Lipid bilayer

A thin membrane structure formed by two layers of lipids, with water-attracting heads facing aqueous surroundings and water-repelling tails facing inward. It creates a flexible barrier around cells and cellular compartments.

Amphiphile: A molecule with both water-attracting and water-repelling regions. Lipid molecules form bilayers because their two contrasting regions interact differently with water.
Phospholipid: A lipid with a phosphate-containing polar head group and hydrophobic fatty-acid tails. Phospholipids are the principal structural molecules in many biological bilayers.
Cell membrane: The selectively permeable boundary separating a cell’s interior from its environment. A lipid bilayer forms the structural basis of the cell membrane.
Lipid monolayer: A single layer of amphiphilic molecules arranged at an interface between water and air or oil. Unlike a bilayer, a monolayer has only one lipid layer and is stable at an interface.
Hydrophobic effect: The tendency of nonpolar substances to aggregate in water, reducing disruption of water’s hydrogen-bond network. This effect drives lipid tails away from water and toward the bilayer interior.
Cholesterol: A sterol found in animal membranes, with a small polar group and a rigid hydrophobic body. Cholesterol inserts among phospholipids and modifies bilayer packing and fluidity.
Organelle membrane: A membrane that encloses or forms compartments within a eukaryotic cell. Bilayers create the boundaries that keep many organelle environments distinct.
Lipid vesicle: A closed compartment bounded by a lipid bilayer. A vesicle is a bilayer arrangement that encloses an aqueous interior.
Membrane fluidity: The ease with which molecules move within a biological membrane. Lipid composition and temperature determine how readily bilayer components move.
Sphingolipid: A lipid built on a sphingoid base, often bearing a polar head group. Sphingolipids are bilayer components that contribute to membrane organization and signaling.

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