Structure of Gram negative cell wall with diagram.
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Answer
A labelled diagram cannot be rendered in this text-based answer; the description below covers the key structural/labelling features of the Gram-negative bacterial cell wall.
Structure (from outside in):
Outer membrane — a distinctive feature unique to Gram-negative bacteria (absent in Gram-positives), a lipid bilayer containing:
Lipopolysaccharide (LPS) — on the outer leaflet, composed of Lipid A (the toxic component, responsible for endotoxin activity), a core polysaccharide, and the O-antigen (a repeating polysaccharide chain extending outward, the basis for serotyping, e.g., E. coli O157).
Porins — transmembrane protein channels allowing passage of small hydrophilic molecules (including some antibiotics) across the outer membrane.
Phospholipids — on the inner leaflet of the outer membrane.
Periplasmic space — a gel-like compartment between the outer membrane and the inner (cytoplasmic) membrane, containing a thin layer of peptidoglycan (only 1–2 layers thick, much thinner than in Gram-positive bacteria) and various periplasmic enzymes (including beta-lactamases, relevant to antibiotic resistance).
Cytoplasmic (inner/plasma) membrane — a phospholipid bilayer, the innermost layer, site of many metabolic/transport functions.
Key labelling points distinguishing it from the Gram-positive cell wall: presence of an outer membrane with LPS (absent in Gram-positive bacteria); a thin peptidoglycan layer confined to the periplasmic space (versus a thick peptidoglycan layer directly external to the plasma membrane in Gram-positive bacteria); absence of teichoic/lipoteichoic acids (present in Gram-positive walls).
Clinical/biological significance: the LPS (endotoxin), particularly its Lipid A component, is responsible for the systemic toxicity of Gram-negative sepsis (fever, hypotension, DIC) when released on bacterial lysis; the outer membrane acts as a permeability barrier, contributing to the intrinsic resistance of many Gram-negative bacteria to certain antibiotics (e.g., vancomycin, which is too large to cross porins) and to disinfectants; porins are also a site of antibiotic-resistance mutations (porin loss reducing drug entry).
