This slide describe about introduction, physical properties, chemical properties, classification and biological functions of lipids.

1. Overview of Lipids
Dr. Anil V Dusane
Sir Parashurambhau College
Pune
anildusane@gmail.com
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2. Introduction
• Lipids are very diverse in both their respective structures and
functions.
• Lipids are a heterogeneous group of compounds related to the fatty
acids and insoluble in water but soluble in solvents such as ether,
chloroform and benzene.
• Lipids comprise a large group of structurally distinct organic
compounds including fats, waxes, phospholipids, glycolipids, etc.
• Definition: Lipids are the esters of fatty acids and alcohols.
• Lipids serve a variety of important functions in living organisms. They
act as chemical messengers, serve as valuable energy sources, provide
insulation, and are the main components of membranes. 2

3. Chemical nature of lipids
• Lipids are the complex compounds.
• These are made up of C, H, and O2 but poor in O2
contents.
• Lipids are fatty esters of glycerols.
• Lipids= fatty acids + glycerols
• Although the term "lipid" is sometimes used as a synonym
for fats, the fats are a subgroup of lipids called
triglycerides.
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4. Physical properties
1. Solubility: Lipids are insoluble in water. Fats and fatty acids are soluble
in organic solvents such as petroleum ether, benzene and chloroform
2. Saturation: Saturated fatty acids are solid at room temperature while
unsaturated fatty acids are liquid. Unsaturated fatty acids show cis-
trans isomerism due to presence of double bonds.
3. Heat conductivity: Lipids are the bad conductors of heat.
4. Melting point: Saturated glycerides containing fats require high
temperature for melting while unsaturated glycerides containing fats
require relatively lower temperature for its melting.
5. Specific gravity: Solid fat has specific gravity 0.86.
6. Tasteless, odorless and colourless: The lipids are generally tasteless,
colourless and odourless.
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5. Chemical properties
1. Hydrolysis: Fats undergoes hydrolysis when they are treated with mineral
acids, alkalis or enzymes (lipase) or hydrolases to yield glycerol and the
constituent fatty acids.
2. Hydrogenation: Oils containing unsaturated fatty acids can be
hydrogenated in presence of high temperature, pressure and nickel
(catalyst). By this process the oils are converted into solid fats (glycerides
of saturated fatty acids).
3. Emulsification: Process of breaking of large sized fat molecules into
smaller ones is known as emulsification.
4. Saponification value: It is defined as the number of milligrams of KOH
required to neutralize the fatty acids resulting from the complete
hydrolysis of 1 g oil or fat.This value gives idea about its molecular weight.5

6. Chemical properties
5. Iodine number: This is the amount ( in grams) of iodine absorbed by
100 g of fat. This value gives an idea about the degree of unsaturation of
fat or oil.
6. Rancidity: All-natural fats are oxidized when exposed to air, light,
moisture, particularly if warm developing unpleasant odour and taste.
7. Acid number: Number of milligrams of KOH required neutralizing the
free acids of 1 g pf fat. This value gives an idea of the amount of free
acids present in given oil or fat.
8. Reichert-Meissl value: It is defined as the number of milliliters of
0.1N KOH solution required to neutralize the volatile water-soluble acids
obtained by the hydrolysis of 5 g of fat. This value is usually lower for
adulterated ghee than for pure ghee.

7. Classification of lipids
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There are many ways to classify the lipids. There no single classification is universally accepted

8. Classification of lipids
1. Fatty acids: Esters of fatty acids with glycerols.
2. Saturated fatty acids: solid at room temp and having
fewer double bonds e.g. Palmatic acid and stearic
acid.
3. Unsaturated fatty acids: Liquid at room temp and
having more double bonds e.g. Oleic acid and linoleic
acids.
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9. Classification of lipids
Glycerol lipids:
• These are esters of fatty acids with glycerol but more complexes.
Neutral lipids (triglycerols)
• 3 group of glycerols are attached to fatty acids. Function - energy
stored in body in this form
Phospholipids
• Phosphate group is attached to glycerols
• E.g. Lecithins (present in Plasma membrane).
Plasmogens
• These are phospholipids but with enol-ether linkages Mostly occurs
in animals.
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10. Classification of lipids
Lipids devoid (lacking) of glycerols: Esters of fatty acids with out
glycerol
Shignolipids: Complex in nature and contains sphinogocine i.e. 18
carbon hydrocarbon chain with N2 bases e.g. Ceratamides.
Glycolipids: Contain a variety of sugars but devoid phosphate
Waxes: Esters of high molecular weight fatty acids with alcohol
(other than glycerols) e.g. Bee’s wax
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11. Classification of lipids
Steroids
• Group of compounds which is structurally and functionally unrelated to lipids but
included in lipids because of similar physical properties.
• These contain alcohol group at C-3 position and have a side chain of 8-10 carbons at
C-17
• Steroids are manufactured from lipid precursors in the cells.
• Each steroid molecule possesses a fused four ring (A,B,C and D) skeleton known as
cyclopentanohydrophenanthrene
• Steroids are the members of the group triterpenoids
• Cholesterol is the most important and common sterol found in mammals.
• It has also been isolated from red algae.
Terpenes
• It contains 10 carbon.
• It has a characteristic odour.
• e.g. Menthol, camphor, essential oils, etc.
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12. Classification of lipids
Complex lipids: Consists of other compounds such as proteins, peptides
and polysaccharides in addition to lipids.
Lipoproteins: It contains protein along with lipids. These are most
complex because in the living systems they are found in the form of
soluble liquid drops and build the plasmamembrane and membranes cell
organelles like mitochondria, chloroplast, lysosomes, goligicomplex, etc.
Lipoproteins of membranes may be water soluble or fat-soluble
Ergosterol: It occurs in ergot and yeast, it is the precursor of vit D, and it
acquires antirachitic properties with the opening of ring B when irradiated
with ultraviolet light.
Glycogen (animal starch): It is a reserve food material fund in liver and
muscles of animals and human beings. It also found in the plants which
have no chlorophyll (fungi and yeasts) but not in green plants.
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13. Biological functions of fat
• Source of energy: In the body fat serves as an efficient source of energy
when stored in adipose tissue. Oxidation of fats results in the release of
a lot of energy 1 g of fat when oxidized releases 9 Kcal energy. It is
almost double of carbohydrates and proteins.
• Seeds contain 30-50% of fat: In a small space large amount of the
energy is stored.
• Components of biomembranes: Phospholipids are the most important
components of biomembranes.
• Plant protective coat: Lipid acts as a plant protective coat e.g. wax,
cutin, and suberin.
• Excellent insulator: Fat is a bad conductor of heat. It provides excellent
insulation.
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14. • Protect internal organs: Fats serves as padding for the internal organs.
• Formation brain and nervous system: Lipids has significant role in
development of brain and nervous system.
• Ion exchange, intercellular transport and cellular excretion:
Phospholipids has vital role in these activities.
• Hormones: Male and female hormones like androgens, ergosterols,
progesterons, etc. are chemically steroids (fats).
• Constituents of essential oils: Terpenes are the constituents of essential
oils.
• Role in digestion: Dietary fat is necessary for sufficient absorption of the
essential fatty acids and fat-soluble vitamins A, D, E, and K from the
gastrointestinal tract.
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15. Questions
Q1. What are fatty acids? Write about its physical and chemical
properties.
Q.2 Write about classification of fats. Add a note on biological
functions of fats.
Q3. Short notes
i) Physical properties of fats
ii) Chemical properties of fats
iii) Steroids
iv) Lipoproteins
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16. Thanks
Dr. Anil V Dusane
anildsuane@gmail.com
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