2. Lipids are organic compounds which are mainly composed of fatty
acids & glycerols.
Characteristics
1. Soluble in organic or non-polar solvents (e.g. oil, ether, alcohol)
2. Contain many non-polar C-C & C-H bonds & a few polar bonds,
resulting in their water insolubility
3. They are ester of fatty acids or fatty acids derivatives
4. Mainly contains C, H, O molecules & also contain N, P or S
5. May be solid or liquid at room Temperature
6. May be saturated or unsaturated
7. Unlike carbs or proteins, they aren't polymers
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3. Functions
Primary:
1. Store energy in adipose tissues
2. Make biological membrane
Others :
1. Act as a structural component of body
2. Layers of subcutaneous fat under the skin also help in insulation,
protection from cold & prevent evaporation of H2O from body
3. Source of fat soluble vitamins- (A, D, E & K) which are essential
nutrients with numerous functions
4. Precursor of hormones including estrogen, testosterone, cck &
cortisol. These are all necessary to control immune system &
metabolism
5. Have high energy value(9 kcal/gm) that is relatively more than
carbs & proteins
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5. Lipids can be classified into substances that are either hydrolyzable &
non-hydrolyzable :
1. Hydrolyzable : Lipids contain an ester functional group that can be
converted into smaller molecules through aqueous hydroysis.
e.g. simple lipids & complex lipids.
2. Non-hydrolyzable lipids : Lipids lack of an ester functional group
that can’t be converted into smaller molecules.
e.g. derived lipids
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6. Fatty acids
• Fatty acids are carboxylic acids with long hc chain. They are
simplest form of lipids. General formula : R-(CH2)n- COOH.
• Fa usually consists of 12-20 molecules of C. They are divided into 2
portions- Hydrophobic tail & Hydrophilic head. Although they
contain polar carboxylic group in their structure, however they're
insoluble in water. Because of their hydrophobic portion is much
bigger than the hydrophilic portion.
nonpolar tail polar head
A fatty acid
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7. Physical Properties of Fatty acids
1. Solubility in water :
• Fatty acids containing up to 6 carbons are completely soluble in
water.
• Longer chain fatty acids are insoluble in water but soluble in
fat solvents.
2. Physical state at room T :
• The lower members of saturated fa are liquid at room T &
volatile. They have irritant odour & bad taste.
• Those higher than 10 carbons are solids.
• Unsaturated long chain fa are liquids due to the presence of cis
double bonds
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8. Nomenclature of Fatty Acids
• C atoms are numbered from the carboxyl carbon (carbon No. 1).
The C atoms adjacent to the carboxyl carbon are numbered as 2,
3…etc & are also known as α, β…etc, carbons respectively.
• The terminal methyl group is known as the ω(omega) carbon
which is used to indicate the site of a double bond. For example:
ω9 indicates a double bond on the 9th C counting from the
terminal methyl group.
• Examples:
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9. Common fatty acids
No of
C
atoms
No of
double
bonds
Name Formula MP Source
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11. 1. Saturated fatty acids
• They contain only single bonds in their structure. They are generally
solids in room T & have high bp & mp
• They are pack together in a tightly regular pattern, which allow a
strong attraction to occur between C chains. Since there are single
bonds & no double bonds, there are enough H atoms in it, i.e. this
fat is saturated with H atoms. As a result, the vander waals force
between molecules is very robust & stable. This makes the fats
remain solid at room T .
• Sources : Animal foods such as meat, poultry, full-fat dairy
products.
• Increased intake of saturated fatty acids may lead to increase in
plasma cholesterol levels & incidence of heart diseases.
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12. 2. Unsaturated fatty acids
• They contain 1 or more double bonds in their structure. They are mostly
liquids at room T & have lower bp & mp
• They are pack together in a irregular pattern, which allow a low attraction
to occur between C chains. Since there is presence of double bonds, the
amount of H in the fa chain gets reduced. Furthermore, the C atoms in ufa
don’t form a straight chain-the chain gets bent. This results in the fa chain
being weak & unstable. As result of these two things, the Vander waals
force between molecules isn’t that robust or strong. Hence ufa remain
liquid at room T.
• They may be -
1. Mono-unsaturated : containing 1 double bond
2. Poly-unsaturated : containing 2 or more double bonds
Ufa may occur in 2 distinct structural configurations –
1. Cis isomers: The H atoms attached to the C double bond are on the
same side
2. Trans isomers: The H atoms attached to the C double bond are on
different side taf
13. Cis-fatty acids
• Most of the double bonds present in USFA are of the cis type
& they are liquid at room T. A trans bond creates a straight
chain, whereas a cis bond results in a chain that is bent. This
disrupt the vandar waal forces by preventing the tails from packing
close to one another. So, they can't bunch tightly together. The
bend helps the fat stay liquid rather than solid.
• Sources : Vegetable oils such as olive, corn, soybean, peanut
• They are important for synthesis of phospholipids. 2- Formation
of eicosanoids such as prostaglandins, prostacyclins,
thromboxanes, leukotrienes & lipoxins.
• Intake of cis-fa decrease the incidence of plasma cholesterol & high
bp.
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14. Trans-fatty acids
• A trans bond creates a straight chain & molecules in chain are
tightly pack together. So, USFA containing trans-double bonds are
solid at room T. Their bp & mp is relatively higher than cis-fa.
• Sources : Fast boods, backed foods, packaging foods, frozen foods,
chips, cookies, candies, beverages etc.
• Studies have shown that trans fats may act similarly to saturated
fats. Trans fats are well known to cause bad cholesterol, heart
disease, & obesity
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15. Nutritional Classification of Fatty Acids
1. Essential fatty acids
Efa defined as the fa that our body can't synthesize & they should be
applied through diet.
Linoleic A- C17H31COOH (omega-6-fa) & Linolenic A- C17H29COOH (omega-3-
fa) are 2 important Efa for our body. They are found in vegetables oils like
cottonseed, castor, olive or peanut oil. Significance :
• Components of cell membrane
• Required for brain growth & development
• Precursors of eicosanoids
• Play an important role in vision
Deficiency of Efa may lead to dermatitis, wt loss, growth retardation etc.
2. Non Essential Fatty Acids: They include all other fatty acids
because they are formed in our body in good amounts mainly from
carbohydrates. It is not essential to take them in diet.
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16. Chemical reactions of fatty acids
Esterification
Fatty acid esters are a type of ester that result from the combination
of a fa with an alcohol. When the alcohol component is glycerol, the
fatty acid esters produced can be monoglycerides, diglycerides, or
triglycerides.
(Palmitic A)
(acid)
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17. Hydrogenation
H2 adds to the double bonds of unsaturated fats. Each double bond
reacts with 2 H atoms to give the corresponding saturated fa as
follows-
As a result bp & mp is increased of the product. Liquid oils are
converted to semi-solid fats.
Ex- Oleic A + H2 Stearic A
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18. Addition of oxygen:
The presence of double bond makes fa sensitive to oxidation. Double
bonds react with O2 to form corresponding peroxides-
Further oxidation produces splitting of the fa chain & results in formation
of lower chain aldehydes & acids. Therefore, oxidation of USFA by
hydrogen peroxide produces destruction of lipoproteins of plasma & cell
membranes (lipid peroxidation).
Reduction
The reduction of fa results in formation of fatty alcohol. proceeds through
a formation of fatty aldehyde as intermediates.
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19. Salt formation
Fa when reacted with alkalies form their salts.Salts of long-chain
fatty acids are known as soaps
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20. Simple lipids
Simple lipids are ester of fa with alcohols.
Triglycerides
Triglycerides are simple lipids. They are actually ester of 3 fa along with
glycerol.
Triglycerides are the most constituents of body fat in human & other
animals. They are formed by esterification of glycerol with 3 fa. Glycerols
have -OH group & fa have -COOH group. They're formed when the -OH
group of glycerol react with the -COOH groups of fa with elimination of
water molecules.
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21. Fats Oils
Triglycerides that are solid at room T Triglycerides that are liquid at room The
Mainly composed of SFA Mainly composed of USFA
Contain no double bonds, molecules
pack together in a tightly regular
pattern
Contain double bonds, molecules pack
together in a irregular pattern
High bp & mp Low bp & mp
Mainly originates from animal sources.
e.g. butter, cream, fish, meat, egg, yolk
Mainly originates from plant sources.
e.g. clove oil, cottonseed oil, mustard oil
Stored in adipose tissues of liver Stored in seeds & fruits of plants
Increase cholesterol level & risk of cvd
development
Improve cholesterol level
Oxidative rancidity is high Oxidative rancidity is low
Triglycerides are mainly 2 forms : fats & oils
https://bit.ly/3qeYNoD
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22. Chemical reactions of triglycerides
Saponification
Saponification reaction is reverse of Esterification reaction. In
Esterification a carboxylic acid & an alcohol combine to form a Ester
along in presence of ester ; Whereas in Saponification an ester reacts
with a base to form a carboxylic acid & an alcohol.
It’s a hydration reaction where free hydroxide breaks the ester bonds
between the glycerol & fa of a triglyceride, resulting in free fa & glycerol,”
which are each soluble in aqueous solutions.
The saponification value is the amount of base required to saponify a fat
sample
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24. Rancidification
Rancidification is the process of degradation of fats & oils when exposed to
high T, R, air, light, or moisture or by bacterial action, resulting in unpleasant
taste & odour. Specifically, it is the hydrolysis or autoxidation of fats into short-
chain aldehydes & ketones, which are objectionable in taste & odour. When
these processes occur in food, undesirable odours & flavours can result.
• Types of Rancidity:
a) Hydrolytic rancidity: It is due to the hydrolysis of TAG by lipase enzyme
especially in presence of high T & moisture. Lipase causes release of short
chain fa which are volatile & have bad odor.
b) Oxidative rancidity: It is associated with the degradation by O2 in the air.
Oils which are rich in USFA are more liable to develop this type of rancidity.
Oxidation of USFA produces peroxides, lower chain fatty acids, fatty aldehydes
& ketones. They have bad odor & bitter taste.
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25. Protection against rancidity:
• Addition of antioxidants e.g. phenols, quinones, BHA, BHT, TBHQ,
propyl gallete help to protect the fats & oils against oxidation &
decrease the rate of development of rancidity. Natural antioxidants
include Zn, Sn, vit E, vit C or ascorbic acid can also be used for this
purpose.
• Rancidification can be decreased by storing fats & oils in a cool,
dark place with little exposure to oxygen or free radicals.
• In addition, Antimicrobial agents can also delay or prevent
rancidification by inhibiting the growth of bacteria or other mos
that affect the process.
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26. Waxes
• Waxes are ester of fa with long chain alcohols (except glycerols).
• They have high mw. They are saturated & solid at room T. Their mp
& bp is higher than triglycerides because of their long C chains.
They are hydrophobic, insoluble in water but soluble in fatty
solvent.
• Wax formation proceeds through a dehydration reaction. The
oxygen of the alcohol forms a bond to the acid at the carbon with
the double bond oxygen. This forms the wax containing ester
functional group.
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27. Significance
1. Form a protective coating in animals that protects the outerlayer
of skin
2. Prevent excess evaporation of water in plants
3. Protect against parasites
4. Beeswax & carnuba wax is used to give a protective coating to
furnitures
5. Jojoba wax is used in making c&les & cosmetics
6. Waxes used as excepient & emollient in many pharmaceuticals
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28. Complex lipids
They are ester of fa with alcohol & contain additional groups. They are
divided into as follows-
1. Phospholipids : Compounds containing fa, glycerol & phosphoric A.
They are classified according to the alcohol present into them-
A- Glycerophospholipids: Containing glycerol.
B- Sphingomyelin: Containing sphingosine (sphingol).
1. Glycolipids : Compounds containing fa, glycerol & carbohydrates.
2. Sulfolipids : Compounds containing fa, glycerol & sulphur
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29. Glycerophospholipids
They are phospholipids containing 2 fa, 1 phosphate group & a alcohol
which is glycerol. They include phosphatidic acid & its derivatives as
follows:
1. Phosphatidic acid : On hydrolysis it gives 1 glycerol, 1 saturated fa,
1 unsaturated fa & phosphoric acid. It plays very important role in
phototransduction. They provide arachidonic acid for synthesis of
eicosanoids.
2. Lecithin : It is formed of phosphatidic acid & choline. It is usually
present in the cell membranes especially in the liver, lung & brain.
Lecithin help to increase good HDL cholesterol & lower bad LDL
cholesterol
3. Cephalin : It is formed of phosphatidic acid & ethanolamine. It is
present in the cell membranes & blood plasma. They have a role in
blood coagulation. They accelerate blood clotting because they enter
in the structure of thromboplastine, which is essential for blood
clotting. taf
30. 4. Phosphatidylserine: It is formed of phosphatidic acid & serine
amino acid. It is present in cell membranes. It contributes to
cellular signaling. They are important constituents of plasma
lipoproteins.
6. Plasmalogens : Plasmalogens are a subclass of ether
phospholipids that are commonly found in cell membranes in the
nervous, immune & cardiovascular systems.
Plasmalogens possess antioxidative potential that can protect
mammalian cells against the damaging effects of reactive oxygen
species e.g. peroxides, superoxides.
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31. Sphingophospholipids
• They are glycolipids containing a fa, a phosphate group, & an
alcohol, which is sphingosine.
• This type is present in cell membranes specially of the lungs &
brain mainly in the myelin sheath. It contains sphingosine
(sphingol) which is an 18C amino alcohol. Fatty acids are linked to
sphingosine by an amide bond to form ceramide, which is
connected to phoshocholine to form sphingomyelin.
• They make large portion of myelin sheath. They also play an
important roles in signal transduction & cell recognition.
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32. Comparison between Glycerophospholipids & Sphingophospholipids
Simmilarities
• Both contain fatty acids.
• Both are constituents of cell membranes.
• Both are distributed asymmetrically in the lipid bilayer.
• Both are amphipathic, contain hydrophilic & hydrophobic parts
Dissimilarities
Glycerophospholipids Sphingophospholipids
contain glycerol backbone contain sphingosine backbone
major component of lipids in the cell
membrane
second major component of lipids in
the cell membrane.
hydrophobic regions are composed of
two fatty acids joined to glycerol
hydrophobic regions are composed of
1fatty acids joined to glycerol
have phosphate groups May/may not contain phosphate groups
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33. Glycolipids
Glycolipids are lipids with a carbohydrate attached by a glycosidic
bond. Their role is to maintain the stability of the cell membrane & to
facilitate cellular recognition, which is crucial to the immune
response & in the connections that allow cells to connect to one
another to form tissues.
They include the following types:
1. Cerebrosides : These types of glycolipids are found primarily in
the brain & in the peripheral nervous tissue. It acts as an insulator
& is mainly involved in providing a protective coating to the nerve
cells. .
2. Gangliosides : These types of glycolipids are neutral compounds
& are composed of sialic acid residues. They are the main
components of the animal’s cell membrane & are abundantly
found in the plasma membrane of the neurons.
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34. Functions of Glycolipid
The main functions of Glycolipid are:
1. It provides energy to the cells.
2. It is an essential part of cell membranes.
3. It helps in determining the blood group of an individual.
4. It acts as receptors at the surface of the red blood cells.
5. It also functions by assisting the immune system by destroying &
eliminating the pathogen from the body
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35. Derived lipids
They are produced by hydrolysis of either simple or conjugated lipids.
Steroids
• Steroids are derived lipids containing steroid nucleus. This nucleus is
composed of 4 fused rings with 17 C atoms.
• Steroids are hydrophobic & insoluble in water. They don't resemble
lipids since they have a structure composed of 4 fused rings. They
don't contain any fa.
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36. Classification of steroids
1- Sterols - Sterols mean solid alcohols. They include the following :
a- Zoo sterols: They are present in animals & humans e.g. cholesterol.
b- Phytosterols: They are present in higher plants e.g. sitosterols.
c- Mycosterols: They are present in lower plants (yeast & fungi) e.g.
ergosterol.
2- Bile acids
3- Steroid hormones
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38. Sources: Exogenous (Dietary)-The richest sources are egg yolk, red
meat, liver, kidney, butter & brain.
Endogenous- Every cell can synthesize its own cholesterol. Plasma
cholesterol is synthesized in the liver & intestine from fats, carbs &
proteins.
Distribution of cholesterol: It is widely distributed in all tissues but
higher concentrations are present in the nervous tissue, liver, adrenals,
gonads, skin & adipose tissue.
Plasma level of cholesterol: Normally it ranges from 120-200 mg/dL
(30% as free cholesterol & 70% as cholesteryl-esters).
Excretion: It is mainly excreted from the body in bile in the form of bile
salts. Less amounts are excreted as cholesteryl-esters &
dihydrocholesterol. In the large intestine cholesterol is reduced by
intestinal bacteria to give coprostanol which is excreted mainly in stool.
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39. Functions of cholesterol
1. It is converted into bile in the liver. Bile aids in digestion. It breaks
down fats into fatty acids, which can be taken into the body by the
digestive tract.
2. Precursor of steroid hormones including corticoids, sex hormones.
3. Essential for making the cell membrane & cell structures
4. Helps to maintain the integrity & fluidity of cell membranes
-At temperatures, cholesterol makes the membrane less fluid by limiting
the movement of phospholipids.
-At low temperature cholesterol decreases the close packing of
phospholipids, increasing fluidity & decreasing gel formation.
5. Important for vitamin D synthesis
6. It insulates nerve fibers
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40. Lipoproteins
• Lipoproteins are water soluble form of lipids. They contain both
lipids & proteins. There main function is to transport hydrophobic
lipids e.g. cholesterol, triglycerides, phospholipids.
• Cholesterol can't travel freely through the bloodstream since it's
insoluble in blood. It travels through the blood on proteins, which
are Lipoproteins. There are 3 types of lipoproteins-
1. LDL (Low Density Lp) : Known as 'bad cholesterol' as it carries
cholesterol from the liver into bloodstream; where it can stick to
the blood vessels. This can lead to atherosclerosis & further cvd.
The optimum amount of LDL in body is <100 mg/dl
2. HDL (High Density Lp) : Known as 'Good cholesterol 'as it carries
cholesterol from the other parts of body into the liver, where it
get metabolized. The optimum amount of HDL in body is >40
mg/dl.
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41. 3. VLDL (Very LDL) : It mainly carries triglycerides & phospholipids
& stores them into adipose tissues.
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42. Bile Salts
• Bile salts are one of the primary components of bile. They are
produced from cholesterol in liver & stored in gallbladder.
• Glycocholate, taurocholate, & other bile salts are released from the
gallbladder into the small intestine, where they aid digestion of
fats by forming emulsions with dietary lipids.
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43. Steroid hormone
• Steroid hormone, any of a group of hormones that belong to the
class of chemical compounds known as steroids
• They are secreted by 3 steroid glands—the adrenal cortex, testes,
& ovaries; & during pregnancy by the placenta. All steroid
hormones are derived from cholesterol.
• Steroid hormones can be grouped into 2 classes: corticosteroids
(typically made in the adrenal cortex, hence corticoids) & sex
steroids (typically made in the gonads or placenta).
• Steroid hormones help control metabolism, inflammation, immune
functions, salt & water balance, development of sexual
characteristics, & the ability to withstand illness & injury
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45. • Corticosteroids are a class of steroid hormones that are produced
in the adrenal cortex. Corticosteroids hormones balance stress
response, energy flow, body temperature, water balance, &
other essential processes.
• The estrogens, control development of secondary sex
characteristics, regulate the menstrual cycle, & are made in the
ovaries.
• The progesterone is called the “pregnancy hormone”; it is
responsible for the preparation of the uterus for implantation of
a fertilized egg.
• Testosterone made in the testes. They control the development
of secondary sex characteristics in males.
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46. Eicosanoids
• Eicosanoids are hormone like molecules act as autocoids in the body.
They are derived from 20C PUFA, e.g. arachidonic acid,
eicosapentaenoic acid.
• These fa undergo chemical reaction that transforms them into various
classes of eicosanoids - such as prostaglandins, thromboxanes,
leukotrienes, & prostocyclin. For example, arachidonic acid can be
transformed into the 3 eicosanoids shown below-
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47. Classification
They are classified into 2 main groups:
A. Cyclic compounds (prostanoids):
1- Prostaglandins (PG)
2- Prostacyclins (PGI)
3- Thromboxanes (TX)
B. Acyclic compounds:
1- Leukotrienes (LT)
2- Lipoxins (LX)
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