1. A small rounded mass within the cell nucleus where ribonucleoprotein is produced; it is usually single, but there may be several accessory nucleoli besides the principal one. The n. is composed of a meshwork (nucleolonema) of microfilaments and granules and the pars amorpha, now shown to have microfilaments also. 2. A more or less central body in the vesicular nucleus of certain protozoa in which an endosome is lacking but one or more Feulgen-positive (DNA+) nucleoli are present; characteristic of certain sporozoans, flagellates, opalinids, dinoflagellates, and radiolarians among the Protozoa. The chromatin material is distributed throughout the nucleus rather than peripherally, as in the endosome type of nucleus of Entamoeba. [L. dim of nucleus, a nut, kernel]
- chromatin n. SYN: karyosome.
- false n. SYN: karyosome.

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nu·cle·o·lus n(y)ü-'klē-ə-ləs n, pl -li -.lī a spherical body of the nucleus of most eukaryotes that becomes enlarged during protein synthesis, is associated with a nucleolus organizer, and contains the DNA templates for ribosomal RNA called also plasmosome

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n. (pl. nucleoli)
a dense spherical structure within the cell nucleus that disappears during cell division. The nucleolus contains RNA for the synthesis of ribosome and plays an important part in RNA and protein synthesis.

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nu·cle·o·lus (noo-kleґə-ləs″) gen. and pl. nucleґoli [L., dim. of nucleus] a rounded, dense body, present in the nucleus of eukaryotic cells during interphase, that is the site of ribosomal RNA (rRNA) synthesis and ribosomal subunit assembly. It consists of (a) a fibrillar center, containing the rRNA genes, surrounded by (b) the pars fibrosa, a dense fibrillar component where transcription occurs, and (c) the pars granulosa, a granular component where the ribosomal subunits are assembled. Multiple nucleoli occur in some cells. nucleolar adj

Prominent nucleoli (arrows) in the eccentric nuclei of ganglion cells.

Medical dictionary. 2011.

Look at other dictionaries:

  • Nucleolus — (Plur. Nucleoli), Kernkörperchen, im Karyoplasma des Zellkerns liegender, dichter Bezirk, meist doppelt, zellspezifisch aber auch einfach oder mehrfach vorhanden; enthält ca. 80% Proteine (keine Histone), DNA und RNA; synthetisiert und speichert… …   Deutsch wörterbuch der biologie

  • nucleolus — (n.) 1845, from L. nucleolus, lit. a little nut, dim. of nucleus (see NUCLEUS (Cf. nucleus)) …   Etymology dictionary

  • Nucleolus — Nu*cle o*lus, n.; pl. {Nucleoli}. [L., a little nut, dim. of nucleus.] 1. A little nucleus. [1913 Webster] 2. (Biol.) A small rounded body contained in the nucleus of a cell or a protozoan. [1913 Webster] Note: It was termed by Agassiz the… …   The Collaborative International Dictionary of English

  • nucleolus — nucleolus. См. ядрышко. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Nucleŏlus — Nucleŏlus, Kernkörper, s. Zelle …   Meyers Großes Konversations-Lexikon

  • Nucleolus — vgl. Nukleolus …   Das Wörterbuch medizinischer Fachausdrücke

  • nucleolus — [no͞o′klē ōl΄, nyo͞o′klē ōl΄no͞o klē′ə ləs, nyo͞oklē′ə ləs] n. pl. nucleoli [no͞o klē′əlī΄, nyo͞oklē′əlī΄] [ModL < LL, dim. of L nucleus] a conspicuous, usually spherical, dense body in the nucleus of most cells, consisting of protein and RNA …   English World dictionary

  • Nucleolus — The nucleolus is contained within the cell nucleus …   Wikipedia

  • Nucleolus — Übergeordnet Zellkern Karyoplasma Untergeordnet Ribosomale DNA Pars granulo …   Deutsch Wikipedia

  • nucleolus — noun (plural nucleoli) Etymology: New Latin, from Latin, diminutive of nucleus Date: 1845 a spherical body of the nucleus of most eukaryotes that becomes enlarged during protein synthesis, is associated with a nucleolus organizer, and contains… …   New Collegiate Dictionary

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