Structural lipids, including phospholipids and glycolipids, are essential components of biological membranes. Phospholipids, characterized by their hydrophilic heads and hydrophobic tails, are classified into glycerophospholipids and sphingophospholipids, with various specific types that serve crucial functions in cellular processes and membrane integrity. Glycolipids, which consist of fatty acids, alcohols, and monosaccharides, play important roles in cell communication and structural organization.

2. STRUCTURAL LIPIDS
Phospholipids and glycolipids are important
structural lipids and are constituents of biological
membranes.

4. Phospholipids - Introduction
LIPIDS:
 Lipids are macrobiomolecule that are insoluble in water, but
soluble in organic solvents like ether, benzene, chloroform
etc.
PHOSPHOLIPIDS:
 Phospholipids are a class of lipids whose molecule has a
hydrophilic "head" and hydrophobic "tails".
 Phospholipids are compound lipids contain fatty acids,
alcohol, phosphoric acid and nitrogenous base.

6. Phospholipids - Structure

7. Phospholipids - Introduction
 Phospholipids are the major component of biological
membranes.
 Phospholipids are compound lipids contain fatty acids, alcohol,
phosphoric acid and nitrogenous base.
 There are two classes of phospholipids
Glycerophospholipids – contain glycerol as alcohol
Sphingophospholipids - contain sphingosine as alcohol

9. Phospholipids - Glycerophospholipids
 Glycerophospholipids are the major lipids that occur in biological
membranes.
 They contain glycerol, fatty acids, phosphoric acid and a
nitrogenous base.

10. Glycerophospholipids
o Glycerophospholipids are the major lipids that
occur in biological membranes.
o They contain glycerol, fatty acids, phosphoric
acid and a nitrogenous base.

11. The general formula of glycerophospholipids
is:

12. Glycerophospholipids
o Usually C-1 contans a saturated fatty acid
while C-2 contains an unsaturated fatty acid.
o The simplest of phospholipids is phosphatidic
acid.
o It contains a glycerol, fatty acids and
phosphate.

13. Phospholipids - Types
 Depending on the alcoholic residue attached, they are
named as:
 Phosphatidyl choline (lecithin),
 Phosphatidyl ethanolamine (cephalin),
 Phosphatidyl serine,
 Phosphatidyl inositol,
 Phosphatidyl glycerol and
 Diphosphatidyl glycerol (cardiolipin).

14. Phospholipids - Types
Lecithins are the most abundant group of
phospholipids in the cell membranes and have
metabolic and structural functions.
Dipalmitoyl lecithin is an important surface
active agent in lungs.

15. Phospholipids - Types

16. Phospholipids - Types
Cephalins are also membrane phospholipids and have the
base ethanolamine.
Phosphatidylinositol is involved in signal transduction.
Cardiolipin was first isolated from heart muscle. It
consists of two phosphatidic acid held by an additional
glycerol. It is an important component of inner
mitochondrial membrane.

17. Phospholipids - Types
Phosphatidylglycerol is a major phospholipid
in thylakoid membrane of chloroplast.
Phosphatidyl serine is a minor component of
most membranes. It is found to take part in cell
signaling and in apoptosis.

18. Phospholipids – Functions
In association with proteins, phospholipids form the
structural components of membranes and regulate
membrane permeability.
Phospholipids (lecithin, cephalin, and cardiolipin) in
the mitochondria are responsible for maintaining
the conformation of electron transport chain
components and thus cellular respiration.

19. Phospholipids – Functions
Due to their amphipathic nature, phospholipids can
combine with polar and non-polar compounds in the
cell.
Phospholipids participate in the absorption of fat from
the intestine.
Phospholipids are essential for the synthesis of
different lipoproteins and thus participate in the
transport of lipids.

20. Phospholipids – Functions
Arachidonic acid liberated from phospholipids
serves as a precursor for the synthesis of
eicosanoids (prostaglandins, prostacyclins,
thromboxanes, etc.)
Dipalmitoyl lecithin is an important lung
surfactant.
Cephalins participate in blood clotting.

21. Phospholipids – Functions
Phospholipids are essential components of bile
where they act as detergents and helps in
solubilization of cholesterol.
Phosphatidyl inositol is involved in signal
transmission across membranes.

22. Sphingophospholipids
Sphingophospholipids contain phosphate and
fatty acid attached to the alcohol, sphingosine
or its derivatives (dihydrosphingosine,
phytosphingosine).
 Eg: Sphingomyelins

23. Sphingophospholipids

24. Sphingophospholipids
The fatty acids are attached through an amide
linkage rather than the ester linkage.
The base present is normally choline.
Sugar residue may also be linked to phosphoric
acid group.

26. Sphingophospholipids
When fatty acid and sphingosine is linked by amide
bond, a ceramide is formed.
Ceramide is the fundamental unit in all
sphingolipids.
Sphingomyelins are found in large amount in the
brain and nerve tissues.
Sphingophospholipids are also found in the seeds
of several plant species.

27. GLYCOLIPIDS
Glycolipids contain an alcohol (sphingosine or
glycerol), fatty acid and a monosaccharide.
They are O-glycosides of either sphingosine or
glycerol derivative.
The commonly attached monosaccharides are D-
glucose, D-galactose or N-acetyl D-galactosamine.

29. GLYCOLIPIDS
Monogalactosyl diglycerides and
digalactosyldiglycerides have been shown to be
present in many higher plant tissues especially in
chloroplast membrane.
Glycolipids present in animal cells help in cell
to cell communication