## Bacterial Cell Wall Structure **Key Point:** The cell wall is the rigid outer layer of bacteria that provides structural support and maintains cell shape. It is composed primarily of peptidoglycan (murein), a polymer of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) cross-linked by short peptide chains. ## Composition and Function | Structure | Composition | Primary Function | | --- | --- | --- | | Cell wall | Peptidoglycan + teichoic acids (Gram+) or lipopolysaccharide (Gram−) | Rigidity, shape maintenance, protection | | Cell membrane | Phospholipid bilayer | Selective permeability, transport | | Capsule | Polysaccharide or protein | Virulence, protection from desiccation | | Pili | Protein | Attachment, conjugation | **High-Yield:** Peptidoglycan is unique to bacteria and is the target of β-lactam antibiotics (penicillins, cephalosporins), which inhibit cross-linking of peptidoglycan strands by binding penicillin-binding proteins (PBPs). **Clinical Pearl:** The thickness and composition of the cell wall differ between Gram-positive and Gram-negative bacteria: - **Gram-positive:** Thick peptidoglycan layer (20–80 nm) with teichoic acids - **Gram-negative:** Thin peptidoglycan layer (5–10 nm) sandwiched between inner and outer membranes **Mnemonic:** **CWPF** = Cell Wall, Peptidoglycan, Firmness, Fixation (the cell wall gives bacteria their fixed shape and structural integrity).
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