Components of a phospholipid
Phospholipids are lipids that form a major part of cell membranes. They contain one glycerol molecule, two fatty-acid chains and a phosphate-containing group.
Compared with a triglyceride, the phospholipid has two fatty acids rather than three because a phosphate-containing group occupies the remaining attachment site on glycerol.
- The two fatty-acid chains are non-polar and hydrophobic.
- The phosphate-containing region is polar and hydrophilic.
- Each fatty-acid chain is linked to glycerol through an ester linkage.
- The remaining glycerol position connects to the phosphate-containing region through a phosphoester linkage.
- An additional polar group, such as choline, may be associated with the phosphate group.
A molecule containing both a hydrophilic region and hydrophobic regions is described as amphipathic. In a phospholipid, the phosphate-containing region forms the hydrophilic head, while the fatty-acid chains form the hydrophobic tails.
Exam Tip: A complete structural description should identify one glycerol, two fatty acids and a phosphate-containing group and distinguish the hydrophilic head from the hydrophobic tails.