Practice question

Although both bacterial and archaeal plasma membranes adopt fluid mosaic architecture with proteins diffusing within lipid matrix, chemical composition diverges dramatically. Bacteria synthesize phospholipid fatty acid esters attached to glycerol-3-phosphate, containing straight-chain fatty acids that can be saturated or unsaturated, regulated to maintain fluidity via desaturases and branched chain synthesis. They sometimes produce hopanoids or carotenoids for ordering, while sterols, cholesterol, and sphingolipids are generally absent except in some mycoplasmas that scavenge cholesterol. Archaea uniquely employ isoprenoid hydrocarbon chains, often C20 phytanyl or C40 biphytanyl, joined via ether bonds to glycerol-1-phosphate enantiomer, opposite stereochemistry to bacteria. These ether bonds resist hydrolysis by heat, acid, and phospholipases, and when tetraether forms span membrane as monolayer, proton leak is dramatically reduced. Hence presence of ether-linked isoprenoid lipids is defining chemical distinction, used as biomarker for archaeal domain in environmental lipidomics and underlying ability to thrive at extremes. Phospholipid concept remains, but linkage type and chain chemistry are inverted relative to bacteria.