Download Lipids (Typed notes of Ma`am Saba by Dr. M. Hassan)

LIPIDS
By
Dr. M.Hassan
Introduction
Derived from a greek word lipos [fat]
They are the substance of biomedical importance
They are soluble in organic solvents such as
chloroform and methanol and are sparingly
soluble in H2O
Chemically they are esters of different alcohols.
Inaddition to alcohols and fatty acids , some of the
lipids may contain phosphoric acid , nitrogenous
base and carbohydrates
Characteristics
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They are insoluble in H2O
They are soluble in organic solvent
Chemically they are esters glycerols with
higher fatty acid
CLASSIFICATION [According to
Bloor]
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A SIMPLE Lipids
These are the esters of fatty acids with
various alcohols
These consist of following subgroups
1.Fats [Neutral fats or
Triacylglycerol]
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These are the esters of fatty acids with
glycerol
The term triacyl glycerol is being used
now days rather than triglycerides
2.Waxes
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These are the esters of fatty acids with
alcohol of higher molecular weight other
than glycerol.These alcohols are
monohydric
B.Compound Lipids
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These are the esters of fatty acids
containing group in addition alcohol and
fatty acid
These are subdivided as follows
1.Glycolipids [glyco sphingolipids]
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These contain sphingosine , fatty acid and
a monosaccharide or oligosaccharide unit.
They contain special alcohol sphingol or
sphingosine , a nitrogenous base in
addition to fatty acids.
They does not contain phosphoric acid
They are of two types
A.cerebrosides
B.gangliosides
2.Sulfo lipids
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Lipids containing sulphate group
3.Aminolipids
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They are also called as proteolipids
They are attached with protein molecule
In them the parent molecule is lipid
4.Lipoproteins
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In them lipids are the prosthetic group in
protein
The parrent is protein
5.Phospholipids
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These are lipids that contain a phosphoric
acid , fatty acid and alcohol
On the basis of type of alcohol
phospholipids are of two types
1.If alcohol is
glycerol>>>Glycerophospholipid
2.If alcohol is
sphingosin>>>sphingophospholipid
C..DERIVED LIPIDS
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These are obtained by the hydrolysis of simple and
compound lipids
These are
A.[fatty acids]:may be saturated or unsaturated or cyclic
B.[monoglycerides]:
C:Diglyceride
D:[Alcohols] straight chain alcohols obtained on
hydrolysis of waxes
Cholesterol and other steroids including vitamin D
Vitamin A
Carotenoids
Glycerol
D.Miscellaneous
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Vitamin E and Vitamin K
Carotenoids
Aliphatic hydrocarbon in liver fat and
certain hydrocarbon in liver fat and certain
hydrocarbons found in bees wax and plant
wax
Fatty Acids
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INTRODUCTION
Fatty acids are carboxylic acids with long chain hydrocarbons side
groups
They occur rarely freely in nature , but rather occur in estrified form
as a major components of various lipids
In higher plants and animals , predominant fatty acid residues those
of the C16 and C18 species palmitic , oleic , linoleic and steric acids
Fatty acids with 14 and 20 carbon atoms are uncommon
Most fatty acids are even number of carbon atom because usually
they are biosynthesized by catenation of C2 units
Over half of the residues [fatty acids] of plants and animals lipids
are unsaturated and often polyunsaturated
Some important fatty acids are discussed below
1.Saturated Fatty Acids
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They have no double bond in their hydrocarbon chain
Symbol of saturated fattyacids have two numbers
1 represent the # of carbon atoms
2 represent number of double bonds with oxygen
Fatty acids with greater than 10 carbon atoms are given
a systematic names e,g palmitic acid ,oleic acid etc.
Palmitic and stearic acids are the two most abundant
fatty acids in human being
Lignoceric is component of cerebrosides
2.Unsaturated Fatty Acids
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They posses one or more double bonds in their
hydrocarbon chain
They are more reactive than saturated fatty acid
Fatty acid containing one double bond is called
as monoenoic/monounsaturated>>oleic and
palmitoteic acid
Fatty acids containing more than one double
bond called as polyenoic/polyunsaturated
>2 double bond dienoic
>3 double bond trienoic
Physical Properties Of Fatty Acids
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1.Melting Point
A. Saturated Fatty Acids
The melting point of saturated F.acids
increase with the increase in chain length
Melting Point Of Unsaturated Fatty
Acids
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It decrease with increase in unsaturation
Because fatty acid double bond almost have cis
configuration.This put a rigid 30 degree bend in the
hydrocarbon chain of unsaturated fatty acids that
interferes with their efficient packing to fill space
E,g oleic acid---14 degree centigrade[1 double bond]
Linoleic acid----5 degree centigrade[2 double bonds]
Linolenic acid--- -10 degree centigrades[3 double bonds]
Vegetable oils---room temp—liquid---unsaturated
2.On hydrogenation under pressure and in the presence
of Ni catalyst these oils are soldified
2.Solubility Of Fatty acids
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1.Anionic group provides hydrophillic property to the fatty acids
making them H2O soluble.
2. At physiological pH carboxyl group (COOH) ionizes becoming
COO-.
3.Hydrocarbon chain being hydrophobic tend to make fatty acid
hydrophobic.
4.Chain length of hydrocarbons determine the solubility of fatty
acids into H2O.
5.As the chain length increass it decreases the solubility of fatty
acids into H2O.
6.E.g CH3COOH has only one methyl group i.e it has short
hydrocarbon chain length so, it is completely miscible with H2O.
7.Unsaturation also increases the solubility.
8.E.g palmitoleic acid more soluble than palmitic acid.
Isomerism in Fatty Acids
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(a). Saturated Fatty Acids.They does not show
isomerism. They may be straight chain or branched.
(b).Unsaturated Fatty Acids.Due to the presence of
double bond they show isomerism.(i.e cis and trans
configuration)
1.All naturally occuring unsaturated fatty acids of
mammals are of cis configuration. Cis bond does not
permit rotation around C=C and thus introduce rigid
bend or kink.
2.Trans bond occur naturally and are also produced
when unsaturated fatty acids are hydrogenated.
NOTE Trans bonds have high ,melting point than cis
bonds.