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Archaea and bacteria have generally similar cell structure, but cell composition and organization set the archaea apart. Like bacteria, archaea lack interior membranes and organelles . [ 68 ] Like bacteria, the cell membranes of archaea are usually bounded by a cell wall and they swim using one or more flagella . [ 119 ]
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.
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]
A speculatively rooted tree for RNA genes, showing major branches Bacteria, Archaea, and Eukaryota The three-domain tree and the eocyte hypothesis (two-domain tree), 2008. [7] Phylogenetic tree showing the relationship between the eukaryotes and other forms of life, 2006. [8] Eukaryotes are colored red, archaea green, and bacteria blue.
For the Prokaryotes (Bacteria and Archaea) the rank kingdom has not been used till 2024 [115] (although some authors referred to phyla as kingdoms [73]). The category of kingdom was included into the Bacteriological Code in November 2023, [ 116 ] the first four proposals ( Bacillati , Fusobacteriati , Pseudomonadati , Thermotogati ) were ...
Because both bacteria and archaea have differences in the structure of phospholipids and cell wall, ion pumping, most proteins involved in DNA replication, and glycolysis, it is inferred that LUCA had a permeable membrane without an ion pump.
The key difference from earlier classifications is the splitting of archaea from bacteria. microbial mats Microbial mats are the earliest form of life on Earth for which there is good fossil evidence.
Archaea are most closely related to eukaryotes due to tRNA present in archaea, but not in bacteria. Archaea have the same ribosomes as eukaryotes that synthesize into proteins. [26] Aside from the morphology of archaea and bacteria, there are other differences between these domains.