Phospholipid

A phospholipid is a lipid that is a primary component of animal cell membranes.

Phospholipids consist of a water-soluble head (a positively charged (polar) group), linked to two water-insoluble nonpolar tails (by a negatively charged phosphate group). Both tails consist of a fatty acid, each 14-24 carbon groups long.

Common types of phospholipids are: phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidic acid (PA) and phosphatidylcholine (PC) Phospholipids are also present in lecithin. Approximate level of phospholipids in lecithin is 50%.

Due to its polar nature, the head of a phospholipid is attracted to water (it is hydrophilic). The nonpolar head is not attracted to water and is said to be hydrophobic. When placed in water, phospholipids form a bilayer, where the hydrophobic tails line up against each other. This forms a membrane with hydrophilic heads on both sides. This membrane is partially permeable and very flexible.

See also: biochemistry, lipid, lipid bilayer, antiphospholipid syndrome;