Nucleolus

The ribosome factory: three nested components, no membrane, and a size and number that depend on which cell you are looking at.

What it does

the nuclear domain where ribosomal RNA is synthesised, processed, and assembled with ribosomal proteins

mammalian · review of structure and function · Hernandez-Verdun D 2010, WIREs RNA · source

Tripartite organisation

fibrillar centre, dense fibrillar component and granular component, the three reflecting ribosomal gene transcription and pre-rRNA processing efficiency

mammalian · review · Hernandez-Verdun D 2010, WIREs RNA · source

Not universal

bipartite in yeast, tripartite in humans, so the three-part arrangement is a property of the lineage rather than of nucleoli in general

yeast against human · review across evolution · Hernandez-Verdun D 2010, WIREs RNA · source

Size and number

cell-specific rather than fixed. This page gives no count per cell for that reason

human · organellar proteomics of a T-cell line · Jarboui MA 2011, Mol Immunol · source

Protein content

872 nucleolar proteins identified in one human T-cell line, a set that reaches well beyond ribosome biogenesis and RNA processing

human, Jurkat T-cell line · organellar proteomic approach · Jarboui MA 2011, Mol Immunol · source

Not shown yet

Diameter

no abstract read for this page gives one with a method, and the sources say size is cell-specific, so a single figure would misrepresent them. The copy is drawn at the caller's scale.

Number of fibrillar centres

the copy draws four because a body needs some number to be drawn at all. No source read here states how many a human nucleolus has.

Behind the copy

The nucleolus is the ribosome factory: the nuclear domain where ribosomal RNA is synthesised, processed, and assembled with ribosomal proteins. In mammals it has a classical tripartite organisation, and the three parts reflect the stages of that work: fibrillar centre, dense fibrillar component, and granular component. The arrangement is not universal, and the comparison is informative: yeast build a bipartite nucleolus and humans a tripartite one. Size, number and organisation are cell-specific rather than fixed, and a proteomic survey of one human T-cell line identified 872 nucleolar proteins, many of them with no role in making ribosomes at all.

source 1, source 2

Other organelles

All · Autophagosome · Centrosome · Cilia and flagella · Cytoskeleton · Endosomes and vesicles · Golgi · Lipid droplet · Lysosome · Mitochondrion · Nuclear envelope · Nucleus · Peroxisome · Plasma membrane · Proteasome · Ribosome · Rough ER · Smooth endoplasmic reticulum

Building the copy.

Selected

Click a part of the copy or its label.

Look

Stain

No stain on cyto.site's table names a part this copy draws.

Real pictures

Representative electron micrographs illustrating the ultrastructural nucleolar characteristics of dorsal root ganglia neurons after administration of miR-30c-5p mimic or inhibitor to SNI rats. Sham (A) and SNI rats treated with miR-30c-5p inhibitor (C) exhibit the typical nucleolar organisation of DRG neurons, characterised by the presence of numerous small-sized fibrillar centres (*, FCs), surrounded by a ring of dense fibrillar component (DFC), and areas of granular component (GC), preferentially at the nucleolar periphery. SNI rats treated with vehicle (B) or with miR-30c-5p mimic (D) present severe nucleolar alterations, including the formation of enlarged FCs and segregation of large masses of GC and DFC at the nucleolar periphery. Scale bar: 2 um. Frances, Mata-Garrido, Lafarga et al 2024, International Journal of Molecular Sciences. Figure 4, CC BY 4.0 · source · transmission electron micrograph, composite of four panels: A (Sham) and C (SNI + miR-30c-5p inhibitor) show typical nucleolar organisation with fibrillar centres, dense fibrillar component and granular component labelled; B (SNI) and D (SNI + miR-30c-5p mimic) show nucleolar alterations in the injury model

Panel a, "DMSO" row: DAPI (blue), fibrillarin (red, dense fibrillar component marker) and NPM1 (green, granular component marker) in HCT116 cells at baseline, showing normal nucleolar substructure. Part of a composite figure on nucleolar stress from DNA-damaging agents. Chen, Xiao, Hao et al 2026, Communications Biology, CC BY 4.0 · source · immunofluorescence, composite figure