Lipids and Their Biological Functions

 Mr.Mote G.D.
 AGCOP,Satara
1

 Define lipids and its occurrence
 State the biological significance of fats
 Define chemical composition of fats
 Define physical properties of fats
 Define chemical properties of fats
 Classify lipids into fatty acids, triglycerides,
steroids
 Define phospholipids
 Describe the chemistry and functions of
cholesterol
 Explain lipoproteins
3

 Group of naturally occurring substances
 Consists of higher fatty acids
 Insoluble in water
 Soluble in: Ether, chloroform, benzene and
acetone (organic solvents)
4

 LIPIDS: Fatty acids, Triacylglycerols, Ketone
bodies, Cholesterol, Phospholipids &
Sphingolipids
 “Fats” and “Oils” – crude lipid mixtures from
natural sources.
 Fats (solid) & Oil (liquid) at room temperature
5

 Widely distributed in plants and animals.
 Plants: nuts, seeds and oils
 The Nervous system of Animals: cholesterol,
phospholipids and glycolipids
 Blood: contains lipoproteins
6

 Fat depots (large amount of
fats):
◦ Subcutaneous tissues
◦ Mesenteric tissues
◦ Fatty tissues around the kidney
◦ Yellow bone marrow
 Food sources:
◦ Milk, Egg, Meat, Liver
◦ Fish oils, nuts, seeds and oils
7

 State the biological significance of
fats
 Classify lipids into fatty acids, triglycerides, steroids
 Describe the chemistry and functions of cholesterol
8

 Acts as fuel in the body. (caloric value: 9
Kcals/gm)
 Deposits of fats underneath the skin = exert
insulating effects.
 The mesenteric fat around organs (kidney) =
padding and protecting internal organs.
 Building materials. (cholesterol – hormone
synthesis)
9

 Lipids supply the essential fatty acids which cannot
be synthesized in the body..
 The Nervous system is particularly rich in lipids.
 Vitamins A, D, E and K are fat soluble.
( lipid/fat is needed for absorbing these vitamins)
 Lipoproteins and phospholipids are important
constituents of cell wall & mitochondria.
10

 Adult: ingests 60-150g of lipids per day of which
90% is triacylglycerol (TAG).
 Balance: cholesterol, cholestryl, esters,
phospholipids and free fatty acids (FFA)
11

Lipoprotein &
Phospholipids (cell
wall &
mitochondrion
constituents)
Vitamin
A,D,E,K fat
soluble
vitamins
Acts as fuel in
the body
Supply essential
fatty acids
Nervous
system: Rich
in lipids
Building
Materials
(hormones
)
Padding &
protection of
internal organs
Insulating
effect
12

13
LIPIDS
Simple Lipids
Substances Associated with
Lipids
Derived Lipids
Compound Lipids

14
Classification Definition Examples
Simple Lipids
Esters of fatty acids
with various
alcohols
* Neutral fats (F.A. + alcohol)
* Glycerol (alcohol in fats)
* Anything other than glycerol
(alcohol in waxes)

15
Classification Description 4 Sub-Divisions
Compound
Lipids
Contains other chemical
groups in addition to alcohol
and fatty acids
•Phospholipids
•Glycolipids
•Sulpholipids
•Lipoprotein
•Phospholipids
•Glycolipids
•Sulpholipids
•Lipoprotein
•Contains fatty acids, glycerol, phosphoric
acid & nitrogenous compound (lecithin,
cephalin)
•Lipids + carbohydrate + nitrogen but no
phosphoric acid & glycerol
•Lipids containing sulphate groups
•Attached to proteins (present in plasma &
tissues)

16
Classification Description
Derived Lipids Substances derived from simple &
compound by hydrolysis.
Examples
Derived Lipids
•Fatty acids
•Alcohols other than glycerol
•Glycerides
•Bases (choline, serine)

17
Classification Examples
Substances
Associated with
Lipids
•Carotenoids
•Tocopherols
•Vitamins A, D, E and K
•Steroids (Cholesterol)

 Define chemical composition of
fats
18

19
ANIMALS AND VEGETABLE FATS
Complex
mixtures
of
glycerides
Esters of glycerol & fatty acids
Triglyceride
s
(TAG)-
Neutral fats
3 molecules of fatty acids - glycerol
Triglyceride
s
One molecule of glycerol + 3
molecules
of fatty acids (condensation)

21

 Greasy to touch and leaves an oily
impression on paper.
 Are insoluble in water but soluble in organic
solvents.
 Have less specific gravity than water (solid
fat= 0.86), (liquid fat = 0.95)
 Pure glycerides are tasteless, odorless,
colorless and neutral in reaction (acidic-
yellow color (hydrolysis & oxidation)
22

 Flavor of butter is due to the presence of bacterial
flora; color of butter, human fat and egg yolk (due
to presence of carotene & xanthophil).
 Hardness and consistency depends on the
amount of saturated and unsaturated fatty acids
present. Saturated fatty acids are solid (room
temperature) while Unsaturated fatty acids are
liquid (room temperature) (e.g. oils)
23

 Fats have definite melting points.
 When liquid fat is placed on water- it spreads
uniformly over the surface of water. If the quantity
is small – it forms a layer of 1 molecule thickness
(effect: to lower surface tension- help transport fat)
 Though fat is insoluble in water- can be broken
down into minute droplets and dispersed in water
(emulsification)
24

25

• Acrolein Formation – glycerol  heat +
potassium bisulphate
• Hydrogenation – unsaturated fats (+nickel-
catalyst) – saturated fats (“hardening”) e.g
vegetable oil – commercial cooking oil
• Saponification – hydrolysis of fat by alkali
(glycerol + alkali salts = soap)
• Rancidity – chemical change resulting in
unpleasant odor and taste on storage when fats
are exposed to light, heat, air and moisture.
– E.g. Ascorbic acid (Vitamin C) and Vitamin E are
antioxidants (prevents rancidity)
26

 Classify lipids into fatty acids,
triglycerides, steroids
27

28
Lipids Examples Sources
Polyunsaturated
Fatty Acids
•Linoleic acid
•Linolenic acid
•Arachidonic acid
(not synthesized by the
body- must be taken in the
diet)
•Linseed
•Cotton seeds
•Peanuts
•Corn oils
•Linoleic acid – the only
fatty acid which is absolutely
indispensable.

 Neutral fat
 Concentrated source of energy
• used primarily for energy; most common lipid in the
body
• contain C, H, and O but less O than carbohydrates
(C57H110O6)
• building blocks are 1 glycerol and 3 fatty acids per
molecule saturated and unsaturated
29

 Are non-saponifiable lipids
 Are biological compounds with diverse
physiological activities
 Are compounds having a
cyclopentanoperhydrophenanthrene ring system
 Has only a hydroxyl group (-OH) as its functional
group (sterol, e.g. cholesterol)
30

31

 Lipids containing phosphorus
 Are good emulsifying agents
 Found in cell membranes and in subcellular
structures (lipid & water interaction)
32

 Describe the chemistry and
functions of cholesterol
33

 Are light yellow
crystalline solid
 Are soluble in
chloroform and
other fat solvents
 Polyunsaturated
acids – lower the
plasma cholesterol
level
 The most abundant
lipid in the human
body
34
 Are synthesized in the liver,
adrenal cortex, intestines,
testes and skin.
 Play an important role as a
component of
biomembranes and has a
modulating effect on the
fluid state of the
membrane.
 Can be estimated by color
reactions (e.g. Liebermann-
Burchard reaction) – blue
or green color

• An important tissue
component
(modulating effect,
integrity &
permeability)
• Play an important role
in insulating nerves
and brain structure
• For transport of fatty
acids in the body
• It is a part of
lipoproteins
35
 It neutralizes the
hemolytic action of
various agents such as
venom, bacterial toxins
 It gives rise to
“provitamin D”
 It is a precursor of cholic
acid in the body as also
bile salts.
 It gives rise to sex
hormones

36
CHOLESTERO
L
Atherosclerosis
Plaque around
The artery
Hardening &
Narrowing
Hyperthyroidis
m
Diabetes
Mellitus
Xanthomatosi
s
(fat storage
disorder)
Myxoedema
(Hypothyroidism
)
Nephrotic syndrome
(kidney disorder)
Obstructive jaundice

37

 Are conjugated proteins involved in transport and
delivery of lipids to tissues.
E.g. Lipids (Cholesterol & triglycerides) + water
soluble carrier proteins
 It transport neutral lipids in the blood.
 It has lower density than the ordinary protein
molecule.
38

39
LIPOPROTEINS
Nucleus,
Mitochondria
Microsome
Thromboplastin
(prothrombin-
thrombin)
Cell membranes
Rhodopsin
(combination of
protein, opsin and
retinal aldehyde of
Vit. A
Plasma
Cholesterol,
Phospholipids, neutral
fat, traces of fat
soluble vitamins
Steroid hormone
Fat droplets in milk
Egg yolk
(HDL & LDL)

40
Type Density
g/ml
Protein Triglycerid
es
(TAG)
Cholesterol Phospholipids
Free Ester
Chylomicron
s
< 0.95 1 85-95 1-2 1-2 3-6
Very low
density
lipoprotein
VLDL
0.95-
1.006
10 50-60 4-8 10 15-20
Low density
lipoproteins
LDL
1.006-
1.063
22 10 10 38 20
High density
lipoproteins
HDL
1.063-
1.21
45-60 3 5 15-20 25-30

41
 Give at least 3 importance of lipids.
 What are the 4 major groups of lipids?
 Give 2 examples of lipids?
 What are the functions of cholesterol?
 Differentiate steroid from cholesterol?
 Name 3 physical properties of fats?

The lipids are a heterogeneous group of
compounds, including fats, oils, steroids, waxes,
and related compounds, that are related more by
their physical than by their chemical properties.
They have the common property of being
(1) relatively insoluble in water and (2) soluble
in nonpolar solvents such as ether and
chloroform.
44

 Storage form of energy
 Important dietary components because of
their high energy value and also because of
the fat-soluble vitamins and the essential
fatty acids contained in the fat of natural
foods.
 Structural components of biomembranes
 Serve as thermal insulators in the
subcutaneous tissues and around certain
organs
 Nonpolar lipids act as electrical insulators,
allowing rapid propagation of depolarization
waves along myelinated nerves
45

 Provide shape and contour to the body
 Act as metabolic regulators
 Combinations of lipid and protein
(lipoproteins) are important cellular
constituents, occurring both in the cell
membrane and in the mitochondria, and
serving also as the means of transporting
lipids in the blood.
46

Following diseases are associated with
abnormal chemistry or metabolism of lipids-
Obesity
Atherosclerosis
Diabetes Mellitus
Hyperlipoproteinemia
Fatty liver
Lipid storage diseases
47

Simple lipids: Esters of fatty acids with various
alcohols.
a. Fats: Esters of fatty acids with glycerol. Oils are
fats in the liquid state.
b. Waxes: Esters of fatty acids with higher
molecular weight monohydric alcohols.
48

2. Complex lipids: Esters of fatty acids containing
groups in addition to an alcohol and a fatty acid.
a. Phospholipids: Lipids containing, in addition to fatty
acids and an alcohol, a phosphoric acid residue. They
frequently have nitrogen-containing bases and other
substituents, eg, in glycerophospholipids the alcohol is
glycerol and in sphingophospholipids the alcohol is
sphingosine.
b. Glycolipids (glycosphingolipids): Lipids containing a
fatty acid, sphingosine, and carbohydrate.
c. Other complex lipids: Lipids such as sulfolipids and
aminolipids. Lipoproteins may also be placed in this
category.
49

3) Precursor and derived lipids: These
include-
 fatty acids
 glycerol
 steroids
 other alcohols
 fatty aldehyde
 ketone bodies
 hydrocarbons, lipid-soluble vitamins, and
hormones.
50

Fatty acids are aliphatic carboxylic acids
Have the general formula R-(CH2)n-COOH
They occur mainly as esters in natural fats
and oils but do occur in the unesterified form
as free fatty acids, a transport form found in
the plasma.
Fatty acids that occur in natural fats are
usually straight-chain derivatives containing
an even number of carbon atoms.
The chain may be saturated (containing no
double bonds) or unsaturated (containing
one or more double bonds).
51

Fatty acids can be classified in many ways-
1) According to nature of the hydrophobic
chain-
a) Saturated
b) Unsaturated
c) Branched chain fatty acids
d) Substituted Fatty acids
Saturated fatty acids do not contain double
bonds, while unsaturated fatty acids contain
double bonds
52

Saturated fatty acids may be envisaged as
based on acetic acid (CH3 —COOH) as the
first member of the series in which —CH2 —
is progressively added between the terminal
CH3 — and —COOH groups.
Fatty acids in biological systems usually
contain an even number of carbon atoms,
typically between 14 and 24. The 16- and
18-carbon fatty acids are most common.
The hydrocarbon chain is almost invariably
unbranched in animal fatty acids. A few
branched-chain fatty acids have also been
isolated from both plant and animal sources.
53

Number of C
atoms
Common Name Systemic Name Formula
2 Acetic acid Ethanoic acid CH3COOH
4 Butyric acid Butanoic acid CH3(CH2)2COOH
6 Caproic acid Hexanoic acid CH3(CH2)4COOH
8 Caprylic acid Octanoic acid CH3(CH2)6COOH
10 Capric acid Decanoic acid CH3(CH2)8COOH
12 Lauric acid Dodecanoic acid CH3(CH2)10COOH
14 Myristic acid Tetradecanoic
acid
CH3(CH2)12COOH
16 Palmitic acid Hexadecanoic
acid
CH3(CH2)14COOH
18 Stearic acid Octadecanoic
acid
CH3(CH2)16COOH
20 Arachidic acid Eicosanoic acid CH3(CH2)18COOH
22 Behenic acid Docosanoic acid CH3(CH2)20COOH 54

Unsaturated fatty acids may further be divided as
follows-
(1) Monounsaturated (monoethenoid, monoenoic) acids,
containing one double bond.
(2) Polyunsaturated (polyethenoid, polyenoic) acids,
containing two or more double bonds.
The configuration of the double bonds in most
unsaturated fatty acids is cis.
The double bonds in polyunsaturated fatty acids are
separated by at least one methylene group.
55

The systematic name for a fatty acid is derived
from the name of its parent hydrocarbon by the
substitution of oic
for the final e.
For example, the C18 saturated fatty acid is
called octadecanoic acid because the parent
hydrocarbon is octadecane.
A C18 fatty acid with one double bond is called
octadecenoic acid; with two double bonds,
octadecadienoic acid; and with three double
bonds, octadecatrienoic acid.
The notation 18:0 denotes a C18 fatty acid with
no double bonds, whereas 18:2 signifies that there
are two double bonds.
57

Carbon atoms are numbered from the
carboxyl carbon (carbon No. 1). The carbon
atoms adjacent to the carboxyl carbon (Nos.
2, 3, and 4) are also known as the α ,β , and
carbons, respectively, and the terminal
methyl carbon is known as theω or n-carbon.
The position of a double bond is represented
by the symbol ∆followed by a superscript
number.
eg, ∆ 9 indicates a double bond between
carbons 9 and 10 of the fatty acid;
58

Alternatively, the position of a double bond can be
denoted by counting from the distal end, with the ω-
carbon atom (the methyl carbon) as number 1.
ω9 indicates a double bond on the ninth carbon counting
from the ω-carbon.
In animals, additional double bonds are introduced only
between the existing double bond (eg, 9, 6, or 3) and the
carboxyl carbon, leading to three series of fatty acids
known as the ω9, ω6, and ω3 families, respectively.
59

S.No. Number of C
atoms,
number and
location of
double bonds
Family Common
Name
Systemic
Name
[A] Monoenoic
acids (one
double bond)
1. 16:1;9 ω 7 Palmitoleic
acid
cis-9-
Hexadecenoic
2. 18:1;9 ω 9 Oleic Acid cis-9-
Octadecenoic
3. 18:1;9 ω 9 Elaidic acid trans 9-
Octadecanoic
[B] Dienoic acids
(two double
bonds)
1. 18:2;9,12 ω 6 Linoleic acid all-cis-9,12-
Octadecadieno60

S.No. Number of C
atoms,
number and
location of
double bonds
Family Common
Name
Systemic
Name
[c] Trienoic acids
(three double
bonds)
1. 18:3;6,9,12 ω 6 Y- Linolenic
acid
all-cis-
6,9,12-
Octadecatrien
oic
2. 18:3;9,12,15 ω 3 α-Linolenic all-cis-
9,12,15Octad
ecatrienoic
[D] Tetraenoic
acid(Four
double bonds)
20:4;5,8,11, ω6 Arachidonic all-cis- 61

S.No. Number of C
atoms,
number and
location of
double bonds
Family Common
Name
Systemic
Name
[E] Pentaenoic
acids (Five
double
bonds)
1. 20:5;5,8,11,1
4,17
ω 3 Timnodonic
acid
all-cis-
5,8,11,14,17-
Eicosapenta
enoic
[F] Hexaenoic
acid(Four
double bonds)
22:6;4,7,10,1
3,16,19
ω3 Cervonic acid all-cis-
4,7,10,13,16,
19-
62

 Depending upon the orientation of the
radicals around the axis of the double bond-
 Cis- If the radicals are on the same side of
the double bond
 Trans- If the radicals are on the opposite side
 Oleic acid and Elaidic acid have the same
formula but Oleic acid is cis while Elaidic acid
is Trans Fatty acid
64

The hydrocarbon chains in saturated
fatty acids are, fairly straight and can
pack closely together, making these
fats solid at room temperature.
Oils, mostly from plant sources, have
some double bonds between some of
the carbons in the hydrocarbon tail,
causing bends or “kinks” in the shape
of the molecules.
Increase in the number of cis double
bonds in a fatty acid leads to a variety
of possible spatial configurations of
the molecule—eg, Arachidonic acid,
with four cis double bonds, has "kinks"
or a U shape.
65

 Because of the kinks in the hydrocarbon tails, unsaturated
fats can’t pack as closely together, making them liquid at
room temperature.
 The membrane lipids, which must be fluid at all
environmental temperatures, are more unsaturated than
storage lipids.
 Lipids in tissues that are subject to cooling, eg, in
hibernators or in the extremities of animals, are more
unsaturated.
 At higher temperatures, some bonds rotate, causing chain
shortening, which explains why biomembranes become
thinner with increases in temperature.
 The carbon chains of saturated fatty acids form a zigzag
pattern when extended, as at low temperatures.
66

 Trans fatty acids are present in certain foods,
arising as a by-product of the saturation of fatty
acids during hydrogenation, or "hardening," of
natural oils in the manufacture of margarine.
 An additional small contribution comes from the
ingestion of ruminant fat that contains trans fatty
acids arising from the action of microorganisms
in the rumen.
 Naturally-occurring unsaturated vegetable oils
have almost all cis bonds, but using oil for frying
causes some of the cis bonds to convert to trans
bonds.
67

 Phytanic acid present in butter
Sebum also contains branched chain fatty
acids
There may be even or odd chain fatty acids.
Even chain fatty acids are predominantly
present.
d) Cyclic fatty acids-
 Chaulmoogric acid and Hydnocarpic acid
e) Substituted fatty acids
 Cerebronic acid- OH fatty acid
c)Branched Chain Fatty acids
68

 Short chain-with 2-6 carbon atoms
 Medium chain- with 8-14 carbon atoms
 Long chain- with 16-18 carbon atoms
 Very long chain fatty acids- with 20 or more
carbon atoms
69

1-Fatty acids are the building blocks of dietary
fats. The human body stores such fats in the
form of triglycerides.
2)- Fatty acids are also required for the
formation of membrane lipids such as
phospholipids and glycolipids.
3) -They are required for the esterificaton of
cholesterol to form cholesteryl esters.
4) They act as fuel molecules and are oxidized to
produce energy.
70

Polyunsaturated fatty acids such as Linoleic and
Linolenic acids are essential for normal life
functions. They are therefore characterized as
essential fatty acids.
Arachidonic acid is considered as semi essential
fatty acid since it can be synthesized from
Linoleic acid .
Essential polyunsaturated fatty acids can be
classified as belonging to one of two "families",
the omega-6 family or the omega-3 family.
Fatty acids belonging to these two families
differ not only in their chemistry, but also in
their natural occurrence and biological functions.
71

Components of cell membranes, structural elements of
gonads and mitochondrial membrane
Required for brain growth and development
Precursors of Eicosanoids
Play important role in vision
They have a cardio protective role- Lower serum
cholesterol and increase HDL levels
Prevent fatty liver formation
Deficiencies of essential polyunsaturated fatty acids may
cause a wide variety of symptoms, including retarded
growth in children, reduced fertility and pathologic
changes in the skin.
72

Also called ‘Glycerin’.
Trihydric alcohol as it contains three
hydroxyl groups
Can be obtained from diet, from lipolysis of
fats in adipose tissue and from glycolysis.
 Can be utilized for the synthesis of
triacylglycerols, phospholipids, glucose or
can be oxidized to provide energy
 Used as a solvent in the preparation of
drugs and cosmetics
Nitroglycerine is used as a vasodilator
73

To number the carbon atoms of glycerol
unambiguously, the -sn (stereochemical
numbering) system is used.
Carbons 1 and 3 of glycerol are not identical
when viewed in three dimensions.
Enzymes readily distinguish between them
and are nearly always specific for one or the
other carbon; eg, glycerol is always
phosphorylated on sn-3 by glycerol kinase to
give glycerol 3-phosphate and not glycerol 1-
phosphate.
74

Most important sterol in
human body
 Molecular formula-C27H45
OH
Possesses a cyclo pentano
perhydrophenatherene ring
nucleus
Has an -OH group at C3
 A double bond between C5
and C6
 Two- CH3 groups at C10
and C13
An eight carbon side chain
attached to C17
75

Cholesterol occurs both as free form or in ester form
 In cholesteryl ester, the hydroxyl group on position 3 is esterified with
a long-chain fatty acid.
Cholesterol esters are formed by the transfer of acyl group by Acyl
transferases-(LCAT and ACAT)
In plasma, both forms are transported in lipoproteins
Plasma low-density lipoprotein (LDL) is the vehicle of uptake of
cholesterol and cholesteryl ester into many tissues.
Free cholesterol is removed from tissues by plasma high-density
lipoprotein (HDL) and transported to the liver, where it is eliminated
from the body either unchanged or after conversion to bile acids in the
process known as reverse cholesterol transport
A sum total of free and ester cholesterol in serum is called serum total
cholesterol
76

Cholesterol is widely distributed in all cells of the
body but particularly in nervous tissue.
It is a major constituent of the plasma membrane
and of plasma lipoproteins.
It is synthesized in many tissues from acetyl-CoA
and is the precursor of all other steroids in the body,
including corticosteroids, sex hormones, bile acids,
and vitamin D.
Cholesterol is a major constituent of gallstones.
Its chief role in pathologic processes is as a factor
in the genesis of atherosclerosis of vital arteries,
causing cerebrovascular, coronary, and peripheral
vascular disease.
77

Normal level of serum total cholesterol
ranges between 150-220 mg/dL
 Physiological variations-
Low at the time of birth, increases with
advancing age.
The level is increased during pregnancy
Pathological Variations-
a) Low cholesterol (Hypocholesterolemia)-
Thyrotoxicosis, anemia, hemolytic jaundice,
wasting diseases and malabsorption
syndrome.
78

B) Hypercholesterolemia-
 Nephrotic syndrome
Diabetes Mellitus
Obstructive Jaundice
Myxoedema
Xanthomatous biliary cirrhosis
Hypopituitarism
Familial Hypercholesterolemia
Idiopathic
79

7- dehydrocholesterol- also called as
Provitamin D3 (Precursor of vitamin D)
Ergo sterol-plant sterol (First isolated from
Ergot- Fungus of Rye)
Stigmasterol and Sitosterol- Plant sterols
Coprosterol (Coprostanol)- Reduced
products of cholesterol- found in feces
Other steroids- Bile acids, adrenocortical
hormones, gonadal hormones, D vitamins and
Cardiac glycosides.
80

 Neutral fats or Triacyl Glycerides-
The triacylglycerols are esters of the
trihydric alcohol, glycerol and fatty acids.
Mono- and Diacylglycerol, wherein one or
two fatty acids are esterified with glycerol,
are also found in the tissues.
 Naturally occurring fats and oils are
mixtures of triglycerides.
If all the OH groups are esterified to
same fatty acids- It is Simple Triglyceride
If different fatty acids are esterified- it is
known as Mixed triglyceride.
Polyunsaturated fatty acid is esterified at
2nd position.
81

Colourless, odourless and tasteless
Insoluble in water
Specific gravity is less than 1.0,
consequently all fats float in water
Oils are liquids at 200C, they contain higher
proportion of Unsaturated fatty acids
Fats are solid at room temperature and
contain saturated long chain fatty acids
Triglycerides are the storage form of energy
in adipose tissue
Triglycerides in the body are hydrolyzed by
Lipases 82

 Lipases are enzymes which catalyze
hydrolysis of triglycerides yielding fatty acids
and glycerol
 Lipases are present in following places-
Lingual Lipase-In saliva
Gastric lipase- in gastric juice
Pancreatic lipase –in pancreatic juice
Intestinal lipase- in intestinal epithelial cells
Hormone sensitive lipase – in adipose tissue
83

Saponification-When the triglycerides are hydrolyzed by
alkali the process is known as Saponification.
Rancidity-Fats and oils have a tendency to become rancid.
Rancidity refers to the appearance of unpleasant taste and
smell of fats.
Hydrolytic rancidity is due to partial hydrolysis of
triglycerides due to traces of lipases present in the given fat
Oxidative rancidity is due to partial oxidation of
unsaturated fatty acids with the resultant formation of
epoxides and peroxides by free radicals.
Preserving the fats with antioxidants can prevent rancidity
84

They are esters of higher fatty acids with higher
mono hydroxy aliphatic alcohols(e.g. Cetyl alcohol)
 Have very long straight chain of 60-100 carbon
atoms
They can take up water without getting dissolved in
it
Used as bases for the preparation of cosmetics,
ointments, polishes, lubricants and candles.
 In nature, they are found on the surface of plants
and insects.
85

Lipid index Details Significance
Saponification number Number of mg of KOH
required to saponify the
free and combined fatty
acids in 1G. of a given fat
Indicates molecular
weight and is inversely
proportional to it.
Iodine number Number of grams of
iodine absorbed by 100
gm of fat
It is a measure of degree
of unsaturation of a fat
Acid number Number of mg of KOH
required to neutralize the
fatty acids in a gram of a
fat
Indicates the degree of
rancidity of a fat
86

Lipid index Details Significance
Polenske number Number of ml of 0.1
normal KOH required to
neutralize the insoluble
fatty acids from 5 gram
of fat
Indicates the presence of
non volatile fatty acids in
a given fat
Reichert-Meissl Number Number of ml of 0.1 N
alkali required to
neutralize the soluble
fatty acids distilled from
5 G of fat
Measures the amount of
volatile soluble fatty
acids.
Acetyl Number Number of mg of KOH
required to neutralize the
acetic acid obtained by
saponification of 1G.of
fat after it has been
acetylated.
Measures the number of
–OH groups present in a
fatty acid
87

a)Phospholipids-
Contain in addition to fatty acids and
glycerol/or other alcohol, a phosphoric acid
residue, nitrogen containing base and other
substituents.
Phospholipids may be regarded as
derivatives of phosphatidic acid , in which
the phosphate is esterified with the —OH of a
suitable alcohol.
They are amphipathic molecules containing
a polar head and a hydrophobic portion
88

Based on nature of alcohol-
1)Glycerophospholipids- Glycerol is the alcohol group.
Examples-
o Phosphatidyl choline
o Phosphatidyl ethanolamine
o Phosphatidyl serine
o Phosphatidyl inositol
o Phosphatidic acid
o Cardiolipin
o Plasmalogen
o Platelet activating factor
o Phosphatidyl Glycerol
2)Sphingophospholipids- Sphingol is the alcohol group
Example- Sphingomyelin
90

1) Phosphatidylcholines (Lecithins )
Phosphoacylglycerols containing choline are the
most abundant phospholipids of the cell
membrane
 Are present a large proportion of the body's
store of choline. Choline is important in nervous
transmission, as acetylcholine, and as a store of
labile methyl groups
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.
91

2) Phosphatidyl ethanolamine (cephalin)-
 Structurally similar to Lecithin with the exception
that the base Ethanolamine replaces choline
Brain and nervous tissue are rich in Cephalin
3) Phosphatidyl Serine-(found in most tissues) differ
from phosphatidylcholine only in that serine replaces
choline
4) Phosphatidylinositol -The inositol is present in
phosphatidylinositol as the stereoisomer,
myoinositol.Phosphatidylinositol 4,5-bisphosphate is
an important constituent of cell membrane
phospholipids; upon stimulation by a suitable
hormone agonist, it is cleaved into diacylglycerol and
inositol trisphosphate, both of which act as internal
signals or second messengers.
93

5) Cardiolipin –
Abundantly found in mitochondrial membrane.
This is the only phospholipid with antigenic
properties.
6) Plasmalogens –
constitute as much as 10% of the phospholipids
of brain and muscle.
Structurally, the plasmalogens resemble
phosphatidylethanolamine but possess an ether
link on the sn-1 carbon instead of the ester link
found in acylglycerols.
Typically, the alkyl radical is an unsaturated
alcohol .
In some instances, choline, serine, or inositol may
be substituted for ethanolamine. 95

7) Platelet activating factor (PAF)-
Ether glycerophospholipid
Contains an unsaturated alkyl group in an ether link to carbon -1
An acetyl residue at carbon 2 of the glycerol backbone.
Synthesized and released by various cell types
PAF activates inflammatory cells and mediates hypersensitivity,
acute inflammatory and anaphylactic reactions
Causes platelets to aggregate and degranulate and neutrophils
and alveolar macrophages to generate superoxide radicals
8) Phosphatidyl Glycerol-
Formed by esterification of phosphatidic acid with glycerol
Diphosphatidyl glycerol, cardiolipin is found in the mitochondrial
membrane
96

Sphingomyelin-
Backbone is sphingosine
(amino alcohol)
A long chain fatty acid is
attached to amino group of
sphingosine to form Ceramide
The alcohol group at carbon-
1of sphingosine is esterified to
phosphoryl choline, producing
sphingomyelin
Sphingomyelin is an
important component of
myelin of nerve fibers
97

Components of cell membrane, mitochondrial membrane and
lipoproteins
Participate in lipid absorption and transportation from intestine
Play important role in blood coagulation
 Required for enzyme action- especially in mitochondrial
electron transport chain
Choline acts as a lipotropic agent
Membrane phospholipids acts as source of Arachidonic acid
Act as reservoir of second messenger- Phosphatidyl Inositol
Act as cofactor for the activity of Lipoprotein lipase
Phospholipids of myelin sheath provide insulation around the
nerve fobers
Dipalmitoyl lecithin acts as a surfactant
98

L/S Ratio in amniotic fluid is used for the evaluation
of fetal lung maturity
Prior to 34 weeks gestation, lecithin and
sphingomyelin concentrations are equal but
afterwards there is marked increase in Lecithin
concentration.
A L/S ratio of> 2 or > 5 indicates adequate fetal
lung maturity
Delivery of a premature,low birth weight baby with
low L/S ratio (1 or<1) predisposes the child to
respiratory distress syndrome
99

Glycolipids differ from sphingomyelins in that they
do not contain phosphoric acid and the polar head
function is provided by monosaccharide or
oligosaccharide attached directly to ceramide by an
O- glycosidic linkage.
The number and type of carbohydrate moieties
present, determine the type of glycosphingolipid.
There are two types of Glycolipids-
A) Neutral glycosphingolipids
B) Acidic glycosphingolipids
10
0

Cerebrosides- These are ceramide
monosaccharides, that contain either a
molecule of galactose(Galactocerebroside)or
glucose(Glucocerebroside)
Found predominantly in the brain and
nervous tissue with high concentration in
myelin sheath
Ceramide oligosaccharides (Globosides) are
produced by attaching additional
monosaccharides to Glucocerebroside.
Lactosyl ceramide contains lactose
(Galactose and Glucose attached to ceramide)
10
1

Cerebrosides (Contd.) – Individual
cerebrosides are differentiated on the basis
of kind of fatty acids in the molecule. Four
types are commonly observed-
a) Kerasin- contains Lignoceric acid
b) Cerebron- Contains cerebronic acid
c) Nervon- contains Nervonic acid
d) Oxynervon- contains hydroxy derivative
of nervonic acid
10
2

They are negatively charged at physiological pH
The negative charge is imparted by N- acetyl
Neuraminic acid(Sialic acid)
Brain gangliosides may contain up to four Sialic acid
residues and based on that they are-GM, GD, GT and
GQ, containing 1,2,3 or 4 Sialic acid residues
Four important types of Gm series are-
GM1, GM2 and GM3
GM1 is complex of all
10
4

They occur particularly in the outer leaflet of the
plasma membrane, where they contribute to cell
surface carbohydrates.
They act as cell surface receptors for various
hormones, and growth factors
Play important role in cellular interactions, growth
and development
They are source of blood group antigens and
various embryonic antigens
GM1 acts as a receptor for cholera toxin in human
intestine
10
6

 They are cerebrosides that contain sulfated
galactosyl residues
Negatively charged at physiological pH
Found predominantly in nerve tissue and
kidney
Failure of degradation causes them to
accumulate in nervous tissues
10
7

Disease Enzyme deficiency Nature of lipid
accumulated
Clinical
Symptoms
Tay Sach’s Disease Hexosaminidase A GM2 Ganglioside Mental
retardation,
blindness,
muscular
weakness
Fabry's disease α-Galactosidase Globotriaosylceramide Skin rash, kidney
failure (full
symptoms only in
males; X-linked
recessive).
Metachromatic
leukodystrophy
Arylsulfatase A Sulfogalactosylceramid
e
Mental retardation
and Psychologic
disturbances in
adults;
demyelination.
10
8

Disease Enzyme
deficiency
Nature of lipid
accumulated
Clinical
symptoms
Krabbe's disease β-Galactosidase Galactosylceramide Mental retardation;
myelin almost
absent.
Gaucher's disease β -Glycosidase Glucosyl ceramide Enlarged liver and
spleen, erosion of
long bones, mental
retardation in
infants.
Niemann-Pick
disease
Sphingomyelinase Sphigomyelin Enlarged liver and
spleen, mental
retardation; fatal in
early life.
Farber's disease Ceramidase Ceramide Hoarseness,
dermatitis, skeletal
deformation,
mental retardation;
fatal in early life 10
9

 Fatty acids, phospholipids, sphingolipids, bile
salts, and, to a lesser extent, cholesterol
contain polar groups. Therefore, part of the
molecule is hydrophobic, or water-insoluble;
and part is hydrophilic, or water-soluble.
Such molecules are described as amphipathic
 They become oriented at oil:water interfaces
with the polar group in the water phase and
the nonpolar group in the oil phase.
 A bilayer of such amphipathic lipids is the
basic structure in biologic membranes
11
0

 Liposomes-Liposomes may be formed by
sonicating an amphipathic lipid in an aqueous
medium.
 They consist of spheres of lipid bilayers that
enclose part of the aqueous medium.
 Liposomes are of potential clinical use—
particularly when combined with tissue-specific
antibodies—as carriers of drugs in the
circulation, targeted to specific organs, eg, in
cancer therapy.
 In addition, they are used for gene transfer into
vascular cells and as carriers for topical and
transdermal delivery of drugs and cosmetics.
11
1

 Emulsions -are much larger particles,
 formed usually by nonpolar lipids in an
aqueous medium.
 These are stabilized by emulsifying agents
such as amphipathic lipids (eg, lecithin),
which form a surface layer separating the
main bulk of the nonpolar material from the
aqueous phase .
11
2

11
4
CH2OH
Vitamin A
2-(8,8-dimethyl-1,2,5,6,7,8-hexahydrophenanthren-2-yl)ethanol
CH2OH
CH3 CH3
Vitamin A

11
5
H3C CH3
CH3
CH3 CH3
H3C CH3
H3CCH3CH3
H2O
CH2OH
CH3 CH3
Vitamin A
B-carotene

 Molecular formula C20H30O,
 Formation of ester shows the nature of oxygen as
alcoholic.
 Oxidation of vitamin gives an aldehyde indicating
that the alcohol is primary one.
 On catalytic reduction retinol absorbs five
molecules of hydrogen forming perhydroretinol
indicates pressence of 5 double bond which is
confirmed by uv spectrum
 Ozonolysis of vitamin A produces one molecule
of geranic acid.
11
6

 Oxidation of retinol with KMnO4 at high
temperature yields two of acetic acid
indicating presence of two -C(CH3)= groups
in side chain. It means that it contains two
isoprene units
11
7
CH2OH
Vitamin A
2-(8,8-dimethyl-1,2,5,6,7,8-hexahydrophenanthren-2-yl)ethanol

 Vitamin A is necessary for variety of functions
such as vision, proper growth and
differentiation, reproduction and
maintenance of epithelial cells.
 Vitamin A and vision: Rhodopsin cycle or
wald’s cycle
11
8

11
9
opsin
Rhodopsin(11 Cis
Retinal)
all trans
retinal
All Trans
-retinol
11-Cis
retinol
11-cis
retinal
Nerve impulses
light
Alcohol dehydrogenase
isomerase
Alcohol dehydrogenase

 On exposure to light,isomerization of 11-cis
retinal to All trans retinal this leads to
genration of nerve impulses.this nerve
impulse transferred to brain for visualisation
or sensation of colors.
 All trans retinal is transferred to liver and is
converted to all trans retinol by alcohol
dehydrogenase
 All trans retinol is isomerised to 11-cis retnol
with the help of isomerase
 11-cis retinol is converted to 11-cis retinal
12
0

 Retinol and retinoic acid function like steroid
hormone. They regulate the protein synthesis
 Vitamin A maintains healthy epithelial tissue,as
they prevent keratin synthesis
 Retinyl phosphate is necessary for synthesis of
certain glycoprotein
 Retinol is involved in synthesis of transferin(iron
transport protein)
 Vitamin A is considered to be essential for
maintenance of proper immune system
 Cholesterol synthesis requires vitamin A
 It act as antioxidants
12
1

 Lanosterol is closely related to sterol.
 It is optically active compounds occurs in fat.
 It is isolated from yeast and also forms a
latex along with pericyclic triterpene
12
2
HO

 From elemental analysis,molecular formula of
lanosterol has been found to be C30H50O
 Lanosterol has been shown to possess two
double bonds, one active while another inert
 When lanosterol is oxidised,it yields acetone and
aldehyde,formation this products confirms that
lanosterol contains -CH=C(CH3)2
 Lanosterol gives positive reaction for alcoholic
functional group
 Lanoterol on reduction yields lanostenol which
on oxidation yields lanostenone,it confirms
alcohol is secondary
12
3

(E)
O
OH
O
HO
OH
Prostaglandin E1
(E)
O
OH
O
OH
Prostaglandin A2

 The term prostaglandins is used for a group of naturally occurring
unsaturated, hydroxy or hydroxyketo fatty acids
 The prostaglandins are C-20 carboxylic acid with a cyclopentane ring
 The cyclopentane ring with two side chains is having generally a β-ketone .
or
 The cyclopentane ring with two side chain with two hydroxy functionality
 The side chains are unsaturated because those are having one,two or
three double bonds
 An α hydroxy group at C-15 is present in all bioactive prostaglandins
 Occurrence: it is produced by prostate gland
 Isolation: by extraction of vesicular glands of sheep.

(Z) (Z)
COOH
(Z) (Z)
Arachidonic acid
O2
O
O (E)
(E)
COOH
Endoparoxide
(E)
O
OH
O
HO
OH
Prostaglandin E1

 They serve as local modulators of cell
functions
 They play vital role in the regulation of
endocrine,nervous,digestive,Haemostatic
fuctions
 They control lipid and carbohydrate
metabolism
 If there is alteration in prostaglandin
production or metabolism this result in
hypertension, bronchial asthma,pain fever,
inflammation and ulcer

 On the basis of physical methods,it was found
that PGE1 has been a C-20 carboxylic acid with
one carboxyl group,two hydroxyl group and a
double bond
 On the basis of IR spectra 1740 cm-1 indicate
cyclopentanone ring
 The double bond was non conjugated. Because
PGE1 doesnot show any UV absorption at 210-
225 mu
 Alkaline hydrolysis of PGE1 showed a UV
absorption at 278 nm
 Final confirmation of structure of PGF1 was done
on the basis of X-ray differaction studies
 The structure of all degradation products was
found by mass spectroscopy

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Lipids and Their Biological Functions