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 ?
The next step, Baia said, is to determine the exact genes activated by the arrival of YAP1 in the cell nuclei.
The feat is the first recovery of genetic material from cell nuclei of fossils that haven't been sheathed in permafrost.
To check for pollen-introduced genes in the beets, the researchers looked for particular patterns of DNA markers in the cell nuclei.
It's still unclear how a mutant lamin A and the misshaped cell nuclei lead to the symptoms of progeria, but Huber Warner of the National Institute on Aging in Bethesda speculates that such a defect could prevent so-called stem cells from replacing worn-out or damaged cells and tissues.
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The microscope also revealed cell nuclei, the cell membranes of spiral-shaped bacteria and the spore coats of other microbes.
356) does show nonlinearity of cell damage from alpha radiation in the dose range studied, but the lowest dose studied (5 percent of all cell nuclei hit) is probably several orders of magnitude above the mean lethal dose for any organism.