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Lipids
The term Lipid applies to a class of
compounds that are soluble in organic
solvent and nearly in soluble in water.
Chemically:
Lipids are either compounds that yield fatty
acids on hydrolysis or complex alcohols that
can combine with fatty acids to form esters.
Lipids

Some lipids contain non lipid groups such as
sialic, phosphoryl, amino or sulphate groups.

These molecules gives lipid molecules an
affinity for both water and organic solvents which
is important in the formation of biological
membranes.
Classification of clinically
important lipids
Sterol Derivatives:
Cholesterol and Cholesterol esters.
Steroid hormones.
Bile acids
Vitamin D.
Fatty Acids:
Short chain (2 to 4 carbon atoms).
Medium chain (6to 10 carbon atoms).
Long chain (12 to 26carbon atoms)
{Prostaglandin}.
Glycerol Esters:
Triglycerides, diglycerides, and monoglycerides
(acyleglycerol).
Phosphglycerides.
Sphingosine Derivatives:
Sphingomyellin.
Glycosphing lipids.
Terpenes (Isoprene Polymers):
Vitamin A.
Vitamin E.
Vitamin K.
Cholesterol
Is a steroid alcohol with 27 carbon atoms that are
arranged in a tetracyclical
perhydrocyclopentanophenantherene
(sterane) skeleton.
Sterols are steroid backbones that have a hydroxyl
group at position 3 and a branched aliphatic
chain of 8 or more carbons at position 17.
12
11
1
2
3
HO
A
4
13
C 14
9
10
5
B
6
8
7
17
D 16
15
Cholesterol
 It
is found exclusively in animals, in
which virtually all cells and body
fluids contain some cholesterol.
 Knowledge of the numbering system of
carbon atoms found in cholesterol is
important because it is the initial
starting point in other metabolic
pathways, including vit D, steroid
hormones and bile acid synthesis.
Fatty acids
RCOOH is a general chemical formula for a fatty acid
where R is alkyl chain.
Fatty acid chain lengths vary and commonly are classified
according to the number of carbon atom present.
The defined groups of fatty acids are:-
Short chain (2 to 4 carbon atoms).
Medium chain (6to 10 carbon atoms).
Long chain (12 to 26carbon atoms).
Those of importance in human nutrition and
metabolism are
of the long chain class
containing.
Fatty acids
Fatty acids are classified further according to
their degree of saturation:
 Saturated Fatty acids have no double bonds
between carbon atoms.
 Monounsaturated Fatty acids contain one double
bond .
 Polyunsaturated Fatty acids contain more than
one double bond .
The double bonds in polyunsaturated fatty acids of
both animals and plant origin are usually three
carbon atoms apart.
Fatty acids


Humans can synthesize most fatty acids, including
saturated, monounsaturated, and some polyunsaturated
fats.
However , some fatty acids cannot be synthesized like
linolenic acid which is found only in plants.
 Because it is not synthesized but is
,
, and
fatty acid.
vital for
, it is termed essential
Types of Lipids

Lipids with fatty acids
Waxes
Fats and oils (trigycerides)
Phospholipids
Sphingolipids

Lipids without fatty acids
Steroids
11
Fatty Acids
Long-chain carboxylic acids
 Insoluble in water
 Typically 12-18 carbon atoms (even number)
 Some contain double bonds

corn oil contains 86%
unsaturated fatty acids and
14% saturated fatty acids
12
Saturated and Unsaturated Fatty
Acids
Saturated = C–C bonds
Unsaturated = one or more C=C bonds
COOH
palmitic acid, a saturated acid
COOH
palmitoleic acid, an unsaturated fatty acid
13
Structures
Saturated fatty acids
 Fit closely in regular pattern
COOH
COOH
COOH
Unsaturated fatty acids
 Cis double bonds
H
H
C C
cis double bond
COOH
14
Properties of Saturated
Fatty Acids

Contain only single C–C bonds

Closely packed

Strong attractions between chains

High melting points

Solids at room temperature
15
Properties of Unsaturated
Fatty Acids





Contain one or more double C=C bonds
Nonlinear chains do not allow molecules
to pack closely
Few interactions between chains
Low melting points
Liquids at room temperature
16
Fats and Oils
Formed from glycerol and fatty acids
O
CH2 OH
CH
OH
CH2
OH
glycerol
HO C
O
+
(CH2)14CH3
HO C (CH2)14CH3
O
HO C
(CH2)14CH3
palmitic acid (a fatty acid)
17
Triglycerides (triacylglcerols)
Esters of glycerol and fatty acids
ester bonds
O
CH2
O
C
(CH2)14CH3 + H2O
O
CH
CH2
O
O
C (CH2)14CH3
O
C
+ H 2O
(CH2)14CH3 +
H 2O
18
Properties of Triglycerides
Hydrogenation
Unsaturated compounds react with H2
 Ni catalyst
 C=C bonds
C–C bonds

Hydrolysis
Split by water and acid or enzyme catalyst
 Produce glycerol and 3 fatty acids

19
Hydrogenation
O
CH2
O
C
(CH2)5CH CH(CH2)7CH3
O
CH
CH2
O
O
C (CH2)5CH CH(CH2)7CH3
O
C
+ 3 H2
Ni
(CH2)5CH CH(CH2)7CH3
20
Product of Hydrogenation

Hydrogenation converts double bonds in
oils to single bonds.
 The
solid products are used to make
margarine and other hydrogenated items.
O
CH 2
O
C
(CH 2)14CH 3
O
CH
CH 2
O
O
C (CH 2)14CH 3
O
C
(CH 2)14CH 3
21
Hydrolysis
Triglycerides split into glycerol and three
fatty acids (H+ or enzyme catalyst)
O
CH2
O
C
(CH2)14CH3
O
CH
CH2
O
O
H+
C (CH2)14CH3
O
C
+3 H2O
(CH2)14CH3
CH2 OH
CH
OH
CH2
OH
O
+
3 HO C
(CH2)14CH3
22
Saponification and Soap
Hydrolysis with a strong base
 Triglycerides split into glycerol and the
salts of fatty acids
 The salts of fatty acids are “soaps”
 KOH gives softer soaps

23
Saponification
O
CH2
O
C
(CH2)16CH3
O
CH
CH2
O
O
C
O
C
(CH2)16CH3 + 3 NaOH
(CH2)16CH3
CH2 OH
CH
CH2
O
+OH + 3 Na O C (CH2)14CH3
salts of fatty acids (soaps)
OH
24
Glycerol esters (acylglycerols)
Glycerol is a three-carbon alcohol that contains a
hydroxyl group on each of its carbon atom.
Each hydroxyl can be esterified with a fatty acid.
H
H
H
C
OH
H
C
O
CO
(CH2)n
CH3
H
C
OH
H
C
O
CO
(CH2)n
CH3
H
C
OH
H
C
O
CO
(CH2)n
CH3
H
Glycerol
H
Triglyceride
The class of acyglycerol (glyceride) is
determind by the number of fatty acyl-groups
present; (monoglycerides,diglycerides and
Triglycerides
In human nutrition, triglycerides
constitute 95% of tissue storage fat
and are the predominant form of
glyceryl ester found in plasma.
The fatty acid residues found in
(monoglycerides, diglycerides, or
triglycerides) vary considerably and
usually include combinations of the
long-chain fatty acids.
Triglycerides
Triglycerides from plants tend to have large
amount of C18:2 or linoleic residues and are
liquid at room temperature (RT).
Triglycerides from animals especially
ruminants, tend to have C12:0 through C18:0 fattyacid residues (saturated fats) and are solid at RT.
Some plant triglyceride, such as coconut oil, are
highly saturated and may be solid at RT.
PHOSPHOLIPID
Phospholipids are complex lipids, resembling
triglycerides, but containing phosphate and a
nitrogenous base in place of one of the fatty
acids.
They are important components of cell
membranes and lipoproteins, maintaining the
solubility of non-polar lipids and cholesterol.