Lipids composition- Glycerol and fatty acids. Classification of fatty acids

1. LIPIDS
(COMPONENTS)
FORTH SEM BIOCHEMISTRY

2. LIPIDS
 The term ‘Lipids’ first coined by German Biochemist Bloor in 1943
 Lipids are important heterogenous group of organic substances in plant and
animal tissue
 Chief concentrated storage form of energy
 These are related either actually or potentially to the fatty acids
 Chemically these are esters of alcohol (commonly glycerol)with fatty acids
 Insoluble in water and soluble in nonpolar organic solvents like ether,
chloroform, acetone, benzene etc( fat solvents)
 Hydrophobic in nature
 Oily or greasy substances
 Unlike carbohydrates and proteins these are not polymers
 Lipids are mostly small molecules
 In addition to alcohol and fatty acids, some of the lipids may contain
phosphoric acid, nitrogenous base and carbohydrates.
“Lipids may be regarded as organic substances relatively insoluble in water, soluble in organic
solvents actually or potentially related to fatty acids and utilized by the living cells.”

3. Functions of lipids
 Storage form of energy (triglycerides)
 Structural components of biomembranes (phospholipids and cholesterol)
 Metabolic regulators (steroid hormones and prostaglandins)
 Act as surfactants, detergents and emulsifying agents (amphipathic lipids)
 Act as electric insulators in neurons
 Provide insulation against changes in external temperature (subcutaneous
fat)
 Give shape and contour to the body
 Protect internal organs by providing a cushioning effect (pads of fat)
 Help in absorption of fat soluble vitamins (A, D, E and K)
 Improve taste and palatability of food.

4. Composition of lipids1.ALCOHOL
 The alcohol found in lipids are saturated
 It include glycerol and higher alcohol such as cetyl alcohol, myricyl
alcohol etc
 The unsaturated alcohol present in lipids are pigments like phytol
(constituent of chlorophyll), lycophyll (pigment in tomato)
 Glycerol is the most common alcohol present in lipids
 Glycerol is a 3C compound. The 1st and 3rd C atom are identical
Glycerol
Cetyl alcohol
CH3-(CH2)14-CH2OH
Myricyl alcohol
CH3-(CH2)28-CH2OH

5. Composition of lipids2.FATTYACID
 Fatty acids (FA)are the carboxylic acids with hydrocarbon side chain
 General formula, R—CO—OH, where COOH (carboxylic group) represents
the functional group
 Depending on the R group (the hydrocarbon chain), the physical properties of
fatty acids may vary
 These are long chain organic acids having usually 4- 30 carbon atoms
 It contains only one carboxylic group (monocarboxylic)
 The nonpolar hydrocarbon tail makes the lipids hydrophobic in nature and
oily or greasy
 Contains even number of carbon atoms as these are synthesized from 2C
units.
 These are usually straight chain derivatives. Still other possess ring structure
(cyclic FA)
 Some contains hydroxyl groups (hydroxy or oxygenated fatty acids)
 Do not occur in free state in tissues ,found in covalently bound form
 If free, the carboxyl group of fatty acid will be ionized

6. Fatty acids

7. Nomenclature of fatty acid
 The systemic name is based on the hydrocarbon from which is derived
(Genevan system)
 The saturated fatty acid end with a suffix –anoic (eg: octanoic acid) while the
unsatuated fatty acid end with suffix –enoic (eg: octadecenoic acid)
 The position of C atom in the fatty acid chain is indicated either by numbering
(1,2,3 etc) or by use of Greek letters (α,β etc)
 The numbering starts from the carboxyl carbon (from the –COOH carbon) –
carbon No.1. (C1)
 The carbon adjacent to –COOH group - carbon number 2 (α-carbon), then
carbon atom 3 (β-carbon) and so on.
 The end –CH3 carbon is known as the ω-carbon (‘Omega’ carbon).
 starting from the methyl end, the carbon atoms may be numbered as omega
(ω)-1,2,3, etc.
6 5 4 3 2 1
CH3 — CH2 — CH2 — CH2— CH2 — COOH
ω1 ω2 ω3 ω4 ω5
6 5 4 3 2 1
CH3 — CH2 — CH2 — CH2— CH2 — COOH
ω δ γ β α

8. Nomenclature of fatty acid (conts…)
 Widely used convention to indicate the number and position of the double bond(s) in
the case of unsaturated fatty acids is to write the number of carbon atoms, the number
of double bond(s) and the position of the double bonds(s) below the name of the acid.
 For example,
1. Oleic acid having 18 carbon atoms and a double bond between carbon atoms 9 and 10
is written as 18:1; 9.
2. Linoleic acid (18 carbon atoms and 2 double bonds at C 9 and C 12) is written as 18:2;
9, 12.
 An alternative method to write the name of an unsaturated fatty acid is to write first
the position of double bond(s) in numerals and then the total number of carbon atoms
in Roman followed by the suffix -enoic acid.
 Eg :
1. Oleic acid written as 9-octadecenoic acid and
2. Linoleic acid written as 9, 12-octadecadienoic acid.
 Other representations
∆ represents double bonds-eg: ∆9 indicates double bond is between 9 and 10
ω – eg: ω6 series indicates double bond is between 6 and 7 from the ω end.

9. Classification of fatty acids
1.Based on the presence or absence of double bond
• Saturated FA (no =bond)
• Unsaturated FA (1 or more =bond)
2. Based on nature of chain
• Straight chain FA
• Branched chain FA
• Cyclic fatty acids
• Hydroxy or oxygenated fatty acids
3. Based on total number of carbon atoms
• Even chain FA
• Odd chain FA
4. Based non length of hydrocarbon chain
• Short chain FA (2 to 6 carbon atoms)
• Medium chain FA (8 to 14 carbon atoms)
• Long chain FA (16 to 22 carbon atoms)
• Very long chain FA (>24 carbon atoms)

10. 1.Based on the presence or absence of double bond
1. SATURATED FATTY ACIDS
>Contains only single bonds
>The general formula for these acids is CnH2n+1COOH.
>Eg: butanoic acid (C4) - C3H7COOH or CH3-CH2-COOH or
CH3-(CH2)2-COOH
>Saturated fatty acids may found in
a. Straight chain fatty acids
#Even numbered-eg:palmitic acid(16C), stearic acid (18C)
#Odd numbered- eg: propionic acid(3C), Valeric acid(5C)
b. Branched chain fatty acids
#Even numbered –eg: Isopalmitic acid(16C)
#Odd numbered- eg: Anteisopalmitic acid(17C),
Tuberculostearic acid (19C)

11. STRAIGHT CHAIN - EVEN NUMBERED FATTY ACIDS
Trivial name Systemic name Carbon
skeleton
structure Common source
Acetic acid Ethanoic acid 2 : 0 CH3COOH Vinegar
Butyric acid n-Butanoic acid 4 : 0 CH3 (CH2)2COOH Butter
Caproic acid n-Hexanoic acid 6 : 0 CH3 (CH2)4COOH Butter, Coconut oil and
palm oils
Caprylic acid n-Octanoic acid 8 : 0 CH3 (CH2)6COOH Coconut oil and
palm oils
Capric acid n-Decanoic acid 10 : 0 CH3 (CH2)8COOH Coconut oil and
palm oils
Lauric acid (laurus=laurel
plant)
n-Dodecanoic acid 12 : 0 CH3 (CH2)10COOH Laurel oil,
Spermaceti
Myristic acid
(Myristica=nutmeg)
n-Tetradecanoic acid 14 : 0 CH3 (CH2)12COOH Butter and wool
Fats
Palmitic acid
(palma = palm tree)
n-Hexadecanoic acid 16 : 0 CH3 (CH2)14COOH Body fat
Stearic acid
(stear = hard fat)
n-Octadecanoic acid 18 : 0 CH3 (CH2)16COOH Body fat
Arachidic acid
(Arachis = legume )
n-Eicosanoic acid 20 : 0 CH3 (CH2)18COOH Peanut oil (Arachis oil)
Behenic acid n-Docosanoic acid 22 : 0 CH3 (CH2)20COOH Groundnut oil
Lignoceric acid
(lignum=wood; cera = wax)
n-Tetracosanoic acid 24 : 0 CH3 (CH2)22COOH Groundnut oil and
Rapeseed oils
Cerotic acid n-Hexacosanoic 26 : 0 CH3 (CH2)24COOH Wool fat
Montanic acid n-Octacosanoic 28 : 0 CH3 (CH2)26COOH

12. STRAIGHT CHAIN - ODD NUMBERED FATTY ACIDS
Trivial name Systemic name Carbon
skeleton
structure Common
source
Prpionic acid n-Propanoic acid 3 : 0 CH3CH2COOH Metabolic
intermediate
Valeric acid n-Pentanoic acid 5 : 0 CH3 (CH2)3COOH Metabolic
intermediate
BRANCHED CHAIN - EVEN NUMBERED FATTY ACIDS
Isopalmitic acid n-Isohexadecanoic
acid
16 : 0 Wool fat
BRANCHED CHAIN - ODD NUMBERED FATTY ACIDS
Anteisopalmitic
acid
n-Methyl
hexadecanoic acid
17 : 0 Wool fat
Tuberculostearic
acid
n-Methyl
octadecanoic acid
19 : 0 Bacteria

13. 1.Based on the presence or absence of double bond
2. UNSATURATED FATTY ACIDS
>Contains one ore more double bonds
>These may be classified, based on the degree of unsaturation.
A. Monoethenoid acids — Contains one double bond
CnH2n–1COOH;
eg: oleic acid.
B. Diethenoid acids —Contain Two double bonds;
CnH2n−3COOH;
eg: Linoleic acid.
C. Triethenoid acids — ContainThree double bonds;
CnH2n−5COOH;
eg:Linolenic acid.
D. Tetraethenoid acids — Contain Four double bonds;
CnH2n−7COOH;
eg: Arachidonic acid
>Monoethenoid acids are commonly called as monounsaturated fatty acids (MUFAs)
and the remaining ones as polyunsaturated fatty acids (PUFAs).

14. ISOMERISM
1. Exhibit geometric isomerism;
If the atoms or acyl groups on same side of double bond- cis configuration
If the groups on opposite side of double bond- trans configuration.
➢cis-isomers are less stable than trans-isomers.
➢Most of naturally occurring unsaturated fatty acids exist as cis isomer
➢Eg:
2. Positional Isomers: A variation in the location of the double bonds along the
unsaturated fatty acids chain produces isomer of that compound. Thus, oleic
acid could have 15 different positional isomers.

15. ➢DOCOSAHEXAENOIC ACID: DHA (Ω3, 22:6)
➢Docosahexaenoic acid (DHA) is a polyunsaturated
fatty acid which is synthesized from α-linolenic or
obtained directly from dietary fish oil. This fatty acid is
present in high concentrations in retina, cerebral cortex,
and sperms.
➢DHA is particularly needed for development of the
brain and retina and is supplied via the placenta and
milk. In EFA deficiency, nonessential polyenoic acids of
the ω9 family replace the essential fatty acids in
phospholipids (PL), other complex lipids and
membranes.

16. OLEIC ACID
18 : 1 ; 9 (ω9 Fatty acid)
C17H33COOH
18CH3-17CH2- 16CH2- 15CH2- 14CH2- 13CH2-12 CH2-11 CH2- 10CH=9CH- 8CH2- 7CH2- 6CH2-5CH2-4CH2- 3CH2-
1COOH-2CH2
LINOLEIC ACID
18 : 2 ; 9, 12 , (ω6 Fatty acid)
C17H31COOH
18CH3-17CH2- 16CH2- 15CH2- 14CH2- 13CH=12CH-11 CH2- 10CH=9CH- 8CH2- 7CH2-6CH2- 5CH2-4CH2-3CH2-2CH2-
1COOH-
ARACHIDONIC ACID
20 : 4 ; 5, 8, 11, 14 (ω6 Fatty acid)
C19H31COOH
20CH3-19CH2- 18CH2- 17CH2- 16CH2-15CH=14CH- 13CH2-12 CH=11 CH- 10CH2-9CH=8CH- 7CH2-6CH= 5CH-4CH2-
1COOH-2CH2-3CH2
LINOLENIC ACID
18 : 3 ; 9, 12, 15 ( ω3 Fatty acid)
C17H29COOH
18CH3-17CH2- 16CH= 15CH- 14CH2- 13CH=12 CH-11 CH2- 10CH=9CH- 8CH2- 7CH2-6CH2- 5CH2-4CH2-3CH2-
1COOH-2CH2

17. MONO UNSATURATED FATTY ACIDS
TRIVIAL NAME SYSTEMIC NAME C SKELETON STRUCTURE COMMON SOURC
Crotonic acid 2-butenoic acid 4 : 1 ; 2 CH3CH=CHCOOH Croton oil
Myristoleic acid 9-tetradecenoic acid 14 : 1 ; 9 CH3(CH2)3CH=CH(CH2)7COOH Pycnanthyus
Palmitoleic acid 9-hexadecenoic acid 16 : 1 ; 9 CH3(CH2)5CH=CH(CH2)7COOH Animal and plant
fats
Oleic acid
(oleum = oil)
9-octadecenoic acid 18 : 1 ; 9 CH3(CH2)7CH=CH(CH2)7COOH Animal and plant
fats
Vaccenic acid 11-octadecenoic acid 18 : 1 : 11 CH3(CH2)5CH=CH(CH2)9COOH Bacterial fat
POLY UNSATURATED FATTY ACIDS
Linoleic acid
(linon = flax)
9, 12-octadecadienoic
acid
18 : 2 ; 9, 12 CH3(CH2)4CH=CHCH2CH=CH
(CH2)7COOH
Linseed and cotton
seed oils
Eleostearic acid 9, 11, 13-
octadecatrienoic acid
18 : 3 ; 9, 11,
13
CH3(CH2)3CH=CH-CH=CH-
CH=CH(CH2)7COOH
Tung oil
Linolenic acid 9, 12, 15-
octadecatrienoic acid
18 : 3 ; 9, 12,
15
CH3CH2CH=CHCH2CH=CHCH2CH=CH(C
H2)7COOH
Linseed oil
Arachidonic acid 5, 8, 11, 14-
eicosatetraenoic acid
20 : 4 ; 5, 8,
11, 14
CH3(CH2)4CH=CHCH2CH=CHCH2
CH=CHCH2CH=CH(CH2)3 COOH
Animal fat

18. Unusual unsaturated fatty acid
Nemotinic acid (16C)
It is excreted in the growth medium by a citrivorium
mould.
This fatty acid is unique in that it contains the single,
double and triple C—C linkages.
Nemotinic acid is one of the few naturally-occurring
compounds containing the allene group

19. 2. Based on nature of chain
1.STRAIGHT CHAIN FATTY ACIDS
Linear chain
Eg:
1.Palmitic acid (C16)
16CH3-15CH2-14CH2-13CH2-12CH2-11CH2-10CH2-9CH2-8CH2- 7CH2-
1COOH-2CH2- 3CH2-4CH2--5CH2-6CH2
2. Stearic acid (C18)
2.BRANCHED CHAIN FATTY ACIDS
Eg: Anteisopalmitic acid (C17)(Methyl hexadecanoic acid)
18CH3-17CH2-16CH215CH2-14CH2-13CH2-12CH2-11CH2-10CH2-9CH2-8CH2-7CH2-6CH2-
1COOH-2CH2--3CH2-4CH25CH2

20. 2. Based on nature of chain
3.HYDROXY OR OXYGENATED FATTY ACIDS
Ricinoleic acid (found in castor oil -87%). It is a C 18 acid with a double bond at C9 and an
OH group on C12.
Cerebronic acid, a C 24 acid obtained from animal lipid, is another important hydroxy acid
with an OH group on C2.
9, 10 dihydroxystearic acid(C18). A common oxygenated fatty acid, isolated from plants and
bacterial lipids.
9, 10-epoxystearic acid (C18) is isolated from rust spore lipids (20%).

21. 4. CYCLIC FATTY ACIDS
These are of rare occurrence.
Hydnocarpic acid and Chaulmoogric acid. Chaulmoogra oil, obtained from the plant
Hydnocarpus kurzil and used in the treatment of leprosy, contains 2 such acids. Chaulmoogric
acid has a cyclopentenyl ring in its 18-carbon structure..
Lactobacillic acid, Lipids from the lactobacilli contain a fatty acid, with a cyclopropyl group.
This fatty acid may result from the addition of a methylene group across the double bond
of vaccenic acid.
Sterculic acid from plant sources has a comparable structure, with a suggested relationship
to oleic acid. It may be derived from oleic acid by the addition of a methylene group
across the double bond in a manner that the unsaturated nature is not altered, unlike the
lactobacillic acid.
2. Based on nature of chain

22. 3. Based on total number of carbon atoms
1. EVEN CHAIN FATTY ACIDS
Eg: palmitic acid(16C)
Stearic acid (18C)
Isopalmitic acid(16C)
2. ODD CHAIN FATTY ACIDS
Eg: Valeric acid (5C)
Propionic acid (3C)
Tuberculostearic acid(19C)

23. 4. Based non length of hydrocarbon chain
• Short chain FA (2 to 6 carbon atoms)
• Acetic acid(2C), Caproic acid(6C)
• Medium chain FA (8 to 14 carbon atoms)
• Caprylic acid (8C), Myristic acid (14C)
• Long chain FA (16 to 22 carbon atoms)
• Palmitic acid(16C), Behenic acid(22C)
• Very long chain FA (>24 carbon atoms)
• Cerotic acid(26C)

24. ESSENTIAL FATTY ACIDS
The fatty acids that cannot be synthesized by
the body and therefore, should be supplied
through diet is known as essential fatty
acids(EFA)
 Chemically they are polyunsaturated fatty acids(PUFA)
 Eg: linoleic acid(ω6, 18C, Δ 9,12)
Linolenic acid(ω3, 18C, Δ 9,12,15)
Arachidonic acid(ω3, 20C, Δ 5,8,11,14)
 Normal dietary allowance of PUFA is 2-3% of total
calories.

25. ESSENTIAL FATTY ACIDS(conts..)

26. ESSENTIAL FATTY ACIDS(conts..)
BIOCHEMICAL BASIS OF ESSENTIALITY
 Humans lack the enzyme that can introduce double
bonds beyond carbons 9 to 10
 Introduction of additional double bonds in unsaturated
fatty acid is limited to the area between – COOH
group and the existing double bond and that it is not
possible to introduce a double bond between the –
CH3 group at the opposite end of the molecule and the
first unsaturated linkage. This would explain body’s
inability to synthesise an EFA from oleic acid.

27. ESSENTIAL FATTY ACIDS(conts..)
Functions of EFA
 Structural elements of tissues: Polyunsaturated fatty acids occur in higher concentration in lipids associated
with structural elements of tissues.
 Structural element of gonads: Lipids of gonads also contain a high concentration of polyunsaturated fatty
acids, which suggests importance of these compounds in reproductive function.
 Synthesis of prostaglandins and other compounds: Prostaglandins are synthesised from Arachidonic acid
by cyclooxygenase enzyme system. Leucotrienes are conjugated trienes formed from arachidonic acid in
leucocytes by the Lipoxygenase pathway.
 Structural element of mitochondrial membrane: A deficiency of EFA causes swelling of mitochondrial
membrane and reduction in efficiency of oxidative phosphorylation. This may explain for increased heat
production noted in EFA deficient animals.
 Serum level of cholesterol: Fats with high content of polyunsaturated fatty acids tends to lower serum level
of cholesterol.
 Effect on clotting time: Prolongation of clotting time is noted in ingestion of fats rich in EFA.
 Effect on fibrinolytic activity: An increase in fibrinolytic activity follows the ingestion of fats rich in EFA.
 Role of EFA in fatty liver: Deficiency of EFA produces fatty liver.
 Role in vision: Docosahexaenoic acid is the most abundant polyenoic fatty acids present in retinal
photoreceptor membranes. Docosahexaenoic acid is formed from dietary linolenic acid. It enhances the
electrical response of the photoreceptors to illumination. Hence linolenic acid is necessary in the diet for
optimal vision.

28. ESSENTIAL FATTY ACIDS(conts..)
DEFICIENCY MANIFESTATIONS:
 A deficiency of EFA has notyet been unequivocally demonstrated in humans.
 In weaning animals, symptoms of EFA deficiency are readily produced. They are:
 Cessation of growth.
 Skin lesions: Acanthosis (hypertrophy of prickle cells) and hyperkeratosis
(hypertrophy of stratum corneum). Skin becomes abnormally permeable to water.
Increased loss of water increases BMR.
 Abnormalities of pregnancy and lactation in adult females.
 Fatty liver accompanied by increased rates of fatty acids synthesis, lessened
resistance to stress.
 Kidney damage.
FATE OF EFA
 EFA undergoes β-oxidation after necessary isomerisation and
epimerisation, like other unsaturated fatty acids

29. REFERENCE
 Dr. M.N. Chatterjea, and Rana Shinde; Extbook of Medical
Biochemistry; Eighth Edition ;Jaypee Brothers Medical
Publishers (P) Ltd
 D.M .Vasudevan, Sreekumari S., and Kannan Vaidyanathan;
Textbook of Biochemistry, For Medical Students; Sixth
Edition; Jaypee Brothers Medical Publishers (P) Ltd
 J.L. Jain, Sunjay Jain and Nitin Jain; Fundamentals of
Biochemistry for University and College Students in India
and Abroad; Sixth Edition; S. Chand & Company Ltd.; 2005
 Dr. U. Satyanarayana and U. Chakrapani; Biochemistry;
Fourth Edition; Elsevier India Pvt. Ltd; 2013