Download Lipids

Lipids
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References:
*Organic and biochemistry
for today by Spencer.
*Biochemistry by
Armstrong.
*Modern biochemistry by
Werner.
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* Definition and classification.
* Fatty acids.
* Triglycerides neutral fats and oils.
* Triglycerides reactions.
* Waxes.
*Phospholipids.
*Sphingolipids.
*Biological membrane.
*Isoprenoids.
*Steroids.
*Prostaglandines.
Lipids
Lipid is made up of substances with widely different
compositions and structures , it defined in term of
physical property (solubility) , insoluble in water but
soluble in non polar solvents.
Lipids are the waxy, greasy or oily compounds found in
plants and animals .lipid repel water ,a useful
characteristic of protective wax coatings found in
some plants.
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Fats and oils are energy rich , it can storage in plants and
animals and structural component like cell
membrans. Lipid can be grouped into two main
classes:
*Saponifiable lipids.
*NonSaponifiable lipids.
Saponification: the process in which esters are
hydrolyzed under basic conditions (NaOH,KOH).
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Saponifiable lipids like:
* Triglycerides.
* Waxes.
* Phospholipids.
* Sphingolipids .
Nonsaponifiable lipids: are not esters and can not
hydrolyzed like:
*Isoprenoids.
*Steroids.
*Prostaglandines.
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Saponifiable lipids can be classefied also into:
*Simple lipids (fatty acid+ alcohol) and includes
waxes and triglyceride.
*Complex lipids (fatty acid + alcohol + other
compounds) and includes phosphoglycerides and
sphingolipids.
Fatty acids : The fundamental building blocks of many
lipids and are long chain carboxylic acid. The long
nonpolar tail of F.A.that are responsible for most of
the fatty or oily characteristics of fats.
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Carboxylic group, polar head of F.A is very hydrophilic
under conditions of physiological pH and it exists as the
carboxylate anion COO¯.
-
 A 16-C fatty acid: CH3(CH2)14 COO
Non polar
-
polar
 A 16-C fatty acid with one cis double bond between C
atoms 9-10 may be represented as 16:1 cis D9.
In aqueous solution the ion of F.As associated with one
another and form spherical clusters called Micelles: in
which the non polar chain extend toward the interior of
the structure a way from water and the polar carboxylate
groups face outward in contact with the water (some time
contain hundreds or thousands of F.As).
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F.As held together by weak dispersion forces . Micelle
is important in transport of insoluble lipids in the
blood.
CH3—CH2—CH2—CH2—CH2—CH2—CH2—COOH
↓
↓
Non polar hydrophobic
tail water insoluble
Polar hydrophilic head
(water soluble)
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Micelle
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The F.As found in natural lipids have several
characteristics:
1. They are usually straight chain carboxylic acids (no
branching).
2. The size of F.As range 10-20 carbons.
3. F.As usually have even number of carbon atoms
including carbonyl carbon.
4. F.As can be saturated (no double bonds)or
unsaturated contain one or more double bonds and
found in cis configuration.
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This configuration creates a long characteristic bend
or kink in F.As chains that is not found in saturated
F.As.
These kinks prevent unsaturated F.As chains from
packing together as do the chains of saturated F.As.
As a result, the intermolecular forces are weaker and
unsaturated F.As have lower melting points and are
usually liquids at room temperature.
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13
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The presence of double bond and the length of F.A chain in
membrane lipids partly explain the fluidity of biological
membranes.
Human body can synthesis all F.As except two (linoleic acid ,
linolenic acid) which are polyunsaturated F.As that
contain 18 C atom, it must be obtained from the diet they
are called Essential F.As: A fatty acid needed by the body
but not synthesized within the body ,it distributed in
plants and fish oils.
In body ,both acids used to produce hormone like
substances that regulate a wide range of functions and
characteristic including blood pruessre, blood clotting
,blood lipid level ,immune response to injury and
infections.
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Linolenic acid called omega-3 F.A which mean the
endmost double bond is three carbons from the
methyl end chain.
linolenic acid (fish oil)
CH3─CH2─(CH=CH─CH2)3─(CH2)6─COOH
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Linoleic acid an omega-6 F.A the endmost double bond
is located six carbons from the methyl end of the
chain.
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and the both acids can be converted to other omega-3 and -6
F.As.
linoleic acid (vegetable oil )
CH3─(CH2)4─CH=CH─CH2─CH=CH─(CH2)7─COOH
Some fatty acids and their common names:
14:0 myristic acid; 16:0 palmitic acid; 18:0 stearic acid;
18:1 cisD9 oleic acid
18:2 cisD9,12 linoleic acid
18:3 cisD9,12,15 a-linonenic acid
20:4 cisD5,8,11,14 arachidonic acid
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Animal fats and vegetable oils are the most widely
occurring lipids. Fats and oils are both esters, ester
consist of an alcohol portion and an acid portion.
Formation of an ester:
O
R'OH
+
HO-C-R"
O
R'-O-C-R'' +
H2O
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Natural T.g (fats and oils) are usually mixture of different
T.g molecules,for example butter fat contains 14
different F.As components.
Fat: A triglyceride that is a solid at room temperature
and come from animals it contain long chain
saturated F.As(higher melting points).
Oil: A triglyceride that is a liquid at room temperature
and come from plant or fish.
Vegetable oil such as corn, sunflower oils consists of
unsaturated F.A(lower melting point).
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Olive oil
Contains a high percentage of oleic acid, which is a
monounsaturated fatty acid with one cis double bond.
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Triglyceride reactions:
1.Hydrolysis: most important reaction in fats and oils it’s the
reveres to ester formation. Enzymes (lipases) of the
digestive system also catalyze the hydrolysis to supply
energy.
O
CH2
CH
CH2
O
O
O
C
O
(CH2)14CH3
C (CH2)14CH3 +3 H2O
O
C
(CH2)14CH3
H+
CH2
OH
O
CH
OH
+3 HO C
CH2
OH
(CH2)14CH3
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2.Saponification:(soap making)
soap:A salt of a F.A often used as a cleaning agent.
Sodium salts →hard salt → cake soap
used in home.
Potassium salts →soft salt →sharing creams and liquid
soap.
O
H2 C O C R
O
HC O C R
O
H2 C O C R
H2 C OH
+
3 KOH
HC
OH
H2 C OH
+
O
3 R C OK
“soap”
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O
CH2 O C (CH2)14CH3
CH2 OH
O
CH O C (CH2)14CH3
O
+ 3NaOH
CH OH +3Na+ -O C (CH ) CH
2 14 3
O
CH2 O C (CH2)14CH3
“soap”
CH2 OH
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3. Hydrogenation:
double bond can be reduced to single bond by
treatment with hydrogen H2 in the presence of
catalyst .
It is commercial reaction of fats and oils and therefore
increase the melting point ,it is most often used in
the production of semisolid cooking shortening
(margarines) from liquid vegetable oils.
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Hydrogenation:
O
CH2 O
C
+ 3H2
O
CH
O
CH2
O
C (CH2)5CH CH(CH2)7CH3
O
C
Ni
(CH2)5CH CH(CH2)7CH3
O
CH2
O
(tripalmitolean)
(CH2)14CH3
O
(CH2)5CH CH(CH2)7CH3
glyceryl tripalmitoleate
C
CH
CH2
O
O
C (CH2)14CH3
O
C
(CH2)14CH3
glyceryl tripalmitate
(tripalmitin)
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Some cis F.A in hydrogenation isomerizes to trans
F.A (Bad F.A).
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Waxes : An ester of a long chain F.A and long chain
alcohol (13-32 carbon).Waxes insoluble in water and
not as easily hydrolyzed as fat and oil ,they occur
naturally in nature as protective coating on feathers,
skin , fruits,leaves.
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Phosphoglycerides (Phospholipids) :A complex lipid
contains glycerol, F.As, phosphoric acid , and an
amino alcohol component.
Fatty acid
Glycerol
Fatty acid
PO4
Amino
alcohol
Phosphoglycerides are the major component of cell
membranes.
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Phosphoglycerides have different amino alcohol
groups like:
CH3
│+
HO−CH2−CH2−N−CH3
│
choline
CH3
+
HO−CH2−CH2−NH3
ethanolamine
+
NH3
│
HO−CH2−CH−COO−
Amino alcohols
serine
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Lecithin and cephalin are glycerophospholipids
 Abundant in brain and nerve tissues.
 Found in egg yolk, wheat germ, and yeast.
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Sphingolipids: A complex lipid contain sphingosine compound
(along-chain unsaturated amino alcohol ,an 18-carbon
alcohol ) instead of glycerol, F.As, phosphoric acid , and
an amino alcohol component. they found in cell
membrane like: sphingomyelin , glycolipid.
fatty acid
sphingosine
PO4
Amino
alcohol
CH3−(CH2)12 −CH=CH−CH−OH
│
sphingosine
CH−NH2
│
CH2−OH
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Sphingomyelin: a sphingolipid found in brain and nerve
tissue and in protective myelin sheath that surrounds
nerves. It is acomplex lipid contain a siphingosin
,F.A,cholin. There is an amide bond between a fatty
acid and sphingosine.
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Glycolipids: A complex lipid contain a siphingosin ,F.A ,a
carbohydrate (glucose or galactose)and often called
cerebrosides because of their abundance in brain
tissues.
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Biological membrane :
Membranes performed two vital functions in living
organisms :
 The external cell membrane: acts as a selective
barrier between the living cell and its environment.
 The internal membrane: surround some organelles
,creating cellular compartments that have separate
organization and functions.
Lipid bilayer: A structure found in membranes,
consisting of two sheets of lipid molecules arranged
so that the hydrophobic portions are facing each
other.
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Cell membranes contain lipid , protein and carbohydrates.
Phosphoglycerides such as (lecithin, cephalin) and
sphingomyelin,cholesterol are lipids found in membranes.
The lipids are organized in a bilayer in which the
hydrophobic chains extend toward the inside of bilayer
and the hydrophilic groups(the phosphate groups and
other polar groups ) are oriented toward the outside,
where they come in contact with water, like the micelle.
Membrane lipids usually contain unsaturated F.As chains
that fit into bilayer more loosely than do saturated F.As.
This increases the flexibility or fluidity of the membrane.
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Fluid Mosaic Model of Cell Membranes
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Isoprenoids : Are a vast array of biomlecules that contain
repeating five-carbon structural units known as
isoprene (methylbutadiene) units.The isoprenoids
consist of terpenes and steroids.
Terpenes : They are linear or cyclic compounds formed
by condensation of two or more isoprene units and
are found largely in the essential oils of plants (have
been used in perfumes and medicine), like vitamin
A,K,E , carotenes , sequaline.
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Terpenes
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Steroids:They are completely different from the lipids,
and defined: are compound contain four rings fused
in a particular pattern (three six-membered rings
and a single five membered ring fused together) ,like:
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1. Cholesterol: most abundant lipid in human body
(cellular membranes , myelin sheath, brain, and nerve
tissues) and has a rigid ring system and a short
branched hydrocarbon tail.
Cholesterol is largely hydrophobic.But it has one polar
group, a hydroxyl, making it amphipathic.
Cholesterol inserts into bilayer membranes with its
hydroxyl group oriented toward the aqueous phase & its
hydrophobic ring system adjacent to fatty acid chains of
phospholipids.
The OH group of cholesterol forms hydrogen bonds
with polar phospholipid head groups.
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HO
Cholesterol
Cholesterol
in membrane
Cholesterol is a precursor for other important steroids
including :
 Bile salts
 Hormones
 Vitamin D
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Usually; saturated fat in diet cause high blood cholesterol
level and these consider risk factor of coronary heart
diseases.
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2. Bile salt :is a yellowish-brown or green liver secretion
that is stored and concentrated in the gallbladder . It
is important in lipid digestion.
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glycine, an amino acid
cholic acid, a bile acid
CH3
OH
CH3
O
C
CH2
N
COO- Na+
H
CH3
Polar region
HO
OH
Non polar region
sodium glycocholate, a bile salt
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3.Steroid Hormons:
Hormons: A chemical messenger secreted by specific
glands and carried by the blood to a target tissue,
where it triggers a particular response.
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Adrenocorticoid Hs.:
Adernal glands are small mounds of tissue located at the
top of each kidney.The outer layer of the gland , the
adrenal cortex , produse a number of potent steroid
Hs., the adrenocorticoids are classified in to:
↙
↘
Mineralocrticoids
Glucocorticoids
regulate concentrations enhance carbohydrates
of Na⁺ in body fluids
metabolism
( aldosterone )
(cortisol)
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aldosterone, which regulates electrolytes and water
balance by the kidneys.
cortisone, a glucocorticoid, which increases blood glucose
level and stimulates the synthesis of glycogen in the liver .
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Sex hormons: the tests and ovaries produce steroids that
functions as sex Hs,which are responsable of
secondary sex characteristic appearnase.
Tests in male produce
sperm and male sex H.
testesrone (androgen).
Ovaries in female produce
estrogen and progesterone.
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Prostaglandines (PGs):
This group of compounds was given its name because
the first prostaglandins were identified from the
secretion of the male prostate gland , there are about
20 prostaglandins in a variety of tissues within both
male and female.
Prostaglandin: A substance derived from unsaturated
F.A with hormone like effects on a number of body
tissues and is a cyclic compound synthesized in the
body from the 20 carbon unsaturated F.A
arachidonic acid , like prostaglandin E 2 (PGE 2).
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Clinically, PGs have many functions as stimulate blood
clotting ,involved in every phase of reproductive
process.
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Prostaglandins are:
• Produced by injured tissues.
• Involved in pain, fever, and inflammation.
• Not produced when anti-inflammatory drugs such as
aspirin inhibit their synthesis.
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