Practice question

Gram-negative cell wall is thin but complex, optimized for protection while maintaining permeability for nutrients. It comprises inner plasma membrane, narrow periplasmic space containing single or few layers of peptidoglycan only about 2 to 6 nanometers thick, and outer membrane distinguished by asymmetry. Outer membrane outer leaflet consists of lipopolysaccharide anchored by lipid A, while inner leaflet contains phospholipids; integral outer membrane proteins such as porins, TonB-dependent receptors, and OmpA form beta-barrels. Lipopolysaccharide confers negative charge, stabilizes outer membrane via bridging divalent cations, and provides endotoxin activity and serotype specificity. Thick peptidoglycan, characteristic of Gram-positives, is absent; instead, thin layer provides shape but contributes less mechanical strength than in Gram-positives. Monolayer lipid and teichoic acid-only models do not reflect Gram-negative dual membrane architecture. Assembly of outer membrane requires Lpt pathway transporting LPS from inner membrane across periplasm to outer leaflet and Bam complex folding beta-barrel proteins. This organization explains staining behavior, antibiotic susceptibility, and resistance to detergents and bile in enteric organisms.