Phospholipid Bilayer


ninja icon


•  Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules

phospholipid structure

Structure of Phospholipids:

  • Consist of a polar head (hydrophilic) composed of a glycerol and a phosphate molecule
  • Consist of two non-polar tails (hydrophobic) composed of fatty acid (hydrocarbon) chains
  • Because phospholipids contain both hydrophilic (water-loving) and lipophilic (fat-loving) regions, they are classed as amphipathic

Arrangement in Membranes:

  • Phospholipids spontaneously arrange into a bilayer
  • The hydrophobic tail regions face inwards and are shielded from the surrounding polar fluids, while the two hydrophilic head regions associate with the cytosolic and extracellular fluids respectively

Properties of the Phospholipid Bilayer:

  • The bilayer is held together by weak hydrophobic interactions between the tails
  • Hydrophilic / hydrophobic layers restrict the passage of many substances
  • Individual phospholipids can move within the bilayer, allowing for membrane fluidity and flexibility
  • This fluidity allows for the spontaneous breaking and reforming of membranes (endocytosis / exocytosis)