Main part of surfactant is formed by -
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. Lysophospholipids=glycerophospholipid-1 fatty acid or lysophospholipids=glyceral + phosphoric acid + 1 fatty acid + nitrogenous base). Most common of these are lysophosphatidylcholine (lysolecithine) and lysophosphatidylethanolamine (lysocephalin).7) Cardiolipin (Diphosphatidy lglyeerol)Cardiolipin' 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.
Dipalmitovl phosphatidyl choline
Phospbotidyl-inositol
Dipalmitovl cephaline
Dipalmitovl serine
Lipids