Ribosome biogenesis is the process of making ribosome

Ribosome

A ribosome is a component of cells that assembles the twenty specific amino acid molecules to form the particular protein molecule determined by the nucleotide sequence of an RNA molecule....

s. In prokaryotic cells, it takes place in the cytoplasm with the transcription of many ribosome gene operons. In eukaryotes, it takes place both in the cell cytoplasm

Cytoplasm

The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

 and in the nucleolus

Nucleolus

The nucleolus is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Ribosomal RNA is transcribed and assembled within 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.This organelle also involve in the protein synthesis during translation process within the cytoplasm of a cell.

In Prokaryotes

There are 52 genes that encode the ribosomal proteins and they can be found in 20 operons within prokaryotic DNA. Regulation of ribosome synthesis hinges on the regulation of the rRNA itself.

First, a reduction in aminoacyl-tRNA

Aminoacyl-tRNA

Aminoacyl-tRNA is tRNA to which its cognated amino acid is adhered. Its role is to deliver the amino acid to the ribosome where it will be incorporated into the polypeptide chain that is being produced...

 will cause the prokaryotic cell to respond by lowering transcription

Transcription (genetics)

Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...

 and translation

Translation

Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. Whereas interpreting undoubtedly antedates writing, translation began only after the appearance of written literature; there exist partial translations of the Sumerian Epic of...

. This occurs through a series of steps, beginning with stringent factor binding to ribosomes and catalyzing the reaction:

GTP + ATP --> pppGpp + AMP

The γ-phosphate is then removed and ppGpp will bind to and inhibit RNA polymerase. This binding causes a reduction in rRNA transcription. A reduced amount of rRNA means that ribosomal proteins (r-proteins) will be translated but will not have an rRNA to bind to. Instead, they will negatively feedback and bind to their own mRNA, repressing r-protein synthesis. Note that r-proteins preferentially bind to its complementary rRNA if it is present, rather than mRNA.

The ribosome operons also include the genes for RNA polymerase

RNA polymerase

RNA polymerase is an enzyme that produces RNA. In cells, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses...

 and elongation factors (used in RNA translation). Regulation of all of these genes at once illustrate the coupling between transcription and translation in prokaryotes.

In Eukaryotes

Ribosomal protein synthesis in eukaryotes occurs, like most protein synthesis, in the cytoplasm just outside the nucleus. Individual large and small units are synthesized and imported into the nucleus through nuclear pores. These pores have a diameter of 120 nm 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 transcribed at the nucleolus

Nucleolus

The nucleolus is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus. Ribosomal RNA is transcribed and assembled within the nucleolus...

, at a high speed, which contains all 45S rRNA genes. The only exception is the 5S rRNA which is transcribed outside the nucleolus. 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.