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CHEMISTRY OF LIPID
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INTRODUCTION
Lipids are a chemically diverse group of compounds.
Insoluble in water & soluble in non-polar solvents
like chloroform, ether and benzene.
Hydrophobic in nature.
It include fats, oils, steroids, waxes & related
compounds.
DEFINITION They are esters of fatty acids with alcohol or are
substances capable of forming such esters & are
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CLASSIFICATION
A. Simple lipid.
B. Complex or compound lipid.C. Derived lipid.
A. Simple lipid
Esters of fatty acids with various alcohols. Classified as following depending on the type of
alcohol present-
i. Neutral fats.ii. Waxes.
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1.NEUTRAL FATS Esters of fatty acids with alcohol glycerol.
eg tripalmitin.
Uncharged.2. WAXES
a. True waxes:-
These are esters of fatty acids with highermolecular weight monohydric long chain alcohol.
eg- lanolin (from lamb,s wool).
Bees-wax
spermacetic oil ( from whales).
b. other waxes:- Esters of fatty acid with alcohol.
eg:- Cholesterol forms cholesterol ester.
Retinol form vitamin A ester
Cholecalciferol (vitamin D) forms vitamin D ester
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B. COMPLEX LIPID
These are esters of fatty acid with alcohol containing
additional (prosthetic ) groups.
Classification:- according to the type of prostheticgroup present:-
a) Phospholipids
b) Glycolipidsc) Lipoproteins.
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a. Phospholipids
They contain phosphoric acid & frequently a nitrogenous
base as additional group. Classification:- on the basis of the type of alcohol
present:-
1. Glycerophospholipids.
2. Sphingophospholipids.
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1. Glycerophospholipids
The alcohol present is glycerol. Eg:-
I. Phosphatidyl choline (lecithin)
II. Phosphatidyl ethenolamine (cephalin)
III. Phosphatidyl serine
IV. Phosphatidyl inositol
V. LysophospholipidVI. Plasmalogen
VII. Cardiolipins.
2. Sphingophospholipids
The alcohol present in sphingosine.
Eg:- Sphingomyelins.
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b. Glycolipids
Additional residue are carbohydrate with
nitrogenous base.Eg:- Cerebrosides
Gangliosides.
c. Lipoproteins
Lipoproteins are formed by combination of lipid with
a prosthetic group protein.
Eg:- Chylomicrons
Very low density lipoprotein(VLDL) Low density lipoprotein(LDL)
High density lipoprotein(HDL)
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C. DERIVED LIPIDS
Include the products obtained after the hydrolysis
of simple & compound lipids. Eg:- Fatty acids
Glycerol
Steroids
Cholesterol
Vitamins A & D.
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FUNCTION
Storage form of energy.
Structural lipid.eg:- phospholipid, glycolipid,& sterols.
Cholesterol is a precursor of many steroid hormones.
Activators of enzymes: eg:- glucose-6 phosphatase,mono-oxygenases & mitochondrial enzyme B-hydroxybutyric dehydrogenase, requirephophatidylcholine for activation.
Help in absorption of fat soluble vitamin & act as asolvent for the transport of the fat soluble vitamin.
In the mitochondria cardiolipin is necessary for optimum
function of electron transport process.
Phosphatidyl inositol triphosphate is serve as a keyprecurser in the formation of a second messenger.
Steroid hormone & prostaglandins are modulator of
physiological activity.
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Nervous tissue are particularly rich in lipids which serve
an important role in their function.
Bile salt derived from cholesterol act as a emulsifying
agent & facilitate the digestion & absorption of lipids.
Important dietary consituents.
Non polar lipids act as electrical insulator.
Thermal insulator in the subcutaneous tissue & certainorgans.
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FATTY ACIDS
Fatty acid are carboxylic acid with hydrocarbon chains &
represented by a chemical formula R-COOH. The fatty acid are amphiphatic in nature.
Fatty acid occurs mainly as esters of glycerols in neutral fat &
oil.
Classification:- Four major classes:-
A. Straight chain fatty acid
B. Branched chain fatty acid
C. Substituted fatty acidD. Cyclic fatty acid
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A. Straight chain fatty acid :-
Fatty acid in which the carbon are arranged linearly.
Sub classified into two classes:-
1. Saturated fatty acid
2. Unsaturated fatty acid
1. Saturated fatty acids:- There is no double bond in thehydrocarbon chain of these fatty acids ,so can be packed together
into a compact structure.
It is sub classified into :-
a. Even carbon acid:- palmitic acid & stearic acid. b. Odd carbon acid:- Propionic acid.
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2. Unsaturated fatty acid:- They contain double bond
in their hydrocarbon chains.
They are in cis configuration.
Sub classified into following type according to the
number of double bonds present in the structure.
a. Monounsaturated fatty acid
b. Poly unsaturated fatty acid
c. Ecosanoids .
B. Branched chain fatty acid:- eg. Isovaleric acid &Isobutyric acid.
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C. Substituted fatty acid:- In this one or more hydrogen
atom have been replaced by another group.
Eg: Lactic acid, cerebronic acid
D. Cyclic fatty acid:- eg. Prostaglandins.
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Essential fatty acids (EFA) Human can not synthesize 2 main types of PUFA.
Linolenic acid & Linoleic acid . Arachidonic acid , fatty acid derived from linoleic acid is an
essential precursor of regulatory lipids eicosanoids in man ,which include :- Prostaglandins, Thromboxanes, Prostacyclin,leukotrines.
FUNCTION OF EFA:- 1. Synthesis of eicosanoids 2. Maintenance of structural integrity
3. Development of retina & brain
4. Antiatherogenic effect
5. Transport of cholesterol & formation of lipoproteins.
Deficiency of EFA:- 1. Phrynoderma or toad skin. 2. Dermatitis
3. Poor wound healing
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CHOLESTEROL:- cholesterol is the major sterol in
animal tissues. but not in the plant fats. It consists of
steroid nucleus (CPP). fUNCTIONS:- Major structural constituent of cell
membrane & plasma lipoproteins.
Precursors of :-
steroid hormones.
Bile acids
Vitamin D