Which lipid is absent in most prokaryotic and plant membranes?
Evolutionary lipidomics reveals sterol distribution discontinuous across domains life reflecting oxygen dependent biosynthesis pathway complexity. Eukaryotes animals synthesize cholesterol via HMGCoA reductase squalene monooxygenase epoxidase lanosterol fourteen demethylase CYP51 DHCR enzymes pathway requiring molecular oxygen maintaining thirty to forty percent plasma membrane buffering fluidity organizing rafts signaling. Fungi use ergosterol additional double bonds methyl group phytosterol plants stigmasterol sitosterol campesterol from cycloartenol SMT sterol methyltransferase modification. Most bacteria lack sterol biosynthetic enzymes squalene cyclization and sterol auxotrophy; membranes composed phosphatidylethanolamine phosphatidylglycerol cardiolipin hopanoids pentacyclic triterpenoids surrogate sterol function rigidify Methylococcus planctomycetes providing order stability. Mycoplasma pneumoniae lacking cell wall scavenges cholesterol host serum incorporating membrane requiring exogenous cholesterol growth. Sphingomyelin also predominantly animal glycosphingolipid rare prokaryotes. Therefore cholesterol truly absent most prokaryotic plant membranes explaining differential susceptibility cholesterol binding toxins perfringolysin O Streptolysin O polyenes amphotericin B selective antimicrobial strategies. Phylogeny underlies membrane evolution topics microbiology textbooks and cell biology comparisons across kingdoms for structure function diversity.
Ref: Nes WD, Chem Rev 2011, Sterol biosynthesis diversity bacterial absence cholesterol and hopanoids.