This document discusses phospholipids and their subclasses. Phospholipids contain fatty acids, phosphoric acid, and nitrogenous bases or alcohols. The two main classes are glycerophospholipids, containing glycerol, and sphingophospholipids, containing sphingosine. Lecithin and cephalin are important glycerophospholipids. Phospholipids form cell membranes and regulate permeability. They also participate in fat absorption and transport and removal of cholesterol from the body. The document also briefly discusses glycolipids, lipoproteins, steroids like cholesterol, and their structure and functions.

1. Lecture 9
Phospholipids

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

6. Phosphotidylserine:
The amino acid serine is attached in this group

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

11. Glycolipids

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

13. Lipoproteins

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

15. Steroids

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

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