Liposome structure, illustration. A liposome (top right) is an artificially-constructed, spherical vesicle that possesses a selectively-permeable wall that closely resembles the membrane of a living cell. The membrane consists of a dual layer of phospholipids (bottom right). Each phospholipid molecule (top left and centre) consists of a hydrophilic (water-soluble) phosphate group head (round) and a hydrophobic (water-insoluble) fatty acid tail. Liposomes can be used to carry drugs or genes to target cells. This is particularly useful for highly toxic cancer drugs as it reduces unpleasant side effects.