The Three Domain System

Domain:  In 1978 Carl Woese proposed this level of

classification above kingdom.

There are three domains based on the following

distinguishing criteria: 

• Cell wall composition 
• Membrane lipids 
• RNA sequence 
• Protein synthesis 
• Antibiotic sensitivity

I. Domain Eubacteria: “True bacteria”. 

•   Cell wall contains peptidoglycan.  
• Sensitive to antibiotics.

II. Domain Archaeabacteria: “Ancient bacteria”

• Cell walls lack peptidoglycan, resistant to antibiotics.
• Live in extreme environments
• Three kingdoms:

1. Methanogens: Strict anaerobes that produce methane.

2. Extreme Halophiles: Require high salt concentrations.

3. Thermoacidophiles: Live in hot, acidic environments.

III. Domain Eucarya: All eucaryotes: Protista, Fungi, 

Plantae, and Animalia.