chemistry of lipid biochemistry

1. chemistry

2. TRIACYLGLYCEROLS

3. TRIACYLGLYCEROLS
The triacylglycerols are esters of the trihydric alcohol
glycerol and fatty acids.

4.  Mono- and diacylglycerols wherein one or two
fatty acids are esterified with glycerol are also
found in the tissues.
 They are significant in the synthesis and
hydrolysis of triacyl glycerols

6.  Triacyl glycerol are the main storage form of
energy.
 Simple triacyl glycerol- all the three hydroxyl
groups of the glycerol are esterified to the same fatty
acids. tripalmitin
 Mixed triacyl glycerol – different fatty acids are
esterified to the hydroxyl groups of glycerol. 1,3-
dipalmitoyl – 2-olein.

7. Rancidity
 Hydrolytic rancidity
 Due to partial hydrolysis of the TAG due to traces of
hydrolytic enzymes present in naturally occurring fats
and oils.
 Oxidative rancidity
 Result of partial oxidation of unsaturated fatty acids
with resultant formation of epoxides and peroxides.

8. Physical properties of TAG
 Oils are liquids at 20oC
 Oils contain higher proportions of
unsaturated fatty acids or short chain
triglycerides.
 Oils are usually plant origin.

9.  Fats are solid at room temperature and contain
mainly saturated fatty acids
 Fats are mainly animal origin.
 When the constituent fatty acids have a higher chain
length and are predominantly saturated, hard fat is
produced. Eg, pig fat

10. Hydrolysis of fats
 Occurs during digestion of dietary fat and
mobilization of TAG from adipose tissue.
 Hydrolyzed by lipases
 Sequentially hydolyzed to diacyl glycerol,
monoacyl glycerol and glycerol and fatty acids.

11.  Saponification : it is defined as the number of mg of
KOH required to saponify one gram of fat.
 It is an indication of molecular weight of the fat and
is inversely proportional to it.
 Human fat has a saponification number of 194-198,
and coconut oil has 253-262.

12.  Iodine number : iodine number of a fat is defined as
the number of gram of iodine taken up by 100 gm of
fat.
 It is an index of the degree of unsaturation and is
directly proportional to the content of unsaturated
fatty acids.
 Higher the iodine number, higher is the degree of
unsaturation eg, iodine number of butter is 28, and
that of sunflower oil is 130.

13. Phospholipids
 Phospholipids-lipids containing phosphoric
acid residue in addition to fatty acids and an
alcohol

14.  Phospholipids are important constituents of
cell membrane.

15.  Phosphatidic acid
 Phosphatidyl choline
 Phosphatidyl ethanolamine
 Phosphatidyl serine
 Phosphotidyl inositol
 Diphosphotidyl glycerol
 Plasmalogans
 Sphingomylein

16.  Phospholipids may be regarded as derivatives of
phosphatidic acid , in which the phosphate is
esterified with the OH of a suitable alcohol.

17.  Phosphatidic acid is important as an
intermediate in the synthesis of
triacylglycerols as well as phosphoglycerols
but is not found in any great quantity in tissues.

18. Phosphatidylcholines (Lecithins)
 Most abundant phospholipids of the cell
membrane and represent a large proportion of
the body’s store of choline.

20.  Phosphatidylethanolamine (cephalin) and
phosphatidylserine (found in most tissues) differ
from phosphatidylcholine only in that
ethanolamine or serine, respectively, replaces
choline.

21.  Dipalmitoyl lecithin is a very effective surface
active agent and a major constituent of the
surfactant preventing adherence, due to surface
tension, of the inner surfaces of the lungs. Its absence
from the lungs of premature infants causes
respiratory distress syndrome.

22. Functions of lecithin
 Predominant glycerophospholipid in cell membrane.
 Act as the storage depot of body’s choline reserve.
 Choline takes part in various transmethylation
reactions.
 Choline plays a role in nerve conduction.
 Choline helps cholesterol dissolve in bile

23.  Lecithin help in emulsifying lipid water mixtures.
 Lecithin help in the esterification of free cholesterol to
form cholesterol ester.
 Lecithin provides arachidonic acid for eicosanoid
synthesis.
 Lecithin act as a component of cytochrome P450
system which plays a role in detoxification.

24. Lysophospholipids
 These are phosphoacylglycerols containing only
oneacyl radical, eg, lysophosphatidylcholine
(lysolecithin), important in the metabolism and
interconversion of phospholipids

26.  It is also found in oxidized lipoproteins and has
been implicated in some of their effects in
promoting atherosclerosis.

27. Functions of cephalin
 It is a component of membrane.
 It plays a role in blood coagulation

29. Phosphatidylinositol
 The inositol is present in phosphatidylinositol as
the stereoisomer, myoinositol.

31. Functions of phosphatidyl
inositol
 Phosphatidyl inositol 4,5 bisphosphate is an important
constituent of cell membrane.
 Phospholipase C act on phosphotidyl 4,5
bisphosphate and cleaves it into diacyl glycerol and
inositol triphosphate both of which act as second
messengers

32.  Phosphatidylinositol 4,5-bisphosphate is an
important constituent of cell membrane
phospholipids.
 On stimulation by a suitable hormone agonist, it is
cleaved into diacylglycerol and inositol
trisphosphate, both of which act as internal
signals or second messengers.

33. Functions of phosphatidyl
serine
 They are components of biological membranes.

35. Cardiolipin
 Cardiolipin is made up of two molecules of
phosphatidic acid linked by a molecule of glycerol.
 It is first isolated in cardiac muscle and hence
derived the name.

36.  Cardiolipin-
 Diphosphatidyl Glycerol – found in inner Mt.
Membrane, important component of electron
transport chain .
 It occurs in most other tissues as well.
 it also exhibits antigenic properties.

37.  Detection of anticardiolipin antibodies(ACA) have a
diagnostic role in embryo transfers and organ
transplantation.

38. Plasmalogens
 The Plasmalogens resemble phosphatidylethanolamine
but possess an ether link on the sn-1 carbon instead of the
ester linkage.
 Alkyl radical is an unsaturated alcohol.
 In some instances, choline, serine, or inositol may be
substituted for ethanolamine.
 Plasmalogens are rich in brain and muscle tissues.

40. Platelet activating factor
 It has an ether linked alkyl chain at C1 of glycerol C2 is
ester linked to acetic acid which makes PAF more
water soluble than other glycerophospholipids.
 PAF plays a significant role in inflammation,
chemotaxis and allergic responses.

41. Phospholipids
Alcohol
Parent
Compound
Examples:
Glycerophospholipid
Glycerol
Phosphatidic acid
1,2 Diacyl Glycerol3
Po4
Lecithin,Cephalins
Phosphatidyl Inositol
Plasmalogen,Cardiolipin
Sphingophospholipid
Sphingosine
Ceramide
Acyl Sphingosine
Sphingomyelin
(Cer-P-Choline)

42. Sphingomyelins
 Sphingomyelins are found in large quantities in brain
and nerve tissue.
 On hydrolysis, the sphingomyelins yield a fatty acid,
phosphoric acid, choline, and a complex amino
alcohol, sphingosine.

43. SPHINGOMYELIN CATABOLISM

45.  No glycerol is present.
 The combination of sphingosine plus fatty acid is
known as ceramide, a structure also found in
the glycosphingolipids

46.  Aminogroup of sphingosine acylated to form ceramide
 Phosphoryl choline + ceramide –sphingomyelin

48. 
The sphingomyelins are synthesized by the
transfer of phosphorylcholine from
phosphatidylcholine to a ceramide in a reaction
catalyzed by sphingomyelin synthase

50. GLYCOLIPIDS (GLYCOSPHINGOLIPIDS)
 Glycolipids are widely distributed in nervous tissue
such as brain.
 They occur particularly in the outer leaflet of the
plasma membrane.
 They contain ceramide and one or more sugars.

51.  The four glycosphingolipids are
 Cerebrosides
 Globosides
 Gangliosides
 sulfatides

52. Glycolipids
Cerebroside Cer - Glc/Gal
NANA
Ganglioside GM 1 Cer-Glc-Gal-Gal NAc-Gal
NANA
GM2 Cer-Glc-Gal-Gal NAc
NANA
GM3 Cer-Glc-Gal
Globoside Cer-Glc-Gal- Gal NAc

54. Cerebrosides -single sugar groups linked
to ceramide
 Galactocerebrosides
 Found predominantly in neuronal cell membranes.
 Most common
 Glucocerebrosides-
 Intermediates in the synthesis or degradation of more
complex glycosphingolipids
 extraneural tissues, also seen in brain

55. Globosides
 Cerebrosides containing additional carbohydrates like
glucose, galactose or GalNAc
 Lactosyl ceramide-human erythrocyte membrane
 Ceramide trihexoside-

57.  Gangliosides are complex glycosphingolipids
derived from glucosylceramide that contain in
addition one or more molecules of a sialic acid.

58.  Gangliosides are also present in nervous tissues in high
concentration.
 They appear to have receptor

59.  The simplest ganglioside found in tissues is GM3,
which contains ceramide, one molecule of glucose,
one molecule of galactose, and one molecule of
NeuAc.

60.  G represents ganglioside;
 M is a monosialocontaining species;
 The subscript 3 is a number assigned on the basis
of chromatographic migration.

61.  GM1 -receptor in human intestine for cholera
toxin

62.  Gangliosides which contain one to five molecules
of sialic acid, giving rise to di-, trisialogangliosides,
etc.

63. sulfatides
 Sulfuric acid esters of glycosphingolipids
 Synthesized from glycosphingolipids and PAPS

64. Micelle
 When phospholipids are distributed in water, their
hydrophobic parts keep away from water, forming
molecular aggregates called micelle.

67.  Emulsifiers
 Detergents
 solubilisation of lipids in aqueous media
 Absorption of fat-soluble vitamins and complicated
lipids within the human body

68.  Aggregation of bile salts into micelles and the
formation of mixed micelle with the products
of fat digestion are important in facilitating
absorption of lipids from the intestine.

69. liposomes
 Liposomes may be formed by sonicating an
amphipathic lipid in an aqueous medium.
 They consists of spheres of lipid bilayers that
encloses part of the aqueous medium.

70. Liposomes

72.  Drugs, proteins, enzymes, etc. may be
encapsulated by the liposomes which could act
as carriers for these substances to target organs.

73.  Liposomes are of potential clinical use –eg, in
cancer therapy.
 In addition, they are used for gene transfer into
vascular cells
 carriers for topical and transdermal delivery of
drugs and cosmetics.