<prompt> Main part of surfactant is formed by -Dipalmitovl phosphatidyl cholinePhospbotidyl-inositolDipalmitovl cephalineDipalmitovl serine  <response>: Ans. is a i.e., Dipalmitoyl phosphatidyl cholineo Important glycerophospholipids are :-1 Phosphatidylcholine lecithin:- These glycerophospholipids contain choline. These are most abundant phospholipids in cell membrane. Dipalmitoyl lecithin dipalmitoyl phosphatidylcholine is an important phosphatidylcholine found in lungs, secreted by type II pneumocytes. It acts as a lung surfactant and is necessary for normal lung compliance. It reduces surface tension in alveoli and prevents alveolar collapse. Acute pulmonary respiratory distress syndrome RDS in premature infants is due to inefficient production of surfactant dipalmitoyl lecithin dipalmitoyl phosphatidylcholine.2 Phosphatidylethanolamine cephaline They have ethanolamine instead of choline. Thromboplastin coagulation factor III is composed of cephaline. Like lecithin, Phosphatidylethanolamine is also a component of cell membrane.3 Phosphafidylserine:- They have serine nitrogenous base. Phosphatidylserine is also a componant of cell membrane. It plays a role in apoptosis.4 Phosphatidylinositol:- They have inositol as the stereoisomers, myoinositol. Pkosphatidyiinositol 4,5- bisphosphate is an important constituent of cell membrane phospholipids, upon stimulation by a suitable hormone agonist, it is cleaved into diacylglycerol and inositol triphosphate both of which act as second messengers.5 Plasmalogens:- Plasmalogens are similar to other glycerophospholipids but fatty acid at Cl of glycerol is linked through an ether, rather than ester bond as occurs in other glycerophospholipids. So, plasmalogen is called ether glyceroiipid. Plasmalogens are found in brain myelin and cardiac muscles. Plasmalogen is a platelet activating factor PAF and involved in platelet aggregation and degranulation.6 Lysophospholipids:- Lysophospholipids are formed when one of the two fatty acid is removed from glycerophospholipids i.e. Lysophospholipidsglycerophospholipid-1 fatty acid or lysophospholipidsglyceral phosphoric acid 1 fatty acid nitrogenous base. Most common of these are lysophosphatidylcholine lysolecithine and lysophosphatidylethanolamine lysocephalin.7 Cardiolipin Diphosphatidy lglyeerolCardiolipin is composed of two molecules of phosphatidic acid connec ted by a molecule of glycerol, i.e. cardiolipin phosphatidic acid glycerol phosphatidic acid. There is no nitrogenous base. Cardiolipin is a major lipid of inner mitochondrial membrane and is necessary for optimum functioning of ETC. 