2. Phospholipids
These are complex or compound lipids containing
phosphoric acid, in addition to fatty acids,
nitrogenous base and alcohol
There are two classes of phospholipids
Glycerophospholipids (containing glycerol as the
alcohol)
Sphingophospholipids (containing sphingosine as
the alcohol)
3. 1. Glycerophospholipids
They are the major lipids that occur in biological
membranes
They consist of glycerol-3-phosphate esterified at its
C1 and C2 with fatty acids
Phosphatidic acid:
This is simplest phospholipids
Does not occur in good
concentration in tissues
It is an intermediate in
the synthesis of TAG and
phospholipids
4. lecithins:
These are the most abundant
group of phospholipids in the
cell membrane
Chemically lecithin
(Greek: Lecithos-Egg yolk) is a
phophatidic acid with choline as a base
Cephalins:
Ethanolamine is the
nitrogenous base present
in cephalins
5. Phosphotidylinositol (PI):
Inositol is attached to phosphatidic acid to give PI
This is an important component of cell membranes
The action of certain hormone is mediated through
PI
7. Plasmalogens:
When fatty acid is attached by ether
linkage at C1 of glycerol in
Glycerophospholipids, the resultant
compound is plasmalogen
Cardiolipin:
It was first isolated from the
heart muscles
It consist of two molecules of
phosphotidic acid held by an
additional glycerol through phosphate
group
An important component of inner mitochondrial membrane
8. 2.Sphingomyelins:
Sphingosine is atttached by an amide linkage to a
fatty acid to produce Ceramide
They are the important constituents of myelin and
are found in good quantity in brain and nervous
tissues
Ceramide act as a second messenger by
regulating programmed cell death
A ceramide containing 30-carbon fatty acid is a
major component of skin and it regulates skin’s
water permeability
9. Functions of phospholipids
1. In association with proteins phospholipids form the
structural components of membranes and regulate
membrane permeability
2. Phospholipids in the mitochondria maintain the
conformation of electron transport chain
components and thus cellular respiration
3. They participate in the absorption of fats from the
intestine
4. They are essential for the synthesis of different
lipoproteins and thus participate in transport of lipids
5. The prevent accumulation of fats in liver (lipotropic
factors)
10. 6.They participate in the transport of cholesterol
and thus help in the removal of cholesterol from
the body
7.They act as surfactants (respiratory distress
syndrome)
8. Cephalin participate in the blood clotting
9. Phosphotidyl inositol is the source of second
messenger that are involved in the action of some
hormones
12. Thy are the important constituents of cell
membrane and nervous tissues
Cerobrosides is the simplest glycolipids
The contain ceramide and one or more sugars
Gangliosides are primarily found in ganglions
14. They are molecular complexes of lipids with
proteins
They are transport vehicles for lipids in the
circulation
There are five types of lipoproteins
Chylomicrons
VLDL
HDL
Free fatty acid albumin complex
16. They are the compounds containing cyclic steroid
nucleus (or ring) namely CPPP
It consists of phenanathrene nucleus (ring A, B
and C) to which a cyclopentane ring (D) is
attached
There are several steroids in the biological
system. These include cholesterol, bile acids,
vitamin D, sex hormones
If the steroid contains one or more hydroxyl
groups it is commonly known as sterol
17.
18. Cholesterol
Exclusively found in animals is the most abundant
animal sterol
It is widely distributed in all cells and is a major
component of cell membranes and lipoproteins
Cholesterol (Greek: Chole-bile) as first isolated
from bile
Cholesterol literally means “solid alcohol from
bile”
19. Structure and occurrence
C27H46O
As a structural component of plasma membranes,
cholesterol is an important determinant of
membrane permeability properties
It is yellowish crystalline solid
It is insoluble in water and soluble in organic
solvents
20. Functions
It is a poor conductor of heat and electricity
It is present in abundance in nervous tissues
It appears that cholesterol function as an
insulating cover for the transmission of electrical
impulses in the nervous tissues
It has a role in synthesis of bile acids, hormones
and vitamin D