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.

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