The document provides a comprehensive overview of lipids, detailing their classification, structure, properties, and biological functions in living organisms. It explains the types of lipids, including simple, compound, and derived lipids, along with the classification and significance of fatty acids. Additionally, it discusses the metabolic disorders associated with lipids and their roles in energy storage, cell membrane structure, and hormone production.

1. Shivanee Vyas
Assistant Professor 1

2. “These are the naturally Organic compounds, insoluble in water, soluble in organic solvents
(alcohol, ether, etc.), they are potentially related to fatty acids & utilized by living cells”.
• Lipids are a heterogeneous group of compounds.
• They are esters of fatty acids. Lipids occur widely in plants and animals. Lipids Include fats, oils,
waxes, and related compounds.
• Lipids are a family of organic compounds, composed of fats and oils. These molecules yield high
energy and are responsible for different functions within the human body.
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3. 1. Lipids are oily or greasy nonpolar molecules, stored in the adipose tissue of the body.
2. Lipids are a heterogeneous group of compounds, mainly composed of hydrocarbon chains.
3. Lipids are energy-rich organic molecules, which provide energy for different life processes.
4. Lipids are a class of compounds characterized by their solubility in nonpolar solvents and insolubility
in water.
5. Lipids form a mechanical barrier known as a cell membrane that protects a cell from the external
environment.
PROPERTIES OF LIPIDS
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4. CLASSIFICATION OF LIPIDS
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5. Lipids are classified into three main groups based on hydrolysis.
1. SIMPLE LIPIDS: Simple lipids are the esters of fatty acids with various
alcohols.
A. Fats: (Triglycerides and triacylglycerols) - These are esters of fatty acids with
trihydroxy alcohol (glycerol). A fat is solid at ordinary room temperature, an oil is
liquid. e.g. Butter fat, beef fat. Oils are e.g. Coconut oil, castor oil, olive oil.
Fats Oils
Fats are solids or semisolids at room 25°C. Oils are liquid at room temperature.
Fats have a higher melting point than oils. Oils have lower melting point than fats.
Fats contain higher proportion of saturated
fatty acids.
Oils contain higher proportion of unsaturated fatty
acids.
Fats have high Reichert-Meissel number. Oils have low Reichert-Meissel number.
Fats are stored in liver and bone marrow. Oils are stored in seeds and fruits.
e.g. Butter fat, beef fat. e.g., Olive oil, Castor oil, Soyabean oil, Corn oil.
R-COOH + R-OH R-COOR
Fatty
acids
Alcohol Ester of fatty acid
(Simple lipids)
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6. B. Waxes- are the esters of fatty acids with monohydroxy alcohols. They are insoluble in water.
They are usually solids or semisolids and have high melting points. They are chemically
inert in nature. Example: Beeswax, Carnauba wax.
Fats Waxes
The esters of fatty acids with alcohols are
called as fats.
The esters of fatty acids with higher alcohol are
called waxes.
Fats are not secretions. Waxes are secretions.
Fats act as food reservoir. Waxes act as protective in function.
Fats are oxidized by atmospheric oxygen. Waxes resist oxidation by atmospheric oxygen.
e.g. Butter fat, beef fat. e.g. Carnauba wax, beeswax, lanoline,
spermaceti wax.
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7. 2. COMPOUND LIPIDS: These are esters of fatty acids with alcohol-containing additional groups
also. (phosphate, Nitrogenous base, protein)
A. Phospholipids: They consist of phosphoric acids, nitrogen bases, alcohol, and fatty acids. These compound
lipids are major components of the cell membrane. In cell membranes, these phospholipids have a hydrophilic
head and a hydrophobic tail, which forms the inside of the bilayer.
• Functions of phospholipid:
1. It is the structural component of membranes & regulates membrane permeability.
2. In mitochondria, they are responsible for maintaining the conformation of electron transfer chain components,
& thus cellular respiration.
3. It is participate in the absorption of fat from the intestine.
4. Cephalins, an imp group of phospholipids participate in blood clotting.
5. Phospholipids help in blood coagulation.
6. Accumulation of fat in the liver can be prevented by Phospholipids E.g.: lecithin, and cephalins.
a. Glycerophospholipids: They contain glycerol as the alcohol. Example: Lecithin, Cephalins
plasmalogens.
a. Sphingophospholipids: Sphingosine is the alcohol in this group of phospholipids.
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9. B. Glycolipids: contain fatty acids, carbohydrates, and nitrogen but not phosphoric acid.
C. Lipoproteins: Macromolecular complexes of lipids with protein.
(Chylomicrons, VLDL, LDL, HDL)
3. DERIVED LIPIDS: Derived lipids are substances derived from simple and compound lipids by hydrolysis.
A. Steroids Our bodies possess chemical messengers known as hormones, which are basically organic compounds
synthesized in glands and transported by the bloodstream to various tissues in order to trigger or hinder the
desired process. Examples: progesterone, estrogen, testosterone.
B. Terpenes in majority found in plants. Example: Natural rubber.
C. Carotenoids are tetra terpenes. They are widely distributed in both plants and animals. They are
exclusive of plant origin, they are coloured - red or yellow. Examples: carotenes, Xanthophyll's.
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10. STRUCTURE AND PROPERTIES OF TRIGLYCERIDES
These are esters derived from glycerol and three fatty acids.
• The fats & oils that are widely distributed in both plants & animals are chemically
Triacylglycerols.
• Triacylglycerols primarily function as fuel reserves for animals. Adipose tissue is
specialized for the storage of Triacylglycerols.
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11. PROPERTIES OF TRIACYLGLYCEROLS
 PHYSICAL PROPERTIES OF TRIGLYCERIDES:
1. Pure fats have no colour, taste, or odour.
2. At room temperature, fat of plant origin remains oil, because it contains more unsaturated fatty acids
while animal fat remains solid because it contains mostly saturated fatty acids.
3. They are optically active.
 CHEMICAL PROPERTIES:
1. Hydrolysis: Fats are hydrolyzed into glycerol and fatty acids by boiling with water at high temperatures.
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12. 2. SAPONIFICATION AND SOAP: When fats are boiled with a strong base like sodium hydroxide or potassium
hydroxide it gives glycerol and salt of fatty acid which is also called soap.
SAPONIFICATION NUMBER: The saponification number is a milligram of KOH required to saponify 1 gram of fat
or oil. it gives an idea about the molecular weight of fat. since it is inversely proportional to the molecular
weight. higher the molecular weight lower will be its saponification number. For example, butter has a high
saponification number of 200-203.
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13. 3. RANCIDITY: When fats and oils are exposed to light, air, and heat for a long. It develops a disagreeable
objectionable odour. Such oil or fat is said to be rancid and the phenomenon is called rancidification.
Rancidification can be prevented by antioxidants like vitamin E, butylated hydroxytoluene, phenols,
hydroquinone, tannins etc.
4. ACID NUMBER: The acid value can be defined as the number of milligrams of KOH required to neutralize free
fatty acid present in one gram of fat or oil.
5. REICHERT-MEISSL NUMBER: The reichert-meissl number can be defined as the number of litres of 0.1 N KOH
required to neutralize steam volatile water-soluble fatty acid contained in 5 grams of fat or oily it gives an idea
about the amount of steam volatile fatty acids present in the fat or oil.
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14.  COMPOSITION OF LIPID
• Lipoproteins are globular, micelle-like particles made up of a hydrophobic core of triacylglycerols and
cholesterol esters surrounded by an amphipathic coat of protein, phospholipid, and cholesterol.
• The apolipoproteins on the surface of the lipoproteins help to solubilize the lipids and target the
lipoproteins to the correct tissues.
• There are different types of lipoprotein, classified according to their functional and physical properties:
chylomicrons, very low-density lipoproteins (VLDLs), low-density lipoproteins (LDLs), and high-density
lipoproteins (HDLs).
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15. CLASSIFICATION OF FATTY ACIDS
Fatty acids are derived lipids and are obtained by hydrolysis of fats and other lipids.
Fatty acids are carboxylic acids, usually with long aliphatic long chains. Depending upon straight-chain
of fatty acids, are classified as follows.
I. Saturated Fatty Acids: These are fatty acids containing a long chain of carbon and a carboxylic
group and contain a single bond in their structure. They have the general formula CnH2n+1 COOH.
Palmitic acid-
C15H31COOH
Stearic acid-
C17H35COOH
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16. II. Unsaturated Fatty Acids: These contain one or more double or triple bonds in their structure. They
have the general formula CnH2n-1 COOH. Based on the degree of unsaturation, they may be
classified as below:
• Fatty acids with one double bond: Oleic acid.
• Fatty acids with two double bonds: Linoleic acid.
• Fatty acids with three double bonds: Linolenic acid.
• Fatty acids with four double bonds: Arachidonic acid.
Due to the presence of double bonds, unsaturated fatty acids are more reactive than saturated fatty
acids. The reactivity increases with an increasing number of double bonds.
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17. • Classification of Fatty Acids based on Nutritional Requirements
1. Essential Fatty Acids: The unsaturated fatty acids that are not synthesized in the body and are
required for the normal growth of the body are called, essential fatty acids. e.g. Arachidonic acid,
Linoleic acid, Linolenic acid etc.
2. Non-essential Fatty Acids: The saturated fatty acids are synthesized in the body and contain only
single bonds called non-essential fatty acids. e.g. Palmitic acid, Stearic acid, Arachidic acid etc.
• Significance of Essential Fatty Acids:
1. Essential fatty acids are required for the synthesis of phospholipids which are essential to maintain
the integrity of the cell and plasma membrane.
2. They are involved in the proper functioning of the reproductive system.
3. They have an important role in the blood clotting process.
4. They retard atherosclerosis.
5. They cure skin lesions.
6. A deficiency of essential fatty acids in babies can cause eczema.
7. Essential fatty acids are also required for the synthesis of prostaglandins.
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18. • Cholesterol is a steroid lipid. It is widely distributed in all cells of the body. It is found in the brain,
nervous tissue, and spinal cord.
• It is not synthesized in plants, Hence, can only be supplied by animal sources e.g. eggs, meat, etc.
• Increased blood cholesterol levels can be an indication of functional impairment of the liver
(jaundice), diabetes and CVS Increased blood cholesterol levels with other lipids can lead to
atherosclerosis.
STRUCTURE AND FUNCTIONS OF CHOLESTEROL IN THE BODY
• Structure:
 Molecular formula: C27H46O
 Normal conc. in serum: 150-250 mg/dl
 Chemically, cholesterol is 3-hydroxy-5, 6- cholestane
 Ring: Cyclopentano-per-hydrophenanthrene
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19. • Functions of Cholesterol:
1. Cholesterol is an essential component of cell membranes, which are the structures that border every cell in
the human body.
2. Cholesterol is also needed for the manufacturing of steroid-based hormones, like testosterone and
progesterone.
3. Some other hormones, produced mainly by the adrenal gland, also require cholesterol for production.
Aldosterone and cortisol are two examples.
4. Cholesterol must also be present for the skin to manufacture vitamin D, which plays a role in how the body
handles calcium and assists in maintaining bone density.
5. Cholesterol also enables the body to form bile acids, which are needed to help break down fats in the
digestive tract so that they can be absorbed into the body.
6. In addition, triglycerides are an important source of energy for the body particularly when glucose is
deficient.
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20. • Qualitative Tests
1. Solubility Test: Lipids are insoluble in water and soluble in hot alcohol, chloroform and ether.
2. Grease Spot Test: Lipids have the property to produce a greasy translucent spot when applied on
paper.
3. Litmus Paper Test: On the basis of unesterified fatty acid in the lipid, lipids can be acidic or neutral
to litmus change in the colour of litmus paper from red to blue indicates lipids contain free fatty acids
4. Saponification Test: To Fatty acids formed after hydrolysis of fat can be treated with alkali to form
salts of fatty acids having soap-forming properties. In a test, tube adds 10 drops of oil and 20 drops
of 40% NaOH. Boil for 30 min. It forms a stable froth or foam.
5. Emulsification Test: Lipids can facilitate the mixing of oil and water forming a stable emulsion. Take
2 ml of water and 2 ml of bile salt solution in a separate test tube. To each test type, add 3 drops of
oil. Shake and compare the stability of the mixture formed in two test tub, This test gives the idea
that fat or oil form an emulsion that can be stabilized by the addition of emulsifying agent like bile
salt.
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21. • Functions of Lipids
1. Source of Energy: Lipids are an efficient source of energy when stored in adipose tissue.
2. Insulator: Lipids protect internal organs of the body from shock.
3. Prevention of Blood Loss: Lipids like phospholipids of blood platelets are involved in blood clotting and
help in preventing blood loss from the injury.
4. Vehicle: Lipids serve as vehicles for fat-soluble vitamins.
5. Permeability: Lipids regulate membrane permeability.
6. Hormones: Some hormones and vitamins are lipids.
7. Essential Fatty Acids: Lipids, taken in the diet provide essential fatty acids which are synthesized in the
body.
8. Fats serve as surfactants by reducing surface tension.
9. Lipids present in myelinated nerves act as insulators for the propagation of depolarization waves.
10.Some saturated fatty acids are antimicrobial and antifungal agents.
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22. • METABOLIC DISORDERS OF LIPIDS
1. Obesity is due to the accumulation of excess body fat.
2. Lipidosis: Abnormal lipoproteins in blood or specific lipids in blood tissue.
3. Hyperlipidemia: Increase in plasma cholesterol or plasma triglycerides.
4. Hyper lipoprotenemia: Increase in lipoproteins.
5. Ketosis: Formation of ketone bodies in blood or urine due to excessive oxidation of fatty acid.
6. Lipid storage diseases (Enlargement of liver and spleen, leads to mental retardation)
7. Niemann Pick disease
8. Gaucher's disease
9. Metachromatic leukodystrophy
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