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The three-domain system adds a level of classification (the domains) "above" the kingdoms present in the previously used five- or six-kingdom systems.This classification system recognizes the fundamental divide between the two prokaryotic groups, insofar as Archaea appear to be more closely related to eukaryotes than they are to other prokaryotes – bacteria-like organisms with no cell nucleus.
Woese argued that the bacteria, archaea, and eukaryotes represent separate lines of descent that diverged early on from an ancestral colony of organisms. [ 64 ] [ 65 ] One possibility [ 65 ] [ 66 ] is that this occurred before the evolution of cells , when the lack of a typical cell membrane allowed unrestricted lateral gene transfer , and that ...
The two-domain system is a biological classification by which all organisms in the tree of life are classified into two domains, Bacteria and Archaea. [1] [2] [3] It emerged from development of knowledge of archaea diversity and challenges the widely accepted three-domain system that classifies life into Bacteria, Archaea, and Eukarya. [4]
Halophiles (organisms that thrive in highly salty environments) and hyperthermophiles (organisms that thrive in extremely hot environments) are examples of Archaea. [1] Archaea are relatively small. They range from 0.1 μm to 15 μm diameter and up to 200 μm long, about the size of bacteria and the mitochondria found in
Woese argued that the bacteria, archaea, and eukaryotes represent separate lines of descent that diverged early on from an ancestral colony of organisms. [ 45 ] [ 46 ] However, a few biologists argue that the Archaea and Eukaryota arose from a group of bacteria. [ 47 ]
Like all other organisms, bacteria contain ribosomes for the production of proteins, but the structure of the bacterial ribosome is different from that of eukaryotes and archaea. [69] Some bacteria produce intracellular nutrient storage granules, such as glycogen, [70] polyphosphate, [71] sulfur [72] or polyhydroxyalkanoates. [73]
While the existence of Eukarya and Prokarya were already accepted, Woese was responsible for the distinction between Bacteria and Archaea. [3] Despite initial criticism and controversy surrounding his claims, Woese's three domain system, based on his work regarding the role of rRNA in the evolution of modern life, has become widely accepted. [4]
Metagenomic analyses recover a two-domain system with the domains Archaea and Bacteria; in this view of the tree of life, Eukaryotes are derived from Archaea. [ 58 ] [ 59 ] [ 60 ] With the later gene pool of LUCA's descendants, sharing a common framework of the AT/GC rule and the standard twenty amino acids, horizontal gene transfer would have ...