Ribosome biogenesis

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Ribosome biogenesis, the process of making ribosomes, takes place both in the cell cytoplasm and in the nucleolus of eukaryotic cells. It involves the coordinated function of over 200 proteins in the synthesis and processing of the four rRNAs, as well as assembly of those rRNAs with the ribosomal proteins.

Ribosomal protein synthesis occurs in the cytoplasm just outside the nucleus. Individual large and small units are translated and imported into the nucleus through nuclear pores. These pores have a diameter of 120nm and import 560 000 ribosomal proteins per minute into the nucleus with active transport. See nuclear import for more about the movement of the ribosomal proteins into the nucleus.

Ribosomal RNA (rRNA) is transcripted at the nucleolus, at a high speed, which contains all 45s rRNA genes. After transcription, the rRNA is put together with the ribosomal subunits to make a functioning ribosome. See nuclear export for more about the movement of the ribosomal subunit out of the nucleus.