Nucleolus nucleus, nuclei

Nucleus Nucleus, nucleolus Steroid hormone receptors Immune-mediated disease ... 

The main feature of normal animal cell is its compartmentalization [7]. The DNA of the animal cell is restricted to the nucleus at all cell cycle stages except during metaphase when no nucleus exists. The synthesis of RNA occurs in the nucleus and most of it remains there, but messenger RNA and transfer RNA migrate to the cytoplasm. Ribosomal RNA is synthesized in the nucleolus the two ribosomal subunits are partly assembled in the nucleolus and nucleus then migrate to the cytoplasm. All protein synthesis proceed in the cytoplasm. The mitochondria, which is located only in the cytoplasm, contains DNA-s, RNA- and protein-synthesizing systems of their own [7]. 

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. 

The nucleus, nucleolus, and nuclear envelope of plant cells are like those of animal cells. 

Kem-isomer, n. nuclear isomer, ring isomer, -isomerie, /. nucleus (or nuclear) isomerism, -kbrper, m., -korperchen, n. nucleolus, -la-dung,/. nuclear charge main charge, -la-dungszahl, /. nuclear-charge number, atomic number, -leder, n. butt or bend leather. 

Fig. 2.6 The moqjhological events of sporulation in Saccharomyces cerevisiae. (a) starved cell V, vacuole LG, lipid granule ER, endoplasmic reticulum CW, cell wall M, mitochondrion S, spindle pole SM, spindle microtubules N, nucleus NO, nucleolus, (b) Synaptonemal complex (SX) and development of polycomplex body (PB) along with division of spindle pole body in (c). (d) First meiotic division which is completed in (e). (f) Prepararation for meiosis II. (g) Enlargement of prospore wall, culminating in enclosure of separate haploid nuclei (h). (i) Spore coat (SC) materials produced and deposited, giving rise to the distinct outer spore coat (OSC) seen in the completed spores of the mature ascus (j). Reproduced from the review by Dickinson (1988) with permission from Blackwell Science Ltd.

Like other cells, a neuron has a nucleus with genetic DNA, although nerve cells cannot divide (replicate) after maturity, and a prominent nucleolus for ribosome synthesis. There are also mitochondria for energy supply as well as a smooth and a rough endoplasmic reticulum for lipid and protein synthesis, and a Golgi apparatus. These are all in a fluid cytosol (cytoplasm), containing enzymes for cell metabolism and NT synthesis and which is surrounded by a phospholipid plasma membrane, impermeable to ions and water-soluble substances. In order to cross the membrane, substances either have to be very lipid soluble or transported by special carrier proteins. It is also the site for NT receptors and the various ion channels important in the control of neuronal excitability. 

These cells are relatively undifferentiated and have a large nucleus, distinguishable nucleolus but few, if any, cytoplasmic granules. Myeloblasts arise from a precursor pool of stem cells, and both the rough endoplasmic reticulum and the Golgi apparatus stain for peroxidase, indicating that this enzyme is beginning to be synthesised. This cell type is capable of proliferation. 

Microscopic examination of the mature neutrophils reveals two striking features a single multilobed nucleus and a dense, granular appearance of the cytoplasm (see Fig. 1.1a). The nucleus typically comprises two to four segments, and within this organelle the chromatin is coarsely clumped. Until recently, this abnormal chromatin structure was taken as evidence that the nucleus was transcriptionally inactive however, it is now appreciated that the mature neutrophil does perform active transcription ( 7.3), although rates of biosynthesis are somewhat lower than those observed in cells such as monocytes. There is no detectable nucleolus, so there can be only limited synthesis of ribosomal RNA in these cells. 

Figure 7. A series of monoclonal antibodies raised against nuclear proteins. HeLa cells fixed with 4% paraformaldehyde were immunostained with monoclonal antibodies raised against nuclear proteins. The intracellular localization of these antigens are (a) dot inside the nucleolus, (b) whole nucleolus, (c) nuclear foci, (d) nucleoplasm, (e) the edge of the nucleus, (f) cytoplasm, (g) cytoskeleton, (h) plasma membrane, (i) mitochondria, (j) nucleus and cytoplasm, (k) nucleus and the paranuclear structure, and (1) paranuclear structure and nucleoplasm...

The eukaryotic nuclei once referred to as merely a bag of chromatin has now been recognized to be a highly ordered structure or a hub of cellular activities. The nucleus is seen as a three dimensional mosaic of nucleolus, inter-chromatin regions and condensed chromatin, dispersed in a nuclear ground substance... 

Euchromatin generally corresponds to looped 30-nm fibers. Heterochromatin is more highly condensed. Figure 1-1-14 shows an electron micrograph of an interphase nucleus containing euchromatin, heterochromatin, and a nucleolus. The nudeolus is a nuclear region spedalized for ribosome assembly (discussed in Chapter 3). 

Almost all of the RNA in the cell is synthesized in the nucleus, in this process, known as transcription, the information stored in DNA is transcribed into RNA (see p. 242). As mentioned above, ribosomal RNA (rRNA) is mainly produced in the nucleolus, while messenger and transfer RNA (mRNA and tRNA) are formed in the region of the euchromatin. Enzymatic duplication of DNA—replication—also only takes place in the nucleus (see p. 240). 

The nucleus is not capable of synthesizing proteins. All of the nuclear proteins therefore have to be imported—the histones with which DNA is associated in chromatin, and also the so-called non-histone proteins (DNA polymerases and RNA polymerases, auxiliary and structural proteins, transcription factors, and ribosomal proteins). Ribosomal RNA (rRNA) already associates with proteins in the nucleolus to form ribosome precursors. 

A special metabolic task carried out by the nucleus is biosynthesis of NADT The immediate precursor of this coenzyme, nicotinamide mononucleotide (NMN""), arises in the cytoplasm and is then transported into the nucleolus, where it is enzymatically converted into the dinucleotide NADT Finally, NAD"" then returns to the cytoplasm. 

D. Ranitidine is an H2-receptor antagonist. H2-receptors are found in the cell membrane of parietal cells, not in the nucleus, nucleolus, or cytoplasm. Mammalian cells do not have cell walls. 

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... 

Molecular communication between the nucleus and the cytosol requires the movement of macromolecules through nuclear pores. RNA molecules synthesized in the nucleus are exported to the cytosol. Ribosomal proteins synthesized on cytosolic ribosomes are imported into the nucleus and assembled into 60S and 40S ribosomal subunits in the nucleolus completed subunits are then exported back to the cytosol. A variety of nuclear proteins (RNA and DNA polymerases, histones, topo-isomerases, proteins that regulate gene expression, and so forth) are synthesized in the cytosol and imported into the nucleus. This traffic is modulated by a complex system of molecular signals and transport proteins that is gradually being elucidated. 

There are three distinct classes of RNA polymerase in the nucleus of eukaryotic cells. RNA polymerase I synthesizes the precursor of large rRNAs in the nucleolus. RNA polymerase II synthesizes the precursors for mRNAs, and RNA polymerase III produces the precursors of tRNAs and some other small RNAs in the nucleoplasm. 

As is indicated in Fig. 28-15, transcription is thought to occur from the loops of DNA that form the nucleolar organizing region. The 100-kDa nucleolin, the major protein of the nucleolus, binds to the non-transcribed spacer sequences in the DNA.529-530 It also binds to the newly formed transcripts, as do various proteins that enter the nucleus from the cytoplasm.524531 More than 270 proteins, many of which participate in synthesis of ribosomes, have been detected in the nucleolus.5313 Some of these proteins, acting together with the snoRNAs discussed in the next section, catalyze hydrolytic cleavage of the pre-rRNA molecules. For completion of pre-ribosomal particles additional protein molecules enter the nucleolus and associate with the pre-rRNA particles, then diffuse out of the nucleus. 

A somewhat spherical or oblong body in most living cells. This nucleus contains the chromosomes, which, in turn, bear the genes of heredity. The nucleus also contains a nucleolus, or sometimes two or more nucleoli and a basic ground substance, the nucleoplasm. A nuclear membrane surrounds it on the outside, but this membrane is very porous, allowing materials to pass through rather freely. 

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... 

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