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
McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
*Research utilizing human pluripotent stem cells that were derived using somatic cell nuclear transfer, i.e., the transfer of a human somatic cell nucleus into a human or animal egg;
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The DNA in the cell nucleus is packaged into chromatin in a form that prevents access to genetic information.
Spector and colleagues began by observing the location within the cell nucleus of various genes known to be important in stem cells.
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Reviewing current knowledge about the organization and functional compartmentalization of the cell nucleus, the 27 articles in this collection are arranged in five sections on the nuclear periphery, chromosomes and chromatin, nuclear bodies, functional organization, and nuclear architecture during differentiation and disease.