Lipids

LIPIDS
In pursuit of quality education
DR. USMAN SALEEM
Pharm.D, M.Phil. Scholar, R.Ph,
Lecturer Pharmaceutical Biochemistry
Rashid Latif College of Pharmacy

CHAPTER OUTLINES
 Chemistry of Fatty acids and Lipids
 Classification
 Saponifiable and non-saponifiable lipids
 Simple, Complex and Derived lipids
 Reactions of Fatty acids and other Lipids,
 Essential fatty acids,
 Biological and pharmaceutical importance of lipids.

1. Define and List the Functions of Lipids
Learning
Objective

DEFINITION
 The lipids are a heterogeneous group of compounds
related to fatty acids and include fats, oils, waxes and
other related substances.
 These are oily or greasy organic substances, relatively
insoluble in water, and considerably soluble in organic
solvents like ether, chloroform and benzene.
 The term ‘lipid’ was first used by the German biochemist
Bloor in 1943 for a major class of tissue components and
foodstuffs.

FUNCTIONS OR BIOLOGICAL IMPORTANCE
1. Storage form of energy (triacylglycerol)
2. Structural components of biomembranes (phospholipids and cholesterol)
3. Metabolic regulators (steroid hormones and prostaglandins)
4. Act as surfactants, detergents and emulsifying agents (amphipathic lipids)
5. Act as electric insulators in neurons

FUNCTIONS OR BIOLOGICAL IMPORTANCE
6. Provide insulation against changes in external temperature (subcutaneous
fat)
7. Give shape and contour to the body
8. Protect internal organs by providing a cushioning effect (pads of fat)
9. Help in absorption of fat soluble vitamins (A, D, E and K)
10. Improve taste and palatability of food.

2. Classify Lipids as Simple, Complex and
Derived, and as Saponifiable or
Nonsaponifiable.
Learning
Objective

CLASSIFICATION OF LIPIDS
 Two commonly used classification systems exist for lipids:
 A system based on chemical composition of lipids (Bloor’s Classification),
and
 A system based on particular chemical reaction (Saponification) that lipids
undergo.

 Bloor has proposed the following classification of lipids based on their
chemical composition.
1. Simple lipids: These are esters of fatty acids with various alcohols.
a) Neutral Fats (Triacylglycerol, TAG):
 These are esters of fatty acids with trihydroxy alcohol, glycerol. Oils are fats
in the liquid state.
b) Waxes:
 These are esters of fatty acids with higher molecular weight monohydric
alcohols.

2. Compound lipids: These are esters of fatty acids with alcohol and possess
additional group(s) also.
a) Phospholipids:
 These are lipids containing, in addition to fatty acids and glycerol, a
phosphoric acid, a nitrogen base and other substituents. For example, in
glycerophospholipids the alcohol is glycerol and in sphingophospholipids, the
alcohol is sphingosine.
b) Glycolipids:
 These are lipids containing a fatty acid, sphingosine, and carbohydrate.

3. Derived Lipids: These are compounds obtained by hydrolysis of simple of
compound lipids. These include fatty acids, alcohols, mono- and diglycerides,
steroids, terpenes and carotenoids.
 Glycerides and cholesterol esters, because of their uncharged nature, are
also called neutral lipids.

 Lipids are grouped into two main classes in the chemical reaction
(saponification) classification system:
1) Saponifiable lipids
2) Nonsaponifiable lipids.
 Saponification refers to the process in which esters are hydrolyzed under
basic conditions.

Saponifiable Lipids
 Saponifiable lipids are esters that
undergo hydrolysis in basic solution
to yield two or more smaller
product molecules.
 Triglycerides, waxes, phospholipids,
and sphingolipids are all belong to
this class.
Non-Saponifiable Lipids
 Nonsaponifiable lipids are not
esters and cannot be hydrolyzed
into smaller components.
 Steroids and prostaglandins belong
to this class.

3. Describe chemistry and classification
of fatty acids.
Learning
Objective

FATTY ACIDS
 Fatty acids are long, unbranched hydrocarbon chains with a carboxylic acid group at
one end.
 It is represented by a chemical formula R-COOH, where R stands for
hydrocarbon chain.
 Fatty acids are amphipathic compounds because the carboxyl group is
hydrophilic and the hydrocarbon tail is hydrophobic.
 The carboxyl group can ionize as the carboxylate anion (–COO- ) under the
proper conditions of physiological pH.

FIGURE: The molecular structure of fatty acid. A. Lauric acid and B. a simplified
diagram of a fatty acid with a nonpolar tail and a polar head.

FATTY ACIDS
• In aqueous solution, the ions of fatty
acids associate to form spherical
clusters, called micelles.
• In micelles, the nonpolar chains
extend toward the interior of the
structure away from water, and the
polar carboxylate groups face
outward in contact with the water.

FATTY ACIDS
 The fatty acids found in natural lipids have several characteristics in common:
1. They are usually straight-chain carboxylic acids (no branching).
2. The sizes of most common fatty acids range from 10 to 20 carbons.
3. Fatty acids usually have an even number of carbon atoms (including the
carboxyl group carbon).
4. Fatty acids can be saturated (containing no double bonds between
carbons) or unsaturated (containing one or more double bonds between
carbons).

FATTY ACIDS
5. In terms of carbon chain length, fatty acids are characterized as:
 Long-chain fatty acids (C12 to C26),
 Medium chain fatty acids (C8 and C10), or
 Short-chain fatty acids (C4 and C6).
6. Fatty acids are rarely found free in nature but rather occur as part of the
structure of more complex lipid molecules.

CLASSIFICATION OF FATTY ACIDS
 The hydrocarbon chain of a fatty acid may or may not contain carbon–carbon
double bonds.
 On the basis of this consideration, fatty acids are classified as:
1. Saturated fatty acids (SFAs),
2. Unsaturated Fatty Acids
3. Monounsaturated fatty acids (MUFAs), and
4. Polyunsaturated fatty acids (PUFAs).

1. Saturated Fatty Acids
 A saturated fatty acid is a fatty acid with a carbon chain in which all carbon–
carbon bonds are single bonds.
 Examples include:
 Propionic acid
 Palmitic acid
 Stearic acid

2. Unsaturated Fatty Acids
 They are classified further according to degree of unsaturation.
a) Monounsaturated Fatty Acids (MUFA’s)
b) Polyunsaturated Fatty Acids (PUFA’s)

a) Monounsaturated Fatty Acids
 A monounsaturated fatty acid
is a fatty acid with a carbon chain
in which one carbon–carbon
double bond is present.
 For example, Oleic acid is a
monounsaturated fatty acid,
that is found in nearly all fats.

b) Polyunsaturated Fatty Acids
 A polyunsaturated fatty acid is a fatty acid with a carbon chain in which
two or more carbon–carbon double bonds are present.
 Up to six double bonds are found in biochemically important PUFAs; they
include:
• Dienoic acids series have two double bonds, e.g. linoleic acid
• Trienoic acids series have three double bonds, e.g. linolenic acid
• Tetraenoic acid series with four double bonds, e.g. arachidonic acid

NOMENCLATURE OF FATTY ACIDS
 The systematic nomenclature of the fatty acids is based on the Genevan
system.
 According to this system, the fatty acid is named after the hydrocarbon with
the same number of carbon atoms.
 The suffix -oic is written in place of the final letter e in the name of the
hydrocarbon.
The names of saturated fatty acids end with the suffix –anoic e.g.,
Octadecanoic acid.
The names of unsaturated fatty acids end with the suffix –enoic e.g.,
Octadecenoic acid (Oleic acid).

 The position of carbon atoms in the
fatty acid chain is indicated either:
 By numbering - in which case the
carboxyl carbon is numbered as C1,
the carbon adjacent to C1 as C2 and
so on; or
 By the use of Greek letters - in which
case C2 is denoted as a-carbon, C3 as
b-carbon and so on, while the
terminal methyl (-CH3) carbon is
known as w-carbon.

 The notation most commonly used for fatty acids indicates the:
• Number of carbon atoms, and
• Number of double bonds.
 The notation 18:0 denotes an C18 fatty acid with no double bonds, while 18:1
signifies an C18 fatty acid with one double bond.

 To specify double-bond positioning within the carbon chain of an
unsaturated fatty acid, the preceding notation is expanded by adding the
Greek capital letter delta (D) followed by one or more superscript numbers.
 The notation 18:3(D9,12,15) denotes a C18 PUFA with three double bonds at
locations between carbons 9 and 10, 12 and 13, and 15 and 16.

SELECTED FATTY ACIDS OF BIOLOGICAL IMPORTANCE
Saturated Fatty Acids
Common Name Structural
Notation
Formula Common Sources
Lauric Acid 12:0
CH3(CH2)10COOH Laurel oil, Spermaceti
Myristic Acid 14:0
CH3(CH2)12COOH Butter and wool fat
Palmitic Acid 16:0
CH3(CH2)14COOH Palm Oil
Stearic Acid 18:0
CH3(CH2)16COOH Animal and plant fats
Arachidic Acid 20:0
CH3(CH2)18COOH Peanut Oil

SELECTED FATTY ACIDS OF BIOLOGICAL IMPORTANCE
Unsaturated Fatty Acids
Common
Name
Structural
Notation
Formula Common
Sources
Oleic Acid 18:1 – D9
CH3(CH2)7CH=CH(CH2)7COOH
Animal and plant
fats
Linoleic Acid 18:2 – D9,12
CH3(CH2)4CH=CH(CH2)CH=CH(CH2)7COOH
Peanut &
cottonseed Oil
Linolenic Acid 18:3 – D9,12,15
CH3(CH2CH=CH)3(CH2)7COOH Linseed Oil
Arachidonic
Acid
20:4 – D5,8,11,14
CH3 (CH2)4(CH=CHCH2) 4(CH2)2COOH Animal fats

ISOMERISM IN FATTY ACIDS
 The unsaturated fatty acids exhibit geometric (or cis-trans) isomerism at the
double bonds.
 In biochemically important MUFAs, the configuration about the double bond
is nearly always cis rather than trans.
 ‘Cis’ form is comparatively unstable and is more reactive.
 For example, Oleic acid can exist in two forms: cis-oleic acid and trans-oleic
acid which is also called elaidic acid.

ISOMERISM IN FATTY ACIDS
 ‘Cis’ configuration creates a
rigid 30o
bend, or kink, in the
fatty acid chain that is not
found in saturated fatty acids.
 Such a bend affects the
physical properties of a fatty
acid.

ESSENTIAL FATTY ACIDS
 Essential fatty acids are those polyunsaturated fatty acids that cannot be
synthesized by our cells and we should obtain them from plants through diet.
 Linoleic acid and linolenic acid are the only essential fatty acids for animals.
 Other polyunsaturated fatty acids can be synthesized from these essential
fatty acids.
 For example, arachidonic acid can be synthesized only from linoleic acid.
 Therefore, in deficiency of linoleic acid, arachidonic acid also becomes an
essential fatty acids.

IMPORTANCE OF ESSENTIAL FATTY ACIDS
 Linoleic acid is the starting material for the biosynthesis of arachidonic acid.
 Arachidonic acid is the major starting material for eicosanoids, substances
that help regulate blood pressure, clotting, and several other important body
functions.
 Linolenic acid is the starting material for the biosynthesis of two additional
omega-3 fatty acids.
Linolenic acid (18:3) → EPA (20:5) → DHA (22:6)

IMPORTANCE OF ESSENTIAL FATTY ACIDS
 EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are important
constituents of the communication membranes of the brain and are necessary
for normal brain development.
 EPA and DHA are also active in the retina of the eye.

NEUTRAL FATS
(TRIACYLGLYCEROLS (TAG) OR TRIGLYCERIDES)
 Triacylglycerol, also called triglycerides, are composed of three fatty acids
bonded by an ester linkage to glycerol.

TYPES OF NEUTRAL FATS
 Triacylglycerol are of two types:
1. Simple Triacylglycerol
2. Mixed Triacylglycerol
 Naturally occurring simple triacylglycerols are rare.
 Most biochemically important triacylglycerols are mixed triacylglycerols.

1. Simple Triacylglycerol
 These types of triacylglycerol
contain the same types of fatty
acids at the three carbon atoms.
 The triacylglycerol produced from
glycerol and three molecules of
stearic acid is an example of a
simple triacylglycerol.

ACTIVITY
Draw the structural formula of the triacylglycerol produced from the
reaction between glycerol and three molecules of Lauric acid.

2. Mixed Triacylglycerol
 These types of triacylglycerol
contain more than one kind of
fatty acid molecule.
 Figure shows the structure of a
mixed triacylglycerol in which one
fatty acid is saturated, another
monounsaturated, and the third
polyunsaturated.

FATS AND OILS
FATS
 A fat is a triacylglycerol mixture that
is a solid or a semi-solid at room
temperature (25◦C).
 Generally, fats are obtained from
animal sources.
 All fats, even highly saturated fats,
contain some unsaturated fatty
acids.
OILS
 An oil is a triacylglycerol mixture
that is a liquid at room temperature
(25 ◦C).
 Generally, oils are obtained from
plant sources.
 All oils, even polyunsaturated oils,
contain some saturated fatty acids.

5. Write key reactions for fats and oils.
Learning
Objective

CHEMICAL REACTIONS OF TRIACYLGLYCEROLS
1. Hydrolysis
 Fats can be hydrolyzed in the presence of an acid or a base.
 Under acidic conditions, the hydrolysis products are glycerol and fatty acids.
 Under basic conditions, the hydrolysis products are glycerol and fatty acid
salts.
 Within the human body, triacylglycerol hydrolysis occurs during the process
of digestion by the specific fat-splitting enzymes called lipases, for example
pancreatic lipase.

 Triacylglycerol is sequentially hydrolyzed to diacylglycerol and
monoacylglycerol and finally glycerol plus 3 fatty acids.

2. Saponification
 Hydrolysis of a fat by an alkali such as sodium hydroxide or potassium
hydroxide is called saponification.
 For fats and oils, the products of saponification are glycerol and fatty acid
salts.

3. Hydrogenation
 Hydrogenation involves hydrogen addition across carbon–carbon double
bonds, which increases the degree of saturation as some double bonds are
converted to single bonds.

 Many food products are produced via partial hydrogenation.
 In partial hydrogenation some, but not all, of the double bonds present are
converted into single bonds.
 In this manner, liquids (usually plant oils) are converted into semi-solid
materials.
 This is the basis of Banaspati (Dalda) manufacture, where inedible and cheap
oils like cotton seed oil are hydrogenated and converted to edible solid fat.

4. Oxidation
 Fats very rich in unsaturated fatty acids such as linseed oil undergo spontaneous
oxidation at the double bond forming aldehyde and carboxylic acid products.
 The short-chain aldehydes and carboxylic acids so produced often have
objectionable odors, and fats and oils containing them are said to have become
rancid.
 To avoid this unwanted oxidation process, commercially prepared foods
containing fats and oils always contain antioxidants.
 Two naturally occurring antioxidants are vitamin C and vitamin E.

5. Rancidity
 The unpleasant taste and odor developed by most natural fats on aging is refereed
to as rancidity.
 Hydrolytic rancidity is due to partial hydrolysis of the fats due to traces of
hydrolytic enzymes present in naturally occurring fats and oils.
 Oxidative rancidity is the result of partial oxidation of unsaturated fatty acids
with resultant formation of epoxides and peroxides of small molecular weight fatty
acids by peroxides and free radicals.
 The same process, if it occurs in vivo will affect the integrity of biomembranes,
leading to cell death.

 Many natural vegetable fats and oils may contain antioxidants like vitamin E
which prevent onset of rancidity. Therefore, vegetable fats can be preserved
for a longer time than animal fats.

CHARACTERIZATION OF FAT OR
IDENTIFICATION OF FATS AND OILS (FAT CONSTANTS)
 Fat constants or numbers are test necessary to:
 Identify a pure fat
 Assess the degree of adulteration
 Determine the proportions of different types of fat in a mixture

1. Saponification Number
 Saponification number is defined as the number of milligrams of potassium
hydroxide required to saponify one gram of fat.
 It is inversely proportional to the molecular weight of fat.
 This value is high in fats containing a short chain fatty acids.
 For example, the saponification number of:
 Butter = 220
 Coconut oil = 260

2. Acid Number
 Acid number is the number of milligrams of KOH required to neutralize the free
fatty acids present in one gram of fat.
 It is used for the detection of hydrolytic rancidity because it measures the
amount of free fatty acids present.
 Acid number is directly proportional to the rancidity.

3. Iodine Number
 Iodine number is the number of grams of iodine absorbed by 100 grams of fat.
 It is an index of the degree of unsaturation and is directly proportional to
the content of unsaturated fatty acids.
 Higher the iodine number, higher is the degree of unsaturation, e.g.
 Butter = 28,
 Sunflower oil = 130

4. Acetyl Number
 Acetyl number is the number of milligrams of KOH needed to neutralize the
acetic acid liberated from hydrolysis of 1gm of acetylated fat.
 The natural fat that contains fatty acids with free hydroxyl groups are
converted into acetylated fat by reaction with acetic anhydride.
 Thus, acetyl number is a measure of the amount of hydroxy fatty acids in
fat content.

 Castor oil because of its high content of ricinoleic acid has a high acetyl
number.
 Acetyl number of some oils are:
 Castor oil = 146-150
 Cod Liver oil = 1.1
 Cotton Seed oil = 21-25
 Olive oil = 10.5

4. Reichert Meissl Number
 Reichert-Meissl number is the numbers of milliliters of 0.1N alkali required to
neutralize the volatile acid obtained from 5g of a fat, which has been saponified
then acidified to liberate the fatty acids and then steam distilled.
 It is also known as volatile fatty acid number.
 Reichert Meissl value for:
 Butter = 26
 Coconut oil = 7.

 It is less than one for other edible oils.
 The admixture of certain fats may be used to prepare synthetic butter which
may simulate butter in most of the constants except RM value and hence,
can be detected.

WAXES
 Waxes are esters of long-chain saturated and
unsaturated fatty acids with long-chain
monohydroxy alcohols.
 The fatty acids range in between C14 and C36
and the alcohols range from C16 to C36.

WAXES
 Beeswax, for example, contains a wax (1-triacontyl palmitate) with the following
structure:

WAXES
 Waxes generally have higher melting points than fats (60 to 100°C) and are
harder.
 Animals and plants often use them for protective coatings.
 In plants, waxes are secreted as surface coating to prevent excessive
evaporation and to protect against parasites.
 In animals, waxes are secreted by cutaneous glands as a protective coating to
keep the skin pliable, lubricated and water-proof.

WAXES
 Important waxes include carnauba wax (from a Brazilian
palm tree), lanolin (from lamb’s wool), beeswax, and
spermaceti (from whales).
 These substances are used to make cosmetics, polishes,
candles, and ointments.
 Sperm whale wax (spermaceti) and beeswax are composed
mainly of palmitic acid esterified with either
hexacosanol, CH3(CH2)24.CH2OH or triacontanol,
CH3(CH2)28.CH2OH.

6. What are Complex or Compound
Lipids?
Learning
Objective

7. Describe chemistry and classification
of Phospholipids.
Learning
Objective

PHOSPHOLIPIDS
 Phospholipids are the most abundant membrane lipids.
 They serve primarily as structural components of membranes and are never
stored in large quantities.
 They differ from triglycerides in possessing usually one hydrophilic polar
“head” group and usually two hydrophobic nonpolar “tails”.
 For this reason, they are often called polar lipids.

 There are two classes of phospholipids:
A. Glycerophospholipids or Phosphoglycerides
B. Sphingophospholipids or Phosphosphingosides

PHOSPHOLIPIDS
A. Glycerophospholipids
 In these compounds, glycerol is linked by ester bonds to two fatty acids and
one phosphate, which in turn is linked by ester bond to another alcohol
(usually amino alcohol).
 Phosphoglycerides serve as a major component of cell membranes.

PHOSPHOLIPIDS
 The alcohol attached to the phosphate group in a phosphoglyceride is usually
one of three amino alcohols: choline, ethanolamine, or serine.

PHOSPHOLIPIDS
 Phosphoglycerides containing these three amino alcohols are respectively
known as phosphatidylcholines, phosphatidylethanolamines, and
phosphatidylserines.
 Phosphatidylcholines are also known as lecithins.
 Phosphatidylethanolamines and phosphatidylserines are also known as
cephalins.
 Another important group of glycerophospholipids is the phosphatidylinositols
(PI), in which the alcohol is inositol.
 In phosphatidylinositol, inositol is present as the stereoisomer myoinositol.

PHOSPHOLIPIDS
a) Lecithins
 Various oil seeds like soybean and the yeasts are important sources from
plant world.
 In animals, they are distributed in liver, brain, nerve tissues, sperm and egg
yolk.
 Dipalmitoyl lecithin is an important phosphatidylcholine found in lungs,
secreted by pulmonary type II epithelial cell.
 It acts as a lung surfactant and is necessary for normal lung function.
 It reduces surface tension in the alveoli, thereby prevents alveolar collapse.

ACTIVITY
 Draw the structural formula for the glycerophospholipid that
produces, upon hydrolysis, equimolar amounts of glycerol,
phosphoric acid, and choline, and twice that molar amount of
palmitic acid, the 16:0 fatty acid.

PHOSPHOLIPIDS
b) Cephalins
 Phosphoglycerides in which the alcohol is ethanolamine or serine, rather
than choline, are called cephalins.
 These compounds are found in heart and liver tissue and in high
concentrations in the brain.
 They are also found in blood platelets, where they play an important role in
the blood-clotting process.

PHOSPHOLIPIDS
c) Phosphatidylinositol
 Another important group of glycerophospholipids is the
phosphatidylinositols (PI), in which the alcohol is inositol.
 In phosphatidylinositol, inositol is present as the stereoisomer myoinositol.
 Phosphatidylinositols in their higher phosphorylated form, such as
phosphatidylinositol 4,5-bisphosphates (PIP2), serve as signaling molecules in
chemical communication.

PHOSPHOLIPIDS
 Two less common phosphoglycerides are:
i. Plasmalogens
ii. Cardiolipins

PHOSPHOLIPIDS
d) Plasmalogens
 Plasmalogens constitute about 10% of the phospholipids of the brain and
muscle.
 Structurally, these resemble lecithins and cephalins but have one of the
fatty acids replaced by an unsaturated ether.
 These are found in myelin and in cardiac muscle.
 Plasmalogen is a platelet activating factor (PAF) and involved in platelet
aggregation and degranulation.

PHOSPHOLIPIDS
e) Cardiolipin
 Cardiolipins are present in abundance in inner mitochondrial membranes,
and their complete hydrolysis yields:
 Four molecules of fatty acids
 Three glycerol molecules
 Two phosphate ions

PHOSPHOLIPIDS
B. Phosphosphingosides
 A phosphosphingosides is a lipid that contains one fatty acid and one
phosphate group attached to a sphingosine molecule and an alcohol attached
to the phosphate group.
 All phospholipids derived from sphingosine have:
1. the fatty acid attached to the sphingosine —NH2 group via an amide
linkage,
2. the phosphate group attached to the sphingosine terminal —OH
group via an ester linkage, and
3. an additional alcohol esterified to the phosphate group.

PHOSPHOLIPIDS
B. Phosphosphingosides
 Sphingophospholipids in which
the alcohol esterified to the
phosphate group is choline are
called sphingomyelins.
 Sphingomyelins are found in all
cell membranes and are
important structural
components of the myelin
sheath.

GLYCOLIPIDS OR SPHINGOGLYCOLIPIDS
 A glycolipid is a complex lipid that contains both a fatty acid and a
carbohydrate component attached to a sphingosine molecule.

a. Cerebrosides
 Cerebrosides are the simplest sphingoglycolipid that contain a
single monosaccharide unit—either glucose or galactose and
named as glucocerebrosides and galactocerebrosides.
 Cerebrosides are present in high concentrations in the white
matter of the brain as well as in myelin sheathes.

a. Cerebrosides
 Four types of cerebrosides have been characterized, depending upon the type of
fatty acids they contain.
 Kerasin−contains saturated C 24 lignoceric acid.
 Phrenosin (cerebron)−contains a 2-hydroxy derivative of lignoceric acid called
cerebronic acid.
 Nervon−contains an unsaturated homologue of lignoceric acid called nervonic
acid,
 Oxynervon−contains a 2-hydroxy derivative of nervonic acid called oxynervonic
acid.

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b. Gangliosides
 Gangliosides are more complex glycolipids that contain a branched chain of
up to seven monosaccharide residues.
 Gangliosides also generally contain sialic acid, which is usually N-
acetylneuraminic acid (NANA) attached to ceramide (N-acylsphingosine).
 These substances occur in the gray matter of the brain as well as in the myelin
sheath.

b) Gangliosides
 Several types of gangliosides such as GM1, GM2, GM3, etc. have been isolated
from brain and other tissues.
 The simplest ganglioside found in tissues is GM3.

7. What are Derived Lipids?
Learning
Objective

DERIVED LIPIDS
 Unsponifiable compounds obtained by hydrolysis of simple or compound
lipids are called derived lipids.
 Derived lipids include prostaglandins and related compounds, fat soluble
vitamins and steroids.

EICOSANOIDS
 Eicosanoids are the compounds derived from arachidonic acid that function
as messenger lipids.
 There are three principal types of eicosanoids:
1. Prostaglandins
2. Leukotrienes
3. Thromboxanes

PROSTAGLANDINS
 Prostaglandins were first detected in the seminal fluid, which is produced by
the prostate gland and hence the name.
 Chemically, they are considered to be derived from 20C cyclic saturated fatty
acid, prostanoic acid.

PROSTAGLANDINS
 Some of the functions of prostaglandins are:
• Control of blood pressure
• Stimulation of smooth muscle contraction
• Induction of inflammation
• Inhibition of platelet aggregation

LEUKOTRIENES
 Leukotrienes are compounds that, like prostaglandins, are derived from
arachidonic acid.
 They are found in leukocytes (white blood cells) and have three conjugated
double bonds; these two facts account for the name.

LEUKOTRIENES
 Various inflammatory and hypersensitivity (allergy) responses are associated
with elevated levels of leukotrienes.
 Leukotriene C produce long-lasting muscle contractions, especially in the
lungs, and can cause asthma-like attacks.
 One way to counteract the effects of leukotrienes is to inhibit their uptake by
leukotriene receptors (LTRs) in the body.
 A new antagonist of LTRs, zafirlukast, is used to treat and control chronic
asthma.

THROMBOXANES
 Thromboxanes contain cyclic ethers as part of their structures.
 These compounds were called thromboxanes because they were first isolated
from thrombocytes.
 The most widely studied member of the group, thromboxane A2 (TxA2), is
known to induce platelet aggregation and smooth-muscle contraction.

STEROIDS
 Steroids are a group of compounds that
contain cyclopentanoperhydrophenanthrene
ring structure.
 This ring is present in steroid hormones, bile
acids, cholesterol etc.

CHOLESTEROL
 Cholesterol is a C27 steroid molecule that is a component of cell membranes
and a precursor for other steroid-based lipids.
 Cholesterol is amphipathic, with a:
 Polar head, the hydroxyl group at C3 and a
 Nonpolar the steroid nucleus and hydrocarbon side chain at C17.
 Most of the cholesterol in the body exists as a cholesterol ester, with a fatty
acid attached to the hydroxyl group at C3.

CHOLESTEROL
 Cholesterol is widely distributed in all the cells of the body but particularly in
nervous tissue.
 It is synthesized in our body as well as supplied in the diet.
 Cholesterol serves as the precursor for a variety of biologically important
products, including: steroid hormones, bile acids and fat soluble vitamins.
 It is a major structural constituent of the cell membranes and plasma
lipoproteins.

BILE ACIDS
 A bile acid is a cholesterol derivative that functions as a lipid-emulsifying
agent in the aqueous environment of the digestive tract.
 Approximately one-third of the daily production of cholesterol by the liver is
converted to bile acids.

BILE ACIDS
 Obtained by oxidation of cholesterol, bile acids differ structurally from
cholesterol in three respects:
1. They are tri- or dihydroxy cholesterol derivatives.
2. The carbon 17 side chain of cholesterol has been oxidized to a carboxylic
acid.
3. The oxidized acid side chain is bonded to an amino acid (either glycine or
taurine) through an amide linkage.
 The presence of this amino acid attachment increases both the polarity of the
bile acid and its water solubility.

BILE ACIDS
 The three major types of bile acids produced from cholesterol by biochemical
oxidation are:
 Cholic acid,
 7-deoxycholic acid, and
 12-deoxycholic acid.

Lipids

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