Lipids may be regarded as organic substances which is insoluble in water, soluble in organic solvents (alcohol , ether etc.), Triacylglycerols (formerly triglycerides) are the esters of glycerol with fatty acids.

1. Seminar Presentation
LIPIDS
S. Maheen Abdul Rahman,
M. Pharm.,
Pharmaceutical Chemistry

2. Definition
 Lipids may be regarded as organic substances which
is insoluble in water, soluble in organic solvents
(alcohol , ether etc.), and it is related to fatty acids
and utilized by the living cells.
Unlike the polysaccharides, proteins and nucleic
acids, lipids are not polymers. Further, lipids are
mostly small molecules.

3. Classification
1. Simple lipids: These are defined as the esters of fatty acids with
alcohols. These are mainly two types.
1. Fats and oils (Triacylglycerals): These are esters of fatty acids
with glycerols.
2. Waxes: Esters of fatty acids with alcohols other than
glycerol. This fatty acids generally long chain!
2. Complex or compound lipids: These are esters of fatty acids with
alcohols containing extra groups such as phosphate,
nitrogenous base, carbohydrate, protein etc. They are further
divided as
(i) Phospholipids: They contains phosphoric acids and
frequently a nitrogenous base.
(a) Glycerophospholipids: Glycerol as the alcohol e.g.,
Lecithine and Cephaline
(b) Sphingophospholipids: Sphingosine is the alcohol e.g.,
Sphingomyelin.

4. (ii)Glycolipids: These lipids contain a fatty acid, carbohydrate
and nitrogenous base. The alcohol is sphingosine, hence they
are also called as glycosphingolipids. Glycerol and phosphate are
absent e.g., cerebrosides gangliosides.
(iii) Lipoprotein: Macromolecular complexes of lipids with
proteins e.g., LDL, HDL, VLDL, Chylomicrons
3. Derived Lipids: These are the derivatives obtained on the
hydrolysis of group 1 and group 2 lipids which possess the
characteristics of lipids. E.g., DAG, Steroid, Ketone bodies.
4. Miscellaneous lipids: These include a large number of
coumpounds e.g., Carotinoids, Squalene and terpenes

6. Fatty acids
Fatty acids are carboxylic acids with hydrocarbon side
chain. They are simplest form of lipids. Fatty acids that occur
in natural fats are usually straight chain derivatives containing
an even number of carbon atoms.
The chain may be saturated(contains no double bond)
called saturated fatty acids or the chain may
unsaturated(containing one or more double bonds) called
unsaturated fatty acids.

7. Examples of important fatty acids
Saturated fatty acids
* Acetic acid
* Propionic acid
* Butyric acid
*Caproic acid ,,, etc
Unsaturated fatty acids
*Linolenic acid - ω 3 fatty acids (no. represents the position
of double bond with carbon atom)
*Linoleic acid - ω 6 fatty acids
* Oleic acid - ω 9 fatty acids

8. Essential fatty acids
 The fatty acids that cannot be synthesized by the body
and therefore should be supplied in the diet are known as
essential fatty acids (EFA). Chemically, they are
polyunsaturated fatty acids(PUFA), namely linoleic acid and
Iinolenic acid Arachidonic acid.

9. Triacylglycerols(TAG)
 Triacylglycerols (formerly triglycerides) are the esters of
glycerol with fatty acids. The fat sand oils that are widely
distributed in both plants and animals are chemically
triacylglycerols. They are insoluble in water and non-polar in
character and commonly known as neutral fats

10. Properties of TAG
 Hydrolysis: TAG undergo enzymatic hydrolysis by lipases to
produce FFA and glycerols
 Saponification – By alkali to produce Soaps and glycerols
 Rancidity – Deterioration of fats and oils – unpleasant taste. It
occurs when the fats and oils exposed to air, moisture, light
and bacteria

11. Phospholipids
 These are complex or compound lipids containing Phosphoric
acid, in addition to fatty acids, nitrogenous base and alcohols.
There are 2 classes of phospholipids,
1. Glycerophospholipids
2. Sphingophospholipids
1. Glycerophospholipids:
 These are the major lipids that occur in biological membranes.
They consist of glycerol 3-phosphate(G-3-P) esterified at its C1
and C2 with fatty acids. Usually, C1 contains a saturated fatty
acid while C2 contains an unsaturated fatty acid.
Examples: 1. Phosphatidic acid
2. Lecithin(Phosphatidyl choline)

12. 3. Cephalin(Phosphatidyl ethanolamine)
4. Phosphatidyl inositol
5. Phosphatidyl serine
6. Plasmalogen(Phophatidal ethanolamine)
7. Cardiolipin(Phosphatidyl glycerol)
2. Sphingophospholipids:
Examples: Sphingomyelins
 In this sphingosine is attached to fatty acids by an amide
linkage and also b ceramide also attached. Sphingomyelines
are important constituents of myelin and found in nervous
tissues.

13. Structures of phospholipids

15. .
Glycolipids
 These are important constituents of cell membrane and
nervous tissues(particularly in brain). Cerebrosides are the
simplest form of glycolipids. They cntains a ceramide and one
or more sugars e.g., galactocerebroside and Glucocerebroside
are the most important glycolipids.

16. Lipoproteins
 Lipoproteins are molecular complexes of lipids with proteins.
They are the transport vehicles for lipids in the circulation.
There are five types of lipoproteins, namely chylomicrons,
very low density lipoproteins (VLDL), low density
lipoproteins (LDL), high density Iipoproteins (HDL) and free
fatty acid-albumin complexes.

17. Biomedical Concepts of Lipids:
 Lipids are important to the body as constituents of membranes,
source of fat soluble (A, D, E and K) vitamins
 Triacylglycerols(TAGs) primarily stored in the adipose tissue
are concentrated fuel reserves of the body.
 The unsaturated fatty acids-linoleic and linolenic acid are
essential to humans, the deficiency of which couses
phrynoderma or toad skin.
 The cyclic fatty acid, namely choulmoogric acid, is employed
in the treatment of leprosy.
 Fats and oils on exposure to air, moisture, bacteria etc. undergo
rancidity (deterioration).
 Cephalins participate in blood clotting.
 Lipids are associated with certain disorders----obesityo nd
atherosclerosis.

18. References
1. Satayanarayana, U (2014) Biochemistry,
Publisher: Elsevier; fourth edition
2. Nelson, D., and Cox,M.M.(2017) Lehninger
Principles of Biochemistry. 7th edition

19. .
Thank You…