This document provides information about lipids. It begins by defining lipids as compounds that are relatively insoluble in water but soluble in organic solvents. Lipids are then classified into three main categories: simple lipids like fatty acids and triglycerides, compound lipids containing additional non-lipid components like phospholipids and glycolipids, and derived lipids which are hydrolysis products of other lipids. The document focuses on the structures, functions and examples of important lipids like fatty acids, triglycerides and phospholipids.

2. CONTENTS
 Definition
 Classification
 Functions
 Fatty Acids
 Triglycerides
 Phospholipids and other important Lipids

3. What are lipids ?
“Lipids are heterogeneous group of compounds
relatively insoluble in water (hydrophobic),
soluble in organic solvents such as ether, benzene &
chloroform.”
 Lipids are the esters of fatty acids with alcohol or are
substances capable of forming such esters and are utilised
by living organism

4. How do we classify them?
1. Simple lipids
2. Complex or Compound lipids
3. Derived or precursor lipids

5. 1. Simple lipids – esters of FA + alcohol
 Fats - esters of FA + Glycerol
eg. TAG
Fat in liquid state is known as -----
 Waxes – solid esters of long chain FA
+
high mol.wt MHA
[ monohydric alcohols]
eg. Bees wax
sperm oil
H2COH
HCOH
H2COH

6. TRI ACYL GLYCEROLS (TG/Neutral Fat)
Glycerol + Fatty acid ----> TAG
(Trihydric alcohol)
CH2-OH HOOC-R
CH-OH + HOOC-R’ ------->
CH2-OH HOOC-R’’

7. 2. Compound Lipids:
Esters of FA with different alcohols, but carry in
addition other substances such as –
i) Carbohydrates
ii) Phosphates
iii) Proteins
iv) Nitrogenous base
a) PHOSPHOLIPIDS
b) GLYCOLIPIDS
c) LIPOPROTEINS
Glycerophospholipids
Sphingophospholipids

8. 2. Compound lipids
FA + Alcohol + Non lipid
PL GL LP
FA Alcohol P X
Glycerol Sphingosine

10. a) Phospholipids
 Glycerophospolipids or phosphoglycerides
FA + glycerol + P + X
eg. phosphatidic acid, lecithin, cephalin,
cardiolipin
 Sphingophospholipids
FA + sphingosine + P + choline / ethanolamine
CERAMIDE
eg. sphingomyelin

11. b) Glycolipids (glycosphingolipids)
Ceramide + carbohydrate
No phosphoric acid !
 eg. cerebrosides, gangliosides, sulfatides
c) Lipoproteins – complexes of lipids &proteins
eg. LDL, VLDL, HDL, chylomicrons

12. 3. Derived lipids:
Hydrolysed product of simple and compound lipids
 Fatty acid
 Alcohols- glycerol, sphingosine
 Steroids
 Fat soluble vitamins
 Cholesterol
 Ketone bodies

13. Storage lipids – (neutral lipids )
Triacylglycerols
Cholesterol
Cholesteryl esters
Membrane lipids – (polar lipids)
Phospholipids
Glycolipids

14. FATTY ACIDS
 Included in Derived lipids.
 Aliphatic carboxylic acids – have general
structural formula, R-COOH
‘R’ – represents alkyl chain composed of carbon
& hydrogen atoms.
‘COOH’ represents the functional group.
 FA occurs mainly as esters in natural fat & oils in
esterified form.
 In unesterified form they occur as free fatty acids
(FFA), a transport form found in plasma.

15. FATTY ACIDS ……
 Fatty acids are long-chain hydrocarbon
molecules containing a carboxylic acid
moiety at one end.
CH3-CH2-CH2------------CH2-CH2-COOH

16. CLASSIFICATION
 Based on no. of ‘C’ atoms
based on CH3-COOH and CH3 –(CH2 )-COOH
Even chain FA – ‘C’ atoms 2, 4, 6…. etc
Odd chain FA – ‘C’ 3, 5, 7…
Most of the FA have Even chain
 Based on chain length
- Short chain …2 - 6 ‘C’
- Medium chain…8 -14 ‘C’
- Long chain….16 - 24 ‘C’

17.  Based on the nature of the hydrocarbon chain
- Saturated FA [ - anoic]
- Unsaturated FA [ - enoic]
- Branched chain FA – phytanic acid
- Hydroxy FA – cerebronic, ricinoleic acid
Fatty acids that contain no carbon-carbon
double bonds are termed saturated fatty acids;
those that contain double bonds are
unsaturated fatty acids.

18. Nomenclature:
Systematic naming of a fatty acid is based on
the number of hydrocarbons, with –oic being
substituted for final –a/e.
Saturated fatty acids end in –anoic &
Unsaturated fatty acids end in –enoic acid.
eg: octadecanoic acid (C18:0)
octadecenoic acid (C18:1)

19.  FA with 1 double bond – monoenoic
2 – dienoic,
3 – trienoic,
4 – tetraenoic etc.
 Saturated FA < 8 ‘C’ atoms are liquid at
physiological temperature.
 Those containing > 10 ‘C’ are solid.

20.  Gen formula…CH3 (CH2)n COOH
1) “c” system-The numbering of carbons in fatty
acids begins
with the functional ‘C’- the carboxylate carbon.
6 5 4γ 3β 2α C1 Carboxyl end
CH3 – CH2 – CH2 - CH2 – CH2 – COOH
W1 W2 W3 W4 W5 W6
Methyl end
2)Omega system-Numbering starts from methyl carbon
Omega system is widely used by nutritionists

21. OLEIC ACID
 It’s a C18 fatty acid with one double bond between
carbon 9 and 10.
18 17 10 9 8 Carboxyl end
CH3 – CH2 –------------CH = CH – (CH2 )7 ─COOH
W1 W2 W9 W10 W11
Methyl end
“C” System- C:18:1:Δ9
“W” System- C:18:1: W9

22. LINOLEIC ACID
 It’s a C18 fatty acid with two double bond between
carbon 9 and 10, 12 and 13.
18 13 12 10 9 Carboxyl
CH3 –(CH2)4─CH = CH-CH2–CH=CH-(CH2 )7 ─COOH
W1 W6 W9
Methyl end
“C” System- C:18:2:Δ9,12
“W” System- C:18:2: W6

23. SATURATED FATTY ACIDS
Symbol Common Structure Occurence
Name
14:0 Myristic acid CH3(CH2)12COOH Coconut oil
16:0 Palmitic acid CH3(CH2)14COOH Body fat
18:0 Stearic acid CH3(CH2)16COOH Body fat
Some other common eg. are acetic, propionic, butyric, valeric,
etc.

24. UNSATURATED FATTY ACIDS
Symbol Common Name Occurence
18:1 Δ9 ω9 Oleic acid Body fat
(octadecenoic)
16:1 Δ9 ω7 Palmitoleic acid Body fat
18:2 Δ9,12 ω6 Linoleic acid Vegetable oil
18:3 Δ9,12,15 ω3 Linolenic acid Vegetable oil
20:4 Δ5,8,11,14 ω6 Arachidonic acid Vegetable oil

25. SATURATED FATTY ACID UNSATURATED FATTYACID

26.  Saturated FA-Palm oil, coconut oil
 MUFA- Groundnut oil, mustard oil, sesame oil
 PUFA- Sunflower, cotton seed oil, corn, rice bran

27. FUNCTIONS
 Major fuel for most cells.
 Precursor for all the class of lipids.
 Maintenance of structural integrity
 Antiatherogenic effect(PUFA)
 Devlopement of Retina and Brain

28. ISOMERISM
A type of geometric isomerism occurs in
unsaturated FA depending on orientation of the
atoms or groups around axes of the double bonds
which do not allow rotation.
If acyl chains are on the same side – cis
configuration
&
on the opposite sides – trans configuration

29. Cis-form (Oleic acid)- Natural form
CH3-(CH2)7-CH
║
HOOC-(CH2)7-CH
Trans-form HC-(CH2)7-CH3
║
HOOC-(CH2)7-CH (Elaidic Acid)

31. PROPERTIES OF FATTY ACIDS
 Hydrogenation
• Unsaturated FA------> Corresponding Saturated FA
• Also known as “Hardening”
• e.g. Linolenic----> Stearic acid
• Leads to solidification and saturation (Vanaspathi
ghee)
• Used commercially.

32.  Halogenation
Oleic acid + I2 -------> Di-iodo oleic acid
Iodine No.- The no. of grams of iodine required to
saturate 100gms of given fat is known as Iodine no.
More the Iodine No ----> More Unsaturation
Butter-28
Sunflower Oil-130

33.  Melting Point(Transition temp.)
• With ↑ in length of F.A.---- Solubility ↓
---- Melting Point ↑
Unsaturated fatty acid has lower melting point.
• E.g. Stearic acid- 69°c
• Oleic acid- 13°c

35.  Saponification
• Hydrolysis of fat by alkali is called Saponification
• Sodium and Potassium salt of long chain F.A. are called
soaps.
• Triacylglycerol+NaOH----> Glycerol+ Na salt of FA
(Soap)
• Saponification No.- No. of mg of KOH requires to
saponify one gram of fat
• Butter- 210-230
• Coconut oil – 253-262

36.  Rancidity
“ Unpleasent taste or odour devloped by natural fat
upon aging is referred to as “Rancidity”
1) Due to Hydrolysis
2) Due to Oxidation

37. Compound lipids
FA + Alcohol + Non lipid
PL GL LP
FA Alcohol P X
Glycerol Sphingosine

38. Glycerophospholipids
• Phosphatidylcholine(Lecithin)
• Phosphatidylethanolamine(Cephaline)
• Phosphatidylserine
• Phosphatidylinositol
• Plasmalogens
• Cardiolipin
• Lysophospholipids
Sphingophospholipids
• Sphingomyelin

39. 1. PHOSPHATIDIC ACID

40. 2. PHOSPHATIDYL CHOLINE ( LECITHIN )
 Choline in addition to
phosphatidic acid.
 Most abundant phospholipids of cell membrane &
represent a large proportion of the body’s store of choline.
 Choline is imp. in nerve transmission as acetyl choline.
 Also a store of labile methyl groups.
 Dipalmitoyl lecithin is a major constituent of surfactant
which lines the inner surface of lungs.
Its deficiency in premature infants causes respiratory distress
syndrome.

41.  The term surfactant is a blend of "surface active
agent".
 Pulmonary surfactant is a surface-active
lipoprotein complex formed by type II alveolar cells.
 The main lipid component of surfactant, dipalmitoyl
lecithin reduces surface tension.

42. 3. PHOSPHATIDYL ETHANOLAMINE (CEPHALIN)
 Ethanolamine in addition to
phosphatidic acid.
 Occurs in tissues, in lesser
amounts than phosphatidylcholine,
principal phospholipid present in bacteria.
 Thromoplastin(Factor-III)
4. PHOSPHATIDYL SERINE
 Ethanolamine replaced by serine.
 only amino acid-containing
glycerophospholipid in animal cells.

43. 5. PHOSPHATIDYL INOSITOL
 The carbohydrate myoinositol esterified to phosphatidic
acid.
 Imp. constituent of cell membrane & present as
phosphatidyl inositol 4,5 bisphosphate.
 On stimulation by specific hormone agonists, cleaved into
DAG (diacyl glycerol) & IP3(inositol triphosphate) which act
as secondary messengers - precursor of secondary
messengers.

44. 6. DIPHOSPHATIDYL GLYCEROL (CARDIOLIPIN)
 Two phosphatidic molecules attached to glycerol.
 Major lipid present in inner mitochondrial membrane.
 Only phospholipid with antigenic properties.

45. 7. PLASMALOGENS
 Structurally resemble phosphatidyl ethanolamine.
 Ether linkage on the 1st ‘C’ atom instead of the usual
ester linkage.
Instead of ethanolamine there can be choline, serine,
inositol.
 mainly present in high concentration in the white matter
of the nervous system, heart and the kidney.
 PAF(platelet activating factor)

46. 8. LYSOPHOSPHOLIPIDS
 imp. metabolic intermediates
PL with only 1 acyl radical.
 When one of the acyl groups is
removed, forms lysophosphatidic acid.
 Common – lysolecithin.
 Lysolecithin present in snake venom is responsible
for lysis of RBC.

47. Functions of PL
 major constituents of cellular membrane
 PL in gen & lecithin in particular are amphipathic polar head
– glycerol, phosphocholine, non-polar tail – hydrocarbon
chains of FA.
 As a constituent of lung surfactant- DPL, phosphatidyl
glycerol, sphingomyelin. [LS ratio] >2 indicates lung maturity
Low levels of surfactant – RDS (prematurity)
 Constituent of lipoproteins
 Contain polyenoic FA, esterifies cholesterol.

48.  Insulator of nerve fibres
 PIP-2 is an imp. constituent of membranes. It helps in
mediating hormone action.
 Cardiolipin is a major PL – inner mito. memb, - the only PL
with antigenic properties.
 Lyso PL- lysolecithin is present in snake venom.
 PAF – activates the blood platelets
– causes aggregation
- reduces BP
- mediates inflammation

49. Sphingophospholipids
FA + sphingosine + P + choline / ethanolamine
CERAMIDE

50.  Sphingolipids are generated by transfer of the
phosphocholine moiety of phosphatidylcholine to a
ceramide.
 Sphingosine is a complex amino alcohol &
derived from glycerol. It is N-acetylated by a variety
of FA to form ceramide
 Eg. Sphingomyelin – major SPL found in animals
Sphingolipids predominate in the myelin sheath of
nerve fibers.

51. Glycolipids (glycosphingolipids)
FA + sphingosine + carbohydrate
No phosphoric acid !
i.e., ceramide + carbohydrate
 Cerebrosides – ceramide+ monosaccharide
(glucose or galactose)
 Nervous tissue, Complex glycolipids synthesis
 Sulfatides- ceramide+monosaccharide+Sulfate
 Found high amount in myelin sheath

52. Globosides- Ceramide + Oligosaccharide
 Contain two or more molecules of
Glucose,Galactose or N-Acetylgalactosamine
 Constituents of RBC membrane and Bloodgroups
Gangliosides-Ceramide+Oligosaccharide+N-
Acetyl Neuranimic Acid (NANA)
 Complex derivatives from glucocerebrosides
 Act as a cell membrane receptors for hormones

53. STEROLS
D
 All sterols have similar cyclic nucleus - cyclo
pentano per hydro phenantherene ring.(19 C)
C

54. STRUCTURE OF CHOLESTEROL
Cholesterol is the main steroid in humans.
• There is a OH group on C3.This group is usually esterified
to a FA.
• There is a double bond between the position 5 & 6.
• It has a eight carbon side chain at C17.

55. Functions:
 Cholesterol & its esters are major constituents of
plasma membrane and lipoproteins.
 It is the precursor of steroid hormones, bile acids,
& Vit D.
[Steroid hormones ----adrenal cortex - cortisol,
cortisone & aldosterone, testis- testosterone, ovary-
estradiol, placenta -progesterone.
Bile acids---cholic, chenodeoxycholic, deoxycholic,
lithocholic acids].

56. LIPOPROTEINS
 As lipids are hydrophobic, they are not
soluble in the aqueous medium of plasma.
 They are transported in blood in the form of
lipoproteins

57. Lipoproteins are made up of lipids, e.g.triglycerides,
free cholesterol, cholesteryl esters and
phospholipids, and some specific proteins called
apolipoproteins or apoproteins
 In lipoprotein particles, the more hydrophobic
lipids, e.g. triglycerides and cholesteryl esters,
are present in the interior, surrounded by
amphipathic lipids e.g. phospholipids and free
cholesterol

58.  Phospholipids are present in a monolayer with
the hydrophilic portion facing outwards
 The apoproteins either surround or are
embedded in the phospholipid monolayer

59. Cholesteryl ester
Triglycerides
Phospholipid monolayer
Free cholesterol
Apoprotein

60. The major lipoproteins in plasma are chylomicrons
(CM), very low density lipoproteins (VLDL), low
density lipoproteins (LDL) and high density
lipoproteins (HDL)
 The apoproteins present in them are Apo A-I, A-II,
B-48, B-100, C-I, C-II, C-III, D and E

61.  CM and VLDL are rich in triglycerides
 LDL is rich in cholesterol
 HDL is rich in phospholipids and cholesterol

62. LIPOPROTEIN SITE OF SYNTHESIS FUNCTION
Chylomicrons Intestine Transports dietary lipids
from intestine to
peripheral tissues
VLDL Liver Transports TGs from
liver to peripheral
tissues
LDL From VLDL Transports cholesterol
from liver to peripheral
tissues
HDL Liver and Intestine Transport of cholesterol
from peripheral tissue to
Liver ( Reverse)

65.  Involved in
solubilisation of lipid in
aqueous media and
helps in digestion and
absorption of lipids.

66.  Drugs, proteins,
enzymes, genes can
be delivered by
liposome