Cell walls of Prokaryotes

Domain	Eubacteria	Archaea
membrane	Glycerol-ester lipids	Glycerol-ether lipids
lipids	Amphipathic molecules containing a backbone of glycerol connected to a hydrophilic head group and two hydrophobic long-chain fatty acids. Fatty acids are attached to the glycerol backbone by ester bonds.	Isoprenoid side chain Fatty acids are attached to the glycerol backbone by ether bonds. In some extremophiles, C-40 hydrophobic chains attached to the glycerol backbone are twice normal length and pass completely through the membrane, attaching to a second backbone on the opposite side and adding stability.
chains	linear	branched carbon rings
chirality of glycerol	D-glycerol (R)	L-glycerol (S)
lacking cell wall	Mycoplasma (sterol-like compounds in cell membranes provide osmotic protection)	Thermoplasma, Picrophilaceae

In addition to differences in composition of the cell membrane, Eubacteria and Archaea differ in the composition of the cell wall. Cell walls are rigid to semi-rigid structures that enclose the protoplastic cell membrane, and which are found in bacteria, archaea, fungi, plants, and algae, but not in animals.

 Comparisons of Eubacteria, Archaea, and Eukaryotes

Cell Wall	Gram +ve bacteria	Gram -ve bacteria	Gram +ve Archea	Gram -ve Archaea
outer membrane		Lipoprotein-lipopolysaccharide-phospholipid (LPS) with porins. Braun’s lipoprotein anchors outer membrane to peptidoglycan
peptidoglycan*	thick teichoic acid	none	none pseudomurein or complex carbohydrate	none protein-glycoprotein
S-layer patterned, surface layer of protein or glycoprotein	some bacteria associated with the peptidoglycan	some bacteria adheres directly to outer membrane sole cell-wall component in Planctomyces	commonly constitutes cell wall	commonly constitutes cell wall

*Peptidoglycan comprises N-acetylglucosamine (NAG) bonded to N-acetyl muramic acid (NAM) by a 1,4 glycosidic bond. The N-acetylmuramic acid (NAM) in peptidoglycan is replaced by N-acetyl talosaminouronic acid acid (NAT) in pseudopeptidoglycan (pseudomurein) of Archaea (im). Each glycan is linked by 1,4 glycosidic bonds in peptidoglycan and by 1,3 glycosidic bonds in pseudomurein (NAT). Hyperthermophiles use branched glycerol tetraethers (single-layer membranes) to increase membrane fluidity, so they lack a cell wall. Psychrophiles have plasma membranes with lipids that contain mainly unsaturated fatty acids.