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 (i.e. two parallel layers of phospholipids)
  

• The hydrophobic tail regions face inwards and are shielded from the surrounding polar fluids
  

• The two hydrophilic head regions face outwards and associate with the cytosolic and extracellular fluids respectively
  

Properties of the Bilayer

• The phospholipid bilayer is held together by weak hydrophobic interactions between the tails
  

• The presence of hydrophilic and 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)
  

Phospholipid Properties