Different types of Fatty Oxidation

Different types of fatty acid oxidation

Q. 1

Oxidation of odd-chain fatty acids result in the production of which of the following?

 A

Acetyl CoA

 B

Succinyl CoA

 C

Propionyl CoA

 D

Malonyl CoA

Q. 1

Oxidation of odd-chain fatty acids result in the production of which of the following?

 A

Acetyl CoA

 B

Succinyl CoA

 C

Propionyl CoA

 D

Malonyl CoA

Ans. C

Explanation:

Odd chain fatty acids are also oxidised exactly as even chain fatty acids. However, after successive removal of 2-carbon units, at the end, one 3 carbon unit, propionyl CoA is produced. The propionyl CoA is further metabolised to Succinyl CoA which enters the TCA cycle.
 
Ref: Vasudevan Biochemistry, 3rd Edition, Page 124

 


Q. 2

Fatty acid with even number of carbon atoms on oxidation produces:

 A

Acetyl CoA

 B

Succinyl CoA

 C

Propionyl CoA

 D

All of the above

Q. 2

Fatty acid with even number of carbon atoms on oxidation produces:

 A

Acetyl CoA

 B

Succinyl CoA

 C

Propionyl CoA

 D

All of the above

Ans. A

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. Hence, the propionyl residue from an odd-chain fatty acid is the only part of a fatty acid that is glucogenic
         
Ref: Harper 28th edition, chapter 22.

Q. 3

Very long chain fatty acid is oxidised in:

 A

Mitochondria

 B

Cytoplasm

 C

Peroxisome

 D

All of the above

Q. 3

Very long chain fatty acid is oxidised in:

 A

Mitochondria

 B

Cytoplasm

 C

Peroxisome

 D

All of the above

Ans. C

Explanation:

A modified form of oxidation is found in peroxisomes and leads to the formation of acetyl-CoA and H2O2 (from the flavoprotein-linked dehydrogenase step), which is broken down by catalase.
Thus, this dehydrogenation in peroxisomes is not linked directly to phosphorylation and the generation of ATP. The system facilitates the oxidation of very long chain fatty acids (eg, C20, C22).
These enzymes are induced by high-fat diets and in some species by hypo-lipidemic drugs such as clofibrate.
Ref: Harper 28th edition, chapter 22.

Q. 4

Beta-oxidation of odd-chain fatty acids produces:

 A

Acetyl CoA

 B

Malonyl CoA

 C

Succinyl CoA

 D

Propionyl CoA

Q. 4

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

Quiz In Between


Q. 5

β-oxidation of odd-chain fatty acids produces:

 A

Succinyl CoA

 B

Propionyl CoA

 C

Acetyl CoA

 D

Malonyl CoA

Q. 5

β-oxidation of odd-chain fatty acids produces:

 A

Succinyl CoA

 B

Propionyl CoA

 C

Acetyl CoA

 D

Malonyl CoA

Ans. B

Explanation:

B i.e. Propionyl CoA

13- oxidation of odd chain fatty acid produces acetyl CoA plus a molecule of propionyl –CoAQ. But propionyl CoA is formed only in odd chain fatty acid oxidation (not in even fatty acids)


Q. 6

Short chain fatty acid produced by bacteria are maximally absorbed in :

 A

Duodenum

 B

Colon

 C

Ileum

 D

Jejunum

Q. 6

Short chain fatty acid produced by bacteria are maximally absorbed in :

 A

Duodenum

 B

Colon

 C

Ileum

 D

Jejunum

Ans. B

Explanation:

B i.e. Colon

  • Major fat absorption takes place in upper small intestine except (mainly jejunum & duodenum) short chain fatty acids which is absorbed in colon0.
  • Normal fecal fat excretion is less than 6gm/day, more than 6gm/day indicates malabsorptionQ.
  • Steatorrhea is defined as stool fat > 7gm/dayQ.
  • Daily fecal fat averages 15-25gm/d with small intestinal disease & exceeds 40gm /d with pancreatic exocrine insufficiency
  • Evaluation of fat malabsorption:

Q. 7

Oxidation of very long chain fatty acids takes place in ‑

 A

Cytosol

 B

Mitochondria

 C

Ribosomes

 D

Peroxisomes

Q. 7

Oxidation of very long chain fatty acids takes place in ‑

 A

Cytosol

 B

Mitochondria

 C

Ribosomes

 D

Peroxisomes

Ans. D

Explanation:

Quiz In Between



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