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Oxidation of Fatty Acids

Neelam Maurya

Oxidation of Fatty acids

Q. 1

Oxidation in pentose phosphate pathway utilises:

 A

Oxidative phase
 B

Non oxidative phase
 C

Both of the above
 D

None of the above
Q. 1

Oxidation in pentose phosphate pathway utilises:

 A

Oxidative phase
 B

Non oxidative phase
 C

Both of the above
 D

None of the above
Ans. A
Explanation:
The enzymes of the pentose phosphate pathway act in the sequence of reactions of the pathway may be divided into two phases: an oxidative nonreversible phase and a nonoxidative reversible phase.
           
Ref: Harper 28th edition, Chapter 21.
Q. 2

Fatty acid oxidations produce:

 A

Acetyl CoA
 B

Succinyl CoA
 C

Propionyl CoA
 D

All of the above
Q. 2

Fatty acid oxidations produce:

 A

Acetyl CoA
 B

Succinyl CoA
 C

Propionyl CoA
 D

All of the above
Ans.
D
Explanation:
Fatty acids with an odd number of carbon atoms are oxidized by the pathway of β-oxidation, producing acetyl-CoA, until a three-carbon (propionyl-CoA) residue remains. This compound is converted to succinyl-CoA, a constituent of the citric acid cycle. 
         
Ref: Harper 28th edition, chapter 22.

 

Q. 3

Beta-oxidation of odd-chain fatty acids produces:

 A

Acetyl CoA
 B

Malonyl CoA
 C

Succinyl CoA
 D

Propionyl CoA
Q. 3

Beta-oxidation of odd-chain fatty acids produces:

 A

Acetyl CoA
 B

Malonyl CoA
 C

Succinyl CoA
 D

Propionyl CoA
Ans.
D
Explanation:

Odd chain fatty acids are oxidized in the similar manner as of even chain fatty acid, beta-oxidation.

However, unlike even chain fatty acids which yields only acetyl CoA, odd chain fatty acids will yield Acetyl-CoA and one three carbon acid, Propionyl-CoA.

Propionyl CoA is further converted into succinyl CoA.                                                                                                                                                      
Fatty acids are an important source of energy. ?Oxidation is the process where energy is produced by degradation of fatty acids.
 

Beta Oxidation of fatty acids: The pathway for catabolism of fatty acids is referred to  as the b-oxidation pathway, because oxidation occurs at the b-carbon (C-3).
?The beta oxidation of fatty acids involve three stages:
1. Activation of fatty acids in the cytosol
2. Transport of activated fatty acids into mitochondria (carnitine shuttle)
3. Beta oxidation proper in the mitochondrial matrix.
 
1. Activation of Fatty Acid:
 
This proceeds by Fatty Acid  thiokinase (acyl COA synthetase) present in cytosol. Thiokinase requires ATP, COA SH, Mg++. The product of this reaction is Fatty Acid  acyl COA and water.
2. Transport of fatty acyl CoA from cytosol into mitochondria: (rate-limiting step) ?Long chain acyl CoA traverses the inner mitochondria membrane with a special transport mechanism called Carnitine shuttle.
  • Acyl groups from acyl COA is transferred to carnitine to form acyl carnitine catalyzed by carnitine acyltransferase I, in the outer mitochondrial membrane.
  • Acylcarnitine is then shuttled across the inner mitochondrial membrane by a translocase enzyme.
  • The acyl group is transferred back to CoA in matrix by carnitine acyl transferase II.
  • Finally, carnitine is returned to the cytosolic side by translocase, in exchange for an incoming acyl carnitine.
3. Proper of β – oxidation in the mitochondrial matrix:
There are 4 steps in β – oxidation
  • Step I – Oxidation by FAD linked dehydrogenase: oxidation of acyl CoA by an acyl CoA dehydrogenase to give α-β unsaturated acyl CoA (enoyl CoA). 
  • Step II – Hydration by Hydratase: hydration of the double bond to β-hydroxyacyl CoA (p-hydroxyacyl CoA).
  • Step III – Oxidation by NAD linked dehydrogenase: oxidation of β-hydroxyacyl CoA to produce β-Ketoacyl CoA a NAD-dependent reaction.
  • Step IV – Thiolytic clevage Thiolase:? cleavage of the two carbon fragment by splitting the bond between α and β carbons, by thiolase enzyme.
Beta oxidation of odd chain fatty acids:
Fatty acids that enter beta-oxidation with an even number of carbons are converted entirely to acetyl-CoA. The beta-oxidation of odd chain fatty acid results in a acetyl-CoA and the 3-carbon chain propionyl-CoA. Propionyl Coa is further converted to succinyl CoA.
Ref: Harper’s, Illustrated Biochemistry, 26th edition, Page 182

Q. 4

Enzyme responsible for complete oxidation of glucose to CO2 to water is present in

 A

Cytosol
 B

Mitochondria
 C

Lysosomes
 D

Endoplasmic reticulum
Q. 4

Enzyme responsible for complete oxidation of glucose to CO2 to water is present in

 A

Cytosol
 B

Mitochondria
 C

Lysosomes
 D

Endoplasmic reticulum
Ans.
B
Explanation:

B i.e. Mitochondria

Q. 5

All are true about 0-oxidation except:

 A

Activation of FA is a must
 B

Carnitine palmitoyl transferase I is present in outer mitochondrial membrane
 C

Carnitine palmitoyl trasferase II is present in mitochondrial matrix
 D

FA activation requires 2ATP.
Q. 5

All are true about 0-oxidation except:

 A

Activation of FA is a must
 B

Carnitine palmitoyl transferase I is present in outer mitochondrial membrane
 C

Carnitine palmitoyl trasferase II is present in mitochondrial matrix
 D

FA activation requires 2ATP.
Ans.
C
Explanation:

C i.e. Carnitine palmitoyl trasf erase II is present in mitochondrial matrix

Long chain activated fatty acid penetrate the inner mitochondria( membrane only in combination with carnitineQ. Carnitine, a carrier molecule, acts like a ferry boat and transport long chain acyl- CoA across mitochondiral membrane otherwise inner mitochondrial membrane is impermeable to acyl -CoA.

Q. 6

Beta-Oxidation is peroxisome is differentiated from that occurring in mitochondria by:

 A

Acetyl CoA
 B

H202 formed
 C

Different enzymes are found in different sites
 D

NADH is required
Q. 6

Beta-Oxidation is peroxisome is differentiated from that occurring in mitochondria by:

 A

Acetyl CoA
 B

H202 formed
 C

Different enzymes are found in different sites
 D

NADH is required
Ans.
B
Explanation:

B i.e. H202 formed

Q. 7

Site of β-oxidation is ‑

 A

Cytosol
 B

Mitochondria
 C

Lysosome
 D

Golgi apparatus
Q. 7

Site of β-oxidation is ‑

 A

Cytosol
 B

Mitochondria
 C

Lysosome
 D

Golgi apparatus
Ans.
B
Explanation:

Ans. is ‘b’ i.e., Mitochondria


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