importins and exportins to transport their cargo is regulated by the Ran small G-protein .
This includes the transportation of RNA and ribosomal proteins from the nucleus to the cytoplasm, as well as proteins (such as DNA polymerase and lamins), carbohydrates, signaling molecules, and lipids moving into the nucleus. Notably, the nuclear pore complex (NPC) can actively mediate up to 1000 translocations per complex per second.
Gene expression first involves transcription, in which DNA is used as a template to produce RNA. In the case of genes encoding proteins, that RNA produced from this process is messenger RNA (mRNA), which then needs to be translated by ribosomes to form a protein. As ribosomes are located outside the nucleus, mRNA produced needs to be exported. [60]
Each human cell contains around two metres of DNA, which must be tightly folded to fit inside the cell nucleus.However, in order for the cell to function, proteins must be able to access the sequence information contained within the DNA, in spite of its tightly-packed nature.
Nuclear DNA and mitochondrial DNA differ in many ways, starting with location and structure. Nuclear DNA is located within the nucleus of eukaryote cells and usually has two copies per cell while mitochondrial DNA is located in the mitochondria and contains 100–1,000 copies per cell.
A eukaryotic cell has a nucleus that separates the processes of transcription and translation. Eukaryotic transcription occurs within the nucleus where DNA is packaged into nucleosomes and higher order chromatin structures. The complexity of the eukaryotic genome necessitates a great variety and complexity of gene expression control.
S/MARs (scaffold/matrix attachment regions), the DNA regions that are known to attach genomic DNA to variety of nuclear proteins, show an ever increasing spectrum of established biological activities. There is a known overlap of this large group of sequences with sequences termed LADs (lamina attachment domains).
The nuclear envelope has many nuclear pores that allow materials to move between the cytosol and the nucleus. [4] Intermediate filament proteins called lamins form a structure called the nuclear lamina on the inner aspect of the inner nuclear membrane and give structural support to the nucleus. [4]