Cell nucleus

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Cell nucleus

The largest of the membrane-bounded organelles which characterize eukaryotic cells; it is thought of as the control center since it contains the bulk of the cell's genetic information in the form of deoxyribonucleic acid (DNA). The nucleus has two major functions: (1) It is the site of synthesis of ribonucleic acid (RNA), which in turn directs the formation of the protein molecules on which all life depends; and (2) in any cell preparing for division, the nucleus precisely duplicates its DNA for later distribution to cell progeny. See Deoxyribonucleic acid (DNA), Eukaryotae, Ribonucleic acid (RNA)

The diameter of nuclei ranges from 1 micrometer in intracellular parasites and yeast cells to several millimeters in some insect sperm. Spherical or ellipsoidal nuclei are found in most cell types, although occasionally spindle-shaped, lobulated, disc-shaped, or cup-shaped nuclei may be observed. Although nuclear size and shape are somewhat consistent features of a particular cell type, these features are more variable in cancer cells. In addition, tumor cell nuclei are characterized by indentation, furrowing, elongation, and budding.

The nucleus is bounded by a double membrane (the nuclear envelope) and contains several major components: chromatin, which is composed of DNA and chromosomal proteins; the nucleolus, which is the site of ribosomal RNA (rRNA) synthesis; and nucleoplasmic fibrils and granules, some of which are involved in the processing and transport of messenger RNA out of the nucleus (see illustration). The constituents of the nucleus are contained within a framework referred to as the nuclear matrix.

Transmission electron micrograph of a thin section of a rat liver cell nucleusenlarge picture
Transmission electron micrograph of a thin section of a rat liver cell nucleus
References in periodicals archive ?
Both iPP1 and iPP2 are nucleated samples produced by The Dow Chemical Company using a Ziegler-Natta catalyst, whereas iPP3 and iPP4 are non-nucleated resins obtained from Sigma-Aldrich Corporation.
Huntsman's AP5165 is a nucleated 65-MFR impact copolymer for auto interior trim.
Stress levels are related to SHP values, but in highly nucleated polymers the relationship deviates from the values established for non-nucleated polyesters.
Figure 4 showed the photographs under a cross polarizing light microscope of the virgin iPP and the iPP nucleated with 0.
The WAXS measurement in a transmission mode was applied to determine the total content of the [beta]-phase for the iPP samples nucleated with PA + CS.
t] of the nucleated and nonnucleated POM at 424 K, it can be found that the crystallization time of nucleated POM is much shorter than that of non-nucleated POM, indicating that the addition of the nucleating agent attapulgite accelerates the whole crystallization process because the grooves of attapulgite offer nucleation sites for POM.
Two formulations of PA66, supplied by the Rhodia Nyltech Company, have been studied: a virgin grade and a commercial grade nucleated for injection productivity enhancement.
To this end, the concept of shaping a nucleated polymer/gas solution flow is presented and experimentally verified.
Recently, our group [50] used iPP nucleated with [alpha]/[beta]-CNAs ([alpha]/[beta]-CNAs including the [alpha]-NA of 0.