Phospholipids are lipids containing phosphorus, and they form the basic structure of all cell membranes.
Important points
- Glycerol-based phospholipids are also called phosphoglycerides or glycerophospholipids.
- Phospholipids are the major lipid components of biological membranes.
- Phospholipids are made up of a glycerol esterified at its C1 and C2 positions to fatty acids, and at its C3 position to a phosphate group.
- The phosphoryl group is attached to an ‘X’ group, which determines the type of phospholipid.
- Phospholipids are amphiphilic molecules, with non-polar/ hydrophobic tails made up of the hydrocarbon chains of fatty acids and a polar/ hydrophilic head made up of the phosphate group and the X group.
- The C1 position of phospholipids is usually attached to a saturated fatty acid having 16 or 18 C.
- The C2 position of phospholipids is usually attached to an unsaturated fatty acid having 16 to 20 C.
Lipids are not macromolecules, because their molecular weight is less than 800 Da. They still appear in the acid-insoluble fraction, because cell membranes break up into insoluble vesicles.
Extra information
| Name of X-OH | Formula of -X | Name of phospholipid |
|---|---|---|
| Water | -H | Phosphatidic acid |
| Ethanolamine | -CH2CH2NH3+ | Phosphatidylethanolamine |
| Choline | -CH2CH2N(CH3)3+ | Phosphatidylcholine (lecithin) |
| Serine | -CH2CH(NH3+)COO– | Phosphatidylserine |
Lecithin is NCERT’s example of a phospholipid found in the cell membrane. NCERT also notes that some tissues, especially neural tissue, have lipids with more complex structures.