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1. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Beta Oxidation
Course: Principles of Biochemistry
By;
M. Sheraz Yasin
Lecturer,
Institute of Biochemistry and Biotechnology,
University of Veterinary and Animal Sciences,
Lahore.

2. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Oxidation of Fatty Acids (Carbohydrates and lipids)
A large amount of energy is obtained when fatty acids undergo
•oxidation in the mitochondria to acetyl CoA.
•beta oxidation, (β oxidation) which removes two-carbon
segments containing the alpha and beta carbon from the
carboxyl end of the fatty acid.

Learning Goal Describe the metabolic pathway of β oxidation.

3. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
β Oxidation
A cycle in β oxidation
•produces an acetyl CoA and a fatty acid that is
shorter by two carbons.
•repeats until the original fatty acid is completely
degraded to two-carbon units that form acetyl CoA,
which enters the citric acid cycle.

4. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Fatty Acid Activation
Fatty acids in the cytosol are transported through the inner
mitochondrial membrane to undergo β oxidation in the matrix.
In an activation process,
•a fatty acid is combined with CoA to yield a high-energy
fatty acyl CoA.
•energy is released by the hydrolysis of ATP to AMP and
used to drive the reaction.

5. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Transport of Fatty Acyl CoA
A transport system called the carnitine shuttle carries fatty
acids into the mitochondria from the cytosol.
•Carnitine acyltransferase catalyzes the transfer of a fatty
acyl group to the hydroxyl group of carnitine to produce
fatty acyl carnitine.
•Fatty acyl carnitine then passes through the inner
mitochondrial membrane into the matrix.

6. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Transport of Fatty Acyl CoA

7. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Transport of Fatty Acyl CoA
In the matrix, another carnitine acyltransferase
•catalyzes the reverse reaction that transfers the
fatty acyl group to CoA to reform fatty acyl CoA.
•releases the carnitine and returns to the cytosol.

Thus, the carnitine shuttle moves fatty acyl CoA from
the cytosol into the matrix, where the fatty acid can
undergo β oxidation.

8. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Carnitine Shuttle System
In the carnitine shuttle system, fatty acids are
activated and transported from the cytosol through
the inner mitochondrial membrane into the matrix.

9. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Fatty acyl CoA undergoes beta (β) oxidation in a cycle of
four reactions.
In reaction 1,
•acyl CoA dehydrogenase catalyzes the transfer of
hydrogen atoms from the α and β carbons of the activated
fatty acid.
•a trans C = C bond is formed between α and β carbons,
and the reduced coenzyme FADH
2 is produced.
Beta (β) Oxidation of Fatty Acids:
Reaction 1

10. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Beta (β) Oxidation of Fatty Acids:
Reaction 2
In reaction 2,
•a hydration reaction catalyzed by enoyl CoA hydratase adds
the components of water to the trans double bond.
•a hydroxyl group (—OH) attaches to the β carbon of the
fatty acid, and a hydrogen atom attaches to the α carbon.

11. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Beta (β) Oxidation of Fatty Acids:
Reaction 3
In reaction 3,
•the secondary hydroxyl group on the β carbon (carbon 3)
is oxidized by 3-hydroxyacyl CoA dehydrogenase to yield
a ketone.
•the hydrogen atoms removed in the oxidation are
transferred to NAD
+
to yield a β keto or 3-keto group and
the reduced coenzyme NADH.

12. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Beta (β) Oxidation of Fatty Acids:
Reaction 4
In reaction 4,
•the C
α — C
β bond is cleaved by β-ketoacyl CoA thiolase to yield
a two-carbon acetyl CoA and a new fatty acyl CoA that is
shortened by two carbon atoms.
•the shorter fatty acyl CoA repeats the four steps of the β-
oxidation cycle until the original fatty acid is completely degraded
to two-carbon units of acetyl CoA.

13. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Fatty Acid Length Determines Cycle
Repeats
•The number of carbons in a fatty acid determines the
number of times the cycle repeats and the number of
acetyl-CoA units it produces.
•The total number of times the cycle repeats is one fewer
than the total number of acetyl groups it produces.
•Odd-numbered fatty acids go through the same four steps
of β oxidation until the final cycle, in which the remaining
fatty acyl CoA is cleaved to yield a propionyl CoA (C
3)
group and an acetyl CoA.

14. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Beta (β) Oxidation of Fatty Acids
Capric acid (C
10)
undergoes four oxidation
cycles that repeat
reactions 1 to 4 and yield
five acetyl CoA molecules,
four NADH, and four
FADH
2.

15. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Oxidation of Unsaturated Fatty Acids
•Some fats from our diets contain unsaturated fatty acids,
which have one or more cis double bonds.
•An isomerase converts a cis double bond to a trans double
bond between the α and β carbons so the fatty acid can
undergo hydration.
•It forms a product that enters β oxidation at reaction 2, so
the energy released by the β oxidation of an unsaturated
fatty acid is slightly less because no FADH
2 is produced in
that cycle.

16. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Match the reactions of β oxidation with each of the following:

A.Water is added.
B.FADH
2 forms.
C.A two-carbon unit is removed.
D.A hydroxyl group is oxidized.
E.NADH forms.

1) oxidation 1

2) hydration

3) oxidation 2

4) acetyl CoA cleaved

17. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Match the reactions of β oxidation with each of the following:

A.Water is added. 2) hydration
B.FADH
2 forms. 1) oxidation 1
C.A two-carbon unit is removed. 4) acetyl CoA cleaved
D.A hydroxyl group is oxidized. 3) oxidation 2
E.NADH forms. 3) oxidation 2

18. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
A.How many acetyl CoA groups are produced by the
complete β oxidation of palmitic acid (C
16)?
1) 16 2) 8 3) 7


B.How many oxidation cycles are necessary to completely
oxidize palmitic acid (C
16)?
1) 16 2) 8 3) 7

19. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
A.How many acetyl CoA groups are produced by the
complete β oxidation of palmitic acid (C
16)?
2) 8 (16 C/2 = 8)


B.How many oxidation cycles are necessary to completely
oxidize palmitic acid (C
16)?
3) 7 (16 C/2 – 1 = 7)

20. General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
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