Presentation on introduction of fatty acids and even and odd number of fatty acids

1. Plant biochemistry II
Assignment: Biosynthesis of even and odd number of fatty acids
Semester (3rd)
Department of botany, university of sargodha
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2. Biosynthesis of
even and odd number of
fatty acids
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3. Fatty acids
• Fatty acids are the building blocks of lipids
important component in plants, animals and
microorganisms.
• A fatty acid consists of a straight chain of an even
number of carbon atoms, with hydrogen atoms
along the length of the chain at one end and a
carboxyl group(-COOH) at the other end. Fatty acids
are not found in free state in nature; commonly
they exist in combination with glycerol( an alcohol)
in the form of triglyceride.
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4. Structure of fatty acids
• Fatty acids are synthesized from linear acetogenins of acetate
pathway.
• Fatty acids are carbon chains with a methyl group at one end
of the molecule (designated omega,ω) and a carboxyl group at
the other end.
• The carbon atom next to the carboxyl group is called the α
carbon, and the subsequent one the β carbon.
• The systematic nomenclature of fatty acids may also indicate
the location of double bonds with reference to the carboxyl
group.
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5. • CH3- (CH2)n CH2-CH2- COOH
ω β α
• Fatty acids may be named according to systematic or trivial
nomenclature.
• One systematic way to describe fatty acids is related to the
methyl (ω) end. This is used to describe the position of double
bonds from the end of the fatty acids.
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6. Classification of fatty acids
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7. Saturated fatty acids
• Fatty acid chains that contain only carbon-carbon bonds are
referred to as saturated.
• The common fatty acids contain 12-22 carbon atoms.
Unsaturated fatty acids
 Monounsaturated fatty acids have one carbon-carbon double
bond, which can occur in different positions.
 Polyunsaturated fatty acids have two or more double bonds.
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8.  Monounsaturated fatty acids:
Monounsaturated fatty acids have one double bond and have a chain
length of 16-22 , with cis configuration. This means that the hydrogen
atom on either side of double bond are oriented in the same direction.
Cis fatty acids are thermodynamically less stable than trans form.
Trans isomers may be produced during industrial processing
(hydrogenation) of unsaturated oils.
Example: Oleic acid (C18H34O2)
Natural sources: red meat, nut, olive oil etc.
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9. Polyunsaturated fatty acids:
• In polyunsaturated fatty acids the first double bond may be found
between the third and the forth carbon atom from the ω carbon; these
are called ω-3 fatty acids.
• If the first double bond is between the sixth and seventh carbon atom,
then they are called ω-6 fatty acids.
• The double bond in PUFAs are separated from each other by methylene
grouping.
Help to decrease total cholesterol level.
Example: Linoleic acid (C18H32O2).
Natural resources: corn oil, soybean oil etc.
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11. Nomenclature of fatty acids
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12. Fatty acids biosynthesis
• Fatty acid biosynthesis is the creation of fatty acids from acetyl –CoA
and NADPH through the action of enzymes called fatty acid synthase.
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14. Fatty acid biosynthesis in plants occurs in the chloroplast of green tissue
and in the plastids of non-photosynthetic tissue and not in the cytosol
as in the animal cell.
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15. Production of NADPH
In cytosol of organisms In chloroplast of plants
NADPH is produced in the chloroplasts
by the light-dependent reactions of
photosynthesis.
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16. • In chloroplasts, photosynthesis provides the NADPH required
for the synthesis of fatty acids. In leucoplasts, the NADPH
required for the fatty acid synthesis is provided by the
oxidation of glucose 6-phosphate via the oxidative pentose
phosphate pathway. Glucose 6-phosphate is transported by a
glucose phosphate-phosphate translocator to the plastids.
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17. Enzymes & co factors
Two main enzymes
1)acetyl CoA carboxylase
2)fatty acid synthase
Co factors
1)Biotin
2)NADH
3)Mg+
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18. • Fatty acid synthesis starts with the carboxylation of acetyl CoA
to malonyl CoA by acetyl CoA carboxylase, with the
consumption of ATP.
• CoA is exchanged by acyl carrier protein(ACP). ACP comprises
a serine residue to which a panthetheine is linked via a
phosphate group. The panthetheine is also a functional
constituent of CoA. Both ACP and CoA are covalently bound to
a protein. The enzyme β-ketoacyl-ACP synthase III (KAS III)
catalyzes the condensation of acetyl CoA with malonyl-ACP.
This reaction is irreversible due to the liberation of CO2
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20. Formation of malonyl-CoA
• Irreversible process
• Biotin is covalently linked with its
carboxyl group to the ϵ-amino
group of a lysine residue of the
biotin carboxyl carrier protein,
and its –NH-group can form a
carbamate with HCO3
-
• Biotin is carboxylated at the
expense of ATP by biotin
carboxylase.
• Bicarbonate is transferred to
acetyl CoA by carboxyl
transferase.
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21. Fatty acids on the basis of carbon number
Even numbered chain fatty acids
The most commonly occurring fatty acids have even numbers
of carbon atoms in an unbranched chain of 12-24 carbons.
E.g, palmitic acid(16:0), oleic acid(18:1)
Odd numbered chain fatty acids
Rare , found in some plants & marine organisms. E.g.,
propionic acid(13:0), Heptadecanoic acid or margaric
acid(17:0)
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22. Biosynthesis of even chain fatty acids
Activation
 Fatty acid synthesis starts with the formation of acetyl ACP and malonyl ACP.
 Acetyl transacylase and malonyl transacylase catalyze these reactions.
 Acetyl CoA + ACP → acetyl ACP + CoA
Malonyl CoA + ACP → malonyl ACP + CoA
acetyl ACP malonyl ACP
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23. Condensation reaction
Acetyl ACP and malonyl
ACP react to form
acetoacetyl ACP.
Enzyme: acyl-malonyl ACP
condencing enzyme.
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24. Reduction reaction
Acetoacetyl ACP is reduced to D-3-
hydroxybutyryl ACP.
NADPH is the reducing agent.
Enzyme: β-ketoacyl ACP reductase
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25. Dehydration reaction
D-3-hydroxybutyryl ACP is
dehydrated to form crotonyl
ACP.
Enzyme: 3-hydroxyacyl ACP
dehydratase
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26. Reduction reaction
The final step in the cycle reduces
crotonyl ACP to butyryl ACP.
NADPH is reductant.
Enzyme: -enoyl ACP reductase.
This is the end of first elongation
cycle.
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27. In the second round butyryl
ACP condenses with malonyl
ACP to form a C6-β-ketoacyl
ACP.
Reduction, dehydration, and a
second reduction convert the
C6-β-ketoacyl ACP into a C6-acyl
ACP , which is ready for a third
round of elongation.
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28. Each malonyl group and acetyl group is
activated by a thioester that link it to
fatty acid synthase, a multienzyme
system.
1)Condensation of an activated acyl
group and two carbon derived from
malonyl-CoA, with elimination of CO2
from malonyl group, extends the acyl
chain by two carbons.
2) β-keto group is reduced to an alcohol,
3)Elimination of H2O creates a double
bond,
4)The double bond is reduced to form
corresponding saturated fatty acyl
group.
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29. Termination
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30. Seven cycle of condensation and reduction produce the 16-carbon
saturated palmitoyl group, still bound to ACP. Chain elongation by
synthase complex generally stops at this point and free palmitate is
released from the ACP by a hydrolytic activity (thioesterase; TE) in the
multi-functional protein.
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32. Biosynthesis of odd chain fatty acids
• Rare , found in some plants and marine organisms. For
example, propionic acid(3:0), Heptadecanoic acid or margaric
acid(17:0)
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33. sources
• Ruminant animals derive most of their caloric intake from
acetate and propionate.
• Produced by bacterial fermentation of carbohydrates
(propionibacterium).
• Produced also by oxidation of amino acids isoleucine, valine,
and methionine.
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36. Propionyl –CoA Carboxylase
• Biotin dependent enzyme
• α6β6
• resembles pyruvate decarboxylase reaction
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