They occur in unusual habitats such as hydrothermal vents and terrestrial hot springs.
Peptidoglycan is a component of the cell walls of almost all bacteria; it is absent in the cell walls of archaea and eukaryotes. The archaea have several kinds of cell walls.
Complexity of RNA polymerase: An enzyme called RNA polymerase, which copies a DNA template into an RNA product, is responsible for carrying out transcription in all sorts of organisms. A straightforward RNA polymerase made up of four polypeptides is present in bacteria. However, RNA polymerases with many polypeptides within them are present in both eukaryotes and archaea.
