3. Phospholipids
• Complex lipids
• Containing phosphoric acid, in addition to fatty
acids, nitrogenous base and alcohol
Classification
Phospholipids
Glycerophospholipids Sphingophospholipids
4. Micelles are spherical
structures that have a
nonpolar, hydrophobic
environment in the
core, and a polar,
aqueous environment
on the surface. The bile
salt-lipid complexes
formed in the small
intestine are micelles.
8. Phosphatidyl choline (Lecithin)
• Most abundant phospholipids in cell membrane
• Storage form of body’s choline
• Widely distributed in animals in liver, brain, nerve
tissues, sperm & egg-yolk, having both meatabolic &
structural functions
• On hydrolysis: glycerol, fatty acids, phosphoric acid,
nitrogenous base choline.
9. Properties of lecithin
Physical properties :
• when purified it is a waxy, white substance,
becomes brown when exposed to air
• Soluble in ordinary fat
• hygroscopic
10. Chemical properties
Lecithin
H2O
Phosphatidic acid + Choline
1. When aqueous solution of lecithins are shake with sulphuric
acid, choline is split off, forming phosphatidic acid
Phosphatidic acid Glycerophosphoric acid +
2 Fatty acids
H2O
2.
11. Dipalmitoyl Lecithin
• Important phosphatidylcholine found in lungs
• Acts as a surfectant & lower the surface tension in
lung alveoli
• Absence of DPL, in premature fetus, produces
collapse of lung alveoli, which produces
Respiratory distress syndrome
13. Cephalin
• Ethanolamine is the nitrogenous base
• They occur with lecithin, particularly rich in brain
& nervous tissue
14. Phosphatidyl inositol
• Phosphatidic acid is esterified to inositol
• Important component of cell membrane
• Plays vital role in the mediation of hormone
action
• Inositol as a constituent of phospholipids was
first discovered in acid fast bacilli, later in brain
& nervous tissue
15. Phosphatidyl serine
• Cephalin like phospholipid
• Contains amino acid serine in place of
ethanolamine
• Found in brain, nervous tissue & blood
16. Plasmalogens
• When a fatty acid is attached by an ether linkage at C1 of glycerol in
glycerophospholipid, the resultant compound is plasmalogen
• Unsaturated fatty acid occurs at C1
17. Cardiolipin
• Isolated from heart muscle
• Consists of two molecules of phosphatidic acid held
by an additional glycerol through phosphate groups
• Important component of inner mitochondrial
membrane
• It is only phosphoglyceride that possesses antigenic
properties
18. Sphingophospholipids
• Found in brain & nervous tissue, small amount in other tissues
• Does not contain glycerol
• In place of glycerol, it contains an 18 carbon unsaturated
amino alcohol called sphingosine (sphingol)
• On hydrolysis: sphingomyelin yields: one molecules of fatty
acid, phosphoric acid, 1 complex unsaturated amino alcohol
sphingosine
• Sphingosine is attached by an amide linkage to a fatty acid to
produce ceramide
Example: Sphingomyelins
19.
20. Function of phospholipids
• Structural components of membranes and regulate
membrane permeability
• Role in enzyme action e.g. mitochondrial enzyme
system involved in oxidative phosphorylation
• Role in transport of lipids from intestines
• Role in lipid absorption in intestine
• Role in electron transport
21. Cont…
• Lipotropic action of lecithin
• Membrane phospholipids as source of arachidonic acid
• Role in blood coagulation
• Insulation: phospholipids of myelin sheath provide the
insulation around the nerve
• Cofactor e.g. lipoptotein lipase, triacylglycerol lipase
• Phosphatidylinositol are involved in signal transmission
across membranes
23. Cerebrosides (glycosphingosides)
• Occur large amounts in the white matter of brain & in the
myelin sheaths of nerve
• Structure: no glycerol, no phosphoric acid & no nitrogenous
base. Thus, cerabrosides on hydrolysis yields:
- a sugar, usually galactose but sometimes glucose
- a high mol. Weight fatty acid
- alcohol, sphingosine or dihydrosphingosine
• Contain a ceramide (sphingosine attached to fatty acid) &
one or more sugars
25. Clinical aspect of cerebrosides
Gaucher’s disease:
• Inherited disorder of cerebrosides metabolism
• Autosomal recessive
• Enzyme defect: deficiency of beta
glucocerebrosidase
26. Gangliosides
• Highest concentration found in gray matter of the brain
• Formed when ceramide oligo-sachharides have at least
one molecules of NANA (N-acetyl neuraminic acid, also
called sialic acid) attached to them
• Ceramide-Glucose-Galactose-NANA
• Types of gangliosides: more than 30 types have been
isolated
• Four important types: GM-1, GM-2, GM-3 & GD-3
27. Function: can serve as specific membrane binding sites
(receptor sites) for circulating hormones
Clinical aspect
1. Tay-Sach’s disease (GM2 Gangliosidosis)
• Enzyme defect: deficiency of hexosaminidase A
2. GM1 Gangliosidosis
• Due to deficiency of beta galactosidase
28. Sulfolipids
• Formed when sulfate groups are attached to
ceramide oligosaccharides
• Important component of membranes of nervous
tissue
• Failure in degradation of these compounds results
in accumulation of these complex in CNS, result
in lipid storage diseases
