Welcome to class of

1
Welcome to class of Lipids Dr. Meera Kaur
2
Learning objectives To understand 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 following 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
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
9
(No Transcript)
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
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
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
19
(No Transcript)
20
(No Transcript)
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.

28
(No Transcript)
29
(No Transcript)
30
3-phosphoglycerol (building block for
phosphoglycerides)
31
(No Transcript)
32
General structure of a glycerophospholipid. Note
the glycerol-3-phosphate backbone
33
Glycerophospholipids
34
(No Transcript)
35
(No Transcript)
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
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).

39
(No Transcript)
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
Sperm Whales
Triacylglycerols are biologically useful.
Spermaceti organ contains spermaceti oil, a
mixture of triacylglycerol and waxes. This oil is
liquid at 31degree C, and becomes solid when the
temperature drops several more degrees
52
(No Transcript)
53
Lipids in biomolecules