5. (A) STRUCTURE
Phosphatidic
acid / Phospho
glycerides
Simplest
phospholipid
Hence, all other phosp
holipids are considered
to be derivatives of
Phosphatidic acid
PO4 is esterified to the 3rd –OH group of Glycerol
7. (i) MEMBRANE CONSTITUENTS
Most abundant membrane lipids, accounting for
(55–70%) of the total lipids
Because of their amphipathic nature, they form
lipid bilayer
(C) FUNCTIONS
8. (ii) PULMONARY SURFACTANT
Dipalmitoyl lecithin helps to maintain shape of the
alveoli and prevent their collapse by reducing the
surface tension of alveoli
Composition: 40% DPPC, 35% PC, 10% PG, 10% Prot
eins (SP-A,B,C,D), 5% Neutral lipids
9. (iii) SECONDARY MESSENGERS
Phosphatidylinositol is the source of Inositol triphos
phate & Diacylglycerol, that acts as secondary messe
ngers for Group IIC hormones (e.g. Oxytocin)
(iv) BIOLOGICAL DETERGENTS
In small intestine, they act as biologic detergents
promoting emulsification & micelle formation: A
pre-requisite for lipid digestion & absorption respec.
(v) TRANSPORT OF LIPIDS
Phosphoglycerides are structural components of
lipoproteins (Chylomicrons,VLDL, HDL) which are
involved in transport of lipids
10. (vi) ANCHORING OF PROTEINS
Phosphoglycerides being amphipathic, interact with
the polar group of proteins thereby anchoring them
to biological membranes
(vii) LIPOTROPIC FACTORS
Phospholipids prevent accumulation of fat in the
liver thereby preventing fatty liver, hence
called as lipotropic factors
11. (viii) PRECURSORS OF EICOSANOIDS
Arachidonic acid liberated from membrane phosphol
ipids by action of PhospholipaseA2 serves as a
precursor for the synthesis of eicosanoids
14. Nervous tissue, especially myelin sheath
and RBC membranes are rich in
sphingomyelins
Lignoceric acid & Nervonic acid
(both 24C) are the fatty acids
commonly found in sphingomyelins
L/S ratio is an important parameter
in amniotic fluid to determine
fetal lung maturity
(B) SIGNIFICANCE
