Lipids perform four major physiological functions in the body: 1) as structural components of biological membranes, 2) as energy reserves, 3) as vitamins and hormones, and 4) bile acids aid in lipid solubilization. There are three main classifications of lipids: simple lipids like triglycerides, compound lipids containing additional groups like phospholipids and sphingolipids, and derived lipids which are hydrolysis products of simple and compound lipids. Fatty acids are mono-carboxylic acids that vary in carbon chain length and saturation, and serve as building blocks for more complex lipids. Phospholipids are major structural components of membranes and act as emulsifying agents. Steroids contain a cyclopentanoperhydrophen

1. LIPID
STRUCTURE AND FUNCTION

2. INTRODUCTION
“Biological molecules that are insoluble in aqueous solutions and soluble
in organic solvents, have some relation to fatty acids as esters, and have
potentiality of utilization by living organisms are classified as lipids.”
They perform four major physiological functions:
1. Serve as structural components of biological membranes
2. Provide energy reserves, predominantly in the form of
triacylglycerols
3. Both lipids and lipid derivatives serve as vitamins and
hormones
4. Lipophilic bile acids aid in lipid solubilization

3. Bloor’s Classification
A. Simple lipid - ester of fatty acids with various alcohols
1. Natural fats and oils (triglycerides)
2. Waxes
(a) True waxes: cetyl alcohol esters of fatty acids
(b) Cholesterol esters
(c) Vitamin A esters
(d) Vitamin D esters
B. Compound lipid - esters of fatty acids with alcohol plus other
groups
1. Phospholipids and spingomyelin: contains phosphoric
acid and often a nitrogenous base
2. Spingolipids (also include glycolipids and cerebrosides):
contains aminoalcohol spingosine, carbohydrate, N-base;
glycolipids contains no phosphate
3. Sulfolipids : contains sulfate group
4. Lipoproteins : lipids attached to plasma/other proteins
5. Lipopolysaccharides: lipids attached to polysaccharides
Classification
CH3
OH
CH3
CH3
CH3 CH3
E E E E

4. C. Derived lipids – hydrolytic products of A & B with lipid
characters
1. Saturated & unsaturated fatty acids
2. Monoglycerides and diglycerides
3. Alcohols (β-carotenoid ring, e.g., vitamin A, certain
carotenoids)
4. Vitamin E and K
Classification cont.

5. FIGURE 43
NOMENCLATURE AND
STRUCTURE
Fats and oils:
Vegetable oils are triglycerides that are liquid at room
temp due to their higher unsaturated or shorter-chain fatty
acids
Triglycerides are most abundant natural lipids
Natural fats have D-configuration
Usually R1 and R3 are saturated and R2 is unsaturated
Natural fats are mixture of two or more simple triglycerides

6. FATTY ACIDS
“ A fatty acid may be defined as an acid that occurs in a natural
triglyceride and is a mono carboxylic acid ranging in chain length
From four carbon to 24 carbon atoms and including , with
exceptions, only the even-numbered members of the series ”

7. FIGURE 44
SOME NATURAL FATTY
ACIDS
Hydroxy acids : ricinoleic acid and dihydroxy stearic acid (castor
oil) cerebronic acid (C23H46[OH]COOH, 2 – hydroxy tetracosanoic
acid) (cerebroside of animal tissues)
Cyclic acids: Hydnocarpic and chaunmoogric acids (chaulmoogra
oil, used in treatment of leprosy)
Linoleic acid, linolenic acid and arachidonic acid are essential
fatty acids

8. FIGURE 46
HYDROLYSIS
If Alkali is used (saponification):
Triolein + 3NaOH Glycerol + 3C17H33COO-
Na+
(Sodium oleate, soap)

9. PHOSPHOLIPIDS
They are first and foremost structural components
of membranes
Serves as emulsifying agents and surface active
agents
They are amphipathic molecules
They are of two types : phosphoglycerides and
spingomyelins (contains spingosine instead of
glycerol)
Ceramide is the core structural unit of spingolipids
which is a fatty acid amide derivative of spingosine

10. STEROIDS
Contains cyclopentanoperhydrophenanthrene
ring
It is the nonsaponifiable fraction of lipids
Main constituent of animal tissues and
abundant in brain, nerve tissue and glandular
tissue
Chief component of gallstones
Normal blood level is 200 mg/ml a portion of
which is plasma protein bound