Fatty acids are long chain organic acids that are the building blocks of lipids. They contain a carboxyl group and a long hydrocarbon tail. There are different types including saturated, unsaturated, and branched fatty acids. Lipids include fats, oils, waxes, phospholipids, glycolipids and steroids. They serve important functions like energy storage, insulation, cell structure, and transport. Lipids can be classified as simple or complex. Simple lipids include neutral fats and waxes. Complex lipids include phospholipids, glycolipids and steroids. Fatty acids and lipids have properties like melting point, hydrolysis, hydrogenation, and rancidity. Tests like iodine

1. LIPIDS
MAN BAHADUR RANA
BPH
ACAS,NEPAL

2. Fatty acids
Fatty acids long chain organic acids 2-24 carbon atoms.
single carboxyl group and a long, nonpolar hydrocarbon tail.
building block units of lipids.

3. Fatty acids
Amphipathic molecule
Diverse structures (>100 different
types)

4. Classification of Fatty acids
1. Saturated Fatty acids
2. Unsaturated Fatty acids
3. Branched Fatty acids

5. Classification of Fatty acids
1. Saturated Fatty acids:
derivative of acetic acid  at least 4 carbon atom.
All carbon  fully saturated no double bond is .
2. Unsaturated Fatty acids:
double bonds between any two carbon atoms
. Generally double bonds C-9 and C-10.
•PUFA:
more than 2 double bonds Polyunsaturated fatty acids
(Polyethenoid).
E.g linoleic acid, linolenic acid and arachidonic acid fatty
acids (EFA)

6. Lipids and fatty acids

7. Lipids
esters of fatty acids or are substances such
Esters
heterogenous compound, greasy in nature insoluble in water but
soluble in organic solvents

8. Functions of Lipids
1. Source of energy:
2. Storage of energy:
3. Heat insulation and Mechanical protection:
4. Structural components of cells:
5. transport form

9. Functions of Lipids
4. Structural components of cells:
5. transport form

10. Classification of Lipids

11. Classification of Lipids
I. Simple Lipids
Esters of fatty acids  various alcohols:
(a) Neutral fats (Triacylglycerol, TG):
triesters of fatty acids  glycerol.
(b) Waxes: Testers of fatty acids  higher monohydroxy
aliphatic alcohols.

12. Classification of Lipids
2.Complex lipids: Esters of fatty acids
containing other groups
(a) Phospholipids
substituted fats fatty acid and alcohol
+ a phosphoric acid residue, +
nitrogenous base +other
substituents.
(i) Glycerophospholipid: glycerol 
alcohol. e.g. ,lecithin, cephalin.
(ii) Sphingophospholipids: Sphingosine
 the alcohol e.g. sphingomyelin.

13. Classification of Lipids
(b) Glycolipids
With carbohydrate moiety.
sphingosine or sphingol + nitrogenous + fatty acids
No phosphoric acid and glycerol.
These are of two types:
• Cerebrosides
• Gangliosides

14. Classification of Lipids
C. Steroids
With cyclopentan ring system.
The basic structure of steroids is a four-ring hydrocarbon.
Three parts, Polar head, rigid planar steroid ring and nonpolar
hydrocarbon tail.

15. Classification of Lipids
Importance of cholesterol
• component of some cell membranes and of plasma
lipoproteins.
•precursor of many other biologically important steroids
•
•sterol of higher animals abundant in nerve tissues and in
gallstones.
•High blood atherosclerosis.

16. Properties of Fatty acids and lipids
1. Melting point:
• Shorter chain length
lower melting
• Unsaturated  lower
melting temperatures
18:0 18:1 18:3
70o 13o -17o

17. Properties of Lipids and fatty acids
2. Hydrolysis.
fats a lipases fatty acids and glycerol.
3. Hydrogenation
Unsaturated fatty acids + gaseous hydrogen saturated
(platinum, palladium or nickel)

18. Properties of Lipids and fatty acids
4. Halogenation:
Unsaturated fatty acids and their esters  halogens like Br2
and I2 at their double bond.
5. Rancidity.
Oils or fats  unsaturated fatty acids + O2  short chain
fatty acids (C4 to C10) and aldehydes  a rancid taste and
odour
oxidative rancidity

19. Properties of Lipids and fatty acids
5. Iodine number
grams of iodine to saturate 100 gm of given
iodine  double bonds,
high iodine number  a high degree of unsaturation
Beef fat: 32-47
Human fat: 65
Butter fat: 27
Coconut oil: 8

20. Properties of Lipids and fatty acids
6.Acid Number
number of milligram of KOH neutralize the free
fatty acids.
Acid numbers degree of rancidity of the given fat.
Smaller the acid no. better the fatty acid.
Acid number of  Beef fat: 0.25,
Butter fat: 0.40
Coconut oil: 1.50

21. Properties of Lipids and fatty acids
7. Saponification and Saponification Number:
hydrolysis of fats  saponification.
Saponification number  a number of milligram of KOH required
 neutralization of 1 gm fat.
The shorter the average chain length of the fatty acids
higher is the saponification number.
Saponification No  use of oils in fats