Question

b) Explain Boxidation of fatty acids. Write the amount of energy generated from
complete oxidation of fatty acids​

Answer 1

Answer:

Regulation of Mitochondrial Fatty Acid Oxidation

The rate of fatty acid oxidation changes in response to the nutritional and hormonal state of the animal. The rate of fatty acid oxidation is high during fasting but low in the fed animal. One cause for this change is the higher concentration of unesterified (free) fatty acids in the circulation of the fasting animal as compared to the concentration in the fed animal. An increased concentration of free fatty acids results in higher rates of cellular uptake and oxidation of fatty acids. In liver, which has high capacities for both synthesizing and oxidizing fatty acids, a reciprocal relationship exists between these two processes. After feeding, when carbohydrates are converted to triacylglycerols, the rate of fatty acid synthesis is high because acetyl-CoA carboxylase is active. This enzyme catalyzes the carboxylation of acetyl-CoA to malonyl-CoA, the first committed intermediate in fatty acid synthesis. Malonyl-CoA binds to and effectively inhibits CPT I that initiates the uptake of fatty acids by mitochondria. Thus, when fatty acids are rapidly synthesized, the cytosolic concentration of malonyl-CoA is high and the mitochondrial uptake and oxidation of fatty acids are inhibited. This situation is reversed during fasting when lower blood glucose levels cause the plasma concentration of the hormone glucagon to increase and that of insulin to decrease. Glucagon promotes the phosphorylation and inactivation of acetyl-CoA carboxylase with the result that the cytosolic concentration of malonyl-CoA declines. The lower concentration of malonyl-CoA causes fatty acid synthesis to decrease and fatty acid oxidation to increase. The same regulatory mechanism may be effective in tissues such as heart and skeletal muscle that oxidize fatty acids but do not synthesize them. Although malonyl-CoA is generated in these tissues by acetyl-CoA carboxylase, it seems to be metabolized by decarboxylation catalyzed by malonyl-CoA decarboxylase.

Answer 2

Answer:

Fatty acids provide highly efficient energy storage, delivering more energy per gram than carbohydrates like glucose. In tissues with high energy requirement, such as heart, up to 50–70% of energy, in the form of ATP production, comes from fatty acid (FA) beta-oxidation.

During fatty acid β-oxidation long chain acyl-CoA molecules – the main components of FAs – are broken to acetyl-CoA molecules.

Beta-oxidation:

Beta-oxidation consists of four steps:

1) Dehydrogenation catalyzed by acyl-CoA dehydrogenase, which removes two hydrogens between carbons 2 and 3.

2) Hydration catalyzed by enoyl-CoA hydratase, which adds water across the double bond.

3) Dehydrogenation catalyzed by 3-hydroxyacyl-CoA dehydrogenase, which generates NADH.

4) Thiolytic cleavage catalyzed beta-ketothiolase, which cleaves the terminal acetyl-CoA group and forms a new acyl-CoA which is two carbons shorter than the previous one.

The shortened acyl-CoA then reenters the beta-oxidation pathway.