Lipids
The lipids are a group of substances found in plant and animal tissues. They are
insoluble in water but soluble in common organic solvents such as benzene, ether
and chloroform. They act as electron carriers as substrate carriers in enzymatic
reactions, as components of biological membranes and as sources and stores of
energy.
In animals, lipids are the major form of energy storage, mainly as fat, which may
constitute up to 79 per cent of the adipose tissue of obese animals. The yield of
energy from the complete oxidation of fat is about 39Ml/ Kg DM compared with
about 17 Ml/Kg DM from glycogen, the major carbohydrate form of stored energy. In
addition, stored fat is almost anhydrous, whereas stored glycogen is highly hydrated.
Weight for weight, fat is, therefore, about six times as effective as glycogen as a
stored energy source.
The structural lipids of animal tissues, mainly phosphoglycerides, constitute
between 0.5 and 1 per cent of muscle and adipose tissue; the concentration in the
liver is usually between 2 and 3 per cent. The most important non-glyceride, natural
lipid fraction of animal tissue is made up of cholesterol and its esters, which together
make up 0.06 to 0.09 per cent of muscle and adipose tissue.
Classification of lipids:
Lipids
Non-glycerol based
Glycerol based
Sphingomyelins
Simple
Compound
dd
Cerebrosides
Waxes
Phosphoglyceride
s
Glycolipids
Steroids
Terpenes
Fat
Glucolipid
s
Galactolipid
Lecithin
s
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Cephalins
Eicosanoids
Simple lipids:
Esters of fatty acids with various alcohols, Fats: Esters of fatty acids with glycerol.
Oils are fats in the liquid state.
Compounds lipids:
Lipids constitute a group of naturally occurring molecules that include fats, waxes,
sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), monoglycerides,
diglycerides, triglycerides, phospholipids, and others.
Fat:
Fats and oils are a group of organic compounds that are greasy to touch,
insoluble in water and soluble in alcohol and ether. Fats, together with protein and
carbohydrates, constitute chief structural component of the living cell. Fats and oils
are composed of carbon, hydrogen and oxygen. But the proportion of the hydrogen
and oxygen is not the same as in carbohydrates. Moreover, fats and oils provide
about two and a half times more energy per unit weight compared to carbohydrates.
Fats are in solid state under room temperature, whereas oils are in liquid form.
The animal body contains 17-26% fat. The amount of fat present in the bones of
the adult animal is 4 per cent. Most of the fat present in the animal body is stored
around the walls of the intestine and kidneys and under the skin or adipose tissues
of the body. In addition to this, it is found in muscles and other parts of the body in
small amounts.
Structural of fats:
Fat are esters of fatty acids with the trihydric alcohol glycerol, and are also referred
to as glycerides or acylglycerol. When all three alcohol groups are esterified fatty
acids, the compound is a triacylglycerol (triglyceride).
2
CH2 OH
CH2 OH
CH 2 .O.CO.R
+ 3R.COOH
CH2 OH
Glycerol
CH.O.CO.R
+
3H2 O
CH 2 .O.CO.R
fatty acid
triacylglycerol
Triacylglycerol differ in type according to the nature and position of the fatty acid
residues. Those with three residues of the same fatty acid are termed simple
triacylglycerols as illustrated above. When more than one fatty acid is concerned in
the esterification then a mixed triacylglycerol results:
Functions of fats:
1. The main function of fats is to supply energy to the animal body. One gram of
fat on oxidation produces 9.3 Kcal of heat. It indicates that fats provide about
2.5 times more energy as compared to carbohydrates.
2. Fats are reserve source of energy to the animal body.
3. Food fats provide body fats to the animals.
4. Fats obtained from food take pan in the formation of milk fat in milk animals
and provide necessary taste to milk as well.
5. Fats are also helpful in the absorption of calcium and carotene.
6. Fats are also responsible for supply of vitamin A, D, E and K to the animal
body since these vitamins are only soluble in fats.
7. Fats are essential constituents of the body protoplasm.
8. Fats are essential for the growth and development of calves.
Fatty acids:
A fatty acid is a carboxylic acid with a long aliphatic chain, which is
either saturated or unsaturated. Most naturally occurring fatty acids have a chain of
an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived
from triglycerides or phospholipids. When they are not attached to other molecules,
they are known as "free" fatty acids. Fatty acids are important sources of energy
because, when metabolized, they yield large quantities of ATP. Many cell types can
use either glucose or fatty acids for this purpose. In particular, heart and skeletal
muscle prefer fatty acids. Despite long-standing assertions to the contrary, the brain
can use fatty acids as a source of energy in addition; to glucose and ketone bodies.
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Saturated fatty acids:
Saturated fatty acids are long-chain carboxylic acids that usually have between
12 and 24 carbon atoms and have no double bonds. Thus, saturated fatty acids are
saturated with hydrogen (since double bonds reduce the number of hydrogens on
each carbon). Because saturated fatty acids have only single bonds, each carbon
atom within the chain has 2 hydrogen atoms (except for the omega carbon at the
end that has 3 hydrogens).
Example for saturated fatty acids
Common name
Caprylic acid
Capric acid
Lauric acid
Myristic acid
Palmitic acid
Stearic acid
Arachidic acid
Behenic acid
Lignoceric acid
Cerotic acid
Chemical structure
CH3 (CH2)6 COOH
CH3 (CH2)8 COOH
CH3 (CH2)10 COOH
CH3 (CH2)12 COOH
CH3 (CH2)14 COOH
CH3 (CH2)16 COOH
CH3 (CH2)18 COOH
CH3 (CH2)20 COOH
CH3 (CH2)22 COOH
CH3 (CH2)24 COOH
Unsaturated fatty acids:
Unsaturated fatty acids have one or more double bonds between carbon atoms.
(Pairs of carbon atoms connected by double bonds can be saturated by adding
hydrogen atoms to them, converting the double bonds to single bonds. Therefore,
the double bonds are called unsaturated.
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Examples for unsaturated fatty acid:
Common name
Myristoleic
Palmitoleic acid
Sapienic acid
Oleic acid
Elaidic acid
Chemical structure
CH3 (CH2)3 CH=CH (CH2)7 COOH
CH3 (CH2)5 CH=CH (CH2)7 COOH
CH3 (CH2)8 CH=CH (CH2)4 COOH
CH3 (CH2)7 CH=CH (CH2)7 COOH
CH3 (CH2)7 CH=CH (CH2)7 COOH
Essential fatty acids (EFA):
Fats are compounds of fatty acids and glycerol and they provide essential fatty
acids to body. These EFA are linolic acid, arachidonic acid and linolenic acid. But it
has been proved that linoleic acid is the only EFA, as the animals have the capacity to
synthesize arachidonic and linolenic acid. Linoleic acid, though an essential fatty acid
cannot be synthesized in the body and must be present in the diet. Therefore,
presence of linoleic acid in adequate amounts ultimately eliminates all symptoms of
EFA deficiency. Safflower oil is the best source of linoleic acid followed by soybean
oil.
EFA deficiency in poultry
The first outward sign of EFA deficiency is retarded growth. This can be apparent
within one week of feeding a deficient diet. Male chicks are more susceptible to EFA
deficiency. As the deficiency intensifies, the skin becomes rough and gives a flaky
appearance leading to greater water loss and consequently greater water
consumption. The birds also have a decreased resistance to diseases, a poorer
efficiency of feed utilization and faulty feathering.
Adult birds rarely show signs of abnormality if fed an EFA deficient diet.
However, hens suffer from reduction in the rate of egg production and egg size. Also,
the fertility and hatchability of eggs are depressed. Chicks hatched from deficient
eggs are small.
Importance of lipids in animal diets:
1. The lipids play important role in the absorption of carotenes and vitamin A
found in diet.
2. Assist to the absorption of Ca in the body, also supported the body in energy
which equivalent twice the energy which supported by carbohydrates.
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Symptoms of essential fatty acids deficiency:
 Growth retardation.
 Increase permeability to water and increased water consumption.
 Increased to susceptibility to bacterial infection.
 Sterility.
 Less stable biomembranes.
 Capillary fragility.
 Kidney damage, haematuria and hypertension.
 Decrease visual acuity.
 Decrease ATP synthesis in the liver and heart.
Deficiency of lipids in diets:
1. Dry coat and scaly skin, a reduction of lipids on the skin can cause pyoderma.
2. Wound healing can also be impaired due to the requirement of
phosopholipids within the cells membranes.
3. If there is a chronic deficiency of lipids, especially of the EFA, symptoms of
alopecia, edema and moist dermatitis can occur.
4. Severe deficiencies can result in emaciation of the animal.
5. Deficiencies of Vitamin A can cause night blindness, infertility, crusting
lesions of the nares, seborrhoeic coat conditions, and increased susceptibility
to microbial infections.
6. Deficiencies of vitamin D can cause rickets in the young and osteomalacia in
adults.
7. Deficiencies of vitamin E can cause pancreatitis, skeletal muscle dystrophy,
reproductive failure and impairment of the immune response in dogs,
Deficiencies of vitamin K is rare due to its synthesis in the intestine.
Waxes:
Fatty acids and an alcohol. They are more hyrophobic than fats. And they are the
natural coatings for apples and pears.
Important in fruits:
 Natural protective layer in fruits, vegetables, etc.
 Added in some cases for appearance and protection.
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Phospholipids:
Are a class of lipids, and a major component of all biological membranes, along
with glycolipids, cholesterol and proteins. They have two regions named as head and
tail. Heads are hydrophilic while tails are hydrophobic. Phospholipids are diglycerides
that are covalently bonded to a phosphate group by an ester linkage. The diglyceride
is composed of a glycerol backbone that has esterified to two fatty acids the
phosphate group is ionic and therefore hydrophilic. The fatty acid side groups are
hydrophobic.
Cholesterol:
Is an organic molecule. It is asterol (or modified steroid), and an essential
structural component of animal cell membranes that is required to establish
proper membrane permeability and fluidity. Cholesterol is thus considered within
the class of lipid molecules.
In addition to its importance within cells, cholesterol also serves as a precursor for
the biosynthesis of steroid hormones, bile acids and vitamin D.

Mother molecule for many important molecules in body, including sex
hormones and vitamin D, which is needed for calcium absorption

The liver produces cholesterol, so none is needed in the diet.

“bad” cholesterol is associated with heart diseases.

Dietary recommendation - <300 mg/d.

Sources – egg yolks, liver, shellfish.
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Lipoproteins:
A lipoprotein is a biochemical assembly that contains both proteins and lipids, bound
to the proteins, which allow fats to move through the water inside and outside cells.
The proteins serve to emulsify the lipid (otherwise called fat) molecules.
Many enzymes, transporters, structural proteins,antigens, adhesins, and toxins are
lipoproteins.
Function: Transport of fat soluble substance
Types of lipoproteins:
1- Chylomicron.
 Made by: the small intestines in the fed state
 Absorbed into: the lymph vessels, then --> moves into the blood
 Rich in: TGs
 Function: Deliver TG’s to body cells to be used as fuel.
2- VLDL. Very low density lipoproteins
 Very Low Density Lipoprotein.
 Made in: the liver from excess dietary carbohydrate and protein along with
the Chylomicron remnant.
 Secreted into: the bloodstream.
 Rich in: TGs.
 Function: Deliver TGs to body cells.
 Contains apo B100.
 Similar to Chylomicrons, but made by different tissues.
3- LDL. Low density lipoprotein
 Low Density Lipoprotein.
 Made in: the Liver as VLDL.
 Arise from: VLDL once it has lost a lot of its TG’s.
 Secreted into: the bloodstream.
 Rich in: Cholesterol.
 Function: Deliver cholesterol to all body cells.
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4




HDL. High density lipoprotein.
High Density Lipoprotein.
Made in: the Liver and Small Intestine.
Secreted into: the bloodstream.
Function: Pick up cholesterol from body cells and take it back to the liver =
“reverse cholesterol transport”
Potential to help reverse heart disease.
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