Practice question

Bacterial cell wall architecture includes several hallmark polymers absent in Archaea, reflecting fundamentally different envelope synthesis pathways. Peptidoglycan, composed of alternating N-acetylglucosamine and N-acetylmuramic acid crosslinked by D-amino acid containing peptides, is universal among bacteria but never found in archaea, where pseudomurein or S-layers substitute. Outer membrane containing lipopolysaccharide, characterized by Lipid A endotoxin, core oligosaccharide, and O-antigen, is diagnostic of Gram-negative bacteria and relies on Lpx biosynthetic enzymes absent in archaea. Lipopolysaccharide itself, including its toxic Lipid A moiety, is therefore missing in archaeal membranes which instead contain ether-linked isoprenoids. Additionally, bacterial accessory polymers such as lipoteichoic acid, wall teichoic acid, and mycolic acids are not synthesized by archaea. Because Archaea lack all three listed components, their envelopes are intrinsically resistant to beta-lactams, lysozyme, and polymyxins targeting such structures. This absence underlines why antibiotics effective against bacterial walls generally fail against archaeal isolates and why archaeal lipid biosynthesis represents attractive target for specific inhibitors.