A cell in the active phase of growth has thousands of ribosomes. These are the sites of protein synthesis. Each ribosome is composed of two sub-units 30S (unit Svedberg unit of sedimentation coefficient) and 50S, the whole gives ribosome 70S. The machinery of polymerization of amino acids is composed of at least 3 RNA and 50 different proteins. The Mrna prokaryotes possess a binding site on the ribosome (RBS), called sequence-the Shine Dalgarno sequence (S/D). This element is typically located 3 to 9 nucleotides upstream of the initiation codon, it pairs with the complementary sequence located on the 16S Rrna gene. The large subunit contains the center peptidyl-transferase that is responsible for the formation of peptide bonds. The small subunit contains the decoding center in which the Trna loaded to read or decode the codons of the Mrna. The Ribosomal subunits are composed of one or several Rrna and many proteins

Figure 14 : general Structure of ribosomes prokaryotes. The figure shows the composition of Rrna and protein in the different sub-units, the same as the length of the Rrna and the number of ribosomal proteins.

Table 1 : Structure compared to the ribosomes