Ribosome

The machine that reads the message and builds the protein, assembled from two subunits made in the nucleolus.

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Two subunits, one machine

The nucleolus synthesises and processes precursor rRNA into mature rRNAs and assembles the 40S and 60S subunits, which later join as the 80S ribosome.

eukaryotic, review · review · Ponti D 2025, Int J Mol Sci · source

How fast it reads

13 to 18 amino acids per second, measured on single messages in living cells.

human cells · SunTag labelling of nascent protein, single-molecule imaging · Pichon X et al. 2016, J Cell Biol · source

How many on one message

About 1.3 ribosomes per kilobase of message, so a typical mRNA carries several at once as a polysome.

human cells · single-molecule imaging of endogenous and reporter mRNA · Pichon X et al. 2016, J Cell Biol · source

How many in a tissue

About 2 x 10^13 ribosomes per ml of liver, carried on the rough ER, which is two thirds of the 11 m2 of ER membrane in that volume.

rat liver, in situ · stereology on electron micrographs · Weibel ER et al. 1969, J Cell Biol · source

Structure known to the atom

The first X-ray structure of a eukaryotic ribosome was solved at 3.0 angstrom resolution from yeast, following the bacterial structures before it.

yeast, Saccharomyces cerevisiae · X-ray crystallography · Jenner L et al. 2012, Curr Opin Struct Biol · source

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Diameter

No sourced value for this yet: none of the abstracts read for this page states a ribosome diameter, so the copy's size is a drawing choice and not a measurement.

Number per human cell

No sourced value for this yet: the count above is per millilitre of rat liver tissue, which is not a per-cell figure for any human cell, and converting it would need a cell count this page does not have.

Behind the copy

The ribosome is the machine that reads mRNA and builds protein. Its two subunits, 40S and 60S, are assembled separately in the nucleolus and join on a message as the 80S ribosome. In living human cells translation runs at 13 to 18 amino acids per second, with about 1.3 ribosomes per kilobase of message, so one mRNA usually carries several at once.

source 1, source 2

Real pictures

Gallery and papers in the library

Panel of a six-part figure, cropped to this panel and otherwise unaltered, which CC BY allows with attribution. Human astrocyte differentiated from induced pluripotent stem cells of a healthy donor, 25 days in vitro. The authors describe the protein-synthesising apparatus here as polysomes, marked by the yellow arrow, with several short cisternae of rough ER at the red arrow. At a 0.5 micrometre scale bar the fine dark granules filling the cytoplasm are the ribosomes themselves: this is about as close as conventional electron microscopy brings a reader to one. Kutukova, Ivanov, Novosadova et al 2026, Modern Technologies in Medicine, CC BY 4.0 · source · transmission electron micrograph, panel f of figure 2

3D subtomogram average of a cytoplasmic ribosome optimally positioned for protein import on the OMM shows multiple contact points. (A) Three views of the subtomogram average of a cytoplasmic ribosome positioned with the exit tunnel on the 60S subunit (dark blue) facing the OMM (gray). Three connecting densities (labeled 1, 2, 3 in pink, orange, and green, respectively) are visible between the 60S subunit and the OMM. Chang, Barad, Hamid et al 2025, The Journal of Cell Biology, CC BY 4.0 · source · figure from an open-access paper

Ribosomes colocalize with the SR Representative electron micrographs of adult rat ventricular myocytes show ( A ) ribosome (arrowheads) association with perinuclear membranes (ER), ( B ) peripheral membranes (longitudinal, free SR), ( C ) T-tubules (near junctional SR) and ( D ) in the subsarcolemmal region, specifically at the terminal sarcolemma (TS) of intercalated disc (ID). M, mitochondria; T, T-tubules; N, nucleus. E , coimmunofluorescence imaging of phosphorylated ribosomal protein S6 (p-RPS6; red) and phospholamban (PLN; green) or ( F ) ryanodine receptor type 2 (RyR2) in isolated mouse ventricular myocytes using both confocal microscopy and STED nanoscopy. Zoomed-in images demonstrating the local association of p-RPS6 with individual PLN or RyR2. White rectangles indicate the orientation of the signal intensity profiling. Colocalized signals are indicated in yellow. White boxes in ( A ) and ( B ) indicate magnified regions. Scale bars: 10 µm (cell overview), 1 µm (confocal, STED) and 200 nm (magnified view). STED, stimulated emission depletion microscopy. Sandmann, Brandenburg, Uhlenkamp et al 2026, The Journal of Physiology, CC BY 4.0 · source · figure from an open-access paper

Ribosomes are localized throughout the neonatal and adult ventricular myocyte ER and SR membrane network. A, coimmunofluorescence labelling of neonatal rat ventricular myocytes or (B) adult rat ventricular myocytes with antibodies to the S6 ribosomal protein phosphorylated at Ser 235/236 (p-RPS6) and either an antibody that specifically recognizes proteins containing the KDEL sequence, used as an ER marker, the Ca2+-ATPase of the SR (SERCA), or the cardiac ryanodine receptor (RyR2). C, coimmunofluorescence labelling of isolated adult ventricular myocytes from RiboTag mice, expressing hemagglutinin (HA)-tagged ribosomal protein RPL22, which is incorporated into actively translating polyribosomes. TOPRO, nuclei; scale bars = 20 µm. D, mRNA fluorescence in situ hybridization (FISH) of poly(A)-mRNAs in adult rat cardiac myocytes. Sandmann, Brandenburg, Uhlenkamp et al 2026, The Journal of Physiology, CC BY 4.0 · source · figure from an open-access paper

The Zb is associated with active translation. ( A ) Oocyte at the cluster stage stained for nascent translation by Click chemistry with the puromycin analog OPP (OPP, right column), negative control condition previously treated with puromycin for 1 hour (+puromycin, bottom row). The Zb is visualized through the autofluorescence of its organelles at 488 nm (organelles, left column). ( B ) Top row: Zollo, Zaffagnini, Haidar et al 2026, Science Advances, CC BY 4.0 · source · figure from an open-access paper

Reorganisation of the nucleolus upon stress and the generation of nucleolus-related inclusions. (A) H1299 cells stably expressing RPL11-eGFP (top) and parental H1299 cells (bottom) were stressed with HS (2 h, 43 C) or MG132 (5 uM, 15 h) before being stained for fibrillarin (red, upper part) or ubiquitin (green, lower part). Nuclei are stained with DAPI (blue). Scale bar 5 um. Brunello, Polanowska, Le Tareau et al 2024, The EMBO Journal, CC BY 4.0 · source · figure from an open-access paper

Nucleolar localization of KANSL2. a Immunofluorescence detection of endogenous KANSL2 and nucleolar markers UBF in U87 and FBL in U251 cells. A dashed box corresponding to the zoomed area is shown in greater detail (scale bars: 50 um and 10 um for insets). b Actinomycin D (ACTD) treatment of U87 removed KANSL2 and relocalized UBF immunofluorescence signals from nucleolus. DAPI was used to stain the nucleus. Budnik, Canedo, Morellato et al 2026, Communications Biology, CC BY 4.0 · source · figure from an open-access paper

Quantitative analysis of ribosomal protein expression by immunofluorescence. (A) Representative immunofluorescence images showing subcellular localization of RACK1, RPL27, RPS15a and RPS6 in AECs (CD41- CD43- CD45- CD31+ CD201- Kit- CD44+), HECs (CD41- CD43- CD45- CD31+ CD201+ Kit+ CD44+) and HCs (CD45+ Kit+). Scale bars = 10 um. Tian, Liu, Liu et al 2025, FEBS Open Bio, CC BY 4.0 · source · figure from an open-access paper

Positions and orientations of 60S ribosomal subunits found in a cryo-EM micrograph of cell lysate by two-dimensional template matching (2DTM), with the 60S template shown at left; the right half of panel B of a figure on the in extracto cryo-EM workflow. Scale bar 50 nm. (Figure 1B, right.) Seraj, Zottig, Huang et al 2026, eLife, CC BY 4.0 · source · cryo-EM, cropped from a workflow figure

Representative raw electron micrograph of negatively stained single-cell lysates. Circled particles are representative of the larger particles (about 150-300 Å in diameter) used for subsequent 2D and 3D classification. Scale bar 200 nm. (Figure 2A.) Yi, Verbeke, Chang et al 2019, The Journal of Biological Chemistry, CC BY 4.0 · source · negative-stain electron micrograph, cropped from a larger figure

Bile canaliculi with villi (V) on the biliary side of a camel liver hepatocyte. H--hepatocyte; desmosomes (↑); GC--Golgi complex; M--mitochondria; GER--granular endoplasmic reticulum channels; R--ribosomes and polyribosomes. Electron microphotography. (Bactrian camel (Camelus bactrianus, liver hepatocyte); Figure 6single.) Musina, Lebedeva, Drozdova et al 2025, Animals, CC BY 4.0 · source · figure from an open-access paper, transmission electron microscopy (TEM)

Conformational differences and rotational dynamics of human ribosomes. (A) hES cell 80S ribosome cryo-EM map from hES cells colored in light blue. (B) B cell 80S ribosome cryo-EM map of the 80S ribosome from B cells colored in pink. (human (hES cells and B cells); FIGURE 6, panels A and B (cryo-EM density maps of hES cell and B cell 80S ribosomes; full figure 658x676).) Hiregange, Fedorenko, Ainbinder et al 2026, Frontiers in Molecular Biosciences, CC BY 4.0 · source · figure from an open-access paper, cryo-EM (cryo-electron microscopy density map)

Building the copy.