Nucleus Membrane, pores

Figure 2. Hypothetical scheme to account for acquisition of a eukaryotic nucleus with double membrane, pores and duplicate sets of genetic material by endosymbiotic invasion of one procaryotic cell by a primitive flagellate. The resultant endosome would have a double membrane. The pores and pore apparatus could derive from multiple fusions of the flagellar membranes with the outer membrane of the endosome. The primitive motile apparatus of the invading flagellate could have contributed as well to the origins of the mitotic apparatus of the resulting endosymbiont.

The ER membranes are rich in lipoprotein and about 5 m/tt in thickness, each vesicle being bounded by a single membrane. The electron microscope reveals the nuclear envelope as consisting of two membranes of similar structure and the outer of these two membranes has been shown to be continuous with the membranes of the ER, so that the space (20-40 m/ in width) between the two membranes of the nuclear envelope is continuous with the space system of the ER (Fig. 2.10). The ER offers a great area of contact with the matrix of the cytoplasm which in turn has continuity into the nucleus via pores (20-40 m/u diam.) in the nuclear envelope. 

The smaU nucleus of the yeast ceU is surrounded by a membrane or tonoplast, which has many pores with an average diameter of about 0.085 p.m. 

The nucleus is surrounded by the nuclear envelope, which takes on a lumenal structure connected to the endoplasmic reticulum. The transport of proteins into (and out of) the nucleus occurs through the nuclear pore complex (NPC), a large complex composed of more than 100 different proteins (Talcott and Moore, 1999). Because NPC forms an aqueous pore across the two membranes, small proteins less than 9 nm in diameter can pass through it simply by diffusion. However, most of the transports of both proteins and RNAs are mediated by an active transport mechanism. It is now clear that there is heavy traffic through the NPC in both directions. Proteins are not only imported into the nucleus but also actively exported from it as well. There are many reasons for nuclear export. One reason is to send some shuttle proteins back after their import another is for some viral proteins to export their replicated genomes outside the nucleus. 

Nuclear Envelope The membrane system of the cell nucleus that surrounds the nucleoplasm. It consists of two concentric membranes separated by the perinuclear space. The structures of the envelope where it opens to the cytoplasm are called the nuclear pores (nudear pore). [NIH]... 

Ultrastructural examination of nuclei in situ showed they were not surrounded by a continuous double-layered membrane, but that the membrane was interrupted by pores (Callan and Tomlin, 1950). These were not holes but were highly organized structures involved in transport between the nucleus and the cytosol. 

The neuron contains severai speciaiized components, caiied organeiies, which are anaiogous to the organs of a body. The nucleus is approximateiy 3-18 pm in diameter and contains deoxyribonucleic acid (DNA). The nuciear membrane has pores to aiiow passage of substances in and out of the nucieus. The nucieus aiso has a body within caiied the nucieoius, which manufactures ribosomes and contains ribonucieic acid (RNA), a coating of DNA, and severai enzymes. 

Figure 4 Transfer of DNA from cytoplasm into the nucleoplasm. The DNA-containing complex can enter the nucleus by (1) crossing the membrane during mitotic nuclear membrane breakdown (2) diffusion through nuclear pore for small particles and (3) targeted uptake through the nuclear pore, facilitated by a nuclear localization sequence. Abbreviations NLS, nuclear localization sequence IMP, importin.

The exchange of substances between the nucleus and the cytoplasm is mediated by pore complexes with complicated structures, which traverse the nuclear membrane. The nuclear pores consist of numerous proteins that form several connected rings of varying diameter. Low-molecular structures and small... 

The final principal component of the cell is the nucleus. This is located in the center of the cell and is surrounded by a double membrane, the outer layer being derived from the ER of the cytoplasm and the inner layer coming from the nucleus itself. The two leaflets of the double membrane are fused in places, producing nuclear pores that enable the transfer of macromolecules from the cytoplasm to the nucleus. Two important components of the nucleus are chromatin and the nucleolus. Chromatin represents polymers of DNA complexed with protein. The nucleolus is a complex substructure, composed of ribonucleoprotein granules, that controls the synthesis of RNA destined to form the ribosomes of the cytoplasm. Cells engaged heavily in protein synthesis have... 

Each cell nucleus contains one or more dense nucleoli, regions that are rich in RNA and may contain 10-20% of the total RNA of cells. Nucleoli are sites of synthesis and of temporary storage of ribosomal RNA, which is needed for assembly of ribosomes. The nuclear envelope is a pair of membranes, usually a few tens of nanometers apart, that surround the nucleus. The two membranes of the pair separate off a thin perinuclear space (Fig. 1-7). The membranes contain "pores" -130 ran in diameter with a complex structure (see Fig. 27-8).38/39 There is a central channel -42 ran in diameter, which provides a route for controlled passage of RNA and other large molecules from the nucleus into the cytoplasm and also from the cytoplasm to the nucleus. Smaller -10 nm channels allow passive diffusion of ions and small molecules. 

Nucleus 0.7-3 Surrounded by a double membrane (10 nm), containing pores (40-70 nm wide) flexible and contains cytologically distinguishable chromosomes. Nucleolus about 3 nm... 

Membrane destabilization can be simultaneously monitored by using propidium iodide. This non fluorescent and poorly permeant small molecule enters into the cells only upon membrane permeabilization/ destabilization and becomes fluorescent upon binding to DNA in the nucleus. In the presence of melittin, cells are also rapidly (200 s) red-labeled upon peptide induced membrane permeabilization (Figure 16.4D). It can be seen that the diffusion of propidium iodide inside the cells is correlated with the leak of EGFP. The results show that melittin induces the formation of pores in the plasma membranes allowing the passage of... 

Mineralocorticoids are believed to increase sodium reabsorption by affecting sodium channels and sodium pumps on the epithelial cells lining the renal tubules.18,58 Mineralocorticoids ability to increase the expression of sodium channels is illustrated in Figure 29-5. These hormones enter the tubular epithelial cell, bind to receptors in the cell, and create an activated hormone-receptor complex.18 This complex then travels to the nucleus to initiate transcription of messenger RNA units, which are translated into specific membrane-related proteins.27,58 These proteins in some way either create or help open sodium pores on the cell membrane, thus allowing sodium to leave the tubule and enter the epithelial cell by passive diffusion.27,83 Sodium is then actively transported out of the cell and reabsorbed into the bloodstream. Water reabsorption is increased as water follows the sodium movement back into the bloodstream. As sodium is reabsorbed, potassium is secreted by a sodium-potassium exchange, thus increasing potassium excretion (see Fig. 29-5). 

The nucleus stores the cell s genetic information as DNA in chromosomes. It is bounded by a double membrane but pores in this membrane allow molecules to move in and out of the nucleus. The nucleolus within the nucleus is the site of ribosomal ribonucleic acid (rRNA) synthesis. 

The nucleus is bounded by two membranes, the inner and outer nuclear membranes. These two membranes fuse together at the nuclear pores through... 

The nucleus of eukaryotic cells is a very complex structure, containing various components. It is separated from the rest of the cell by two membranes named the nuclear envelope. At regular intervals, the two membranes of the nuclear envelope form pores with a diameter of around 90 nm. These pores regulate flux of macromolecules to and from the cytoplasm. Inside the nucleus is located the nucleolus, which acts to produce ribonucleic acid (RNA), which is the first step for ribosome synthesis. 

Alterations of the mitochondrial membrane may precede those that occur in the nucleus. These changes can involve both the inner and the outer membrane, leading to a dissipation of the transmembrane potential and/or to the release of intermembrane proteins through the outer membrane. The main group of proteins responsible for mitochondrial alterations consist of the proteins known as Bax, which form pores in the outer membrane, causing the release of cytochrome c to the cytoplasm (Loeffler and Kroemer, 2000 Arden and Betenbaugh, 2004). Western blot techniques can be used to specifically detect the presence of cytochrome c in the cytoplasm of apoptotic cells. However, complex purification protocols are required, and there is the possibility of incomplete separation of mitochondria from the cytoplasm therefore, this technique is not very popular. 

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