Chemistry of lipids

Chemistry of LipidsChemistry of Lipids
Definition:
Lipids are organic compounds.
formed from alcohol and fatty acids
combined together by ester linkage.
CH2R
Fatty alcohol
OH C R
Fatty acid
HO
O
+
H2O
CH2R O C R
O
Esterase (lipase) ester (lipid)

properties
insoluble in water
soluble in fat or organic solvents
(ether, chloroform, benzene,
acetone).
Lipids include fats, oils, waxes and
related compounds.
Found in plants and in animals.

Biological Importance of Lipids:
high-energy value (25% of body needs)
Absorb fat-soluble vitamins (A, D, E and K).
important constituents of the nervous system.
Tissue fat is an essential constituent of cell membrane
and nervous system.

7-Stored lipids
• A store of energy.
• A pad for the internal organs to protect them from
outside shocks.
• A subcutaneous thermal insulator against loss of
body heat.
8-Lipoproteins, which are complex of lipids and
proteins, are important cellular constituents that
present both in the cellular and subcellular
membranes.
9-Cholesterol enters in membrane structure and is
used for synthesis of adrenal cortical hormones,
vitamin D3 and bile acids.
10- Lipids provide bases for dealing with diseases
such as obesity, atherosclerosis, lipid-storage
diseases, essential fatty acid deficiency,
respiratory distress syndrome,

Classification of Lipids
1. Simple lipids (Fats & Waxes)
2. Compound or conjugated
lipids
3. Derived Lipids
4. Lipid-associating substances

Fatty alcoholsFatty alcohols
1-Glycerol:
• It is a tri hydric alcohol - three OH
groups eg glycerin.
• It is synthesized in the body from
glucose.

1. Colorless
2. viscous oily liquid
3. sweet taste.

3-It combines with three molecules of nitric
acid to form trinitroglycerin (TNT) that is
used as explosive and vasodilator.
4-On esterification with fatty acids it gives:
• Monoglyceride or monoacyl-glycerol: one
fatty acid + glycerol.
• Diglyceride or diacyl-glycerol: two fatty
acids + glycerol.
• Triglyceride or triacyl-glycerol: three fatty
acids + glycerol.
5-It has a nutritive value by conversion into
glucose and enters in structure of
phospholipids.

Uses of GlycerolUses of Glycerol::
1. Glycerol enters in pharmaceutical and
cosmetic preparations.
2. Reduces brain edema in cerebrovascular
disease.
3. Nitroglycerin is used as vasodilator
especially for the coronary arteries, thus it
is used in treatment of angina pectoris.
Also, enters in explosives manufacturing.
4. Glycerol is used in treatment of glaucoma
(increased intraocular pressure)due to its
ability to dehydrate the tissue from its
water content.

Fatty Acids
DefinitionDefinition:
• Fatty acids are aliphatic mono-carboxylic
acids that are mostly obtained from the
hydrolysis of natural fats and oils.
• Have the general formula R-(CH2)n-COOH and
mostly have straight chain (a few exceptions
have branched and heterocyclic chains). In
this formula "n" is mostly an even number of
carbon atoms (2-34) with a few exceptions
that have an odd number.
• Fatty acids are classified according to
several bases as follows:

I. According to presence or absence of
double bonds they are classified into:
• A-Saturated Fatty Acids
• they contain no double bonds with 2-24
or more carbons.
• They are solid at room temperature
except if they are short chained.
• They may be even or odd numbered.
• They have the following molecular
formula, CnH2n+1COOH.

Saturated fatty acidsSaturated fatty acids (no double )
A-Short chain Saturated F.A.A-Short chain Saturated F.A. (2-10(2-10
carbon).carbon).
a-Short chain Saturated volatile F.A.(2-6
carbon).
b- Short chain Saturated non volatile F.A.(7-
10 carbon).
B-Long chain Saturated F.AB-Long chain Saturated F.A.(more the10.(more the10
carbon)carbon)

a-Volatile short-chain fatty acids:
• They are liquid in nature and containThey are liquid in nature and contain
((1-6)1-6) carbon atoms.carbon atoms.
• water-soluble and volatile at roomwater-soluble and volatile at room
temperature, e.g., acetic, butyric, andtemperature, e.g., acetic, butyric, and
caproic acids.caproic acids.
• Acetic F.A. (2C ) CHAcetic F.A. (2C ) CH33-COOH.-COOH.
• Butyric F.A. (4C ) CHButyric F.A. (4C ) CH33-(CH-(CH22))22-COOH.-COOH.
• Caproic F.A. (6C ) CHCaproic F.A. (6C ) CH33-(CH-(CH22))44-COOH.-COOH.

b-Non-volatile short-chain fatty acidsb-Non-volatile short-chain fatty acids:
• They are solids at room temperatureThey are solids at room temperature
and containand contain 7-107-10 carbon atoms.carbon atoms.
• They are water-soluble and non-They are water-soluble and non-
volatile at room temperature includevolatile at room temperature include
caprylic and capric F.A.caprylic and capric F.A.
• caprylic (8 C ) CHcaprylic (8 C ) CH33-(CH-(CH22))66-COOH.-COOH.
• Capric (10 C ) CHCapric (10 C ) CH33-(CH-(CH22))88-COOH.-COOH.

B-Long-chain fatty acids:
• They contain more than 10 carbon atoms.
• They occur in hydrogenated oils, animal fats,
butter and coconut and palm oils.
• They are non-volatile and water-insoluble
• Include palmitic, stearic, and lignoceric F.A.
• palmitic(16C) CHpalmitic(16C) CH33-(CH-(CH22))1414-COOH-COOH
• stearic (18 C ) CHstearic (18 C ) CH33-(CH-(CH22))1616-COOH-COOH
• lignoceric (24C ) CHlignoceric (24C ) CH33-(CH-(CH22))2222-COOH-COOH

B-Unsaturated Fatty Acids
They contain double bond
• monounsaturated
they contain one double bonds .
(CnH2n-1 COOH)
• polyunsaturated
they contain more the one double bond
(CnH2n-more than 1 COOH).

1-Monounsaturated fatty acids:
1-Palmitoleic acid :
• It is found in all fats.
• It is C16:1∆9, i.e., has 16 carbons and
one double bond located at carbon
number 9 and involving carbon 10.
CHCH33-( CH-( CH22 ))55CH = CH-(CHCH = CH-(CH22))77 –COOH–COOH

2-Oleic acid
• Is the most common fatty acid inIs the most common fatty acid in
natural fats.natural fats.
• It isIt is C18:1∆9C18:1∆9, i.e., has 18 carbons and, i.e., has 18 carbons and
one double bond located at carbonone double bond located at carbon
number 9 and involving carbon 10.number 9 and involving carbon 10.
CHCH33-(CH-(CH22))77- CH=CH – (CH- CH=CH – (CH22))77-COOH-COOH

3-Nervonic acid
(Unsaturated lignoceric acid).
• It is found in cerebrosides.
• It is C24:1∆15, i.e., has 24 carbons
and one double bond located at
carbon number 15 and involving
carbon 16.
CHCH33 – (CH– (CH22))77 CH= CH – (CHCH= CH – (CH22))1313- COOH- COOH

2-Polyunsaturated fatty acids :
(Essential fatty acids):
• Definition:
• They are 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.
• Deficiency: Their deficiency in the diet
leads to nutrition deficiency disease.
• Its symptoms include: poor growth and
health with susceptibility to infections,
dermatitis, decreased capacity to
reproduce, impaired transport of lipids,
fatty liver, and lowered resistance to
stress.

• Function of Essential Fatty Acids:
1. They are useful in the treatment of atherosclerosis
by help transporting blood cholesterol and
lowering it and transporting triglycerides.
2. The hormones are synthesized from them.
3. They enter in structure of all cellular and
subcellular membranes and the transporting
plasma phospholipids.
4. They are essential for skin integrity, normal growth
and reproduction.
5. They have an important role in blood clotting
(intrinsic factor).
6. Important in preventing and treating fatty liver.
7. Important role in health of the retina and vision.
8. They can be oxidized for energy production.

1-Linoleic:1-Linoleic:
• C18:2∆9, 12.
• It is the most important since other
essential fatty acids can be
synthesized from it in the body.
CHCH33-(CH-(CH22))44-CH = CH-CH-CH = CH-CH22-CH=CH-(CH-CH=CH-(CH22))77--
COOHCOOH

2-Linolenic acid2-Linolenic acid:
• C18:3∆9, 12, 15,
• in corn, linseed, peanut, olive,
cottonseed and soybean oils.
CHCH33-CH-CH22-CH=CH-CH-CH=CH-CH22-CH=CH-CH-CH=CH-CH22--
CH=CH-(CHCH=CH-(CH22))77-COOH-COOH

3-Arachidonic acid3-Arachidonic acid:
• C20:4∆5, 8, 11, 14.
• It is an important component of
phospholipids in animal and in peanut
oil from which prostaglandins are
synthesized.
CHCH33-(CH-(CH22))44-CH=CH-CH-CH=CH-CH22-CH=CH-CH-CH=CH-CH22--
CH=CH-CHCH=CH-CH22-CH=CH-(CH-CH=CH-(CH22))33-COOH-COOH

1-Simple Lipids
A-Neutral Fats and oilsA-Neutral Fats and oils (Triglycerides)(Triglycerides)
Definition:Definition:
• - They are called neutral because they- They are called neutral because they
are uncharged due to absence ofare uncharged due to absence of
ionizable groups in it.ionizable groups in it.
• The neutral fats are the most abundantThe neutral fats are the most abundant
lipids in nature. They constitute aboutlipids in nature. They constitute about
98% of the lipids of adipose tissue, 30%98% of the lipids of adipose tissue, 30%
of plasma or liver lipids, less than 10%of plasma or liver lipids, less than 10%
of erythrocyte lipids.of erythrocyte lipids.

• They are esters of glycerol with various fattyThey are esters of glycerol with various fatty
acids. Since the 3 hydroxyl groups ofacids. Since the 3 hydroxyl groups of
glycerol are esterified, the neutral fats areglycerol are esterified, the neutral fats are
also calledalso called “Triglycerides”.“Triglycerides”.
• Esterification of glycerol with one moleculeEsterification of glycerol with one molecule
of fatty acid givesof fatty acid gives monoglyceridemonoglyceride, and that, and that
with 2 molecules giveswith 2 molecules gives diglyceridediglyceride..
H2C O
C HO
H2C
C
C
O C
R1
R3
R2
O
O
O
+
3 H2O
CH2 OH
C HHO
CH2 OH
HO C R1
O
HO C R3
O
HO C R2
O
Fatty acids Glycerol Triglycerides
(Triacylglycerol)

Types of triglyceridesTypes of triglycerides
1-Simple triglycerides1-Simple triglycerides: If the three fatty acids: If the three fatty acids
connected to glycerol are of the same typeconnected to glycerol are of the same type
the triglyceride is called simple triglyceride,the triglyceride is called simple triglyceride,
e.g., tripalmitin.e.g., tripalmitin.
2-Mixed triglycerides2-Mixed triglycerides: if they are of different: if they are of different
types, it is called mixed triglycerides, e.g.,types, it is called mixed triglycerides, e.g.,
stearo-diolein and palmito-oleo-stearin.stearo-diolein and palmito-oleo-stearin.
• Natural fats are mixtures of mixedNatural fats are mixtures of mixed
triglycerides with a small amount of simpletriglycerides with a small amount of simple
triglycerides.triglycerides.

CH2 O
C HO
CH2
C
C
O C
(CH2)14
O
O
O
Tripalmitin
(simple triacylglycerol)
CH3
(CH2)14CH3
(CH2)14 CH3
CH2 O
C HO
CH2
C
C
O C
(CH2)16
O
O
O
1-Stearo-2,3-diolein
(mixed triacylglycerol)
CH3
(CH2)7CHCH(CH2)7CH3
(CH2)7 CH CH (CH2)7 CH3
CH2 O
C HO
CH2
C
C
O C
(CH2)14
O
O
O
1-palmito-2-oleo-3-stearin
(mixed triacylglycerol)
CH3
(CH2)16 CH3
(CH2)7CHCH(CH2)7CH3

• The commonest fatty acids inThe commonest fatty acids in
animal fats areanimal fats are palmitic, stearicpalmitic, stearic
and oleic acids.and oleic acids.
• The main difference between fatsThe main difference between fats
and oils is forand oils is for oils being liquidoils being liquid atat
room temperature, whereas,room temperature, whereas, fatsfats
are solids.are solids.
• This is mainly due to presence ofThis is mainly due to presence of
larger percentage oflarger percentage of unsaturatedunsaturated
fatty acids in oils than fats that hasfatty acids in oils than fats that has
mostlymostly saturatedsaturated fatty acids.fatty acids.

Physical properties of fat and oils:Physical properties of fat and oils:
1. Freshly prepared fats and oils are
colorless, odorless and tasteless.Any color,
or taste is due to association with other
foreign substances, e.g., the yellow color of
body fat or milk fat is due to carotene
pigments(cow milk).
2. Fats have specific gravity less than 1 and,
therefore, they float on water.
3. Fats are insoluble in water, but soluble in
organic solvents as ether and benzene.
4. Melting points of fats are usually low,
but higher than the solidification
point,

Chemical Properties of fats and oilsChemical Properties of fats and oils:
1-Hydrolysis:1-Hydrolysis:
• They are hydrolyzed into their constituents (They are hydrolyzed into their constituents (fattyfatty
acids and glycerol)acids and glycerol) by the action of super heatedby the action of super heated
steam, acid, alkali or enzyme (e.g., lipase ofsteam, acid, alkali or enzyme (e.g., lipase of
pancreas).pancreas).
• - During their enzymatic and acid hydrolysis glycerol- During their enzymatic and acid hydrolysis glycerol
and free fatty acids are produced.and free fatty acids are produced.
CH2 O
C HO
CH2
C
C
O C
R1
R3
R2
O
O
O
3 H2O
H2C OH
C HHO
H2C OH
OHCR1
O
OHCR3
O
+ OHCR2
OLipase or Acid
Triacylglycerol Glycerol Free fatty acids

2-Saponification. Alkaline hydrolysisAlkaline hydrolysis
produces glycerol and salts of fatty acidsproduces glycerol and salts of fatty acids
((soapssoaps).).
• Soaps cause emulsification of oily materialSoaps cause emulsification of oily material
this help easy washing of the fatty materialsthis help easy washing of the fatty materials
CH2 O
C HO
CH2
C
C
O C
R1
R3
R2
O
O
O
H2C OH
C HHO
H2C OH
ONaCR1
O
ONaCR3
O
+ ONaCR2
O
Triacylglycerol Glycerol Sodium salts of
fatty acids (soap)
3 NaOH

3-Halogenation3-Halogenation
• Neutral fats containing unsaturated fatty acids haveNeutral fats containing unsaturated fatty acids have
the ability of adding halogens (e.g., hydrogen orthe ability of adding halogens (e.g., hydrogen or
hydrogenation and iodine or iodination) at thehydrogenation and iodine or iodination) at the
double bonds.double bonds.
• - It is a very important property to determine the- It is a very important property to determine the
degree of unsaturation of the fat or oil thatdegree of unsaturation of the fat or oil that
determines its biological valuedetermines its biological value
CH (CH2)7 COOHCHCH2CH
Linoleic acid
CH(CH2)4CH3
2 I2
CH (CH2)7 COOHCHCH2CH
Stearate-tetra-iodinate
CH(CH2)4CH3
II I I

4-Hydrogenation or hardening of oils4-Hydrogenation or hardening of oils:
• It is a type of addition reactions acceptingIt is a type of addition reactions accepting
hydrogen at the double bonds of unsaturatedhydrogen at the double bonds of unsaturated
fatty acids.fatty acids.
• The hydrogenation is done under highThe hydrogenation is done under high
pressure of hydrogen and is catalyzed bypressure of hydrogen and is catalyzed by
finely divided nickel or copper and heat.finely divided nickel or copper and heat.
• It is the base of hardening of oils (It is the base of hardening of oils (margarinemargarine
manufacturingmanufacturing), e.g., change of oleic acid of), e.g., change of oleic acid of
fats (liquid) into stearic acid (solid).fats (liquid) into stearic acid (solid).
• It is advisable not to saturate all doubleIt is advisable not to saturate all double
bonds; otherwise margarine produced will bebonds; otherwise margarine produced will be
very hard, of very low biological value andvery hard, of very low biological value and
difficult to digest.difficult to digest.

Advantages for hydrogenated oil or fat are as follows:
1.1. It is more pleasant as cooking fat.It is more pleasant as cooking fat.
2.2. It is digestible and utilizable as normal animal fatsIt is digestible and utilizable as normal animal fats
and oils.and oils.
3.3. It is less liable to cause gastric or intestinalIt is less liable to cause gastric or intestinal
irritation.irritation.
4.4. It is easily stored and transported and less liable toIt is easily stored and transported and less liable to
rancidity.rancidity.
Disadvantages of hydrogenatedDisadvantages of hydrogenated
• fats include lack of fat-soluble vitamins (A, D, E andfats include lack of fat-soluble vitamins (A, D, E and
K) and essential fatty acidsK) and essential fatty acids
Oils
(liquid)
(with unsaturated
fatty acids, e.g., oleic)
Hard fat
(margarine, solid)
(with saturated
fatty acids, e.g., stearic)
Hydrogen, high pressure, nickel

5-Oxidation(Rancidty)5-Oxidation(Rancidty)
• This toxic reaction of triglycerides
leads to unpleasant odour or taste of
oils and fats developing after oxidation
by oxygen of air, bacteria, or moisture.
• Also this is the base of the drying oils
after exposure to atmospheric oxygen.
Example is linseed oil, which is used in
paints and varnishes manufacturing

RancidityRancidity
Definition:Definition:
• It is a physico-chemical change in theIt is a physico-chemical change in the
natural properties of the fat leading tonatural properties of the fat leading to
the development ofthe development of unpleasant odor orunpleasant odor or
taste or abnormal colortaste or abnormal color particularly onparticularly on
aging after exposure to atmosphericaging after exposure to atmospheric
oxygen, light, moisture, bacterial oroxygen, light, moisture, bacterial or
fungal contamination and/or heat.fungal contamination and/or heat.
• Saturated fats resist rancidity moreSaturated fats resist rancidity more
than unsaturated fats that havethan unsaturated fats that have
unsaturated double bonds.unsaturated double bonds.

Types and causes of RancidityTypes and causes of Rancidity:
1.1. Hydrolytic rancidityHydrolytic rancidity
2.2. Oxidative rancidityOxidative rancidity
3.3. Ketonic rancidityKetonic rancidity
1-Hydrolytic rancidity1-Hydrolytic rancidity:
• It results from slight hydrolysis of the fatIt results from slight hydrolysis of the fat
by lipase from bacterial contaminationby lipase from bacterial contamination
leading to the liberation of free fatty acidsleading to the liberation of free fatty acids
and glycerol at high temperature andand glycerol at high temperature and
moisture.moisture.
• Volatile short-chain fatty acids haveVolatile short-chain fatty acids have
unpleasant odor.unpleasant odor.

CH2 O
C HO
CH2
C
C
O C
R1
R3
R2
O
O
O
3 H2O
H2C OH
C HHO
H2C OH
OHCR1
O
OHCR3
O
+ OHCR2
OLipase
Triacylglycerol Glycerol Free fatty acids
(volatile, bad odor)

2-Oxidative Rancidity2-Oxidative Rancidity:
• It is oxidation of fat or oil catalyzed byIt is oxidation of fat or oil catalyzed by
exposure to oxygen, light and/or heatexposure to oxygen, light and/or heat
producing peroxide derivatives whichproducing peroxide derivatives which
on decomposition give substances,on decomposition give substances,
e.g.,e.g., peroxides, aldehydes, ketones andperoxides, aldehydes, ketones and
dicarboxylic acids that are toxic anddicarboxylic acids that are toxic and
have bad odor.have bad odor.
• This occurs due to oxidative addition ofThis occurs due to oxidative addition of
oxygen at the unsaturated double bondoxygen at the unsaturated double bond
of unsaturated fatty acid of oils.of unsaturated fatty acid of oils.

Polyunsaturated fatty acid
Peroxyradical
Oxidant, O2
Hydroperoxide
Hydroxy fatty acid
Cyclic peroxide
Aldehydes
such as malondialdehyde
Other fragments
such as dicarboxylic acids

3-Ketonic Rancidity:
• It is due to the contamination withIt is due to the contamination with
certain fungi such as Asperigillus Nigercertain fungi such as Asperigillus Niger
on fats such as coconut oil.on fats such as coconut oil.
• Ketones, fatty aldehydes, short chainKetones, fatty aldehydes, short chain
fatty acids and fatty alcohols arefatty acids and fatty alcohols are
formed.formed.
• Moisture accelerates ketonic rancidity.Moisture accelerates ketonic rancidity.

• Prevention of rancidity is achieved by:Prevention of rancidity is achieved by:
1.1. Avoidance of the causes (Avoidance of the causes (exposure to light,exposure to light,
oxygen, moisture, high temperature andoxygen, moisture, high temperature and
bacteria or fungal contaminationbacteria or fungal contamination). By). By
keeping fats or oils in well-closed containerskeeping fats or oils in well-closed containers
in cold, dark and dry place (i.e.,in cold, dark and dry place (i.e., goodgood
storage conditions).storage conditions).
2.2. Removal of catalysts such as lead andRemoval of catalysts such as lead and
copper that catalyze rancidity.copper that catalyze rancidity.
3.3. Addition ofAddition of anti-oxidantsanti-oxidants to preventto prevent
peroxidation in fat (i.e., rancidity). Theyperoxidation in fat (i.e., rancidity). They
include phenols, naphthols, tannins andinclude phenols, naphthols, tannins and
hydroquinones.hydroquinones. The most common naturalThe most common natural
antioxidant is vitamin E that is importantantioxidant is vitamin E that is important inin
vitrovitro andand in vivoin vivo..

Hazards of Rancid Fats:
1.1. The products of rancidity are toxic,The products of rancidity are toxic,
i.e., causes food poisoning andi.e., causes food poisoning and
cancer.cancer.
2.2. Rancidity destroys the fat-solubleRancidity destroys the fat-soluble
vitamins (vitamins A, D, K and E).vitamins (vitamins A, D, K and E).
3.3. Rancidity destroys theRancidity destroys the
polyunsaturated essential fatty acids.polyunsaturated essential fatty acids.
4.4. Rancidity causes economical lossRancidity causes economical loss
because rancid fat is inedible.because rancid fat is inedible.

Analysis and Identification of fats and oilsAnalysis and Identification of fats and oils
(Fat Constants(Fat Constants))
• Fat constants or numbers are tests usedFat constants or numbers are tests used
for:for:
1.1. Checking the purity of fat for detection ofChecking the purity of fat for detection of
adulteration.adulteration.
2.2. To quantitatively estimate certain propertiesTo quantitatively estimate certain properties
of fat.of fat.
3.3. To identify the biological value and naturalTo identify the biological value and natural
characteristics of fat.characteristics of fat.
4.4. Detection of fat rancidity and presence ofDetection of fat rancidity and presence of
toxic hydroxy fatty acids.toxic hydroxy fatty acids.

1-Iodine number1-Iodine number (or value):
• Definition: It is the number of grams of
iodine absorbed by 100 grams of fat or
oil.
• Uses: It is a measure for the degree of
unsaturation of the fat, as a natural property
for it.
• Unsaturated fatty acids absorb iodine at their
double bonds, therefore, as the degree of
unsaturation increases iodine number and
hence biological value of the fat increase.
• It is used for identification of the type of fat,
detection of adulteration and determining the
biological value of fat.

2-Saponification number (or value):
• DefinitionDefinition: It is the number ofIt is the number of milligrams ofmilligrams of
KOHKOH required to completely saponifyrequired to completely saponify oneone
gramgram of fatof fat.
• UsesUses:
• Since each carboxyl group of a fatty acidSince each carboxyl group of a fatty acid
reacts with one mole of KOH duringreacts with one mole of KOH during
saponification, therefore,saponification, therefore, the amount of alkalithe amount of alkali
needed to saponify certain weight of fatneeded to saponify certain weight of fat
depends upon the number of fatty acidsdepends upon the number of fatty acids
present per weight.present per weight.
• Thus, fats containing short-chain acids willThus, fats containing short-chain acids will
have more carboxyl groups per gram thanhave more carboxyl groups per gram than
long chain fatty acids and consume morelong chain fatty acids and consume more
alkali, i.e., will have higher saponificationalkali, i.e., will have higher saponification
number.number.

3-Acids Number3-Acids Number (or value):
• DefinitionDefinition::
• It is the number ofIt is the number of milligrams of KOHmilligrams of KOH
required to neutralize the free fattyrequired to neutralize the free fatty
acids present inacids present in one gramone gram of fat.of fat.
• Uses:Uses:
• It is used for detection of hydrolyticIt is used for detection of hydrolytic
rancidity because it measures therancidity because it measures the
amount of free fatty acids present.amount of free fatty acids present.

4-Reichert- Meissl Number4-Reichert- Meissl Number (or value):
• DefinitionDefinition: It is the number of: It is the number of milliliters ofmilliliters of 0.10.1
NN KOHKOH required to neutralize the water-required to neutralize the water-
soluble fatty acids distilled fromsoluble fatty acids distilled from 5 grams5 grams ofof
fat. Short-chain fatty acid (less than 10fat. Short-chain fatty acid (less than 10
carbons) is distillated by steam.carbons) is distillated by steam.
• UsesUses: This studies the natural composition: This studies the natural composition
of the fat and is used for detection of fatof the fat and is used for detection of fat
adulteration.adulteration.
• Butter that has high percentage of short-Butter that has high percentage of short-
chain fatty acids has highest Reichert-Meisslchain fatty acids has highest Reichert-Meissl
number compared to margarine.number compared to margarine.

5-Acetyl Number5-Acetyl Number (or value):
• DefinitionDefinition: It is number ofIt is number of milligrams ofmilligrams of KOHKOH
needed to neutralize the acetic acid liberatedneeded to neutralize the acetic acid liberated
from hydrolysis offrom hydrolysis of 1 gram of acetylated fat1 gram of acetylated fat
(hydroxy fat reacted with acetic anhydride(hydroxy fat reacted with acetic anhydride).
• Uses:Uses: The natural or rancid fat that containsThe natural or rancid fat that contains
fatty acids with free hydroxyl groups arefatty acids with free hydroxyl groups are
converted into acetylated fat by reaction withconverted into acetylated fat by reaction with
acetic anhydride.acetic anhydride.
• Thus, acetyl number is a measure of numberThus, acetyl number is a measure of number
of hydroxyl groups present.of hydroxyl groups present.
• It is used for studying the natural propertiesIt is used for studying the natural properties
of the fat and to detectof the fat and to detect adulterationadulteration andand
rancidity.rancidity.

B-WaxesB-Waxes
• DefinitionDefinition: Waxes are solid simple lipidsWaxes are solid simple lipids
containing a monohydric alcohol (with acontaining a monohydric alcohol (with a
higher molecular weight than glycerol)higher molecular weight than glycerol)
esterified to long-chain fatty acids.esterified to long-chain fatty acids.
Examples of these alcohols areExamples of these alcohols are palmitoylpalmitoyl
alcohol, cholesterol, vitamin A or D.alcohol, cholesterol, vitamin A or D.
• Properties of waxesProperties of waxes: Waxes are insoluble: Waxes are insoluble
in water, but soluble in fat solvents and arein water, but soluble in fat solvents and are
negative for acrolein test.negative for acrolein test.
• Waxes are not easily hydrolyzed as the fatsWaxes are not easily hydrolyzed as the fats
and are indigestible by lipases and are veryand are indigestible by lipases and are very
resistant to rancidity.resistant to rancidity.
• Thus they are of no nutritional value.Thus they are of no nutritional value.

Type of WaxesType of Waxes:
• - Waxes are widely distributed in nature such as
the secretion of certain insects as bees-wax,
protective coatings of the skins and furs of
animals and leaves and fruits of plants. They are
classified into true-waxes and wax-like
compounds as follows:
A-True waxesA-True waxes: include:
• Bees-waxBees-wax is secreted by the honeybees that
use it to form the combs. It is a mixture of
waxes with the chief constituent is mericyl
palmitate.

B-Wax-like compounds:
• Cholesterol estersCholesterol esters: Lanolin (or wool fat)Lanolin (or wool fat)
is prepared from the wool-associated skinis prepared from the wool-associated skin
glands and is secreted by sebaceousglands and is secreted by sebaceous
glands of the skin.glands of the skin.
• It is very complex mixture, contains bothIt is very complex mixture, contains both
free and esterified cholesterol, e.g.,free and esterified cholesterol, e.g.,
cholesterol-palmitate and other sterolscholesterol-palmitate and other sterols.
C15H31 C OH
O
+C30H61OH C15H31 C O
O
C30H61
H2OPalmitic
acid
Mericyl
alcohol
Mericyl
palmitate

Differences between neutral lipids and waxes:
Waxes Neutral lipidsNeutral lipids
1.1.Digestibility:Digestibility: Indigestible (notIndigestible (not
hydrolyzed by lipase).hydrolyzed by lipase).
Digestible (hydrolyzed by lipase).Digestible (hydrolyzed by lipase).
2-Type of2-Type of
alcoholalcohol::
Long-chain monohydricLong-chain monohydric
alcohol + one fatty acid.alcohol + one fatty acid.
Glycerol (trihydric) + 3 fatty acidsGlycerol (trihydric) + 3 fatty acids
3-Type of fatty3-Type of fatty
acidsacids::
Fatty acid mainly palmiticFatty acid mainly palmitic
or stearic acid.or stearic acid.
Long and short chain fatty acids.Long and short chain fatty acids.
4-Acrolein test4-Acrolein test: Negative.Negative. Positive.Positive.
5-Rancidability:5-Rancidability: Never get rancid.Never get rancid. Rancidible.Rancidible.
6-Nature at6-Nature at
roomroom
temperaturetemperature.
Hard solid.Hard solid. Soft solid or liquid.Soft solid or liquid.
7-Saponification7-Saponification Nonsaponifiable.Nonsaponifiable. Saponifiable.Saponifiable.
8-Nutritive8-Nutritive
valuevalue:
No nutritive value.No nutritive value. Nutritive.Nutritive.
9-Example:9-Example: Bee & carnuba waxes.Bee & carnuba waxes. Butter and vegetable oils.Butter and vegetable oils.

2-Compound Lipids2-Compound Lipids
DefinitionDefinition:
• They are lipids that contain additionalThey are lipids that contain additional
substances, e.g., sulfur, phosphorus, aminosubstances, e.g., sulfur, phosphorus, amino
group, carbohydrate, or proteins besidegroup, carbohydrate, or proteins beside
fatty acid and alcohol.fatty acid and alcohol.
• Compound or conjugated lipids areCompound or conjugated lipids are
classified into the following types accordingclassified into the following types according
to the nature of the additional group:to the nature of the additional group:
1.1. PhospholipidsPhospholipids
2.2. Glycolipids.Glycolipids.
3.3. LipoproteinsLipoproteins
4.4. Sulfolipids and amino lipids.Sulfolipids and amino lipids.

A-PhospholipidsA-Phospholipids
Definition:Definition: Phospholipids or phosphatides arePhospholipids or phosphatides are
compound lipids, which contain phosphoric acidcompound lipids, which contain phosphoric acid
group in their structuregroup in their structure..
ImportanceImportance:
1.1. They are present in large amounts in the liver andThey are present in large amounts in the liver and
brain as well as blood. Every animal and plantbrain as well as blood. Every animal and plant
cell contains phospholipids.cell contains phospholipids.
2.2. The membranes bounding cells and subcellularThe membranes bounding cells and subcellular
organelles are composed mainly oforganelles are composed mainly of
phospholipids. Thus, the transfer of substancesphospholipids. Thus, the transfer of substances
through these membranes is controlled bythrough these membranes is controlled by
properties of phospholipids.properties of phospholipids.
3.3. They are important components of the lipoproteinThey are important components of the lipoprotein
coat essential for secretion and transport ofcoat essential for secretion and transport of
plasma lipoprotein complexes. Thus, they areplasma lipoprotein complexes. Thus, they are
lipotropic agents thatlipotropic agents that prevent fatty liverprevent fatty liver..
4.4. Myelin sheath of nerves is rich withMyelin sheath of nerves is rich with
phospholipids.phospholipids.

5-Important in digestion and absorption of5-Important in digestion and absorption of
neutral lipids and excretion ofneutral lipids and excretion of
cholesterol in the bile.cholesterol in the bile.
6-Important function in blood clotting and6-Important function in blood clotting and
platelet aggregation.platelet aggregation.
7-They provide lung alveoli with7-They provide lung alveoli with
surfactants that prevent its irreversiblesurfactants that prevent its irreversible
collapsecollapse..
8-Important role in signal transduction8-Important role in signal transduction
across the cell membrane.across the cell membrane.
9-Phospholipase A2 in snake venom9-Phospholipase A2 in snake venom
hydrolyses membrane phospholipidshydrolyses membrane phospholipids
into hemolytic lysolecithin orinto hemolytic lysolecithin or
lysocephalin.lysocephalin.
10-They are source of polyunsaturated10-They are source of polyunsaturated
fatty acids for synthesis offatty acids for synthesis of
eicosanoids.eicosanoids.

Sources:Sources: They are found in all cellsThey are found in all cells
(plant and animal), milk and egg-yolk(plant and animal), milk and egg-yolk
in the form of lecithins.in the form of lecithins.
StructureStructure: phospholipids are composed of:phospholipids are composed of:
1.1. Fatty acidsFatty acids (a saturated and an(a saturated and an
unsaturated fatty acid).unsaturated fatty acid).
2.2. Nitrogenous baseNitrogenous base (choline, serine,(choline, serine,
threonine, or ethanolamine).threonine, or ethanolamine).
3.3. Phosphoric acid.Phosphoric acid.
4.4. Fatty alcoholsFatty alcohols (glycerol, inositol or(glycerol, inositol or
sphingosine).sphingosine).

• Classification of PhospholipidsClassification of Phospholipids areare
classified into 2 groups according to theclassified into 2 groups according to the
type of thetype of the alcoholalcohol present into two types:present into two types:
A-A-GlycerophospholipidsGlycerophospholipids: They are regarded asThey are regarded as
derivatives of phosphatidic acids that are thederivatives of phosphatidic acids that are the
simplest type of phospholipids and include:simplest type of phospholipids and include:
1.1. Phosphatidic acidsPhosphatidic acids..
2.2. LecithinsLecithins
3.3. CephalinsCephalins..
4.4. PlasmalogensPlasmalogens..
5.5. InositidesInositides..
6.6. CardiolipinCardiolipin.
B-SphingophospholipidsB-Sphingophospholipids: They containThey contain
sphingosine as an alcohol and are namedsphingosine as an alcohol and are named
SphingomyelinsSphingomyelins.

A-GlycerophospholipidsA-Glycerophospholipids
1-Phosphatidic acids:1-Phosphatidic acids:They are metabolic intermediatesThey are metabolic intermediates
in synthesis of triglycerides andin synthesis of triglycerides and
glycerophospholipids in the body and may haveglycerophospholipids in the body and may have
function as afunction as a second messengersecond messenger. They exist in two. They exist in two
forms according to the position of the phosphateforms according to the position of the phosphate
CH2 O
C HO
CH2
C
C
O P
R1
R2
O
O
α-Phosphatidic acid
OH
OH
O
Saturated
fatty acidPolyunsaturated
fatty acid
Phosphate
CH2 O
C H
CH2
C
O
R1
O
β-Phosphatidic acid
Saturated
fatty acid
Polyunsaturated
fatty acid
Phosphate PHO
OH
O
C R2
O
β
β
α
α
α
α
O

2-Lecithins:2-Lecithins:
• DefinitionDefinition: Lecithins areLecithins are
glycerophospholipids that contain choline asglycerophospholipids that contain choline as
a base beside phosphatidic acid. They exista base beside phosphatidic acid. They exist
in 2 formsin 2 forms αα- and- and ββ-lecithins. Lecithins are a-lecithins. Lecithins are a
common cell constituent obtained from braincommon cell constituent obtained from brain
((αα-type), egg yolk (-type), egg yolk (ββ-type), or liver (both-type), or liver (both
types). Lecithins are important in thetypes). Lecithins are important in the
metabolism of fat by the liver.metabolism of fat by the liver.
• Structure:Structure: Glycerol is connected at C2 or C3Glycerol is connected at C2 or C3
with a polyunsaturated fatty acid, at C1 with awith a polyunsaturated fatty acid, at C1 with a
saturated fatty acid, at C3 or C2 bysaturated fatty acid, at C3 or C2 by
phosphate to which the choline base isphosphate to which the choline base is
connected. The common fatty acids inconnected. The common fatty acids in
lecithins are stearic, palmitic, oleic, linoleic,lecithins are stearic, palmitic, oleic, linoleic,
linolenic, clupandonic or arachidonic acids.linolenic, clupandonic or arachidonic acids.

LysolecithinLysolecithin causes hemolysis of RBCs. This partiallycauses hemolysis of RBCs. This partially
explains toxic the effect of snake venom,. Theexplains toxic the effect of snake venom,. The
venom containsvenom contains lecithinaselecithinase, which hydrolyzes the, which hydrolyzes the
polyunsaturated fatty converting lecithin intopolyunsaturated fatty converting lecithin into
lysolecithin. Lysolecithins are intermediates inlysolecithin. Lysolecithins are intermediates in
metabolism of phospholipidsmetabolism of phospholipids.
CH2 O
C HO
CH2
C
C
O P
R1
R2
O
O
α-Lecithin
O
OH
O
CH2 O
C H
CH2
C
O
R1
O
β-Lecithin
P
OH
O
C R2
O
CH2 CH2 N
CH3
CH3
CH3
+
OCH2CH2N
CH3
CH3
CH3
+
Choline
Choline
O

• Lung surfactantLung surfactant
• Is a complex of dipalmitoyl-lecithin, sphingomyelinIs a complex of dipalmitoyl-lecithin, sphingomyelin
and a group of apoproteins called apoprotein A, B,and a group of apoproteins called apoprotein A, B,
C, and D.C, and D.
• It is produced by type II alveolar cells and isIt is produced by type II alveolar cells and is
anchored to the alveolar surface of type II and Ianchored to the alveolar surface of type II and I
cells.cells.
• It lowers alveolar surface tension and improvesIt lowers alveolar surface tension and improves
gas exchange besides activating macrophages togas exchange besides activating macrophages to
kill pathogens.kill pathogens.
• In premature babies, this surfactant is deficientIn premature babies, this surfactant is deficient
and they suffer fromand they suffer from respiratory distressrespiratory distress
syndromesyndrome..
• Glucocorticoids increase the synthesis of theGlucocorticoids increase the synthesis of the
surfactant complex and promote differentiation ofsurfactant complex and promote differentiation of
lung cells.lung cells.

3-Cephalins (or Kephalins):3-Cephalins (or Kephalins):
• DefinitionDefinition: They are phosphatidyl-They are phosphatidyl-
ethanolamine or serine. Cephalinsethanolamine or serine. Cephalins
occur in association with lecithins inoccur in association with lecithins in
tissues and are isolated from the braintissues and are isolated from the brain
((Kephale = head).Kephale = head).
• StructureStructure: Cephalins resemble lecithins: Cephalins resemble lecithins
in structure except that choline isin structure except that choline is
replaced by ethanolamine, serine orreplaced by ethanolamine, serine or
threonine amino acids.threonine amino acids.

• Certain cephalins are constituents of the complexCertain cephalins are constituents of the complex
mixture of phospholipids, cholesterol and fat thatmixture of phospholipids, cholesterol and fat that
constitute the lipid component of the lipoproteinconstitute the lipid component of the lipoprotein
““thromboplastinthromboplastin” which accelerates the clotting of” which accelerates the clotting of
blood by activation of prothrombin to thrombin inblood by activation of prothrombin to thrombin in
presence of calcium ionspresence of calcium ions.
CH2 O
C HO
CH2
C
C
O P
R1
R2
O
O
α-Cephalin
O
OH
O
CH2 CH2 NH2 Ethanolamine
HO CH2 CH COOH Serine
NH2
HO CH CH COOH Threonine
NH2CH3

4-Plasmalogens:4-Plasmalogens:
• Definition:Definition: Plasmalogens are found in the cellPlasmalogens are found in the cell
membrane phospholipids fraction of brainmembrane phospholipids fraction of brain
and muscle (10% of it is plasmalogens), liver,and muscle (10% of it is plasmalogens), liver,
semen and eggs.semen and eggs.
• StructureStructure: Plasmalogens resemble lecithinsPlasmalogens resemble lecithins
and cephalins in structure but differ in theand cephalins in structure but differ in the
presence ofpresence of αα,,ββ-unsaturated fatty alcohol-unsaturated fatty alcohol
rather than a fatty acid at C1 of the glycerolrather than a fatty acid at C1 of the glycerol
connected by ether bond.connected by ether bond.
• At C2 there is an unsaturated long-chainAt C2 there is an unsaturated long-chain
fatty acid, however, it may be a very short-fatty acid, however, it may be a very short-
chain fatty acidchain fatty acid

• Properties: Similar to lecithinsSimilar to lecithins.
CH2
C HO
CH2
C
O P
R2
O
α-Plasmalogen
O
OH
O
CH2 CH2 N
CH3
CH3
CH3
+
α,β-Unsaturated
fatty alcoholCH CH R1O

5-Inositides5-Inositides:
• DefinitionDefinition::
• - They are phosphatidyl inositol.They are phosphatidyl inositol.
• StructureStructure: They are similar to lecithins or cephalinsThey are similar to lecithins or cephalins
but they have the cyclic sugar alcohol,but they have the cyclic sugar alcohol, inositolinositol asas
the base. They are formed of glycerol, one saturatedthe base. They are formed of glycerol, one saturated
fatty acid, one unsaturated fatty acid, phosphoricfatty acid, one unsaturated fatty acid, phosphoric
acid and inositolacid and inositol
CH2
C HO
CH2
C
O P
R2
O
α-Phosphatidylinositol
O
OH
O
C R1O
O
H
H
OH
OH
HOH
H
OHOH
H H
1
2 3
4
56

• SourceSource: Brain tissuesBrain tissues.
• FunctionFunction:
• Phosphatidyl inositol is a major componentPhosphatidyl inositol is a major component
of cell membrane phospholipids particularlyof cell membrane phospholipids particularly
at the inner leaflet of it.at the inner leaflet of it.
• They play a major role as secondThey play a major role as second
messengers during signal transduction formessengers during signal transduction for
certain hormone..certain hormone..
• On hydrolysis by phospholipase C,On hydrolysis by phospholipase C,
phosphatidyl-inositol-4,5-diphosphatephosphatidyl-inositol-4,5-diphosphate
producesproduces diacyl-glycerol and inositol-diacyl-glycerol and inositol-
triphosphatetriphosphate both act to liberate calciumboth act to liberate calcium
from its intracellular stores to mediate thefrom its intracellular stores to mediate the
hormone effects.hormone effects.

6-Cardiolipins:6-Cardiolipins:
• DefinitionDefinition: They are diphosphatidyl-glycerol. TheyThey are diphosphatidyl-glycerol. They
are found in the inner membrane of mitochondriaare found in the inner membrane of mitochondria
initially isolated from heart muscle (cardio). It isinitially isolated from heart muscle (cardio). It is
formed of 3 molecules of glycerol, 4 fatty acids and 2formed of 3 molecules of glycerol, 4 fatty acids and 2
phosphate groupsphosphate groups..
• FunctionFunction:: Used in serological diagnosis ofUsed in serological diagnosis of
autoimmunity diseases.autoimmunity diseases.
CH2
C HO
CH2
C
O P
R2
O
Cardiolipin
O
OH
O
C R1O
O
CH2
CH OH
CH2 CH2
CH O
CH2
C
OP
R3
O
O
OH
O
CR4 O
O

B-SphingophospholipidsB-Sphingophospholipids
1-Sphingomyelins1-Sphingomyelins
• Definition:Definition: Sphingomyelins are found in largeSphingomyelins are found in large
amounts in brain and nerves and in smaller amountsamounts in brain and nerves and in smaller amounts
in lung, spleen, kidney, liver and bloodin lung, spleen, kidney, liver and blood.
• Structure:Structure: Sphingomyelins differ from lecithins andSphingomyelins differ from lecithins and
cephalins in that they contain sphingosine as thecephalins in that they contain sphingosine as the
alcohol instead of glycerol, they contain twoalcohol instead of glycerol, they contain two
nitrogenous bases: sphingosine itself and choline.nitrogenous bases: sphingosine itself and choline.
• Thus, sphingomyelins contain sphingosine base,Thus, sphingomyelins contain sphingosine base,
one long-chain fatty acid, choline and phosphoricone long-chain fatty acid, choline and phosphoric
acid.acid.
• To the amino group of sphingosine the fatty acid isTo the amino group of sphingosine the fatty acid is
attached by an amide linkage.attached by an amide linkage.

• Ceramide This part of sphingomyelin in whichThis part of sphingomyelin in which
the amino group of sphingosine is attached to thethe amino group of sphingosine is attached to the
fatty acid by an amide linkage.fatty acid by an amide linkage.
• Ceramides have been found in the free state in theCeramides have been found in the free state in the
spleen, liver and red cells.spleen, liver and red cells.
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

B-GlycolipidsB-Glycolipids
• DefinitionDefinition: They are lipids that containThey are lipids that contain
carbohydrate residues with sphingosine as thecarbohydrate residues with sphingosine as the
alcohol and a very long-chain fatty acid (24 carbonalcohol and a very long-chain fatty acid (24 carbon
series).series).
• They are present in cerebral tissue, therefore areThey are present in cerebral tissue, therefore are
calledcalled cerebrosidescerebrosides
• ClassificationClassification: According to the number andAccording to the number and
nature of the carbohydrate residue(s) present innature of the carbohydrate residue(s) present in
the glycolipids the following arethe glycolipids the following are
1. Cerebrosides. They have one galactoseThey have one galactose
molecule (galactosides).molecule (galactosides).
2. Sulfatides. They are cerebrosides with sulfate onThey are cerebrosides with sulfate on
the sugar (sulfated cerebrosides).the sugar (sulfated cerebrosides).
3. Gangliosides. They have several sugar andThey have several sugar and
sugaramine residues.sugaramine residues.

1-Cerebrosides:1-Cerebrosides:
• Occurrence: They occur in myelin sheath of nerves and white
matter of the brain tissues and cellular membranes. They are
important for nerve conductance.
• Structure: They contain sugar, usually β-galactose and may be
glucose or lactose, sphingosine and fatty acid, but no
phosphoric acid.
CH CH NH
CH2
CHCH(CH2)12CH3
OH
Sphingosine
C R1
O
O
Psychosin
Fatty acid
Ceramide
Cerebroside
OOH
H H
H
OHH
OH
CH2OH
H
Galactose

• TypesTypes: According to the type of fatty acidAccording to the type of fatty acid
and carbohydrate present, there are 4and carbohydrate present, there are 4
different types of cerebrosides isolateddifferent types of cerebrosides isolated
from the white matter of cerebrum and infrom the white matter of cerebrum and in
myelin sheaths of nerves. Rabbitmyelin sheaths of nerves. Rabbit
cerebrosides contain stearic acid.cerebrosides contain stearic acid.
1.1. KerasinKerasin contains lignoceric acid (24contains lignoceric acid (24
carbons) and galactose.carbons) and galactose.
2.2. Cerebron (Phrenosin)Cerebron (Phrenosin) contains cerebroniccontains cerebronic
acid (2-hydroxylignoceric acid) andacid (2-hydroxylignoceric acid) and
galactose.galactose.
3.3. NervonNervon contains nervonic acid (unsaturatedcontains nervonic acid (unsaturated
lignoceric acid at C15) and galactose.lignoceric acid at C15) and galactose.
4.4. OxynervonOxynervon contains oxynervonic acid (2-contains oxynervonic acid (2-
hydroxynervonic acid) and galactose.hydroxynervonic acid) and galactose.

2-Sulfatides2-Sulfatides:
• They are sulfate esters of kerasin or phrenosin inThey are sulfate esters of kerasin or phrenosin in
which the sulfate group is usually attached to thewhich the sulfate group is usually attached to the
–OH group of C3 or C6 of galactose. Sulfatides are–OH group of C3 or C6 of galactose. Sulfatides are
usually present in the brain, liver, muscles andusually present in the brain, liver, muscles and
testes.testes.
CH CH NH
CH2
CHCH2(CH2)12CH3
OH
C R1
O
O
Sulfatides (sulfated cerebroside)
OOH
H H
H
OHH
OSO3H
CH2OH
H

3-Gangliosides:3-Gangliosides:
• They are more complex glycolipids that occur inThey are more complex glycolipids that occur in
the gray matter of the brain, ganglion cells, andthe gray matter of the brain, ganglion cells, and
RBCs. They transfer biogenic amines across theRBCs. They transfer biogenic amines across the
cell membrane and act as a cell membranecell membrane and act as a cell membrane
receptor.receptor.
• GangliosidesGangliosides containcontain sialic acid (N-sialic acid (N-
acetylneuraminicacetylneuraminic acid),acid), ceramide (sphingosine +ceramide (sphingosine +
fatty acid of 18-24 carbon atom length), 3fatty acid of 18-24 carbon atom length), 3
molecules of hexoses (1 glucose + 2 galactose)molecules of hexoses (1 glucose + 2 galactose)
and hexosamine. The most simple type of it theand hexosamine. The most simple type of it the
monosialoganglioside,. It works as a receptor formonosialoganglioside,. It works as a receptor for
cholera toxin in the human intestine.cholera toxin in the human intestine.Ceramide-Glucose-Galactose-N-acetylgalactosamine-Galactose
Monosialoganglioside
Sialic acid

C-LipoproteinsC-Lipoproteins
• DefinitionDefinition: Lipoproteins are lipids combined withLipoproteins are lipids combined with
proteins in the tissues. The lipid component isproteins in the tissues. The lipid component is
phospholipid, cholesterol or triglycerides. Thephospholipid, cholesterol or triglycerides. The
holding bonds are secondary bonds.holding bonds are secondary bonds.
• They include:They include:
1.1. Structural lipoproteinsStructural lipoproteins: These are widely: These are widely
distributed in tissues being present in cellular anddistributed in tissues being present in cellular and
subcellular membranes. In lung tissues acting assubcellular membranes. In lung tissues acting as
a surfactant in a complex of a protein and lecithin.a surfactant in a complex of a protein and lecithin.
In the eye, rhodopsin of rods is a lipoproteinIn the eye, rhodopsin of rods is a lipoprotein
complex.complex.
• Transport lipoproteinsTransport lipoproteins::
• These are the forms present in blood plasma.These are the forms present in blood plasma.
They are composed of a protein calledThey are composed of a protein called
apolipoproteinapolipoprotein and different types of lipids.and different types of lipids.
(Cholesterol, cholesterol esters, phospholipids(Cholesterol, cholesterol esters, phospholipids
and triglycerides). As the lipid content increases,and triglycerides). As the lipid content increases,
the density of plasma lipoproteins decreasesthe density of plasma lipoproteins decreases

• Plasma lipoproteins can be separated by twoPlasma lipoproteins can be separated by two
methodsmethods:
1.1. Ultra-centrifugationUltra-centrifugation: Using the rate of floatation in: Using the rate of floatation in
sodium chloride solution leading to their sequentialsodium chloride solution leading to their sequential
separation intoseparation into chylomicronschylomicrons, very low density, very low density
lipoproteins (lipoproteins (VLDL or pre-VLDL or pre-ββ-lipoproteins-lipoproteins), low), low
density lipoproteins (density lipoproteins (LDL orLDL or ββ-lipoproteins-lipoproteins), high), high
density lipoproteins (density lipoproteins (HDL orHDL or αα-lipoproteins-lipoproteins) and) and
albumin-free fattyalbumin-free fatty acids complex.acids complex.
2.2. ElectrophoresisElectrophoresis:: is the migration of chargedis the migration of charged
particles in an electric field either to the anode or toparticles in an electric field either to the anode or to
the cathode. It sequentially separates thethe cathode. It sequentially separates the
lipoproteins intolipoproteins into chylomicronschylomicrons,, pre-pre-ββ-,-, ββ-, and-, and αα--
lipoprotein andlipoprotein and albumin-free fattyalbumin-free fatty acids complexacids complex.
Polar lipids
(phospholipids)
Nonpolar lipids
(cholesterol and its esters
and triacylglycerols)
Structure of a plasma lipoprotein complex
Polar apolipoproteins

a) Chylomicronsa) Chylomicrons: They have the largest diameter andThey have the largest diameter and
the least density. They containthe least density. They contain 1-2% protein1-2% protein only andonly and
98-99% fat98-99% fat. The main lipid fraction is triglycerides. The main lipid fraction is triglycerides
absorbed from the intestine and they containabsorbed from the intestine and they contain smallsmall
amountsamounts of the absorbed cholesterol andof the absorbed cholesterol and
phospholipids.phospholipids.
b) Very low-density lipoproteins (VLDL) or pre-b) Very low-density lipoproteins (VLDL) or pre-
ββ-lipoproteins-lipoproteins: Their diameter is smaller thanTheir diameter is smaller than
chylomicrons. They contain aboutchylomicrons. They contain about 7-10% protein7-10% protein andand
90-93% lipid90-93% lipid. The lipid content is mainly triglycerides. The lipid content is mainly triglycerides
formed in the liver. They contain phospholipid andformed in the liver. They contain phospholipid and
cholesterolcholesterol more thanmore than chylomicrons.chylomicrons.
c) Low-density lipoproteins (LDL) or) Low-density lipoproteins (LDL) or ββ--
lipoproteinslipoproteins: They containThey contain 10-20% proteins10-20% proteins in thein the
form of apolipoprotein B. Theirform of apolipoprotein B. Their lipid content varieslipid content varies
from 80-90%.from 80-90%. They contain about 60% of total bloodThey contain about 60% of total blood
cholesterol and 40% of total blood phospholipids. Ascholesterol and 40% of total blood phospholipids. As
their percentage increases, the liability totheir percentage increases, the liability to
atherosclerosis increases.atherosclerosis increases.

d) High-density lipoproteins (HDL) ord) High-density lipoproteins (HDL) or αα--
LipoproteinsLipoproteins: They containThey contain 35-55% proteins35-55% proteins
in the form of apolipoprotein A. They containin the form of apolipoprotein A. They contain
45-65% lipids45-65% lipids formed of cholesterol (formed of cholesterol (40% of40% of
total blood contenttotal blood content) and phospholipids () and phospholipids (60%60%
of total blood contentof total blood content). They act as). They act as
cholesterolcholesterol scavengersscavengers, as their percentage, as their percentage
increases, the liability to atherosclerosisincreases, the liability to atherosclerosis
decreases. They are higher in females than indecreases. They are higher in females than in
males. Due to their high protein content theymales. Due to their high protein content they
possess the highest density.possess the highest density.
e) Albumin-free fatty acids complex:e) Albumin-free fatty acids complex: It is aIt is a
proteolipid complex withproteolipid complex with 99% protein99% protein contentcontent
associated with long-chain free fatty acidsassociated with long-chain free fatty acids
for transporting them.for transporting them.

Cholesterol:Cholesterol:
• Importance:Importance: --
• It is the most important sterol in animal tissues asIt is the most important sterol in animal tissues as
free alcoholfree alcohol or in an esterified form (or in an esterified form (with linoleicwith linoleic,,
oleic, palmitic acids or other fatty acidsoleic, palmitic acids or other fatty acids).).
• Steroid hormones, bile salts and vitamin D areSteroid hormones, bile salts and vitamin D are
derivatives from it.derivatives from it.
• Tissues contain different amounts of it that serve aTissues contain different amounts of it that serve a
structural and metabolic role, e.g.,structural and metabolic role, e.g., adrenal cortexadrenal cortex
content is 10%,content is 10%, whereas,whereas, brain is 2%,brain is 2%, others 0.2-others 0.2-
0.3%.0.3%.
• SourceSource:: - It is synthesized in the body from acetyl-It is synthesized in the body from acetyl-
CoA (1gm/day, cholesterol does not exist in plants)CoA (1gm/day, cholesterol does not exist in plants)
and is also taken in the diet (and is also taken in the diet (0.3 gm/day as in, butter,0.3 gm/day as in, butter,
milk, egg yolk, brain, meat and animal fat).milk, egg yolk, brain, meat and animal fat).

Physical propeties:Physical propeties:It has a hydroxyl group on C3, a
double bond between C5 and C6, 8 asymmetric
carbon atoms and a side chain of 8 carbon atoms.
• It is found in all animal cells, corpus luteum and
adrenal cortex, human brain (17% of the solids).
• In the blood (the total cholesterol amounts about 200
mg/dL of which 2/3 is esterified, chiefly to
unsaturated fatty acids while the remainder occurs
as the free cholesterol.
CH3
CH3
HO
CH3
CH3
CH3
Cholesterol

• Chemical propertiesChemical properties Intestinal bacteria reduceIntestinal bacteria reduce
cholesterol intocholesterol into coprosterol andcoprosterol and
dihydrocholesteroldihydrocholesterol..
• - It is also oxidized into- It is also oxidized into 7-Dehydrocholesterol7-Dehydrocholesterol andand
further unsaturated cholesterol with a secondfurther unsaturated cholesterol with a second
double bond betweendouble bond between C7 and C8.C7 and C8. When the skin isWhen the skin is
irradiated with ultraviolet light 7-irradiated with ultraviolet light 7-
dehydrocholesterol is converted to vitamindehydrocholesterol is converted to vitamin D3.D3.
This explains the value of sun light in preventingThis explains the value of sun light in preventing
ricketsrickets..
CH3
CH3
HO
CH3
CH3
CH3
Coprosterol,
in feces
H
CH3
CH3
HO
CH3
CH3
CH3
Dihydrocholesterol,
in blood and other tissues
H

• ErgosterolErgosterol differs from 7-dehydrocholesterol indiffers from 7-dehydrocholesterol in
the side chain. Ergosterol is converted to vitamin D2the side chain. Ergosterol is converted to vitamin D2
by irradiation with UV Ergosterol and 7-by irradiation with UV Ergosterol and 7-
dehydrocholesterol are called Pro-vitamins D ordehydrocholesterol are called Pro-vitamins D or
precursors of vitamin D.precursors of vitamin D.
• - It was first isolated from ergot, a fungus then from- It was first isolated from ergot, a fungus then from
yeast. Ergosterol is less stable than cholesterolyeast. Ergosterol is less stable than cholesterol
((because of having 3 double bondsbecause of having 3 double bonds).).
CH3
CH3
HO
CH3
CH3
CH3
7-dehydrocholesterol
CH3
CH3
HO
CH3
CH3
CH3
Ergosterol
CH3

SteroidsSteroids
• Steroids constitute an important class ofSteroids constitute an important class of
biological compounds.biological compounds.
• Steroids are usually found in associationSteroids are usually found in association
with fat. They can be separated from fatswith fat. They can be separated from fats
after saponification since they occur in theafter saponification since they occur in the
unsaponifiable residue.unsaponifiable residue.
• They areThey are derivatives of cholesterolderivatives of cholesterol that isthat is
formed of steroid ring or nucleus.formed of steroid ring or nucleus.
• Biologically important groups of substances,Biologically important groups of substances,
which contain this ring, are:which contain this ring, are:
1.1. Sterols.Sterols.
2.2. Adrenal cortical hormones.Adrenal cortical hormones.
3.3. Male and female sex hormones.Male and female sex hormones.
4.4. Vitamin D group.Vitamin D group.
5.5. Bile acids.Bile acids.
6.6. Cardiac glycosides.Cardiac glycosides.

• General consideration about naturally occurring steroidsGeneral consideration about naturally occurring steroids:
A typical member of this groupA typical member of this group is cholesterolis cholesterol. Certain facts. Certain facts
have to be considered when drawing steroid formulahave to be considered when drawing steroid formula:
1) There is always oxygen in the form of1) There is always oxygen in the form of hydroxyl or ketone onhydroxyl or ketone on
C3C3..
2) Rings2) Rings C and D are saturatedC and D are saturated (stable).(stable).
3) Methyl groups at3) Methyl groups at C18 C19C18 C19. In case of vitamin D,. In case of vitamin D, the CH3the CH3
group at C19 becomes a methylene group (=CH2) and the ringgroup at C19 becomes a methylene group (=CH2) and the ring
B is opened, whereas,B is opened, whereas, this methyl group is absent in femalethis methyl group is absent in female
sex hormones (estrogens).sex hormones (estrogens).
4) In estrogens (female sex hormones) ring A is aromatic and4) In estrogens (female sex hormones) ring A is aromatic and
there isthere is no methyl group on C10.no methyl group on C10.
CH3
CH3
HO
Steroid ring
1
2
3 4
5
6 7
8
9
10
11
12
13
14 15
1617
18
19
A B
C D

• Bile acidsBile acids:
• They are produced from oxidation of cholesterol inThey are produced from oxidation of cholesterol in
the liver producingthe liver producing cholic and chenodeoxycholiccholic and chenodeoxycholic
acidsacids that are conjugated withthat are conjugated with glycine or taurineglycine or taurine toto
produceproduce glycocholic,glycocholic, glycochenodeoxycholic,glycochenodeoxycholic,
taurocholictaurocholic and taurochenodeoxycholic acids.and taurochenodeoxycholic acids.
They react with sodium or potassium to produceThey react with sodium or potassium to produce
sodiumsodium oror potassium bile saltspotassium bile salts..
• Their function is as followsTheir function is as follows:
1.1. Emulsification of lipids during digestion.Emulsification of lipids during digestion.
2.2. Help in digestion of the other foodstuffs.Help in digestion of the other foodstuffs.
3.3. Activation of pancreatic lipase.Activation of pancreatic lipase.
4.4. Help digestion and absorption of fat-solubleHelp digestion and absorption of fat-soluble
vitamins.vitamins.
5.5. Solubilizing cholesterol in bile and prevent gallSolubilizing cholesterol in bile and prevent gall
stone formation.stone formation.
6.6. Choleretic action (stimulate their own secretion).Choleretic action (stimulate their own secretion).
7.7. Intestinal antiseptic that prevent putrefactionIntestinal antiseptic that prevent putrefaction

CH3
CH3
HO
CH3
C
Sodium-tauro or
glyco-cholate
CH3
CH3
HO
CH3
C
Sodium-tauro or
glyco-chenodeoxycholate
OH
OH OH
O O
R1 or R2 R1 or R2
(CH2)2 SO3
-Na+H2NCH2 COO-Na+H2N
Sodium taurateSodium glycate
R1 R2

Chemistry of lipids

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