Lipids are water-insoluble organic compounds that include fats, oils, waxes and other compounds. They are composed of fatty acids and glycerol. The most common lipids are triglycerides, which are made of three fatty acids bonded to a glycerol molecule. Lipids serve important functions like energy storage and are a more concentrated source of energy than carbohydrates or proteins. They have properties like being insoluble in water but soluble in organic solvents. Saturated fats are typically solids while unsaturated fats are usually liquids. Lipids transport fat-soluble vitamins and are important components of cell membranes.

1. lipids
• Lipids are water insoluble, oily or greasy
organic compounds soluble in non-polar
organic solvents.
• Chemically, lipids are defined as the esters
of alcohol and fatty acids.

2. • Lipids are composed of 3 fatty acids joined
to an alcohol.
• Fatty acids and alcohol are the building
block components of lipids.
• The lipids are the important constituents of
diet due to their higher energy value.
• One gram of lipid yields 9.3 kilocalones of
heat, while the same amount of
carbohydrate or protein yields 4.5
kilocalories only.

3. • The lipids include a heterogenous group of
compounds related to fatty acids.
• The common lipids are fats. oils, waxes,
phosph olipids, glycolipids, cerebros ides,
sulfolipids, aminolipids, steroids, terpenes,
carotenoids, some hormones and some
vitamins.

4. Lipids have three important
properties.
1. Lipids are insoluble in water but soluble in
non-polar organic solvents, such as
acetone, alcohol, chloroform, benzene and
ether.
• 2. They contain a large proportion of
carbon and hydrogen bonds and release
large amount of energy On breakdown.
• 3. On alkaline hydrolysis lipids yield
alcohol and fattyacids.

5. Lipids are esters* of glycerol and fatty acids.
They are formed by the combination of
alcohol and fatty acids.
• Usually a lipid is made up of a glycerol
and three fatty acids. Such a lipid is called
a triglyceride or a neutral fat.

7. • Ester is a compound formed by the
combination of an acid with a glycerol
with the removal of water.

8. Glycerol, a component of lipid.
It is an alcohol.
It is a trihydric alcohol.
It contains three alcoholic (OH) groups.
Of these three, two are primary alcoholic
groups (CH2OH)
and the third one is secondary (CHOH).

9. • Fatty acid: A long-chain carboxylic acid;
those in animal fats and vegetable oils often
have 12–22 carbon atoms.
• Lipid: A naturally occurring molecule from a
plant or animal soluble in nonpolar organic
solvents.
• Waxes are carboxylic acid esters,
RCOOR’,with long, straight hydrocarbon
chains in both R groups; they are secreted by
sebaceous glands in the skin of animals and
perform mostly external protective functions.

10. Triacylglycerols are carboxylic acid
triesters of glycerol, a three-carbon
trialcohol. They make up the fats stored in
our bodies and most dietary fats and oils.
They are a major source of biochemical
energy.

11. Fatty Acids and Their Esters
• The naturally occurring fats and oils are
triesters formed between glycerol and
fatty acids.
• Saturated fatty acid: A long-chain
carboxylic acid containing only carbon–
carbon single bonds.
• Unsaturated fatty acid: A long-chain
carboxylic acid containing one or more
carbon–carbon double bonds.
• If double bonds are present in naturally
occurring fats and oils, the double bonds
are usually cis rather than trans.

12. Types of Fatty Acids

14. Trans Fatty Acids
The Truly Awful!

15. The
Good!

16. The
Bad!

17. The
Truly
Awful!

18. Fats are Used in Energy Storage and
Production

19. The figure is found at http://courses.cm.utexas.edu/archive/Spring2002/CH339K/Robertus/overheads-2/ch11_lipid-struct.jpg
(Jan 2007)
Strcture of lipids

20. Glycerides
The major form of lipid
in food and in the body

21. The figure was adopted from http://en.wikipedia.org/wiki/Fatty_acid (April 2007)

22. Fatty Acids
• Fatty acids are aliphatic straight chain
hydrocarbon compounds with a terminal
carboxyl group. They are the building
blocks of lipids.

25. • The carbon atoms are numbered from the
carbon of the COOH group.
• In most of the unsaturated fatty acids there is a
single double bond lying between carbon
atoms 9 and 10.
• This is designated as .
• The symbol with the superscript number
• 9 indicates the position of the double bond.

26. • The symbol 18:0 denotes a C,8 fatty acid
with no double bonds. The number 18:2
signifies that there are 2 double bonds.
• Similarly, the symbol 18:2; 9, 12 is used to
denote an 18 carbon acid with two double
bonds in the 9 and 12 positions.
• When two or more double bonds are
present in a fatty acid, the double bonds are
never conjugated But the double bonds
are separated by a methylene group.

27. a) Neutral fat (Triacylglycerol):
• Esters of 3 fatty acids with glycerol
• Glycerol is an alcohol containing 3 OH groups
• Types:
– Simple: contain similar fatty acids e.g., tripalmitin
– Mixed; contain different fatty acids e.g.,
palmito-oleio-stearin
– Either solid, called fats, or liquid, called oils.
b) Waxes:
– Esters of fatty acids with alcohols other than glycerol.
– Important for manufacturing of ointments & cosmetics
– Not digested
1- Simple lipids

28. Simple Lipids (Triglycerides)
• A simple lipid is formed when three
molecules of fatty acids combine with
one molecule of glycerol.
• In this process 3 molecules of water are
released.

29. • Monoglycerides
monopalmitin
• Diglycerides
dipalmitin

30. Polyunsaturated fatty acids have more
than one C=C double bond.
Linoleic and linolenic acids are essential
in the human diet because the body does
not synthesize them and they are needed
for the synthesis of other lipids.

32. Compound lipids
• contain some chemical groups in addition
to fatty acids and glycerol.
• When a lipid contains a phosphate group,
it is called a phospholipid and when a
lipid contains a carbohydrate, it is called a
glycolipid.

33. • Lecithin is a phospholipid. In lecithin, two
hydroxyl groups of glycerol have been
esterified by fatty acids, while the third
hydroxyl group has been replaced by
phosphoric acid which in turn has formed
an ester with choline.

34. Phospholipid
Lecithin, a
common food
additive, is a
phospholipid.
Embedded in
cell
membranes.

35. Derived lipids
• Steroids:
• The steroids have a
1,2_cycIopentanoperhydro phenanthrene
nucleus. It has four rings named as A, B, C
and D. The rings A, B and C are hexagons
called cyclohexane rings.
• The ring D is a pentagon called
cyclopentane.

36. Steroids
• Steroids are solid alcohols.
• They have a
cyclo pentano per hydro phenanthrene
nucleus.
• They are made up of four rings named as
A,B,C and D.
• The rings A, B and C are cyclohexanes.
The ring D is a cyclopentane. The
numbering starts from ring A to D.

37. it has two methyl groups (CH3 ) at carbon
atoms 10 and 13. Usually there is a side
chain at position 17. Cholesterol is a
steroid.

38. Terpenes
• derivatives of isoprene (= 2-methylbuta-1,3-diene)
• found in oils of plants and flowers
• characteristic odour (geraniol, menthol,...)
• steroids are derived from triterpenes

39. • Terpenes
• Terpenes are hydrocarbons. They have less
than 40 carbon atoms.
• Terpenes are constructed out of isoprene
units.
• Each isoprene unit has 5 carbon atoms
and 8 hydrogen atoms (C5H8). Each
isoprene unit has two ends, namely a head
and a tail. The head is the branched end and
the tail is the unbranched

40. Terpenes – classification:
• monoterpenes (C10) 2 x isoprene
• sesquiterpenes (C15) 3 x isoprene
• diterpenes (C20) 4 x isoprene
• triterpenes (C30) 6 x isoprene
• tetraterpenes (C40) 8 x isoprene
 formed by bonding „head to tail“ or „tail to tail“
 different degree of unsaturation
 variety of functional groups

41. • When the terpene contains two isoprene
units, it is called a monoterpene, When it
contains 3 units, it is called a
sesquiterpene.
• When it contains 4 units the terpene is called
• a diterpene.
• A triterpene contains 6 units.
• When there are 8 units the terpene is called
a tetraterpene.
• A polyterpene contains more than 8 isoprene
units.

42. menthol (C10) phytol (C 20)
squalene (C 30)
-carotene (C40)
The figures are adopted from http://en.wikipedia.org (April 2007)
Examples of terpenes

43. • The commercial name for glycerol is
glycerine,
• It soluble in water and insoluble in organic
solvents.
• Glycerol combines with three similar fatty
acids to form a simple lipid called
triglyceride with the release of 3
molecules of water.
Glycerol has two important properties. They are
1. Formation of esters
2. Dehydration

44. • 1. Formation of Esters
• Glycerol reacts with acids, both organic and inorganic
acids, to form esters like monoesters, diesters and
triesters,
• Triesters of glycerol with higher fatty acids constitute lipids
• Monoglycerides act as good detergents and
emulsifying agents. This property helps in the
manufacture of detergents. In animals, emulsifying
property helps the digestion of fats.
• 2. Dehydration
• When glycerol is heated in the presence of a dehydrating
agent like H2S04, phosphorus pentoxide or potassium
hydrogen sulphate (KHSO4), it produces an unsaturated
aldehyde called acrylic aldehyde or acrolein.

47. • The common higher fatty acids are insoluble in
• water.
• But they can be dispersed into micelles in dilute
NaOH Or KOH.
• Micelle is an aggregation of fatty acid molecules
• In water into a globular structure in which their
non-polar
• tails are in the interior and the polar heads are on
the exterior exposed to water.
• NaOH or KOH converts fatty acids into soaps.
Soaps are the salts of fatty acids.

48. • Again, based on their requirement in the diet, fatty
• acids are classified into two types namely
• 1. Essential fatty acids
• 2. non- essential fatty acids
• Thus fatty acids are classified into 6 types. They
are
• 1.unsaturated fatty acids
• 2. saturated fatty acids
• 3. hydroxy or oxygenated fatty acids
• 4. Cyclic fatty acids
• 5. essential fatty acids
• 6. Nonessential fatty acids

51. The hydrocarbon chains in saturated
acids are flexible and uniform in shape,
allowing them to nestle together. By
contrast, the carbon chains in unsaturated
acids have rigid kinks wherever they
contain cis double bonds. The kinks make
it difficult for such chains to fit next to
each other in the orderly fashion
necessary to form a solid.

52. The more double bonds there are in a
triacylglycerol, the harder it is for it to
solidify.

54. Waxes
• Waxes have the general structure
shown here. R` and R represent
long carbon chains of approximately 30
carbons resulting in an extremely
hydrophobic lipid with a high degree of
water repellency.
• An important biological function of a wax
is to act as a protective coating.
The “shine” on these leaves is due
to a thick protective wax coating.

55. • Cholesterol (and other lipids) in the body must be packaged for transport
because lipids will aggregate in the aqueous environment of the
bloodstream. The liver packages dietary lipid into aggregates known as
very-low-density-lipoproteins (VLDL).
• The improper transport of cholesterol in the bloodstream can lead to
atherosclerosis, a metabolic disease
Cholesterol and Atherosclerosis
A cutaway of VLDL.

56. The proper transport of lipids through the bloodstream and distribution to tissues
depend on the following lipoproteins: VLDL (very low density lipoprotein),
LDL (low density lipoprotein) and HDL (high density lipoprotein). These
lipoproteins are shown in the diagram below.

57. properties
• physical State
• Fats containing saturated fatty acids are
solids. Animal fats are solids.
• Fats containing unsaturated fatty acids
are liquids. Plant fats are oils at room
temperature.
• Oily and Greasy
• Lipids are greasy to touch and they leave
an oil impression on paper.

58. Properties of Fats and Oils
• Triacylglycerols in natural fats and oils are
nonpolar, hydrophobic molecules with no
ionic charges.
• Oil: A mixture of triacylglycerols that is
liquid because it contains a high
proportion of unsaturated fatty acids.
• Fat: A mixture of triacylglycerols that is
solid because it contains a high proportion
of saturated fatty acids.

59. Solubility;
• Fats are sparingly soluble in water, i.e. fats are hydrophobic.
• They are highly soluble in organic solvents like alcohol,
ether, etc.
• Solubility decreases with increasing molecular weight.
• Fats containing hydroxyl groups are more soluble than fats
without hydroxyl groups.
Melting point
• Melting point of fatty acids increases with increase in
molecular weight.
• Saturated fatty acids are having higher melting points than
fatty acids with unsaturated bonds.

60. SpecifiC Gravity
• Specific gravity is less than water. So they are
floating on the water surface. Solid fats are lighter
than liquid fats (oil).
isomerism
• Due to the presence of double bonds in
unsaturated fatty acids, geometrical isomerism
(cis-trans) is possible.
insulation
• Fats are bad conductors of heat. Fats in the
subcutaneous tissues provide a sort of blanket for
warm blooded animals. For cold blooded animals
there is a little amount of fat in the subcutaneous
regions. A high temperature is maintained by fat.

61. Emulsification
• In water fats are broken into minute droplets
an dispersed. This is called emulsification.
• Emulsion is a mixture of lipids and water.
Milk is a naturally occurring emulsion.
• Emulsification greatly increases the surfaces
area of fats It is an essential requisite for
digestion of fats. Emulsification is brought
about by mechanical action and by the action
of bile salts.

62. Hydrolysis of fats and oils carried out by
strong aqueous bases to form soaps is
called saponification.

63. Micelle: A spherical cluster formed by the
aggregation of soap or detergent
molecules so that their hydrophobic ends
are in the center and their hydrophilic
ends are on the surface.

64. • Rancidity
• Rancidity is the ill-smelling of fat. It is caused
by rancidification. Rancidification is due to
autooxidation of fats.
• The fat which has become rancid has a
disagreeable odour and taste and is unfit for
consumption.
• Rancidification occurs more frequently in
summer. The chemical changes which occur
during rancidification are called rancidity
• Rancidity occurs in two ways.
• They are hydroxyl rancidity and
oxidative rancidity.

65. Bloor’s Criteria
• According to Bloor, lipids are compounds having
the following characteristics.
• (i) They are insoluble in water.
• (ii) Solubility in one or more organic solvents,
such as ether, chloroform, Benzene, Acetone,
etc—so called ‘fat solvents’.
• (iii) Some relationship to the fatty acids as esters
• —either actual or potential.
• (iv) Possibility of utilisation by living organisms.
• Thus, lipids include fats, oils, waxes and related
compounds.

66. • BREAKDOWN PRODUCT OF FATS ARE
ACETYL CO A USED FOR SYTHESIS OF
CHOLESTEROL AND HORMONES
• Some vitamins like, A, D, E and K are fat
soluble, hence lipid is necessary for these
vitamins.

67. • II. Compound Lipids
• Esters of fatty acids containing groups, other than, and in
addition, to an alcohol and fatty acids.
• (a) Phospholipids: They are substituted fats containing in
addition to fatty acid and glycerol, a phosphoric acid
residue, a nitrogenous base and other substituents.
• Examples—phosphatidyl choline (Lecithin),
phosphatidyl ethanolamine (Cephalin),
phosphatidyl insositols (Lipositols),
phosphatidyl serine, plasmalogens,
sphingomyelins etc.
• (b) Glycolipids: lipids containing carbohydrate moiety are
called glycolipids. They contain a special alcohol called
sphingosine or sphingol and nitrogenous base in addition to
fatty acids But does not contain phosphoric acid o’-glyceroL
These are of two types:
• (i) Cerebrosides
• (ii) Gangliosides

68. • (c) Sulfolipids: Lipids characterized by
possessing sulphate groups.
• (d) Aminolipids (Proteoipids)
• (e) Liproproteins: Lipids as prosthetic group
to proteins.

69. DERIVED LIPIDS
• (a) Saturated FA
• There general formula is CnH2n+1 COOH
Examples:
• Acetic acid CH3COOH
• Propionic acid C2H5COOH
• Butyric acid
• Caproic acid
• Palmitic acid
• Stearic acid

70. 1. Saturated fatty acids:
– Fatty acids containing no double bonds
– Examples of saturated FA:
• Butyric acid (4C): CH3–CH2–CH2–COOH
• Palmitic acid (16C ): CH3–(CH2)14–COOH
• Stearic acid (18C): CH3–(CH2)16–COOH
2. Unsaturated fatty acids:
• Fatty acids containing double bond(s).
• They are either monounsaturated (one double bond) or polyunsaturated
(more than one double bond).
• Double bonds are:
– Nearly always in the cis configuration
– Spaced at 3 carbon interval if the fatty acid has more than one double
bond,
• Example of monounsaturated fatty acids:
– Palmitoleic (16C) is written 16:1Δ9 ,
– Oleic (18C) is written 18:1Δ9
• Examples of polyunsaturated fatty acids :
– Linoleic acid (18C) is written 18: 2 ∆9,12
– Linolenic (18C) is written 18:3 ∆9,12,15
– Arachidonic (20C) is written 20: 4 ∆5,8,11,14

71. Essential Fatty acids:
• They are the polyunsaturated fatty acids:
» linoleic acid 18: 2 ∆9,12
» linolenic acid 18:3 ∆9,12,15
• Must be supplied in the diet because the body can
not form them (we lack enzymes required to
introduce double bonds after C9)
• They are present mainly in vegetable oils
• Arachidonic acid (20C) is formed in the body from
linoleic acid, it becomes essential only if linoleic acid
is deficient
Non essential Fatty acids:
• They can be formed in the body
• They are the saturated & the monounsaturated fatty
acids

72. • Unsaturated FA
• (1) Mono unsaturated (Mono-Ethenoid) fatty
acids are those which contain one double
bond.
• Example: Oleic acid is found in nearly all
fats. (formula: 18: 1; 9).
• (2) Polyunsaturated (Polyethenoid) fatty
acids:
• There are three polyunsaturated fatty acids
of biological importance.

73. • (1) Linoleic acid series (18:2; 9, 12): It contains
two double bonds between C9 and C10; and
between C12 and C13.
• Their general formula is CnH2n-3 COOH Dietary
sources—Linoleic acid is present in sufficient
amounts in peanut oil, corn oil, cotton seed oil,
soybean oil and egg yolk.
• (ii) Linolenic acid series (18 : 3 ; 9, 12, 15): It
contains three double bonds between 9 and 10 ; 12
and 13; and I5 and 16. Their general formula is
CnH2n-5 COOH.
• Dietary Source: Found frequently with linoleic acid,
but particularly present in linseed oil, rape seed oil,
soybean oil, fish visceras and liver oil (cod liver
oil).

74. • (iii) Arachidonic acid series (20 : 4; 5, 8,
11, 14): It contains four double bonds
• Their general formula: Cn,H2n-7COOH
• Dietary source: Found in small quantities
with linoIeic acid and linolenic acid but
particularly found in peanut oil. Also found
in animal fats including Liver fats.

75. Nomenclature
• (i) Saturated acids end in “anoic” e.g.,
octanoic acid and
• (ii) unsaturated acids with double bonds
end in “enoic” e.g., octadecenoic acid
(oleic acid).

76. • lack of EFA in the diet can product growth
retardation and other deficiency
manifestation symptoms.
• Experimental studies:
• Burt and Burr (1929) first observed that rats
maintained on a diet from which fats are
rigidly exciuded—they cease to grow,
develop scaliness of the skin, necrosis of
the tail, kidney damage and impaired
reproductive capabilities. These
abnormalities were prevented/cured when
100 mg/day of Linoleic acid or Arachidonic
acid were included in the diet.

77. • Linoleic acid is most important as,
arachidonic acid can be formed from Linoleic
acid by a three stage reaction by addition of
Acetyl — CoA as follows.
• Pyridoxal phosphate is necessary for this
conversion.
• (i) Activation step: Linoleic acid is activated.
• CoA ester of linoleate undergoes
dehydrogenation to form — Linolenate.
• .

78. • (ii) Addition of two carbon moiety: Linolenate Is
converted to Eicosatrienoate by addition of 2
carbon unit—acetyl —CoA either in
mitochondrion or through malonyl — CoA in
microsome.
• Pyridoxal phosphate is required as cofactor.
• (iii) Dehydrogenation step: By another
dehydrogenation Eicosatrienoate is converted to
Arachidonic acid

79. • 3. Synthesis of prostaglandins and other
compounds: Prostaglandins are
synthesized from Arachidonic acid by
cyclooxygenase enzyme system.
• Leukotrienes are a newly discovered
family of conjugated trienes formed from
Arachidonic acid in leucocytes by the
Lipoxygenase pathway. /

80. • Effect on clotting time: Prolongation of
clotting time is noted in ingestion of fats rich in
EFA.
• Role in vision: Docosahexenoic acid is the
most abundant polyeneoic fatty acids present
in retinal photoreceptor membranes.
• Docosahexenoic acid is formed from dietary
linolenic acid.
• It enhances the electrical response of the
photo- receptors to illumination. Hence
linolenic acid is necessary in the diet for
optimal vision.

81. • Unsaturated Alcohols
• Among the unsaturated alcohols found in fats,
many of them are pigments. These include:
• (a) Phytol (Phytyl alcohol): A constituent of
chlorophyll.
• (b) Lycophyll: A polyunsaturated dihydroxy
alcohol which occurs in tomatoes as a purple
pigment.
• (c) Carotene: Easily split in the body at the central
point of the chain to give two molecules of alcohol,
vitamin A.
• (d) Sphingosine or sphingol: An unsaturated
amino alcohol present in body as a constituent of
phospholipid, sphingomyelin and various
glycolipids.

82. Solid bile

83. • Normal level of serum total cholesterol
in an adult varies from 150 to 250 mg%.
About 40-50 mg% occurs as “free”
cholesterol (approx 30% of total)

84. • Colour Reactions of Sterols
• (a) Liebermann-Burchard Reaction
• A chlorofom solution of a sterol, when
treated with acetic anbydride and
conc.H2SO4 gives a grass-green colour..
• This reaction forms the basis for a
colorimetric estimation of cholesterol by
Sackett’s method.

85. • (b) Salkowski Test
• When a chloroform solution of the sterol is
treated with an equal volume of Conc
H,S04 develops a red to purple colour.
• The heavier acid, which forms a layer below
assumes a yellowish colour with a green
fluorescence, whereas the upper
chloroform layer becomes bluish red first,
and gradually turns violet-red.

86. • (c) Formaldehyde-Sulphuric Acid Test
• On adding a 1:50 mixture of formaldehyde
and sulphuric acid to a
chloroform solution of cholesterol, the
chloroform layer turns cherry-red. Addition
of acetic anhydride to the chloroform layer
(after separating it from the previous
mixture)
• changes the cherry-red colour to blue.

87. • Zak’s Reaction
• When glacial acetic acid,
• aldehyde free, solution of cholesterol
• is treated with
• ferric chloride and conc. H,S04,
• produces a red colour.
• This reaction forms a basis for the
colorimetric estimation ot cholesterol
(Zak’s method).

88. Saponification Number
• Definition: The number of mgms of KOH
required to saponify the free and combined
FA in one gram of a given fat is called its
saponification number.
• Fats containing short chain fatty acids will have
more –COOH group present .and hence will take
up more alkali – high saponification number

89. • Acid Number
• Definition: Number of mgms of KOH
required to neutralise the fatty acids in a
gm. of fat is known as the acid number.
• Significance: The acid number indicates the
degree of rancidity of the given fat.
• Polenske Number
• Definition: The number of milli litre of 0.1
normal KOH required to neutralize the
insoluble fatty acids from 5 gram of fat.

90. • Relchert-Meissl Number
• Definition: it is the number of millilitres of 0.1
(N) alkali required to neutralise the soluble
volatile fatty acids distilled from 5gm. of fat.

91. • Significance:
• The Reichert-Meissl measures the
amount of volatile soluble fatty acids
• Butter fat is the only common fat with a
high Reichert-Meissi number and this
determination, therefore, is of interest in
that it aids the food chemist in detecting
butter substitutes in food products.

92. • Iodine Number
• The unsaturated fatty acids take up iodine and
other halogens at the point of unsaturation,
yielding saturated halogen derivatives.
Consequently,
• the degree of unsaturation of fats may be
determined by ascertaining how much Iodine a
given quantity will absorb.
• The result is called the Iodine number.
• Definition: Iodine number is defined as the
number of grams of iodine absorbed by 100
gms. of fat.

93. • Acetyl Number
• Some of the fatty acid residues in fats contain
• —OH groups.
• In order to determine the proportion of these, they
are acetylated by means of acetic anhydride. Thus an
acetyl group is introduced where ever a free — OH
group is present.
• After washing out the excess acetic anhydride and
acetic acid liberated,
• the acetylated fat can be dried and weighed and
the acetic acid in combination determined by
titration with standard alkali after it has been set
free.
• The acetyl number is thus a measure of the
number of — OH group present

95. • Glycerophosphatides: in this glycerol is the alcohol
group. Examples are
phosphatidyl ethanolamine(cephalin),
phosphatidyl choline (Lecithin),
phospatidyl serine,
plasmalogens,
phosphatidic acid and
cardio-lipins, phosphatides.
• Phospho-inositides: In this group, inositol is the
alcohol e.g., phosphatidyl inositol (lipositol)
• Phospho-sphmgosides: Alcohol present is
sphingosine (also called as sphingol) — an
unsaturated amino alcohol. e.g., sphingomyelin.

97. • Melting Points of Saturated vs. Unsaturated Fatty Acids:
• Note that as a group, the unsaturated fatty acids have lower
melting points than the saturated fatty acids.
• The reason for this phenomenon can be found by a careful
consideration of molecular geometries. The tetrahedral bond angles
on carbon results in a molecular geometry for saturated fatty acids
that is relatively linear although with zigzags. See graphic on the left.
• This molecular structure allows many fatty acid molecules to be
rather closely "stacked" together. As a result, close intermolecular
interactions result in relatively high melting points.
• On the other hand, the introduction of one or more double bonds in
the hydrocarbon chain in unsaturated fatty acids results in one or
more "bends" in the molecule. The geometry of the double bond is
almost always a cis configuration in natural fatty acids. These
molecules do not "stack" very well. The intermolecular interactions
are much weaker than saturated molecules. As a result, the melting
points are much lower for unsaturated fatty acids.