The prototype of the prokaryotic cell is the bacterium. Its average size is between 1 and 10 µm. It is characterized by a simple organization.
The prokaryotic cell is surrounded by a plasma, lipido-protein membrane. Its genetic information, carried by a long circular DNA molecule, is not located in a nucleus but is directly immersed in a region of the cytoplasm called the nucleoid. In addition to this highly entangled DNA molecule, its cytoplasm contains many ribosomes and a few rare cellular filaments. On the other hand, it has no organelles. Only certain invaginations of the plasma membrane, called mesosomes, are present.
Its plasma membrane is covered by a wall whose structure varies according to the type of cells. In Gram+ bacteria, the wall is formed by a layer of peptidoglycans (a combination of polysaccharides and short amino acid chains). In Gram- bacteria, the wall is thicker and more complex. It consists of 3 layers: an outer membrane, a thin inner layer of peptidoglycan and a space separating the thin inner layer from the plasma membrane called periplasm.
Video annotated in french