Ribosomes are corpuscles found by the thousands in the cell cytosol of all organisms. They are composed of two subunits, one large and the other small, separated from each other in the fashion of an open oyster until the ribosome becomes active. Each one of the subunits is constituted, on the one hand, of three types of ribosomal RNA (rRNA) and, on the other, of many dozens of proteins which, in the case of eukaryote cells, have entered the nucleus from the cytosol, where their two parts are formed within a dense corpuscle named nucleolus. From there they move to the cytosol –one by one– through the pores of the nuclear membrane. Then they join in pairs to form the ribosome, which soon closes itself over some piece of messenger RNA (mRNA). Another sort of RNA –very small–, called “transfer RNA” (tRNA), fishes out amino acids one by one, and transport them, stuck to their RNA terminal 3’, to a ribosome, where a particular protein will be synthesized on the model of the messenger RNA. In view of all those synchronized industrial activities, one is clearly entitled to consider ribosomes as veritable sophisticated factories of proteins, the blocks and tools of life.