Archaebacteria

1) Archaebacteria are Monerans and extremophiles which can tolerate extreme conditions

2) Acidophiles live in high acidic conditions (E.g.Sulpholobus)

3) Hyperthermophiles live in high temperature (Eg. Methanopyruskandleri)

4) Halophiles live in high salt concentrations (Eg. Halobacterium) 

5) Methanobacteris or Methanogens live in oxygen lacking or anaerobic  conditions (Eg. Methanobacterium). 

6) Methanogens are present in oxygen lacking conditions like marshes and rumen of cattle to release methane from organic matter. 

7) Archaebacteria have Surface layer known as S-layer with glycoproteins or proteins. It is a monolayer with hexagonal proteins or glycoproteins to resist the host attack from low pH and lytic enzymes.

8) Cell wall lacks mureins, Mucopeptides or Muramic acid, but Pseudomureins are present in the cell wall having Laminoacids as tetrapeptides, N-acetyl glucosamine and N-acetyl TalosamineUronic acid in β1,3 linkage. So lysozyme cannot attack this cell wall. 

9) NAT is associated with L-amino acids such as Glutamic acid, Alanine, Lysine and Glutamic acid.

10) Thermoplasma is without cell wall

11) Cell membrane has L-Glycerol in phospholipids. The fatty acid chain  is linked to the Glycerol by ETHER bonding and the fatty acid chain has branched isoprene units having 5C. This provides very high resistance to archaens. 

12) The lipids are tetraether lipids in thermoplasma which can tolerate high temperatures

13) The genome is circular with double stranded DNA associated with histone proteins.

14) Ribosomes are of 70S type which are sensitive to Diphtheria toxin which inactivates eEF2 on ribosome and inhibits protein synthesis (similarity with eukaryotes).

15) The first amino acid involved in protein synthesis is Methionine like that of Eukryotes.

16) tRNA lacks thymine like that of Eukaryotes.

17) They do not have pathogenic nature. 

18) Chlorophyll based photosynthesis is absent but Chemosynthetic metabolism exists.