This document discusses the structure and classification of lipids. It begins by defining lipids as insoluble in water, soluble in organic solvents, and containing carbon, hydrogen and oxygen. Lipids are classified based on their structure and functions, which include storage, membrane, and cell signaling roles. Membrane lipids include phospholipids, glycolipids, and cholesterol. Phospholipids are the most abundant membrane lipid and include phosphoglycerides like lecithin, cephalins, and phosphoinositides. Glycolipids link a hydrophobic lipid tail to one or more hydrophilic sugar groups. Cholesterol contains four linked hydrocarbon rings and a hydrocarbon tail, and is present in almost all animal membranes.

1. DR. VIBHA KHANNA
Asso. Prof. (Botany)
SPC GOVERNMENT COLLEGE
AJMER (Rajasthan)

2. PLANT BIOCHEMISTRY
• BLOCK 1. : Lipid metabolism
– PRESENTATION 1: Structure and function of lipids,

3. LIPIDS
• Term first used by German biochemist Bloor in 1943.
• The word lipid is derived from a Greek word “lipos” which means Fat.
• They are:
1. Insoluble in water.
2. Soluble in non-polar organic solvents e.g. ether, acetone.
3. Contain carbon, hydrogen and oxygen sometimes contain nitrogen and phosphorous.
4. Neutral lipids upon hydrolysis yield glycerol and fatty acids*.
5. Take part in plant and animal metabolism.
6. In aqueous environment lipid molecules associate by non – covalent interactions to
form supramolecular structures such as monolayers,micelles,bilayers,and vesicles.

4. • FATTY ACIDS*
• Fatty acids are a class of compounds
containing a long hydrophobic
hydrocarbon chain and a terminal
carboxylate group.
• Fatty acid are long chain organic
acids usually from 4 to 30 carbon
atoms.
• Fatty acid which occur in natural fats
are usually monocarboxylic and
contain even number of carbon
atoms as these synthesized from two
carbon units.
• The chain may be saturated or
unsaturated.
• Some fatty acid have hydroxyl group
in the chain and still other may
possess ring structure

5. CLASSIFICATION OF LIPIDS:
On the basis of Structure

6. CLASSIFICATION OF LIPIDS :
On the basis of Functions
LIPIDS
STORAGE
LIPIDS
MEMBRANE
LIPIDS
CELL
SIGNALLING

7. MEMBRANE LIPIDS:
• All living cells are enclosed in
membrane.
• These membrane define the
inner and outer boundary of the
cells and also the
compartmentalisation of
different organelles within the
cell.
• The biological membrane
consists of a double layer of lipids
and the proteins.
• Lipid are hydrophobic in nature
they provide effective barrier to
polar molecules.
• Variety of lipid are known to be
present in biological membrane.

8. MEMBRANE LIPIDS
PHOSPHOLIPIDS
Phosphoglycereids
Phosphoinositides
Phosphosphingosides.
GLYCOLIPIDS
Glycosphingolipids
and
Glycoglycerolipids
CHOLESTROL

9. PHOSPHOLIPID:
• Phospholipid are the most abundant
membrane lipid.
• They serve primarily as structural
components of membrane and are never
stored in large quantities.
• Phospholipids consist of a glycerol molecule,
two fatty acids, and a phosphate group that is
modified by an alcohol.
• They are amphipathic.
– The phosphate group is the
negatively-charged polar head,
which is hydrophilic.
– The fatty acid chains are the
uncharged, nonpolar tails, which
are hydrophobic.
• Phospholipid are compound lipid and are
of three types;
1. Phosphoglycereids
2. Phosphoinositides
3. Phosphosphingosides.

10. PHOSPHOLIPID: Phosphoglycereids
• Phosphoglycerides have three parts:
– a three-carbon backbone of glycerol,
– two long-chain fatty acids esterified (or attached via an ether link in
Archaea) to hydroxyl groups on carbons 1 and 2 (C1 and C2) of the
glycerol and
– a highly polar or charged group ( like phosphoric acid) esterified to
the C3 hydroxyl group of glycerol.
• Lecithin is a phospholipid which consists of glycerol, two fatty acids, a
phosphate group and choline. (Lecithins are widely distributed in
nature, including various oil seeds like soybean and the yeasts .)
• Cephalins contain the amino alcohols serine or ethanolamine(in place
of choline). (Cephalins are found in most cell membranes, in animal
world. They have been identified from soybean oil.)

11. PHOSPHOLIPID: Phosphoinositides
• Phosphatidylinositol is an acidic (anionic) phospholipid that basically,
consists of a phosphatidic acid backbone, linked via the phosphate
group to inositol (hexahydroxycyclohexane).
• Phosphoinositides are the phosphorylated derivatives of
phosphatidylinositol.
• They have three parts:
– a three-carbon backbone of glycerol,
– two long-chain fatty acids esterified to hydroxyl groups on carbons 1 and 2
(C1 and C2) of the glycerol and
– attached to a polar head group (the cyclic hexahydroxy alcohol called
inositol) that extends into the cytoplasm. [The inositol is present as the
stereoisomer, myo-inositol.]
• Examples: phosphatidylinositol 3,4,5-trisphosphate, often called PIP3 ;
phosphatidylinositol 4,5-bisphosphate, often called PIP2
• *Phosphosphingosides: apparently lack in plants and the
microorganisms.

12. GLYCOLIPID
• Glycolipid is a structural lipid.
They are made up of lipids and
carbohydrate.
• It consists of a hydrophobic lipid
tail and one or more hydrophilic
sugar groups linked by a
glycosidic bond.
• Glycolipids are components of
cellular membranes
• They are generally found on the
extracellular face of eukaryotic
cellular membrane.
• They are also present on the
cell surface of some viruses,
bacteria.

13. GLYCOLIPIDS
• The basic structure of a
glycolipid consists of a mono- or
oligosaccharide group attached
to a sphingolipid or a glycerol
group, which can be acetylated
or alkylated, with one or two
fatty acids.
• These make up the two classes
– Glycosphingolipids and
– Glycoglycerolipids
• Glycolipids interact and bind to
the lipid-bilayer through the
hydrophobic nature of the lipid
tail which anchors it to the
surface of the plasma
membrane.

14. Cholesterol
• Cholesterol is a steroid derivative
and is present as membrane lipid in
almost all animal membranes.
• Derivatives of steroids, however, are
also found in plants, fungi, and
some bacteria.
• Cholesterol is a lipid with a
unique structure consisting of four
linked hydrocarbon rings forming
the bulky steroid structure. There is
a hydrocarbon tail linked to one end
of the steroid and a hydroxyl group
linked to the other end.
• The steroid nucleus consist of four
rings numbered A,B,C,D. the first
three rings have 6 carbons whereas
the fourth has only 5 carbons.

15. REFERENCES:
Biochemistry And Molecular Biology Of Plants
: Buchanan, Gruissem, Jones
Plant Physiology : Mohr