The term prokaryote means 'with no nucleus'. All prokaryotes have two sets of cell membranes an outer and an inner. Each of these is a phospholipid bilayer. Sometimes there is a layer of mucopolysaccharide (a mucus like material) which gives added protection to the cell. The DNA of the chromosome lies free in the cytoplasm. The cytoplasm has no complex organelles but does contain ribosomes. At one point the inner membrane is very folded, forming the mesosome. This structure is responsible for the respiratory processes of the organism.

There are often small rings of DNA called plasmids in the cytoplasm. These carry a few extra genes which often confer resistance to antibiotics, or allow the cell to carry out the manufacture of special substances. The cell divides by a process of binary fission, the DNA copying itself and the cell then dividing into two.