Question

list reaction/pathways of fatty acid oxidation and biosynthesis effect by insuline and gulcogan?
( Repeat giving details)

Answer 1

Fatty acid oxidation and biosynthesis

Fats, oils, steroids and cholesterols are examples of fatty acids. The break down of these compounds into two acetyl-CoA units inside mitochondria through aerobic processes is called fatty acid oxidation. The fatty acids are synthesized in the cytosol (outside mitochondria) from acetyl-CoA. Both these processes are entirely different in many aspects.

1) Pathway for Fatty acid oxidation/ Beta oxidation

Various steps involved are

a) Dehydrogenation resulting in the formation of FADH2 and a fatty acyl group having a double bond.

b) Hydration occurs at the carbon 3 with double bond and a hydroxyl group is attached.

c) Oxidation of the hydroxyl group to give a ketone.

d) Acetyl CoA if formed after a thiolytic cleavage along with a fatty acid( two carbons less than the initial one).

The diagram given below gives more clear idea of the above given steps.

).

Effect of Insulin and Glucagon

Insulin decreases fatty acid oxidation by decreasing trigliceride break down, thereby decreasing the substrate availability, where as, Glucagon stimulates fatty acid oxidation in the liver and leads to ketogenesis.

2) Pathway of Biosynthesis of fatty acids

Acetyl CoA formed as the result of beta oxidation is the substrate for the formation of fatty acids. The steps in this reaction are catalysed by enzymes. Main steps involved are,

a) Carboxylation of Acetyl-CoA to Malonyl-CoA with the help of enzyme, acetyl-CoA carboxylase.

b) Carrier protein ACP (acyl carrier protein) replaces CoA portions and forms malonyl-ACP.

c) Malonyl-ACP splits out carboxyl and creates an intermediate.

After this step, there are few similarities with beta oxidation, to be precise, a reverse order.

Effects of Insulin and Glucagon

Insulin stimulates the fatty acid synthesis in the liver, where as, Glucagon inhibits malonyl-CoA formation and thus inhibits the subsequent de novo fatty acid synthesis.

Insulin and Glucagon play major role in fatty acid metabolism. The effect of these enzymes are opposite in each pathways.