Nuclear double membrane

The nucleus is perhaps the most important eukaryotic organelle. A typical nucleus exhibits several important structural features (Figure 1.12). It is surrounded by a nuclear double membrane (usually called the nuclear envelope). One of its prominent features is the nucleolus, which is rich in RNA. The RNA... 

Nucleus The nucleus is separated from the cytosol by a double membrane, the nuclear envelope. The DNA is complexed with basic proteins (histones) to form chromatin fibers, the material from which chromosomes are made. A distinct RNA-rich region, the nucleolus, is the site of ribosome assembly. The nucleus is the repository of genetic information encoded in DNA and organized into chromosomes. During mitosis, the chromosomes are replicated and transmitted to the daughter cells. The genetic information of DNA is transcribed into RNA in the nucleus and passes into the cytosol where it is translated into protein by ribosomes. 

Material within the nucleus (nucleoplasm) is separated from the cytoplasm by the nuclear membrane (also known as an envelope), a double membrane that is continuous... 

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... 

The nucleus of the eukaryotic cell is separated from the cytoplasm by the double-membrane nuclear envelope, which provides a continuous boundary between the nucleoplasm and the cytoplasm, except where it is penetrated by nuclear pores, each of which is surrounded by a disklike structure, the nuclear pore complex. These pores serve an export-import function for an exchange of materials between the nucleus and the cytosol. This is necessary in eukaryotic... 

The NE is an elaborate structure that can be divided into several distinct sub-domains the nuclear pore complexes (NPCs), the lamin polymer, and a double membrane system consisting of the outer nuclear membrane (ONM), inner nuclear membrane (INM), lumen, and pore membrane (PoM) together with their integral proteins (Figure 1 see colour insert). The ONM is not only continuous with the ER, but is also studded with ribosomes indicating that in addition to being the outermost layer of the nucleus it is also a subcompartment of the ER. How much of its complement of integral membrane proteins is unique from more distal ER... 

The nucleus is bound by a double-membrane, which is contiguous through the nuclear pores, known as the nuclear envelope. The pores are required to allow RNA out and membrane lipids in (which is needed for growth during S phase). The inner face of the inner nuclear envelope (INE) is coated by the nuclear lamina, which contains intermediate fibres called lamins A, B and C (atleast in mammals). Phosphorylation of lamins by kinases cause nuclear envelope breakdown during prometaphase. Chromosomes occupy definite positions within the nucleus because of the interaction between lamins and telomeres, for example the Rabl conformation in yeast. 

In the cytoplasm, the endoplasmic reticulum is a complex system of double membranes with a lumen —20 nm wide. These membranes are so fine that they are only visible by electron microscopy. They are probably associated with nearly every organelle, having connections with the nuclear membrane, the plasmalemma, and the mitochondria (for a review, see Ref. 93). It would be surprising were the endoplasmic reticulum not an important structure for metabolic compartmentation. 

Pinerii and coworkers, and a few other groups, have used ESR and Mossbauer spectroscopy as well as SANS, extended x-ray absorption fine structure (EX.AFS), and magnetization and susceptibility data to analyze local. struct.ure in perfluorinated ionomer membranes and the distribution of water within them isee, for inst,ance, (61-65) 1. The application of the KNDOR (electron nuclear double resonance) technique to deuteriated methanol-swollen Scunples of these membranes has been reportesd i-ecentiy (66). Photophysical methods have also tef n applied in hydration. si.udies of these membranes (67-69). Finally, some NMR results on the same hydrated perfluorinat,ed ionomer.s well as on hydrated... 

The nucleus is an organelle surrounded by a double membrane, the nuclear envelope. 

Q Nuclear envelope, a double membrane, encloses the contents of the nucleus the outer nuclear membrane is continuous with the rough ER. 

The nuclear envelope is a double-membrane extension of the rough endoplasmic reticulum containing many nuclear pore... 

Oxidative phosphorylation occurs on membranes. In bacteria, chemiosmotic ATP synthesis occurs at the cytoplasmic membrane. In plant and animal cells, these reactions occur in the mitochondrion, a double-membraned organelle (Figure 11-1). The ancestor of mitochondria was a bacterial cell incorporated into a nucleated cell, which subsequently lost much (although not all) of its DNA. Most mitochondrial proteins are encoded by nuclear DNA. Some respiratory proteins, along with mitochondrial ribosomal RNA and transfer RNAs, are encoded by mitochondrial DNA. 

The genetic information of mammalian cells is almost exclusively located in the nucleus (Figure 17.1). This cell organelle is bounded by a double membrane which contains nuclear pore complexes as the connection to the cytoplasm and it is studded with ribosomes [12]. Replication and transcription of DNA are cellular processes that take place in the nucleus. DNA replication occurs during the mammalian cell cycle, which can be divided into different phases. The gap between mitosis and the initiation of DNA replication is termed G -phase, while the gap between DNA synthesis (S-phase) and mitosis (M-phase) is called G2-phase [13]. 

Reassembly of nuclei can be followed most easily by phase-contrast microscopy. During the course of the assembly reaction clusters of chromosomes will be observed to fuse into single masses of chromatin, which will eventually become spherical in shape as decondensation progresses. At this point, thin-section electron microscopy should reveal the presence of a continuous double membrane studded with nuclear pore complexes surrounding each chromatin mass. Assembly of individual nuclear envelope components such as nuclear lamins or nuclear pore complex proteins can best be analyzed by immunofluorescence microscopy (Burke and Gerace, 1986). This is performed as follows. 

The membranes of the two vesicle populations, and possibly others, form the double membrane of the NE, which must be continuous around the chromatin before the nascent nuclei are able to accumulate imported proteins. Our results indicate that the fusion of NEP-A vesicles with NEP-B vesicles is necessary for the formation of a functional NE, but we have not yet defined the precise contribution(s) of either vesicle population to the fully assembled NE. Proteins in both vesicle populations may be required for the fusion of inner and outer nuclear membranes at the sites of NPC assembly, and for the recruitment of the disassembled subunits of NPCs to the nascent NE. While the recruitment of NPC subunits to the NE membrane could either precede or follow the fusion of inner and outer membranes, some NPC proteins almost certainly associate with the NE after the fusion of inner and outer nuclear membranes. Finlay and Forbes (1990) have shown that the depletion of a subset of NPC proteins using wheat germ agglutinin-conjugated agarose resulted in the assembly of NEs in which inner and outer membranes had fused, but which were unable to import proteins. 

An electron micrograph of a sea urchin male pronucleus swollen in an S o extract as described above is shown in Fig. 4. The chromatin is uniformly decon-densed and enclosed by a nuclear envelope consisting of a double membrane... 

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