Bacterial cell envelope

The layered boundary surrounding a bacterial cell, comprising its cytoplasmic membrane and, depending on the species, a cell wall and outer membrane or other surface layers.

Cytoplasmic membrane: The lipid bilayer that encloses a cell’s cytoplasm and controls exchange with its surroundings. It is the innermost envelope layer and anchors many transport and energy-conversion processes.
Osmotic pressure: The pressure difference produced when water moves across a selectively permeable membrane between solutions of different concentrations. The wall prevents the internal pressure created by water uptake from rupturing the cell.
Gram-positive bacteria: Bacteria whose cell walls retain crystal violet during Gram staining, typically with thick peptidoglycan and no outer membrane. Their envelope has a thick wall outside one cytoplasmic membrane.
Beta-lactam antibiotics: Antibiotics that inhibit bacterial penicillin-binding proteins involved in peptidoglycan cross-linking. They weaken the wall by blocking a central step in its construction.
Peptidoglycan: A mesh-like polymer of sugars and short peptides that gives most bacterial cell walls strength and shape. This polymer is the main load-bearing material in most bacterial cell walls.
Bacterial cell division: The process by which a bacterial cell grows and separates into two daughter cells. New envelope material must be coordinated with constriction as the cell divides.
Gram-negative bacteria: Bacteria that do not retain crystal violet during Gram staining and typically have thin peptidoglycan between two membranes. Their outer membrane and thin wall create a distinct multilayered envelope.
Vancomycin: A glycopeptide antibiotic that binds peptidoglycan precursors and inhibits cell-wall synthesis. Its target is accessible in many Gram-positive bacteria but restricted by the Gram-negative outer membrane.
Outer membrane: An additional membrane outside the peptidoglycan layer in Gram-negative bacteria. It forms the envelope’s outer boundary in Gram-negative bacteria and restricts entry of many substances.
Bacterial secretion system: A protein complex that transports molecules across one or more bacterial membranes. Secretion systems provide routes through envelope layers that otherwise impede large molecules.

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