1. Chemistry of
Lipids

2. What is lipids?
Lipids are a broad group of naturally occurring molecules 
which includes fats, waxes, 
sterols, fat-soluble vitamins,
monoglycerides, diglycerides, 
phospholipids, and others.

3. It is soluble in water.
It is soluble in nonpolar organic solvents such as ether, acetone, CCl4.
It contains C, H, O, sometimes N or K
It yields fatty acids on hydrolysis.

4. What are the functions of lipids?
The importance of lipids can be seen from their varied functions.
They are:

5. What are the functions of lipids?
As membrane structural components
As intracellular storage depots of metabolic fuel
As transport form of metabolic fuel
As regulatory substances (some hormones)
As protective form of the cell walls of many bacteria, of the leaves of higher plants, of the exoskeleton of insects and the skin of vertebrates

6. What are the functions of lipids?
As enzymes cofactors (some vitamins)
As transport form of some neurotransmitters (acetylcholine)
As receptors in nerve ending membranes
As determinants of immunological specificity
As part of the outer coating between the body of the organism and the environment to prevent infection and excessive loss or gain of water

7. BIOMEDICAL IMPORTANCE
Stored as a source of
energy in the body.
1 gram of lipid contains 2.25
as much energy as 1 gram
of Carbohydrate
Lipid (TGL)
Droplets In
Adipose tissue

8. 2. Structural components of biomembranes.

9. Provides insulation against changes in external temperature.
3. Thermal Insulator :
Provides insulation against changes in external temperature.

10. 4. Lipids act as electric insulators
in neurons.

11. 5. Act as metabolic regulators (steroid hormones and prostaglandins).
6. Act as surfactants and prevents collapse of lungs during expiration.
7. Lipids are used as detergents.
8. Lipids used in emulsification and intestinal absorption of non polar nutrients like fatty acids and fat soluble vitamins.
9. Associated with diseases such as
atherosclerosis, diabetes mellitus and obesity.
10. Gives shape and contour to the body.

12. Lipid Classification Lipids Nonsaponifiable Saponifiable Steroids
17.1 Biological Functions of Lipids
Steroids
Prostaglandins
Simple
Complex
Sphingolipids
Phosphoglycerides
Waxes
Triglycerides

13. Classification Simple Lipids a) Fats and Oils b) Waxes
2. Compound Lipids
a) Phospholipids
b) Glycolipids
3. Derived Lipids
a) Fatty acids
b) Alcohol
c) Sterols

14. Second Classification of Lipids
Four Main Groups
Fatty Acids
Saturated
Unsaturated
Glycerides glycerol-containing lipids
Nonglyceride lipids
Sphingolipids
Steroids
Waxes
Complex lipids lipoproteins
17.1 Biological Functions of Lipids

15. A Scheme to Classify Lipids
17.1 Biological Functions of Lipids

16. LIPIDS
1. Simple Lipids
2. Compound Lipids

17. Simple and Complex Lipids
Simple: an ester-containing lipid with just two types of components
An alcohol
One or more fatty acids
Complex: an ester-containing lipid with more than two components
Fatty acids
Plus others
17.1 Biological Functions of Lipids

18. 1. Simple Lipids eg: triglycerides
Esters of fatty acids with various alcohols.
a. Fats :esters of fatty acids with glycerol.
eg: triglycerides
b. Waxes: esters of fatty acids with higher molecular weight monohydric alcohols.
eg: beeswax

19. Triglycerides are most common 3 fatty acids attached to glycerol
held together by ester
linkage

20. Triglycerides are lipids with three fatty acids attached to a glycerol

22. © 2009 Cengage - Wadsworth

23. At 20°C, triglycerides can be classified as fats or oils
Solid = fats
Liquid = oil

24. Fats and oils are triglycerides that are formed by condensation reactions of propane- 1,2,3-triol (glycerol) and fatty acids (long-chain carboxylic acids).

25. Triglycerides are the commonest lipids in living organisms.

26. Chemical properties

27. Chemical Properties
Triglycerides have typical ester and alkene chemical properties as they are composed of these two groups:
Saponification: replace H with salt from a strong base
Hydrolysis: produces the fatty acids and glycerol, a reverse of formation
Hydrogenation: saturates the double bonds
17.3 Glycerides

28. Triglyceride Reactions
Triglycerides undergo three basic reactions
These reactions are identical to those studied in carboxylic acids
Triglyceride
H2, Ni
H2O, H+
NaOH
More saturated
triglyceride
Glycerol
Fatty Acids
Glycerol
Fatty Acid Salts

29. Saponification reaction

30. Hydrolysis Chemical (Autocatalytic) Enzymatical (Lipase) +3H20 O C
triacylglycerol =
- R2
- R3 HC
H2C OH
glycerol HC
H2C
HO - C O
- R1
3 fatty acids +
- R3
- R2
+3H20

31. Hydrolysis reaction

32. Addition reaction
Hydrogenation reduction of some or all of the carbon-carbon double bonds of an unsaturated triglyceride using H2/metal catalyst.

33. Hydrogenation of Unsaturated Fats
Oils can be converted to semi-solids through hydrogenation that converts the double bonds to single bonds
In the process, some double bonds are converted to trans form

35. Estimation of Iodine Value of Fats and Oils
Fatty acids react with a halogen [ iodine]  resulting  in the addition of the halogen at the C=C double bond site. 
In this reaction, iodine monochloride  reacts with the unsaturated bonds to produce a di-halogenated single bond, of which one carbon has bound an atom of iodine. 

36. Estimation of Iodine Value of Fats and Oils

37. Oxidation of Oils and Fats

38. Oxidation of Oils and Fats

39. 2. Compound Lipids
Schematic diagram of simple and complex lipids.

40. Simple lipid + Additional group = = Compound Lipids
Esters of fatty acids with various alcohols along with an additional group.
Simple lipid + Additional group =
= Compound Lipids
a. Phospholipids:
b. Glycolipids:
c. Other Complex Lipids:

41. COMPOUND LIPIDS
Esters of fatty acids with various alcohols along with an additional group.
Phospholipids
Glycolipids
Others
Glycerphospholipids
-Phosphatidyl choline
- Phosphatidyl ethanolamine
- Phosphatidyl serine
- Phosphatidyl inositol
- Cardiolipin
- Plasmalogens
Sphingophospholipids
Lipoproteins
Aminolipids
Cerebrosides
Gangliosides
Globosides

42. Phospho lipids

43. SIGNIFICANCE OF PHOSPHOLIPIDS
Structural components of cell membrane.
Enable enzyme action (mitochondrial enzyme system).
Required for blood coagulation (prothrombin to thrombin, activation of factor 8 by factor 9).

44. SIGNIFICANCE OF PHOSPHOLIPIDS
Transports lipids from intestine and liver.
Choline acts as a lipotropic agent since it prevents the formation of fatty liver.
Phospholipids of myelin sheath provides insulation around nerve fibers.

45. PHOSPHOLIPIDS
Phospholipids are similar in structure to triglycerides but one of the fatty acid groups is replaced with a phosphate group, and are hence known as diglycerides.

47. PHOSPHOLIPIDS

48. PHOSPHOLIPIDS
The phosphate group is ionized and negatively charged, therefore water molecules are attracted to this polar part of the molecule, this end is then hydrophilic and soluble in water.
The two fatty acid chains are insoluble and nonpolar.

49. In cells, these phopholipids occur with proteins and cholesterol in a bilayer in the form of a cell membrane.
Bilayers occur when the hydrophobic tails line up with one another with the hydrophilic heads exposed

51. Membranes
Complex lipids form the membranes around cells and small structures within cells.
In aqueous solution, complex lipids spontaneously form into a lipid bilayer, with a back-to-back arrangement of lipid monolayers.
Polar (hydrophilic) head groups are in contact with the aqueous environment.
Nonpolar (hydrophobic) tails are buried within the bilayer
The arrangement of hydrocarbon tails in the interior can be rigid (if rich in saturated fatty acids) or fluid (if rich in unsaturated fatty acids).

54. Phosphatidyl
Phosphatidyl
Glycerol

55. Phosphatidyl Choline (LECITHIN)
Phosphatidic acid + Choline
Most abundant phospholipid of biomembranes

56. Phosphatidyl Choline (LECITHIN)
Dipalmitoyl Lecithin – Lung surfactant.
Synthesized by Alveolar type - II cells.
Rich in alveolar fluid lining the alveoli
Reduces surface tension of alveolar fluid & prevents collapse during expiration
Deficiency in premature infants leads to collapse - Respiratory Distress syndrome

57. Below is Lecithin, or phosphatidycholine, a major component of biological membranes and can be isolated from egg yolk or soybeans
Focus on the “tails”
and “heads” which
form a membrane

59. Lipids in Membranes: Fluid Mosaic Model
Polar heads and nonpolar tails
Double layer of lipids
amphipathic

60. GLYCOLIPIDS Lipids containing carbohydrate moiety - Glycolipids
Alcoholic component – Sphingosine
Ceramide – Common group of all Glycolipids
Occur in brain, spinal cords and other tissues.
Predominant in outer leaflet of biomembranes

61. Types of Glycolipids 1. Cerebrosides 2. Sulfatides 3. Globosides
4. Gangliosides

62. STEROIDS
Lipids containing Cyclo Pentano Perhydro Phenanthrene (CPPP) ring 18 12 17 11 16 13 D C 19 1 15 9 14 2 10 8 A B 3 7 5 4 6

64. STEROLS Steroids containing alcoholic group - Sterols
Plant Sterols : Ergosterol, Stigmasterol, Sitosterol
Animal Sterols : Cholesterol

65. STEROIDS lipids often found in cell membrane (ex cholesterol)
consist of 4 fused hydrocarbon rings and several different functional groups

67. Double bond between 5th & 6th carbons
CHOLESTEROL
Chemistry:
Has Steroid Nucleus
OH group at 3rd position
Double bond between 5th & 6th carbons
8-Carbon containing side chain at 17th position. 17 3 5 6

68. CHOLESTEROL
Chemical Properties
1. Undergoes rapid oxidation to form cholestenones. 2. Hydroxyl group forms esters with acids to form Cholesterol Esters (cholesterol acetate, palmitate and propionates) 3. Presence of double bond gives hydrogenation reactions (similar to unsaturated fatty acids). 4. Colour reactions: LIEBERMANN BURCHARD, SALKOWSKY, ZAKS.

69. Biomedical Importance
CHOLESTEROL
Biomedical Importance
Structural role – Biomembranes, Lipoproteins
Occur in large amounts in brain and nerve tissues.
Act as insulator against nerve impulses which discharge electric charges.
Biomolecules synthesized from cholesterol
Bile acids
Vitamin D
Steroid hormones : Androgens, Estrogens, Progesterone, Aldosterone etc