Phospholipid

A lipid with a phosphate-bearing polar head and hydrophobic tails. Its amphipathic structure lets many phospholipids assemble into cell-membrane bilayers.

Glycerophospholipid: A phospholipid built on a glycerol backbone, typically with two fatty-acid chains and a phosphate-linked head group. This is the main phospholipid family that forms biological membrane bilayers.
Lipid bilayer: A double layer of amphiphilic lipids with hydrophobic regions inward and polar surfaces facing water. Phospholipids spontaneously arrange into this basic membrane structure in water.
Cell membrane: A selectively permeable boundary that separates a cell from its surroundings and organizes internal compartments. Phospholipid bilayers provide the structural foundation of most cell membranes.
Cholesterol: A sterol lipid found in animal membranes and used to make steroid hormones and bile acids. Unlike phospholipids, cholesterol has a rigid fused-ring structure and modulates bilayer properties.
Sphingomyelin: A sphingolipid with a phosphocholine or phosphoethanolamine head group, abundant in animal-cell membranes. It is a major membrane phospholipid built on a sphingosine rather than glycerol backbone.
Micelle: A spherical aggregate of amphiphilic molecules with hydrophobic regions gathered inside and polar regions outside. Phospholipids can form micelles under conditions where their molecular shape favors curved aggregates.
Liposomal drug delivery: A drug-delivery method that encloses therapeutic compounds in phospholipid vesicles called liposomes. Phospholipids form the vesicle shells that can carry drugs in aqueous interiors or lipid membranes.
Glycolipid: A lipid with one or more carbohydrate groups attached, commonly found on cell surfaces. Glycolipids carry sugar head groups rather than the phosphate-bearing heads characteristic of phospholipids.
Fatty acid: A carboxylic acid with a hydrocarbon chain, used as a building block in many lipids. Its hydrocarbon chain supplies the hydrophobic portion of many phospholipids.
Critical micelle concentration: The concentration above which surfactant molecules begin forming micelles in solution. It describes an aggregation threshold, though bilayer-forming phospholipids often aggregate differently.

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