Chemistry of lipids

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Chemistry of Lipids
R.C. Gupta Professor and Head Dept. of
Biochemistry National Institute of Medical
Sciences Jaipur, India
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Classification
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Fats are rich in saturated fatty acids oils are
rich in unsaturated fatty acids
Fat
Oil
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CH3?(CH2)15?OH
Cetyl alcohol
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Fatty acids
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Fatty acids(contd)
Each fatty acid possesses a carboxy terminal and
a methyl terminal
The carbon atoms are numbered from the carboxy
terminal, the carboxyl atom being numbered 1
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Fatty acids(contd)


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Some saturated fatty acids
Fatty acid Formula Fatty acid
Formula Acetic acid CH3COOH
Propionic acid C2H5COOH Butyric acid
C3H7COOH Caproic acid
C5H11COOH Caprylic acid C7H15COOH
Capric acid C9H19COOH Lauric acid
C11H23COOH Myristic acid
C13H27COOH Palmitic acid C15H31COOH
Stearic acid C17H35COOH Arachidic acid
C19H39COOH Behenic acid
C21H43COOH Lignoceric acid C23H47COOH
Cerotic acid C25H51COOH
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Some fatty acids have a ring in their
acyl chain e.g. chaulmoogric acid

• Chaulmoogric acid was used as an
  anti-leprosy drug in the past

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Monounsaturated fatty acids

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Palmitoleic acid
Formed from palmitic acid
Formula is CH3(CH2)5CHCH(CH2)7COOH
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Polyunsaturated fatty acids
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Polyunsaturated fatty acids (contd)
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Polyunsaturated fatty acids (contd)
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Polyunsaturated fatty acids (contd)
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Essential fatty acids
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• EFA are the precursors of hormone-like
  compounds known as eicosanoids

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Eicosanoids

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Tissue distribution of eicosanoids was later
found to be very wide
They produce profound physiological and
biochemical effects on various organs and systems
Systems affected by them include reproductive
system, cardio-vascular system, central nervous
system, gastro-intestinal tract etc
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The other eicosanoids are thromboxanes and
leukotrienes They also produce profound
physiological effects
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Leukotriene E4 (LTE4)
Leukotriene C4 (LTC4)
Leukotriene D4 (LTD4)
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G
Glycerol
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The fatty acids present in a triglyceride are
generally different from each other
R1, R2 and R3 represent the acyl groups of fatty
acids
The first fatty acid is generally saturated the
second and the third are generally unsaturated
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Two molecules of phosphatidic acid are linked,
through their phosphate groups, with a molecule
of glycerol in diphosphatidyl glycerol
(cardiolipin)
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In plasmalogens, an unsaturated alcohol is linked
with carbon 1 of glycerol by an ether bond
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Sphingophospholipids contain sphingosine as the
alcohol portion Sphingosine is a long chain
amino alcohol which is synthesised from palmitic
acid and serine
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The most important sphingophospholipid in
our body is sphingomyelin
It is a constituent of nervous tissue and
membranes
It is made up of sphingosine, a fatty
acid, phosphoric acid and choline
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Cerebrosides

• Cerebrosides are glycolipids containing
  sphingosine, a fatty acid and galactose

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Kerasin contains
Nervon contains
Oxynervon contains
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Lipoproteins
Lipids are an important source of energy for us
As they are insoluble in water, their
transport in plasma poses a problem
This problem is solved by combining the
more insoluble lipids with more polar ones
and then combining them with some proteins
The complex, so formed, is known as a lipoprotein
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EMB-RCG
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Ultracentrifugation
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After a few hours, four different layers are
formed
From above downwards, these are
Chylomicrons (CM)
Very low density lipoproteins(VLDL)
Low density lipoproteins
(LDL) High density
lipoproteins (HDL)
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Electrophoresis
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Four different bands are formed
From point of application, these
are
Chylomicrons (CM)
b-Lipoproteins
Pre-b-lipoproteins
a-Lipoproteins
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Same as
Pre-b-lipoprotein
VLDL
LDL
Same as
b-Lipoprotein
Same as
a-Lipoprotein
HDL
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Steroids
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• Cholesterol is the precursor of many important
  compounds in our body e.g. vitamin D3, steroid
  hormones, bile acids and bile salts

If an excess of cholesterol is present in plasma,
it tends to get deposited in the walls of
arterioles causing atherosclerosis
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Physical properties of lipids
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• Such lipids are said to be amphipathic i.e. a
  part of the molecule is polar and a part non-polar

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Unsaturated fatty acid with cis double bond
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Chemical reactions of lipids
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Hydrolysis
The ester bonds of lipids can be hydrolysed by
specific enzymes
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Saponification
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Hydrogenation

• Double bonds of unsaturated fatty acids can be
  hydrogenated in the presence of catalysts e.g.
  nickel

H H
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Iodination
Iodine can also reduce the double bonds of
unsaturated fatty acids
I2
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Iodine number of common oils
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Oxidation
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• Fat which undergoes this type of oxidation
  becomes rancid
• Rancid fat is unpleasant in taste and smell, and
  can be toxic
• Rancidity is prevented by anti-oxidants e.g.
  vitamin E

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In Salkowskis reaction, cholesterol is treated
with concentrated sulphuric acid
It is dehydrated to cholestadiene and its
polymers which are red in colour
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In Liebermann-Burchard reaction, cholesterol is
treated with concentrated sulphuric acid and
acetic anhydride
It is dehydrated to cholestadiene and its
polymers which are sulphonated to form a green
or blue complex
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Thank you