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Archaea, Bacteria, and Eukaryota

Cellular organisms are divided into three domains—archaea, bacteria, and eukaryota. These three domains are distinguished by the fact that they have substantially different Ribosomal RNA. Archaea and Bacteria are prokaryotic, that is, they do not have a distinct nucleus. A prokaryote is essentially a bag of molecules, while a eukaryote is a complex set of functional components.

The idea that archaea were as different from bacteria as bacteria were from eukaryotes was first proposed by Carl Woese and George E. Fox in 1977, based on studies of the evolutionary distance between the DNA of species in the three groups. At one time it was thought archaea were extremophiles; that is, they preferred extreme temperatures or high concentrations of salt or sulfur. The theory was that early life forms (archaea) needed to be able to survive in extreme conditions and then later forms (bacteria and eukaryotes) would arise as conditions became milder. In recent years, however, archaea have been found in many different environments and are now considered to be as diverse as bacteria.

The tables below show the archaea, bacteria, and eukaryotes in the Sprout Database. Click on an organism name to see its page in the Genome Viewer.