This document discusses lipids and their classification. It defines lipids as biological molecules that are soluble in organic solvents but insoluble in water. Lipids are classified as simple lipids, complex lipids, and derived lipids. Simple lipids include triglycerides and waxes. Complex lipids include phospholipids, glycolipids, and lipoproteins. Phospholipids such as phosphatidylcholine are important components of cell membranes. Essential fatty acids like linoleic acid and alpha-linolenic acid must be obtained through diet.

2. I love pizza , I love cheese ,
Friends call me --------------- obese

3. Obesity Diabetes Heart disease

4. Chemistry of lipids
Dr. Subodhini Abhang

5. Points to be covered:
 Definition
Biological importance
General classification
Simple lipids
Fatty acids
Functions of essential fatty acid

6. Biological molecules – highly soluble in non
polar (organic) solvents like benzene,
chloroform, ether and alcohol, where as
relatively insoluble in water .
Actually or potentially related to fatty acids.
Definition

8. Physiological importance of lipids
1. Serves as a concentrated source of energy when
stored in adipose tissue.
2. Thermal insulator in sub-cutaneous tissue and
around the organ.
3. Serve as a electrical insulators in myelinated nerves.
receptors
Myelin
Sheath
Axon Terminal

9. 4. Amphipathic lipids: Form important cellular
constituents in cell membrane.
5. Lipoproteins serve as transporter for transporting
lipids in the blood.
6 Activators of enzymes e.g. glucose-6-phosphatase,
mono-oxygenase
Physiological importance of lipids

10. Classification of lipids
Simple lipids Complex lipids Derived lipids
1. Oils and Fats
2. Waxes
1Phospholipids
2 Glycolipids
3.Lipoproteins
4.Sulpholipids
1. Fatty acids
2. Cholesterol
3. Glycerol
4. Sterols

11. Simple Lipids
Esters of fatty acids with various alcohols
A. Neutral fats – Esters of fatty acid with
glycerol. e.g. Triglycerides (Triacyl glycerol)

12. •Uncharged
•All vegetable oils available in
market
•A fat in liquid state - oil e.g.
groundnut oil, mustered oil, corn oil
etc.
•Animal fat – Butter / Ghee
•Dalda– Prepared by hydrogenation
Simple Lipids

13. Simple Lipids
B. Waxes Esters of fatty acids with higher
molecular weight monohydric alcohols
– Cetyl Alcohol (C16H33OH)
• Not important for human metabolism
• E.g. Bee-wax, Lanolin from lamb’s wool
• Waxes has water repellant property . Keep lubricated and water
proof.
• Leaves of tropical plants : prevents excessive evaporation of water
and protect against parasites.
• These are widely used in pharmaceutical for making ointments ,
lubricants ,cosmetic and other industries ( Candals)

14. Fatty acids
Aliphatic carboxylic acids
Occur in the body as natural fats and oils.
Unesterified form is Free fatty acid: transport form in plasma.
Naturally occurring fatty acids contain even number carbon atoms.

15. Numbering of fatty acid carbon atom
C-system numbering start from carboxyl
terminus
16 15 3 2 1
CH3-CH2 - - - - - -CH2-CH2- COOH
ω1 ω2 β α
ω- system numbering start from methyl end
ω-9 represent Ist double bond position at C9- C10
ω-6 represent Ist double bond position at C6- C7
ω-3 represent Ist double bond position at C3- C4

16. Classification of Fatty Acids
Monounsaturated Polyunsaturated
Saturated unsaturated
Odd no. c-
atoms
Eg: Valeric
acid
(c-5) Present
in butter
Even no.c –atoms
Eg: Palmitic acid
(c-16)
Stearic acid
(c-18)
Eg : Oleic
(c-18)
Linoleic 2 double bonds
Linolenic 3 double bonds
Arachidonic 4 double bonds

17. Classification of Fatty Acids
According to Hydrocarbon chain
a) Straight chain : eg. Oleic acid
b) Branched chain :
eg: Isobutyric and Isovaleric
Found in waxes
c) Cyclic chain :
Rare . But identified in lipids of lactobacillus
and certain seed oils.
eg: Chaulmoogric acid found in Chaulmoogra
seed oil.
Used in leprosy treatment.
d) Hydroxy fatty acid : β-hydroxy butyric acid –
Ketone body

18. Monounsaturated fatty acids
Oleic acid
• Most common fatty acid in natural fats.
• C18:1 ∆9, i.e.,
• 18 carbons and one double bond located
between carbon number 9 and 10.
CH3-(CH2)7- CH=CH – (CH2)7-COOH
110 9

19. Polyunsaturated Fatty Acid (PUFA)
Fatty acids containing two or more double bond
• Two double bonds
• e.g. linoleic acid (C:18;2: 9, 12) (ω-6)
present in soybean, sunflower, saffola and
ground nut oils
• Three double bonds
• e.g. linolenic acid (C:18;3: 9, 12,15) ( ω-3)
present in linseed oil
• Four double bonds
• e.g. arachidonic acid (C:20:4: 5,8,11,14) (ω-6)
present in ground nut oil

20. Expression of fatty acids
• Linoleic Acid = 18: 2; 9, 12 (Two double bond, bet. C9 - C10 and C12-C13
from carboxyl end)
CH3-(CH2)4-CH = CH-CH2-CH=CH-(CH2)7-COOH
ω6
• Linolenic Acid = 18: 3; 9, 12, 15 (Three double bond, bet. C9 - C10, C12-C13
and C15-C16)
• CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-COOH
ω3
12 9

21. Isomerism of double bond fatty acid
• A double bond in hydrocarbon chain can occur in cis or
trans configuration
• All double bonds in naturally occurring fatty acids are of
cis configuration
• More than one double bond – Various shapes

22. Poly unsaturated fatty acids are called
essential fatty acids
Because
There is no enzyme in human that can introduce
double bond beyound 9th carbon atom
Hence they are to be supplied in diet.

23. Essential Fatty acids
• Definition:
• Essential fatty acids that can not be
synthesized in the human body and must be
taken in adequate amounts in the diet.
• They are required for normal growth and
metabolism
• Source: vegetable oils such as corn oil, linseed
oil, peanut oil, olive oil, cottonseed oil,
soybean oil and many other plant oils, cod liver
oil and animal fats.

24. Essential Fatty acids
Linoleic Acid:
• Omega-6 (6) : C18:29, 12.
• It is the most important since other essential fatty
acids can be synthesized from this in the body.
CH3-(CH2)4 - CH = CH-CH2-CH=CH-(CH2)7-COOH
ω6
Arachidonic acid a fatty acid derived from linoleic acid . It is
precursor of regulatory lipids eicosanoids.

25. Essential Fatty acids
2-Linolenic acid: Omega-3 (3)
• C18:39, 12, 15,
• in corn, linseed, peanut, olive, cottonseed
and soybean oils.
CH3-CH2-CH=CH-CH2-CH=CH-CH2-CH=CH-(CH2)7-COOH
ω3

26. Essential Fatty acids
3-Arachidonic acid:
• C20:45, 8, 11, 14. Omega-6 (6)
• Important component of phospholipids in animal
• Present in peanut oil
• Precursor for synthesis of prostaglandins
CH3-(CH2)4-CH=CH-CH2-CH=CH-CH2-CH=CH-CH2-
CH=CH-(CH2)3-COOH

28. Poly unsaturated Fatty acids
Docosa-hexaenoic acid (DHA)
Omega-3 (3) 22:6; 4,7,10,13,16,19
• Structural component of brain, cerebral cortex,
skin, sperm, testicles and retina
• Require for the development of the brain and
retina during the neonatal period
• Supply via placenta and milk
• Can be synthesized from linolenic acid
• Present in fish oil

29. Functions of essential fatty acids
 Formation of healthy cell membrane.
 Proper development and functioning of brain and nervous system.
Production of prostaglandins ,leukotriens and thromboxane.
Deficiency leads to : Dry scaly skin (phrynoderma or toad skin) ,Hair loss
Growth rate, Metabolic rate
Abnormalities in ECG
Risk of heart disease
Structural and functional abnormalities in mitochondria.
 Formation of lipoproteins.
 Prevention of fatty liver.

30. Triacyl glycerol
Properties of TG
Tests to check Purity of fats
Classification of Phospholipids
Functions of Phospholipids
Glycolipids
Points to be covered

31. Triacylglycerol
CH₂-O-
CH-OH
CH₂-OH
C - R
O
Monoacylglycerol
Monoacylglycerol +Fatty acid Diacylglycerol
Diacylglycerol + Fatty acid Triacylglycerol
Eg: Tripalmitin , Triolein
1
2
3

32. Mixed Triglycerides
Contain two or three types of fatty acid.
CH₂-O-
CH-O-
CH₂-O
C - R₁
O
C - R ₂
- C - R₃
1,3dipalmitoyl 2-olein
O
O
Palmitic acid
Palmitic acid
Oleic acid

33. Properties of Triacylglycerol
1. Hydrolysis : By Lipase
Triacyl glycerol Glycerol + Fatty acid
Lipase

34. Properties of Triacylglycerol
2 Saponification: Alkali hydrolysis
glycerol and salts of fatty acids (soaps).
• Soaps cause emulsification of oils and fats.
Triacyl glycerol + 3NaOH Glycerol + 3 RCOONa
(soap)

35. Rancidity
• Deterioration .
• Physico-chemical change in the natural properties of
the fat leading to the development of unpleasant
odor or taste or abnormal color
• Occurs after exposure to atmospheric oxygen, light,
moisture, bacterial or fungal contamination etc
• Fats containing unsaturated fats are more susceptible.
• Unsuitable for human consumption

36. Hydrolytic Rancidity And Oxidative Rancidity
Triacylglycerols
Partial hydrolysis by
Bacterial enzymes
Oxidation of
unsaturated fatty acids
Dicarboxylic acids, Aldehydes, Ketones
Unplesant products
Lipid peroxide s + Free Radicals
Oxidative rancidity prevented by Antioxidants.
Trace amount of Vit.E, gallic acid ,αNaphthol are used
commertially in fats and oils .
Lipase

37. Tests to check purity of fats
and oils

38. Iodine number: measure of degree of
unsaturation
• Grams of iodine absorbed by 100 grams of fat/ oil.
• Degree of unsaturation , iodine number .
•
• identifies of the type of fat and detect adulteration
Butter 25-28 Human fat 65-70
Groundnut oil 85-100 Soyabean oil 135-140
Linseed oil 170-200

39. Saponification Number
Milligrams of potassium hydroxide required to
saponify ( hydrolyse) one gram of fat or oil.
 Represents average molecular size of the fatty
acids
Fats containing short-chain acids : Higher
saponification number.
• Human fat : 195 - 200
• Butter : 220 - 230
• Coconut oil : 250-260

40. Acid Number
• Milligrams of KOH required to neutralize the
free fatty acids present in one gram of fat.
• Used for detection of hydrolytic rancidity
• measures the amount of free fatty acids
present.
• Oils with increased acid number are unsafe for
human consumption.

41. Hydrogenation or hardening of oils
• Addition of hydrogen at the double bonds of
unsaturated fatty acids.
• Done under high pressure of hydrogen and
catalyzed by nickel /copper and heat.
• hardening of oils (margarine manufacturing),
e.g., change of oleic acid of fats (liquid) into
stearic acid (solid).
Vanaspati

42. Partial Hydrogenation forms Trans fatty acids
Cis double bonds Trans double bonds
Trans Fatty acid s in Some fast food and snacks
As% of total fatty acids
French fries 28-36 %
Pizza 25 %
Trans fatty acids: Vascular diseases,
TG,LDL cholesterol HDL

43. Compound Lipids
Eg.Lecithine
Cephaline
Glycosphingolipids
Eg: Cerebrosides
Gangliosides
Globosides
Glycerol sphingosine
With PO4 gr. Without PO4 gr.
Phosphosphingolipids
Eg.Sphingomyelins
With without
nitrogenous base nitrogenous base
Eg :Cardiolipin
Phosphotidyl
inositol
Other complex lipids
eg: Sulpholipids
Lipoproteins
Glycerophospholipids

44. Phospholipids
G
L
Y
C
E
R
O
L
Fatty Acid1
Fatty Acid 2
N-BasePO₄
S
P
H
I
N
G
O
S
I
N
E
Fatty Acid
PO₄ N-Base
Glycerophospholipids Sphingophospholipids

45. Glycerophospholipid
• Phospholipid containing glycerol called
phosphoglycerides or glycerophospholipid
Polar Head Nonpolar, hyderophobic tail
glycerol
PO4
Nitrogenous
base
Fatty acid
Fatty acid

46. Phosphatidylcholine (Lecithin)
glycerol
PO4choline
Fatty acid
Fatty acid
Nitrogenous base
Lecithins – Abundant in cell membrane
Fatty acid at second position is PUFA.
Present in brain , egg yolk and liver.
Lecithins are storage form of Choline in body.
Required for esterification of cholesterol.

47. Action of surfactant: Dipalmitoyl Lecithin
The lungs of immature infants do not have enough type II epithelial
cells to synthesize sufficient amount of the dipalmitoyl lecithin
 In its absence the lungs tend to collapse, this condition is known
as Respiratory distress syndrome (RDS).

48. Lysolecithin
• The snake venom contains lecithinase
(phospholipase A), which hydrolyzes the
polyunsaturated fatty acids converting lecithin
into lysolecithin. Lysolecithins are intermediates
in metabolism of phospholipids
• Lysolecithin causes hemolysis of RBCs.
• Demyelination of CNS
• This partially explains toxic effect of snake
venom.
glycerol
PO4Choline
Fatty acid
OH

49. glycerol
PO4Ethanolamine
Fatty acid
Fatty acid
Phosphatidyl ethanolamine
(Cephalin)
 Component of membrane, essential for blood
coagulation
Thromboplastin (factor III) essential to initiate
the clotting process; It is composed of cephalins

50. Phosphatidyl serine/threonine
• Components of biological membranes
• It is found in most of tissue
glycerol
PO4
Serine/
Threonine
Fatty acid
Fatty acid

51. Plasmalogens / Platele activating factors
glycerol
PO4
Ethanolamine/
choline
O-CH=CH-R1
Fatty acid
• The fatty acid chain at C1 of glycerol linked through an
ether linkage
•Plasmlogen : Found in brain and cardiac muscle
•Platelet activating factor is a ‘plasmalogen ‘ involved in
platelet aggregation

52. Phosphatidylinositol
glycerol
PO4
Myoinositol
4,5 biphosphate
Fatty acid
Fatty acid
• Precursor of second messengers
-diacylglycerol and inositol triphosphate
-Eg. Action of oxytocin and vasopressinis mediated
through phosphatidylinositol
• Phspotidylinositol-4,5-bisphosphate is an
important constituent of cell membrane

53. Cardiolipin
• 2 molecules of phosphatidic acid linked by glycerol
• Cardiolipin : major lipid of mitochondrial
membrane; role in cellular respiration
• It is necessary for optimum function of ETC
• Shows antigenic properties – Have diagnostic role
in embryo transfer and organ transplantation
g
l
y
c
e
r
o
l
PO4 Glycerol
Fatty acid
g
l
y
c
e
r
o
l
PO4
Fatty acid
Fatty acid
Fatty acid

54. Sphingophospholipids
• Sphingomyelins : Present in large amounts : brain and
nerves
• Smaller amounts in lung, spleen, kidney, liver and blood
• Alcohol – sphingosine : Amino alcohol (C18)
CH CH NH
CH2
CHCH(CH2)12CH3
OH
Sphingosine
C R1
O
O
P O
OH
O CH2 CH2 N
CH3
CH3
CH3
+
Choline
Fatty acid
Phosphate
Ceramide
Sphingomyelin

55. Sphingophospholipids
• Ceramide : This part of sphingomyelin in which the
amino group of sphingosine is attached to the fatty
acid by an amide linkage.
• Ceramides have been found in the free state in the
spleen, liver and red cells.
Sphingosine Fatty acid
Large accumulation of sphingomyelins in brain ,liver & spleen of the
person suffering from Niemann Pick disease ----deficiency of
sphingomyelinase enzyme.

56. Functions of Phospholipids
 Structural component of the membranes eg. Cellular and mitochondrial
membrane.
 Cephalins ( phophatidyl ethanolamine or serine participate in the process of
blood clotting.
 Dipalmitoyl lecithin acts as a effective lung surfactant.
 Phosphatidyl inositol acts as precursor of second messengers ( involved in
signal transmission across the membrane)in hormone action.
 Play detergent role in bile : helps in solubilization of cholesterol.
 Phopholipids act as a lipotropic factor.
 Cardiolipin is the only phospholipid having antigenic property. This property is
used in the serologic test for syphilis.

57. Fatty Acid
S
P
H
I
N
G
O
S
I
N
E
S
P
H
I
N
G
O
S
I
N
E
Fatty Acid
Glucose or
Galactose
Glucose +
Galactose
Amino
Sugars
NANA
Glycolipids
Cerebrosides Gangliosides

58. Glycolipids
• Lipids that contain carbohydrate residues with
sphingosine as the alcohol and a very long-chain
fatty (Cerebronic) acid.
• They are present in every tissue; high in cerebral
tissue, hence cerebrosides
• Classification: According to the number and
nature of the carbohydrate residue(s) present in
the glycolipids

59. Glycolipids
1. Cerebrosides - One galactose/glucose molecule
(galactocerebrosides/Gluco).
2. Globosides - 2 or more sugars with ceramide
3. Gangliosides – Complex glycosphingolipids
several sugar, sugaramine and sialic acid residues
Cerebrosides: Occur in myelin sheath of nerves and
white matter of the brain tissues and cellular
membranes.
- Important for nerve conductance

60. • Gangliosides contain
–Ceramide (sphingosine + fatty acid of C18-C24)
– Sialic acid (N-acetylneuraminic acid)
– 3 molecules of hexoses (1 glucose + 2
galactose) and a hexosamine.
–The most simple type – monosialoganglioside
(works as a receptor for cholera toxin in the
human intestine)

61. Gangliosides
• Complex glycolipids that occur in the gray matter
of the brain, ganglion cells, and RBCs.
• Present in cell membrane, ceramide (hydrophobic);
sialic acids and sugars (hydrophilic)
• Act as a cell membrane receptor - hormones
• Transfer biogenic amines across the cell
membrane.