Question

where does fatty acid oxidation occur?"

Answer 1

In prokaryotes, fatty acid oxidation takes place in cytosol.

In eukaryotes, majority of fatty acid oxidation takes place in mitochondria, however, very long chain fatty acids (No. of carbon 22 or greater), and fatty acids with blocked beta carbon are oxidized in peroxisomes untill they are oxidized up to octanoyl-CoA, therafter they are again oxidized in to mitochondria. Omega oxidation takes place in smooth endoplasmic reticulam.

After taking meal, fatty acids are stored as triglycerides. When the blood glucose level falls, enzyme lipase hydrolyzes these triglycerides into fatty acids and glycerol and thus fatty acids reach to metabolizing cells through blood stream. As RBCs lack mitochondria, they can not oxidize fatty acids.

After entering into the cell, they get converted to fatty acyl-CoA with the help of enzymes and ATP. Now with the use of carnitine shuttle, these fatty acyl-CoA enters into the mitochondria and get oxidized in the mitochondrial matrix via beta-oxidation.

Methylated Fatty acids (having methyl group at beta carbon) are oxidized via alpha oxidation in to the peroxisomes.

In case of defective mitochondrial beta-oxidation, fatty acids are oxidized via an alternative pathway called omega-oxidation, which takes place in smooth endoplasmic reticulum (particularly in hepatic cells and kidney).

We can conclude that three types of fatty acid oxidation occur in as shown:

Alpha oxidation	Peroxisomes
Beta oxidation (Most common type of fatty acid oxidation)	Mitochondria
Omega oxidation	Smooth ER