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Why are archaea classified in a separate domain from bacteria?
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Archaea
Archaea are found in a diverse range of extreme environments, including the salt deposits on the shores of the Dead Sea.
Archaea are classified in a separate domain from bacteria primarily due to fundamental genetic and biochemical differences discovered through the analysis of ribosomal RNA by microbiologist Carl Woese in 1977. While both groups are prokaryotic—lacking a defined cell nucleus—they represent distinct evolutionary lineages.123
Key distinctions include:
- Cell Wall Composition: Unlike bacteria, which typically contain peptidoglycan in their cell walls, archaea lack this substance.143
- Membrane Lipids: Bacterial membranes consist of fatty acids linked to glycerol by ester bonds. In contrast, archaea possess membrane lipids composed of branched isoprenoids linked to glycerol by ether bonds.14
- Genetic Machinery: The RNA polymerase of archaea is more complex than that of bacteria and more closely resembles the RNA polymerases found in eukaryotes. Additionally, archaeal protein synthesis mechanisms, such as the use of an initiator tRNA with unmodified methionine, align more closely with eukaryotes than with bacteria.1
These findings led to the modern three-domain system of life: Archaea, Bacteria, and Eukarya.12