Complex lipids include phospholipids, glycolipids, and lipoproteins. Phospholipids are the major components of cell membranes and contain a phosphate group. The most abundant phospholipid, phosphatidylcholine or lecithin, plays structural and metabolic roles. Glycolipids consist of cerebrosides found in the brain and gangliosides found in gray matter that serve as receptor sites. Deficiencies in the enzymes that break down glycolipids can cause lipid storage diseases.

1. Complex lipids
• Classification
• Structure & function of phospholipids &
glycolipids
12-10-2011

2. Classification
Phospholipids Glycolipids Lipoproteins Sulfolipids
Complex lipids

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.

5. Glycerophospholipids
• Membrane lipids
• Alcohol is glycerol

7. Glycerophospholipids

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

12. Phospholipase
Lecithin
Phospholipase A2
Lysolecithin + fatty acid
Phospholipase A1
Acyl glycerophosphorylcholine
+ fatty acid
Phospholipase C
Phospholipase D
1,2 diacyl glycerol + phosphoryl choline
Phosphatidic acid + Choline
Lecithin
Lecithin
Lecithin

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

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

22. Glycolipids
1. Cerebrosides (Glycosphingosides)
2. Gangliosides
3. Sulfolipids

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

24. Cont..
• Ceramide + Glucose : Glucocerebroside
• Ceramide + Galactose: Galactocerebroside
Types of cerebrosides:
1. Kerasin
2. Cerebron
3. Nervon
4. Oxynervon
• Function: Nerve conduction in myelin sheath

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

29. Clinical aspect
1. Metachromatic Leukodystrophy
• Enzyme deficiency: sulfatase
2. Fabry’s disease
• Enzyme deficiency: alpha galactosidase
3. Krabbe’s disease
• Enzyme deficiency: galactocerebrosidase