Phospholipids z Pi is in turn esterified to OH of a polar head group (X): e.g., serine, choline, ethanolamine, glycerol, or inositol. z The 2 fatty acids tend to be non-identical. They may differ in length and/or the presence/absence of double bonds. O P O O− O H2C CH H2C R1 C O O O C O R2 X glycerophospholipidPhospholipids z Pi is in turn esterified to OH of a polar head group (X): e.g., serine, choline, ethanolamine, glycerol, or inositol. z The 2 fatty acids tend to be non-identical. They may differ in length and/or the presence/absence of double bonds. O P O O− O H2C CH H2C R1 C O O O C O R2 X glycerophospholipid