Beta oxidation of fatty acid

It is the catabolic process by which fatty acid molecules are broken down in the cytosol in prokaryotes and in the mitochondria in eukaryotes to generate acetyl-CoA.

1. Beta-oxidation of Fatty Acid
AnupMuni Bajracharya

2. •Lipids areesters of fatty acidswith alcohol. ...
•Triglycerides areesters of fatty acidswith glycerol
•They are called triglycerides because they are
formed of glycerol and 3fatty acids.
LIPIDS
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3. A.B

4. Oxidation of Fatty Acids
•Fatty acids are oxidized by β-, α-and ω-oxidation.
•Quantitatively, β-oxidation is the most important pathway.
•The term β-oxidation means the oxidation takes place in the β-carbon of
the fatty acid with the removal of 2 carbon atoms at a time from the
carboxyl end of the molecule.
•The fatty acids containing even number and odd number of carbon atoms
as well as the unsaturated fatty acids are oxidized by β-oxidation.
The last
carbon is
considered
as omega
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5. Beta-oxidation
•Beta-oxidationis thecatabolic
processby whichfatty
acidmolecules are broken downin
the cytosol in prokaryotes and in
themitochondriain eukaryotes to
generateacetyl-CoA.
•Acetyl-CoA enters thecitric acid
cyclewhileNADHandFADH
2, which
are co-enzymes, are used in
theelectron transport chain.
•It is referred as “beta oxidation”
because thebeta carbonof the fatty
acid undergoes oxidation to
acarbonylgroup.
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6. Location
•Beta-Oxidation takes place in the mitochondria of
eukaryotes while in the cytosol in the prokaryotes.
•Substrates:Free fatty acids; H
2O.
•Products:One acetyl CoA, one NADH, and one
FADH
2for every removal of a two-carbon group from
the fatty acid chain.
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7. Steps
The Beta-oxidation of fatty acids involves three
stages
I. Activation of fatty acids occurring in the
cytosol
II. Transport of fatty acids into mitochondria
III. Beta-Oxidation proper in the mitochondrial
matrix.
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8. Step I:Activation of fatty acid
•Fatty acids are activated to acyl
CoA by thiokinasesor acyl CoA
synthetases.
•The reaction occurs in two steps
and requires ATP, coenzyme A and
Mg2+.
•Fatty acid reacts with ATP to form
acyladenylatewhich then
combines with coenzyme A to
produce acyl CoA.
•In the activation, two high energy
phosphates are utilized, since ATP
is converted to pyrophosphate
(PPi).
•The enzyme inorganic
pyrophosphatasehydrolyses PPito
phosphate (Pi).
•The immediate elimination of PPi
makes this reaction totally
irreversible
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9. Step II:Transport of acetyl coAinto mitochondria
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10. Step II:Transport of acetyl coAinto mitochondria
•The inner mitochondrial membrane is impermeable to fatty acids.
•A specialized carnitinecarrier system (carnitineshuttle) operates to
transport activated fatty acids from cytosol to the mitochondria.
•This occurs in four steps.
•1. Acyl group of acyl CoA is transferred to carnitine, catalysedby carnitine
acyl transferase(present on the outer surface of inner mitochondrial
membrane).
•2. The acyl-carnitineis transported across the membrane to mitochondrial
matrix by a specific carrier protein.
•3. Carnitineacyl transferasell(found on the inner surface of inner
mitochondrial membrane) converts acyl-carnitineto acyl CoA.
•4. The carnitinereleased returns to cytosol for reuse.
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11. Step III: β oxidation proper
Each cycle of β -oxidation,
liberating a two carbon
unit-acetyl CoA, occurs in a
sequence of four reactions.
1. Oxidation : Acyl CoA
undergoes
dehydrogenation by FAD-
dependent flavoenzyme,
acyl CoA dehydrogenase. A
double bond is formed
between o and β carbons
(i.e.,2 and 3 carbons).
2. Hydration : EnoylCoA
hydratasebrings about the
hydration of the double
bond to form β -
hydroxyacylCoA.
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12. 3. Oxidation : β -HydroxyacylCoA
dehydrogenase catalysesthe second
oxidation and generates NADH. The
product formed is β -ketoacylCoA.
4. Cleavage : The final reaction in β -
oxidation is the liberation of a 2 carbon
fragment, acetyl CoA from acyl CoA.
This occurs by a thiolyticcleavage
catalysedby β -ketoacylCoA thiolase(or
simply thiolase). The new acyl CoA,
containing two carbons less than the
original, reenters the β -oxidation cycle.
The process continues till the fatty acid is
completely oxidized.
Step III: β oxidation proper
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13. ATP produced in beta oxidation of palmiticacid
•Palmiticacid, or hexadecanoicacidis the most
common saturated fattyacidfound in animals,
plants and microorganisms.
•Its chemical formula is CH3(CH2)14COOH.
•It is a major component of the oil from the
fruit of oil palms (palm oil).
•β-oxidation of palmiticacid will be repeated 7
cycles producing 8 molecules of acetyl COA.
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14. Calculation
In each cycle FADH2 and NADH+H+ is produced and
will be transported to the respiratory chain.
• FADH2 2 ATP
• NADH + H+ 3 ATP
So 7 cycles 5x7 = 35 ATP
Each acetyl COA which is oxidized in citric acid cycle
(TCA Cycle) gives 12 ATP (8 x 12 = 96 ATP)
2 ATP are utilized in the activation of fatty acid (It
occurs once).
Total Energy gain = 35 ATP + 96 ATP -2 ATP = 129 ATP
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15. A.B