Lipids (Greek: lipos, means fat or lard) - are a heterogeneous class of naturally occurring organic substances - have a distinguished functional group or structural features - are insoluble in water and highly soluble in one or more of the solvents: ether, chloroform, benzene and acetone.This property sets them apart from proteins, carbohydrates,, nucleic acids and other biomolecules - are widely distributed in the biological world - play a wide variety of roles in plant and animal tissues

1. Lipids

2. Objectives (Intro)
* various lipids by source, structure and use:
triglycerides, fats and oil and waxes
* the fluid mosaic model to describe the
movement of lipid molecule in membrane
* the source and functions of some sterols:
cholesterol. ergosterol etc.

3. Introduction
 Lipids (Greek: lipos, means fat or lard)
- are a heterogeneous class of naturally occurring organic
substances
- have a distinguished functional group or structural
features
- are insoluble in water and highly soluble in one or more
of the solvents: ether, chloroform, benzene and
acetone.This property sets them apart from proteins,
carbohydrates,, nucleic acids and other biomolecules
- are widely distributed in the biological world
- play a wide variety of roles in plant and animal tissues

4. Functions of lipids
 Lipids are concentrated source of energy. One gram fat gives
9 K calories.
 It serves as a cushion for the vital organs and protects them
from external shocks or injuries.
 Lipids are the structural materials of cells and membranes
 Lipids serves as insulator for our body
 Lipids are the carrier / reservoir of fat soluble vitamins
 In food preparations lipids serves as a binding agent. It also
enhances the palatability of foods

5. Types of lipids
Glycerol (/ˈɡlɪsərɒl/; also called glycerine or glycerin) is a simple polyol compound. It is
a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol
backbone is found in all lipids known as triglycerides. Glycerolis an alcohol with three
carbons, five hydrogens, and three hydroxyl (OH) groups.

6. Storage lipids
 Fats and oils:
◦ are universally used as stored form of energy by living
organism. One gram of fat gives 9 K Calories
◦ are highly reduced compound, derivatives of fatty
acids
◦ fatty acids are hydrocarbon derivatives, which are
long chain carboxylic acids containing up to 24 carbon
atoms
◦ the most common fatty acids in plants and animals are
the even-numbered C16 and C18 species such as
palmitate and stearate
◦ fatty acid are classified as saturated (where all the
carbon are saturated with hydrogen) or unsaturated
( which contain one or more double bonds)

7. Saturated Fatty acids

8. Stearic acid
The packing of fatty
acids depends on their
degree of saturation.
Stearic acid is shown
here in its usual
extended conformation.
Saturated fatty acids
are tightly packed and
stabilized by many
hydrophobic
interactions

10. Unsaturated Fatty acids

11. Oleic acid
The double bond
(shaded)introduces a
rigid bend in the
hydrocarbon tails. Fatty
acids with one or
several such bends
cannot pack together as
tightly as saturated fatty
acids

15. Triglycerides
 The fats and oils found in animals and
plants are triglycerides
 Triglycerides are:
◦ esters of fatty acids and glycerols
◦ simple lipids
◦ important as the storage form of fat in the
human body

16. Glycerol

17. Types of Triglycerides
 Simple triglycerides: They are triesters made
from glycerol and three molecules of one kind
of fatty acids. They are rare.
 Mixed triglycerides: They are triesters with
different fatty acid components. Animal fats
and vegetable oils are many different mixed
triglycerides; e.g., Butterfat contains at least
14 different carboxylic acids.

18. Triglycerides

21. Properties of Fats and Oils…
 Hydrogenation of fats and oils:
◦ The difference between fats and oils is:
 fats are solid in room temperature and oils are
liquid in room temperature.
◦ Hydrogenation is the process of
converting liquid oil to solid fat by adding
hydrogen to some of the double bond of
the unsaturated carbon chain in presence
of nickel as catalyst; e.g., Margarine .

22. Properties of Fats and Oils…
 Rancidity:
◦ Triglycerides soon become rancid, developing an
unpleasant odor and flavor on exposure to moist air at
room temperature. Rancidity is caused by either
hydrolysis of ester bond or oxidation of double bond
◦ Hydrolytic rancidity is due to the hydrolysis of ester
bond by the enzyme lipase present in the airborne
bacteria. It can be prevented by storing food in
refrigerator
◦ Oxidative rancidity is caused by the ruptured of the
double bond due to exposure to warmth air. As a result,
aldehydes with low molecular wt. are formed releasing
off flavor; e.g., Off flavor in cookies. Oxidative rancidity
can be prevented by adding antioxidant (Vitamin C,
Vitamin E, -Tocopherol)

23. Properties of Fats and Oils
 Saponification of fats and oils:
◦ Hydrolysis of fats and oils by boiling with sodium
hydroxide is called saponification. This process is
used to make soap (Latin: sapon means soap).
Soaps are the alkali metal (Na, K or Li) salts of
fatty acids.
◦ Glycerol is an important by-product of
saponification process. It is recovered by
evaporating the water layer. The crude soap is then
purified, and coloring and perfumes are added
according to the market demands.

24. Waxes
 Waxes: Waxes are part of the lipid family. Waxes are esters of
long-chain saturated and unsaturated fatty acids (having 14-
36 carbon atoms) with long-chain alcohol(having 16-30 carbon
atoms).
 Waxes are low- melting, stable solids which appear in nature in
both plants and animals. A wax coat protects surface of many
plant leaves from water loss and attack by microorganisms.
 Carnauba wax, a major ingredients of car wax and floor polish,
comes from the leaves of a South American palm tree.
Beeswax is largely myricyl palmitate , the ester of myricyl
alcohol and palmitic acid
 Waxes also coat skin, hairs and feathers, and help keep them
pliable and water-proof

25. Beeswax
The term ‘wax’ originates in the Old English word weax,
meaning the “material of the honeycomb”.

26. Structural lipids
 Chemical analysis of the isolated materials
shows that lipids are the major components
of most membranes. This lipids are not
triglycerides but another group of
compound called complex lipids.
 There are two types of complex lipids:
◦ Phospho lipids
◦ glycolipids

27. Complex Lipids…
* Phospholipids: They are esters of phosphoric
acids.There are two main types of phospholipids in
cellular membranes:
Phosphoglecerides: They are also known as Phosphaitdyl
choline (lecithin). They are built from long chain fatty acid,
glycerol and phosphoric acids.
sphingomyelins: They do not contain glycerol. Instead,
they contain sphingosine, a long-chain unsaturated amino
alcohol. Only one fatty acid is attached to the sphingisine.
Sphingomylins are found in brain and nervous tissue and in
the myelin sheath, the protective coat of nerves.

30. 3-phosphoglycerol (building block for phosphoglycerides)

32. General structure of a glycerophospholipid. Note the
glycerol-3-phosphate backbone

33. Glycerophospholipids

36. Electron microscopy (EM) of myelinated nerve fibres.
Note spirally wrapped membranes around each nerve
axon. The myeline sheath may be 10-15 layers thick. Its
high lipid content makes it a good electrical insulator
myeline a mixture of
proteins and
phospholipids forming a
whitish insulating sheath
around many nerve fibres,
which increases the speed
at which impulses are
conducted.

37. Complex Lipids
Glycolipids: A lipid molecule that
contains carbohydrates, which is usually a
simple sugar like glucose or galactose
They are also called cerebrosides because
of their abundance in brain.

38. Membrane lipids
 Phospholipids: naturally aggregate in form
of bilayers (which fuse to form spherical
liposomes)
◦ glycerophospholipids
◦ sphingophospholipids
 Sterols:
◦ e.g. cholesterol (animal sterol) ergosterol(
plant sterol).

40. Lipid bilayers
The fundamental component of a biological
membrane is lipid bilayer.
In a vigorously shaked mixture of phosphatidyl
choline and water, the lipid molecules form
microscopic sphere.
These lipid sphere or liposome are packages of
solvent surrounded by a lipid bilayer- a
two layer thick wall of phosphatidyl choline

41. Electron micrograph of a liposome

42. Diagram indicating spherical micelle (b), and effect of crowding in too
many lipid molecules. The micelle could develop a water-filled centre
(c), or could flatten out to collapse the hollow centre but would
develop water-filled spaces (d)

43. Two-tailed amphipathic molecules are more
cylindrical, and tend to naturally form a bilayer
structure (as opposed to a micelle)

44. Model (snapshot) of a lipid bilayer surrounded by water

45. Fluid mosaic model
 The fluid mosaic model of membrane structure
proposes that lipids of the bilayer are in
constant motion, gliding from one part of their
bilayer to another at high speed

46. The fluid mosaic model of membrane structure

47. Steroids
 Steroids are a family of lipids found in plants
and animal
◦ A steroid contains four fused carbon ring: 17 carbon
atoms make the structural unit of steroids known as
steroid nucleus.
◦ Steroid nucleus is found in a number of extremely
important biological molecules: cholesterol,
adrenocorticoid hormones, the sex hormone and bile
acids.

48. Cholesterol
 Cholesterol is found only in animal cells. A
typical animal cell membrane contains about
60% phospholipids and 25% cholesterol.
 Cholesterol imparts rigidity to cell membrane.
The higher the % of chlesterol, the more rigid
the membrane.
 Bile acids contain cholesterol.

49. Cholestorol (membrane sterol)

50. Scanning EM of adipocytes: each contains a fat globule
that occupies nearly the entire cell

51. Triacylglycerols are
biologically useful.
Spermaceti organ
contains spermaceti oil,
a mixture of
triacylglycerol and
waxes. This oil is liquid
at 31o C, and becomes
solid when the
temperature drops
several more degrees
Sperm Whales

52. O
C
O
CH3
(Z)-7-dodecenyl acetate
pheromone of
cabbage looper moth
and
asian elephant

53. Lipids in biomolecules