Different types of fatty acid oxidation
| A | Acetyl CoA | |
| B |
Succinyl CoA |
|
| C |
Propionyl CoA |
|
| D |
Malonyl CoA |
Oxidation of odd-chain fatty acids results in the production of which of the following:
| A |
Acetyl CoA |
|
| B |
Succinyl CoA |
|
| C |
Propionyl CoA |
|
| D |
Malonyl CoA |
A 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 |
The very-long-chain fatty acid is oxidized in:
| A |
Mitochondria |
|
| B |
Cytoplasm |
|
| C |
Peroxisome |
|
| D |
All of the above |
Beta-oxidation of odd-chain fatty acids produces:
| A |
Acetyl CoA |
|
| B |
Malonyl CoA |
|
| C |
Succinyl CoA |
|
| D |
Propionyl CoA |
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.
- 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.
- 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.
| A |
Succinyl CoA |
|
| B |
Propionyl CoA |
|
| C |
Acetyl CoA |
|
| D |
Malonyl CoA |
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)
| A |
Duodenum |
|
| B |
Colon |
|
| C |
Ileum |
|
| D |
Jejunum |
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:
Oxidation of very long chain fatty acids takes place in ‑
| A |
Cytosol |
|
| B |
Mitochondria |
|
| C |
Ribosomes |
|
| D |
Peroxisomes |
- A modified form of β-oxidation is found in peroxisomes and leads to the breakdown of very-long-chain fatty acids (eg, C20, C22) with the formation of acetyl-CoA and H2O2, which is broken down by catalase.
- This system is not linked directly to phosphorylation and the generation of ATP, and also does not attack shorter-chain fatty acids.
- The peroxisomal enzymes are induced by high-fat diets and in some species by hypolipidemic drugs such as clofibrate.
- Another role of peroxisomal β-oxidation is to shorten the side chain of cholesterol in bile acid formation
