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