noun, plural: nucleoli

(cell biology) The round granular structure within the nucleus of a cell, composed of proteins, DNA, and RNA, and functions primarily for the creation of ribosomes


Nucleolus is a round and granular organelle located inside the nucleus. It is composed of proteins, DNA, and RNA. In higher eukaryotes, three major regions are distinct: the fibrillar center, the dense fibrillar component, and the granular component.1 In plants, another structure is recognizable. This is called the nucleolar vacuole, a clear area in the center of the nucleolus.2

The nucleolus is involved with ribosomal RNA synthesis and the formation of ribosomes in eukaryotes. It is also functions in the assembly of signal recognition particles.

Word origin: Latin, diminutive of nucleus (kernel)

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1 Koberna, K., Malínský, J., Pliss, A., Mašata, M., Večeřová, J., Fialová, M., Bednár, J., and Raška, I. (2002). "Ribosomal genes in focus: new transcripts label the dense fibrillar components and form clusters indicative of "Christmas trees" in situ". J. Cell Biol. 157 (5): 743–8.
2 Beven, A. F., Lee, R., Razaz, M., Leader, D. J., Brown, J. W., and Shaw, P. J. (1996). "The organization of ribosomal RNA processing correlates with the distribution of nucleolar snRNAs". J. Cell. Sci. 109 (6): 1241–51.

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