 Diagram of human cell nucleus. Nuclear pore labeled at bottom left
 Nuclear pore. Side view. 1. Nuclear envelope. 2. Outer ring. 3. Spokes. 4. Basket. 5. Filaments. (Drawing is based on electron microscopy images) Nuclear pores are large protein complexes that cross the nuclear envelope, which is the double membrane surrounding the eukaryotic cell nucleus. There are about on average 2000 nuclear pore complexes in the nuclear envelope of a vertebrate cell, but it varies depending on the number of transcriptions of the cell. The proteins that make up the nuclear pore complex are known as nucleoporins. About half of the nucleoporins typically contain either an alpha solenoid or a beta-propeller fold, or in some cases both as separate structural domains. The other half exhibit structural characteristics typical of "natively unfolded" proteins, i.e. they are highly flexible proteins that lack ordered secondary structure.[1] These disordered proteins are the FG nucleoporins, so called because their amino-acid sequence contains many repeats of the peptide phenylalanine—glycine.[2] Image File history File links Diagram_human_cell_nucleus. ...
Image File history File links Diagram_human_cell_nucleus. ...
Image File history File links No higher resolution available. ...
Image File history File links No higher resolution available. ...
A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...
The nuclear envelope (also known as the perinuclear envelope, nuclear membrane, nucleolemma or karyotheca) is the double membrane of the nucleus that encloses genetic material in eukaryotic cells. ...
The endomembrane system is the system of internal membranes within eukaryotic cells that divide the cell into functional and structural compartments, or organelles. ...
Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ...
Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the...
HeLa cells stained for DNA with the Blue Hoechst dye. ...
The nuclear envelope (also known as the perinuclear envelope, nuclear membrane, nucleolemma or karyotheca) is the double membrane of the nucleus that encloses genetic material in eukaryotic cells. ...
A trimer of the peridinin-chlorophyll-containing protein from the dinoflagellate Amphidinium carterae illustrating the alpha solenoid fold. ...
Ribbon diagram of the C-terminal WD40 domain of Tup1 (a transcriptional co-repressor in yeast), which adopts a 7-bladed beta-propeller fold. ...
Within a protein, a structural domain (domain) is an element of overall structure that is self-stabilizing and often folds independently of the rest of the protein chain. ...
Phenyl alanine is an α-amino acid with the formula HO2CCH(NH2)CH2C6H5. ...
For the plant, see Glycine (plant). ...
Nuclear pores allow the transport of water-soluble molecules across the nuclear envelope. This transport includes RNA and ribosomes moving from nucleus to the cytoplasm and proteins (such as DNA polymerase and lamins), carbohydrates, signal molecules and lipids moving into the nucleus. It is notable that the nuclear pore complex (NPC) can actively conduct 1000 translocations per complex per second. Although smaller molecules simply diffuse through the pores, larger molecules may be recognized by specific signal sequences and then be diffused with the help of nucleoporins into or out of the nucleus. This is known as the RAN cycle. Each of the eight protein subunits surrounding the actual pore (the outer ring) projects a spoke-shaped protein into the pore channel. The center of the pore often appears to contains a plug-like structure. It is yet unknown whether this corresponds to an actual plug or is merely cargo caught in transit. Left: An RNA strand, with its nitrogenous bases. ...
Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ...
A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...
3D structure of the DNA-binding helix-hairpin-helix motifs in human DNA polymerase beta A DNA polymerase is an enzyme that assists in DNA replication. ...
A lamin is a fibrous protein that gives the cell nucleus its shape. ...
Carbohydrates (literally hydrates of carbon) are chemical compounds that act as the primary biological means of storing or consuming energy, other forms being fat and protein. ...
Nitric oxide is a quite salient signaling molecule, instrumental in both learning and memory. ...
Figure 1: Basic lipid structure. ...
diffusion (disambiguation). ...
The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...
Ran GTPase is a small GTPase that is involved in transport into and out of the cell nucleus during interphase and also involved in mitosis. ...
Size and complexity The entire pore complex has a diameter of about 120 nm, the diameter of the opening is about 50 nm wide and its "depth" is about 200 nm.[citation needed] The molecular mass of the NPC is about 125 million dalton and contains approximately 50 different proteins components. A nanometre (American spelling: nanometer) is 1. ...
The molecular mass (abbreviated Mr) of a substance, formerly also called molecular weight and abbreviated as MW, is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12). ...
The unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express atomic and molecular masses. ...
Transport through the nuclear pore complex Small particles (< 30 kDa) are able to pass through the nuclear pore complex by passive diffusion. Larger particles are also able to pass through the large diameter of the pore but at almost negligible rates.[3] Efficient passage through the complex requires several protein factors.[4] Karyopherins, which may act as importins or exportins are part of the Importin-β super-family which all share a similar three-dimensional structure. Possible meanings: Kachin Defense Army Kentucky Distillers Association Kongsberg Defence & Aerospace This page expands a three-character combination which might be any or all of: an abbreviation, an acronym, an initialism, a word in English, or a word in another language. ...
Karyopherins are a group of proteins involved in transporting molecules through the nuclear pores of the nuclear envelope. ...
Three models have been suggested to explain the translocation mechanism:
- Affinity gradients along the central plug
- Brownian affinity gating
- Selective phase
Import of proteins Any cargo with a nuclear localization signal (NLS) exposed will be destined for quick and efficient transport through the pore. Several NLS sequences are known, generally containing a conserved polypeptide sequence with basic residues such as PKKKRKV. Any material with an NLS will be taken up by importins to the nucleus. A nuclear localizing sequence (NLS) is an amino acid sequence which acts like a tag on the exposed surface of a protein. ...
The classical scheme of NLS-protein importation begins with Importin-α first binding to the NLS sequence, and acts as a bridge for Importin-β to attach. The importinβ—importinα—cargo complex is then directed towards the nuclear pore and diffuses through it. Once the complex is in the nucleus, RanGTP binds to Importin-β and displaces it from the complex. Then the cellular apoptosis susceptibility protein (CAS), an exportin which in the nucleus is bound to RanGTP, displaces Importin-α from the cargo. The NLS-protein is thus free in the nucleoplasm. The Importinβ-RanGTP and Importinα-CAS-RanGTP complex diffuses back to the cytoplasm where GTPs are hydrolyzed to GDP leading to the release of Importinβ and Importinα which become available for a new NLS-protein import round. The cellular apoptosis susceptibility protein (CAS) is an exportin which in the nucleus is bound to RanGTP. Nuclear_pore#Import_of_proteins MeSH Cellular+Apoptosis+Susceptibility+Protein Cell cycle proteins Cdc2 - Cdc25 - CDK-activating kinase - Cellular apoptosis susceptibility protein - Cyclin (A, B, D, E) - Cyclin-dependent kinase (2, 4, 6) - E2F - Maturation promoting...
Guanosine triphosphate (GTP) is also known as guanosine-5-triphosphate. ...
Although cargo passes through the pore with the assistance of chaperone proteins, the translocation through the pore itself is not energy dependent. However, the whole import cycle needs the hydrolysis of 2 GTPs and is thus energy dependent and has to be considered as active transport. The import cycle is powered by the nucleo-cytoplasmic RanGTP gradient. This gradient arises from the exclusive nuclear localization of RanGEFs, proteins that exchange GDP to GTP on Ran molecules. Thus there is an elevated RanGTP concentration in the nucleus compared to the cytoplasm. Sodium-Potassium pump, an example of Primary active transport secondary active transport Active transport (sometimes called active uptake) is the mediated transport of biochemicals, and other atomic/molecular substances, across membranes. ...
Export of proteins Some nuclear proteins need to be exported from the nucleus to the cytoplasm, as do ribosome subunits and messenger RNAs. Thus there is an export mechanism similar to the import mechanism. Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ...
The life cycle of an mRNA in a eukaryotic cell. ...
In the classical export scheme, proteins with an nuclear export sequence (NES) can bind in the nucleus to form a heterotrimeric complex with an exportin and RanGTP (for example the exportin CRM1). The complex can then diffuse to the cytoplasm where GTP is hydrolysed and the NES-protein is released. CRM1-RanGDP diffuses back to the nucleus where GDP is exchanged to GTP by RanGEFs. This process is also energy dependent as it consumes one GTP. Export with the exportin CRM1 can be inhibited by Leptomycin B. Leptomycin B is a secondary metabolite produced by Streptomyces spp. ...
Export of RNA Different export pathways from NPC for each RNA class exist. RNA export is also signal mediated (NES), the NES is in RNA-binding proteins (except for tRNA which has no adapter). It is notable that all viral RNAs and cellular RNAs (tRNA, rRNA, U snRNA, microRNA) except mRNA are dependent on RanGTP. Conseved mRNA export factors are necessary for mRNA nuclear export. Export factors are Mex67/Tap (large subunit) and Mtr2/p15 (small subunit). An adapter binds to the large export factor subunit mediating the export process. Left: An RNA strand, with its nitrogenous bases. ...
Transfer RNA (abbreviated tRNA) is a small RNA chain (74-93 nucleotides) that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. ...
A non-coding RNA (ncRNA) is any RNA molecule that functions without being translated into a protein. ...
Ribonucleic acid (RNA) is a nucleic acid consisting of a string of covalently-bound nucleotides. ...
The stem-loop secondary structure of a pre-microRNA from Brassica oleracea. ...
Additional images The Ran-GTP cycle Image File history File links Download high-resolution version (2000x1350, 912 KB) The Ran-GTP cycle for the Cell nucleus article. ...
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