This whole process of protein synthesis is also referred to as central dogma.
Usually, the proteins synthesized by the free ribosomes are utilized in the cytoplasm itself, while the protein molecules produced by the bound ribosomes are transported outside the cell.
The best known and studied bacterial toxin is the diphtheria toxin,produced by . Diphtheria toxin is abacterialexotoxin of the A/B prototype. It is produced as single polypeptidechainwith a molecular weight of 60,000 daltons. The function of the proteinis distinguishable into two parts: subunit A, with a m.w. of 21,000daltons,contains the enzymatic activity for inhibition of elongation factor-2involvedin host protein synthesis; subunit B, with a m.w. of 39,000 daltons, isresponsible for binding to the membrane of a susceptible host cell. TheB subunit possesses a region T (translocation) domain which insertsinto the endosome membrane thus securing the release of the enzymaticcomponent into the cytoplasm.
In the cytoplasm, the two subunits of ribosomes bind around the mRNA polymers and synthesize proteins with the help of transfer RNA (tRNA), as per the genetic code.