This document provides an overview of lipids, including their classification, structures, functions, and properties. It discusses the different types of lipids such as simple lipids, compound lipids, and derived lipids. Specific lipid subclasses are described in detail, including fatty acids, glycerolipids, glycerophospholipids, sphingolipids, sterols, and lipoproteins. The roles of lipids in biological structures like cell membranes and as energy stores are summarized. Key physical and chemical properties of lipids are also highlighted.

1. Classification,
Structure,
Functions and
Properties of
LIPIDS
Presented by-
K. Chinmayi

2. Contents • Introduction
• Classification of Lipids
• Functions of Lipids
• Branching of Lipids
• Structures
• Functions
• Properties

3. INTRODUCTION
• “Lipos” in Greek, means fat
• Lipids Esters of Fatty acids and
Alcohols
Definition
The organic substances relatively insoluble in
water and soluble in organic solvents like
alcohol , ether etc.

4. CLASSIFICATION OF LIPIDS
Lipids
Simple
Lipids
Compound
Lipids
Derived
Lipids
Neutral
Lipids
Miscellaneous
Lipids
Esters of Fatty
acids and
Alcohols
Esters of Fatty
acids and
Alcohols
having other
additional
groups.
Also called
Complex Lipids
Hyldrolysed
forms of
Simple and
Compound
Lipids
Uncharged
Lipids
Compounds
which
characteristics
similar to
Lipids

5. Classification of Fatty Acids
Fatty Acids
Unsaturated acids Cyclic acids
Hydroxy and keto
Derivatives
Branched chain
acids
Saturated acids
1. Based on Natural Occurrence

6. 2. Based on number of Carbon
Atoms in the Chain
Fatty Acids
Even ChainOdd Chain Long ChainShort Chain
Medium Chain
Fatty Acids
3. Based on the Chain Length

7. Examples of Fatty Acids based on Chain length
Short Chain Fatty Acids Long Chain Fatty Acids

8. Saturated Fatty Acids

9. Unsaturated Fatty Acids

11. Branched Chain Fatty Acids
Cyclic Acids

12. Glycerol
• It is optically inactive.
• But when it is esterified in positions 1and 3, the carbon in position 2
becomes asymmetric .
• May be considered to be derived from L-glyceraldehyde.

13. Forms of Glycerides

15. Fatty acid Reactions

20. Reactions with Glycerol

24. Formation of Fatty acids from Soap

26. Functions of
Fatty Acids
• Major Source of Energy
• Used in the Soap Industry
• Used as Emulsifiers, Anti-foaming agents,
Texturizers andWetting Agents
• Esters with Complex alcohols are consumed in
foods
• Precursor to Prostaglandins

27. Biological Importance of Fatty Acids
• Cell membranes
• Heart
• Bones
• Liver
• Lungs
• Hormones
• Immune System

28. Functions of Essential fatty
Acids• Synthesis of Hormones
• Components of cellular and sub-cellular components
• Transport plasma phospholipids
• Oxidise to produce energy
• Important in
– Blood clotting(intrinsic factor)
– Retinal health
– Prevent and treat fatty liver
– Skin integrity
– Reproduction
– Normal growth
– Treatment of Atherosclerosis
• Transport blood cholesterol and triglycerides (control)

29. Physical properties of fatty acids
1. Melting point
Increases with increase in chain length.
Introduction of double bond causes lowering of the MP.
Cis-isomer melting lower than the trans isomer.
2. Polymorphism
The higher fatty acids exist in 2 or 3 crystalline forms ,depending on theT and the solvent of crystallization.
They are interconvertible and change to the most stable form when theT approximates the MP.
3. Solubility
It decreases with increasing chain length and increases withT.
4. Boiling point
The BP of the saturated fatty acids increase with increasing chain length.
The BP of the respective methyl esters are usually < 300C than those of free fatty acids .
5. Absorption spectra
The carboxyl group in the free fatty acids absorbs light in the short UV, but this not generally useful.
Properties of Fatty Acids

30. Chemical properties
1. Formation of salts
The fatty acids dissociate in solution and their salts can be prepared.
RCOONa + HCl RCOOH + NaCl
2. Formation of detergents and wetting agents
The soaps of sodium are hard and potassium are soft in nature.
RCOOH + NaOH RCOONa + H2O
3. Formation of esters with the alcohols
The esters of fatty acids with the trihydric alcohol or glycerol are called neutral
fats or triglycerides.
RCOOH + C2H3OH RCOOC2H5 + H2O

31. Chemical Properties
• Hydrolysis
They undergo stepwise enzymatic hydrolysis to give fatty acids and glycerol catalysed by
lipases.
• Saponification
The hydrolysis of triacylglycerols by alkali to produce glycerols and soaps.
Saponification no
- No. of KOH required to saponify the free & combined fatty acids in 1g. of a given
fat.
-A high saponification no. indicates that the fat is made up of low molecular wt. fatty
acids ,etc.

32. • Hydrogenation
Oleic acid( unsaturated ) + 3H2 Stearic acid(saturated glyceride)
• Oxidation of unsaturated glycerides of fats
Rancidity may be due to hydrolysis of fats into free fatty acids and glycerol
hastened by lipolytic enzyme and by oxidative processes.
• Reichert-Meissl no./Volatile fatty acid no.
-The ml. of 0.1 N alkali required to neutralize the volatile acids obtained from
5g. of fat which has been saponified and acidified to liberate the fatty acids
and then steam distilled.
-Butter has RH value of 25-30 while others have <1 , so any adulteration of
butter can be easily identified.

33. WaxesOilsFats
 Natural esters of
glycerol and Fatty
Acids
 Liquid at room
temperature
 Esters of
Glycerol and
Fatty Acids
 Solid at room
temperature
Simple
Lipids
 Esters of Fatty Acids
and Alcohols other
than Glycerol
 Alcohols can be
Aliphatic or Alicyclic
 Examples: Cetyl
Alcohol in candles
Saturated Unsaturated
 Single
bonds
 Maximum
Hydrogen
Atoms
 Double or
triple bonds
between two
or more
Carbon Atoms

34. The are esters of fatty acids with alcohols
Fats

35. Structures of Fats

36. • Efficient source of energy
• Insulator beneath the skin to prevent excessive external conditions
• Solvent for Fat soluble vitamins and hormones
• Constituent of Protoplasm
• Restricts water loss from Skin surface
• Reduces rate of water evaporation and heat loss
General Functions of Lipids

37. Biological Functions of Lipids
Membranes
Glyceropho
spho lipids
Non-
glycerophos
pho lipids
Energy
storage
Adipocytes
Major
source
Cell
signalling
Activation
of nuclear
receptors
Cellular
messengers

38. • Lipid peroxidation in vivo
To produce peroxides and free radicals which can damage the tissue.
• Iodine number
-The number of grams of iodine required to saturate 100g. of a given fat.
-A high iodine number indicates a high degree of unsaturation of the fatty acids in the fat.
Tests for Lipids

39. • Acetyl number
-It is defined as amount of KOH required, to combine with the acetic acid which is
liberated by the saponification of 1g of acetylated fat.
-Indicates the presence of volatile short- chain fatty acids or hydroxylated acids.
• Acid number
-Amount of KOH required to neutralize the free fatty acids in a 1g of fat.
-It indicates the degree of rancidity of the given fat.

40. Waxes
• They are esters of higher fatty acids and of higher monohydroxy alcohols
(aliphatic or aromatic)
Waxes
SpermoilLanolein Carnauba waxBees wax

41. Lanolein/Woolfat
• Containing both free & esterified cholesterol as well as the
sterols lanosterol & agnosterol.
• Used in ointments and cosmetics.
Beeswax
• A complete mixture of esters, some free fatty acids, alcohols
and hydrocarbons.
• It is a palmitic acid ester of myricyl alcohol(C30H61OH).

42. Carnauba wax
• An important plant wax.
• Used in the manufacture of polishes.
Spermoil
• Consists of three fourths of wax esters and one fourth of
triglycerides.
• Used in the manufacture of lubricants .
• Spermaceti- Palmitic acid ester of cetyl alcohol (C16H33OH), used
in the manufacture of candles, polishes and lubricants.

43. Properties of Lipids
They are colorless, odourless,
tasteless substances
Have well defined melting points
and solidifying points
Have low specific gravity and
float on water
They spread on water to form
thin monomolecular layers.
Physical Properties

44. Compound
/Complex Lipids
LipoproteinsGlycolipids Others
Non-
phosphorylated
Lipids
Phospholipids
Fatty acid+
Alcohol+
Phosphoric
acid+
Nitrogenous
base
Fatty acid+
Carbohydrate+
Nitrogenous
base
(NO GLYCEROL
and
PHOSPHATE)
Lipids+
Proteins
Glycero -
phospholipids
Sulpholipids
Sphingo -
phospholipids
Proteolipids
Cerebrosides
Gangliosides
Lipopolysaccharides

45. Glycerophospholipids
• Major lipids that occur in biological membranes.
• They consist of glycerol 3- phosphate esterified at its C1 (contains a saturated fatty
acid)and C2 (contains an unsaturated fatty acid) with the fatty acids.
Examples of Glycero-phospholipids
oPhosphatidic acid
oPhosphatidyl choline ( Lecithins )
Dipalmitoyl lecithin
Lysolecithin
oPhosphatidyl inositol
oPhosphatidyl ethanolamine ( Cephalins )
oPhosphatidyl serine
oPlasmalogens
oCardiolipin

51. Plasmologens

52. Sphingolipids/ Sphingomyelins
• Sphingosine is an amino alcohol present in sphingolipids.
• Sphingosine is attached by an amide linkage to a fatty acid to produce
Ceramide.
• The alcohol group of sphingosine is bound to phosphorylcholine in
Sphingomyelin structure.

54. Ceramide

57. Functions of
Phospholipids
• Structural components of membranes
• Regulates membrane permeability
• Maintains conformation of Electron transport
chain components in the mitochondria
• Maintains cellular respiration
• Helps in absorption of fats from the intestine
• Essential in the synthesis lipoproteins
• Prevents accumulation of fats in the liver

58. The phospholipids self-organize
themselves into:
• Bilayer sheet
• Miscelle
• Liposome

59. Sulpholipids
• Class of lipids which possess a sulphur-containing functional group
• Sulphoquinovosyl diacylglycerol is composed of a glycoside
of sulphoquinovose and diacylglycerol
• Mostly found sulpholipid in nature
• In plants, sulphoquinovosyl diacylglycerides (SQDG) are important
members of the sulphur cycle

61. Proteolipids
• Proteolipids are a different kind of protein-
lipid combination that are insoluble in water.
• Abundant in brain tissue

63. Glycolipids/Glycosphingolipids/Cerebrosides
• These lipids contain a fatty acid ,carbohydrate and nitrogenous
base.
• The alcohol is Sphingosine, hence they are also called as
glycosphingolipids.
• Glycerol and phosphate are absent.

65. Functions of
Glycolipids
• Essential part of cell membranes
• Receptors on the surface of the red blood cells
• Help determine the blood group
• Presence on cell membranes of
microorganisms
– Act as immune system
– Destroy pathogens inside the body

66. • Cerebrosides
– One sugar Molecule
• Galactocerebrosides
• Glucocerebrosides
• Sulphosides or Sulphogalactocerebrosides
– Sulphuric acid ester of Galactocerebroside
• Globosides- Ceramide oligosaccharides
– Lactosylceramides
• Two sugars
• Gangliosides
– Complex oligosaccharide

67. Diseases caused due to Lipid
Accumulation
• Sphingolipidoses
– Accumulation of Phospholipids
– Enzymatic defect in lysosomal degradation pathway of Sphingolipids
• Multiple Sclerosis
– Demyelination
– Loss of Phospholipids and Sphingolipids in white matter
• Infant Respiratory Distress Syndrome (IRDS)
– Deficiency of lung surfactant
• Dipalmitoyl-phosphatidylcholine

68. Examples of Sphingolipidoses

71. Gangliosides
– They are acidic glycosphingolipids
– They contain oligosaccharides with terminal charged N- acetyl neuraminic
acids (NANA)
– Based on the number of NANAs, the ganglioside is named.

72. Functions of
Gangliosides
• Expression of genes relevant to neuronal
function
• Key role in immune defence systems
• Regulate cell signalling
• Receptors of
– Epidermal growth factor
– Interferon
– Nerve growth factor
– Insulin

73. • Functional ligands
• Maintain myelin stability
• Control nerve regeneration
• Mediate interactions in between microbes and host cells during
infections
• Bind specifically to viruses and bacterial toxins
• Cholera
• Tetanus
• Botulinum

74. Functions of
Phospholipids and Glycolipids
• Transportation of lipids in the blood
• Formation of tissue fat
• Source of arachidonic acid
• Anchoring cell surface proteins like alkaline
phosphatase, lipoprotein lipase and
acetylcholine esterase

75. • HDL, LDL, IDL,VLDL, chylomicrons and lipoproteins, according to
density or size.
• Transport of fat in water molecules as in blood & ECF.
• Subgroups of which are primary drivers / modulators of
atherosclerosis, the transmembrane proteins of mitochondria,
chloroplast, and bacterial lipoproteins.
Lipoproteins

76. Functions of
Lipoprotein
• HDL- Collects cholesterol from non-hepatic
tissues and delivers it to the liver
• LDL- Delivers cholesterol derived from liver
synthesis to all the tissues
• VLDL- Delivers fatty acids attached to
triacylglycerol derived from liver synthesis to
non- hepatic tissues
• Chylomicron- Delivers fatty acids as part of
triacylglycerol from dietary fat to muscle
adipose tissue
• Chylomicron remnants- Deliver dietary
cholesterol to the liver

77. Lipopolysaccharides
• Lipopolysaccharides (LPS), also known as
lipoglycans, are large molecules consisting of
a lipid and a polysaccharide
• Lipids Endotoxins
• The term lipooligosaccharide (LOS) is used to
refer to a low-molecular-weight form of
bacterial LPS.
Oxidation

78. Functions of
Lipopolysaccharides
• Immune response
– TLR endotoxemia
– Septic shock
• Auto immune-responses
– Molecular mimicry of LOS
• Link to obesity
– Endo toxin producing bacteria

79. Derived Lipids
Glycerol and
other alcohols
Fatty Acids Steroid
Hormones
Fat soluble
vitamins
Ketone Bodies
Hydrocarbons
Pentacosanes
Compounds having
the cyclic steroid
ring
(CYCLO-
PENTANO-
PERHYDRO-
PHENANTHRENE)
Terpenes

80. Steroids
• Sterol lipids are important components of cell
membranes along with glycerophospholipids and
sphingomyelin
• Roles change with changes in the structure (every bond
makes a difference !)
– C-18 Estrogen
– C-19 Androgen (testosterone and androsterone)
– C-21 Progestogens, glucocorticoids and mineralocorticoids
– Secosteroids (Various forms ofVitamin D)
– Phytosterols
– Bile acids

82. Properties of Steroids
• Derivatives of fully saturated ring system called
cyclopentanoperhydrophenanthrene (sterane)
• The system has 3 non-linear cyclohexane rings (phenanthrene form)
attached to a cyclopentane ring
• They are not saponifiable (no fatty acids in structure)
• They can be separated from fats after saponification (residue)

84. Cholesterol
• Molecular formula- C27H45OH.
• OH group at C3, double bond at C5.
• First isolated in 1784, from human gallstones which consist almost
entirely of cholesterol
• Cholesterol literally means ‘solid alcohol from bile’
• Hydroxyl group is the polar head, rest of the molecule is hydrophobic.
• There are 2 main types of cholesterol
• Low density lipoprotein cholesterol (LDL-C)
• High-density lipoprotein cholesterol (HDL-C).
• Main sources
• Fish liver oils
• Brain and spinal cord of cattle.

85. • It is a white crystalline solid and is optically active, [α]D 39°.
• It has a melting point of 149°C.
• Cholesterol is generally believed to be notorious as a major cause of
heart disease.
• Principle sterol of higher animals
• Abundant in nerve tissues and in gallstones
• Occurs as free or fatty esters in all animal cells.
• Not found in plant fats.
Propertie
s

86. Functions of Cholesterol
• Builds and Maintains Cell membranes
• Prevents crystallization of Hydrocarbons in the Membrane
• Controls the Cell Permeability
• Involves in Production of Androgens and Estrogens
• Essential in production of hormones secreted by adrenal glands
• Aids in production of bile
• Helps in conversion of Sunlight toVitamin D
• Helps in metabolism of Fat solubleVitamins
• Insulation of Nerve Fibres

87. Lanosterol
• Major constituent of wool fat
• Present in minor quantities in liver and yeast.
• C30 compound with twin methyl groups at C4 and a third angular
methyl group on C14
• There are 2 double bonds at C8 and C24
• It is an intermediate in the biosynthesis of cholesterol.

89. Ergosterol (Mycosterol)
• Present in ergot (hence its nomenclature), yeast and
Neurospora (mold).
• Parent hydrocarbon -Ergostane, C28H50.
• Molecular formula- C28H43OH
– OH group at C3
– 3 double bonds at C5, C7 and C22.
• It is optically active
• Derivative of cholestatriene
• When irradiated with UV rays, calciferol, tachysterol,
and many other substances were derived

91. 7-dehydrocholesterol (Animal
sterol)
• Is a Skin lipid
• Precursor toVitamin D3
• Part of commercially prepared cholesterol
• Reacts rapidly with Lieberman-Burchard reagent

93. Stigmasterol
(Phytosterol)
• Occurs in Calabar and soybean oils.
• Parent hydrocarbon - Cholestane
• It can be converted into progesterone under lab conditions

95. Sitosterols
(Phytosterol)
• Complex sterols occurring in oils higher plants
– Wheat germ oil
• Isomers of stigmasterol

96. Bile acids
• Found in bile of higher animals
• Found conjugated with glycine and taurine
• Parent hydrocarbon -Coprostane

99. Terpenes
• Nonsaponifiable lipids found in plants hydrocarbons(<40C)
• Monoterpenes -formulaC10H16 (equivalent to 2 isoprene units)
• Sesquiterpenes- formula C15H24
• Diterpenes-formula C20H32
• Triterpenes-formula C30H48
• Terpenes with 40 carbon atoms (or tetraterpenes) include compounds called
carotenoids.
• The presence of long hydrocarbon chain in carotenoids makes them lipid-
soluble; they are hence also called lipochromes or chromolipids.

101. Functions of
Terpenes
• They are taste and flavour enhancers
• Limonene is an anti-Depressant
• Anti inflammatory
• Anti-cancerous
• Analgesic

102. KETONE BODIES

103. Neutral Lipids
Acyl
Gylcerols
Cholesteryl
Esters
Miscellaneous
Lipids
Carotenoids Squalene

104. Glycerol Fatty Acid
Hydroxyl
Group
Fatty Acid
Hydroxyl
Group
Hydroxyl
Group
Fatty Acid
Glycerol
Mono-acylglycerol Di-acylglycerol
Acylglycerols

105. Note - C1 and C3 are different. Cells posses enzymes that distinguish these two carbons.
• Stereospecific numbering (Sn) of glycerol
• It is adopted to represent the Carbon atoms of glycerol in an unambiguous manner.
• Thus glycerokinase phosphorylates Sn-3, not Sn-1 glycerol to give Sn-glycerol 3
phosphate.
Glycerol
Fatty Acid
Fatty Acid
Fatty AcidTri-acylglycerols

106. • Simple tri acylglycerols
• The same type of fatty acid residue at all three sections of carbons.
• For example, tristearin.
• Mixed tri acylglycerols
• 2 or 3 different types of fatty acid residues .
• Generally fatty acid attached to C1 is saturated, that attached to C2 is
unsaturated while that on C3 can be either.
• TAGS are named according to placement of acyl radical on glycerol.
For example, 1,3 –Palmitoyl, 2-linoleoyl glycerol.

107. • West E.ToddW. Mason H and Brugger J(1947).Text Book of
Biochemistry, 4th edition, Oxford and IBH Publishing Co., Pvt. Ltd.
• Satyanarayana U (2008),Chakrapani U.Biochemistry,3rd edition, Books &
Allied(P) Ltd. Kolkatta, India.
• Ramarao A.V.S.S(1968), Suryalakshmi A.AText Book of Biochemistry,
8th edition, UBS Publishers Distribution Ltd.
• Howard S Mason,Text book of Biochemistry,3rd edition, Oxford
university press.
References

108. Thank you