Three Domains of Life

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Three Domains of Life

Microbes are found in all three domains of life: bacteria, archaea, and eukaryotes.
Diverse species of the three domains are explored in Microbial Biorealm.
You can also explore the three domains through the Taxonomy Index.

	All cells on Earth resemble each other
Chromosomal material	Double-stranded DNA
RNA transcription	Common ancestral RNA polymerase
Translation	Common ancestral rRNAs and elongation factors
Protein	Common ancestral functional domains
Cell structure	Aqueous cell compartment bounded by a membrane
	Bacteria	Archaea	Eukaryotes
	Archaea resemble Bacteria
Cell volume	1 to 100 μm3 (usually)		1 to 106 μm3
DNA chromosome	Circular (usually)		Linear
Gene organization	Multi-gene operons; few introns		Single genes; Many introns
Metabolism	Denitrification, N2 fixation, lithotrophy, respiration and fermentation		Respiration and fermentation
Nuclear membrane	None (nucleoid)		Nuclear membrane
Multicellularity	Simple		Complex
		Archaea resemble Eukaryotes
Monomolecular cell wall	Peptidoglycan (nearly always)	Absent in most species (Methanogens have pseudopeptidoglycan)
Ribosome sensitivity to Cam, Kan, and Str	Sensitive	Resistant
Translation initiator	Formyl-Met	Methionine (except mitochondrial F-Met)
RNA polymerase	Bacterial	Eukaryotic
Transcription factors	Bacterial	Eukaryotic
	Archaea Differ from Bacteria and Eukaryotes
Methanogenesis	No	Yes	No
Highest temperature growth	> 90ºC	> 110ºC	> 60ºC
Photosynthesis	Many species. Bacteriochlorophyll	Halobacteria only; bacteriorhodopsin	Many species; bacterial origin. Chlorophyll, in Chloroplasts (prokaryotic in organization)
Chlorophyll light absorption	Red and blue	Green	Red and blue
Membrane lipids (major)	Ester-linked fatty acids	Ether-linked isoprenoids	Ester-linked fatty acids
Pathogens that infect animals or plants	Many pathogens	No pathogens	Many pathogens