Prokaryotes

The word 'prokaryote' comes directly from Greek - pro meaning primitive and karyon meaning nucleus - and that etymology is a fair description of the group's defining feature. A prokaryotic cell's genetic material is not enclosed inside a true, membrane-bound nucleus at all; instead, it lies as a single mass called the nucleoid, floating freely in the cytoplasm with no nuclear membrane separating it from the rest of the cell. Because there is no real nuclear envelope, biologists describe this as only a 'primitive' type of nuclear organisation - hence 'prokaryote'. A second defining chemical feature is that prokaryotic DNA is not associated with histone proteins, unlike the DNA of eukaryotic chromosomes. Classic example …