I am a student and I'm currently using the IB biology Oxford textbook. A few weeks ago I had a test on biochemistry. I studied on my textbook and it stated the following: "Mitochondrion: (…) fat is digested here if it is being used as an energy resource in the cell" (page 22) "The energy store from them (Triglycerides) can be released by aerobic cell respiration" (page 78). My teacher told me that I was wrong to write these statements in my test. Is there something wrong? Is the term 'fat' too generic? Do different kinds of fats undergo either aerobic or anaerobic respiration? I am currently confused as I do not know who is right and who is wrong… Can someone answer my questions?

Thank you


You are not far off the mark I would say. Strictly speaking it's not correct to say that mitochondria oxidize fat. By "fat" we usually mean triacylglycerides, and these must first be hydrolyzed into free fatty acids (by enzymes known as lipases) that can be oxidized in the mitochondria. But many researchers and textbook authors are not always careful with this distinction.

Most fatty acids are indeed oxidized ("digested" sounds strange to me) in the mitochondria into acetyl-CoA units, in a process known as beta-oxidation. The acetyl-CoA units produced are then further oxidized into CO$_2$ by the TCA cycle. These processes generate NADH and FADH$_2$ which is converted into ATP by the respiratory chain.

There are exceptions though. Very long-chain or branched fatty acids are instead oxidized in peroxisomes, which contain enzymes specialized for this purpose.

There is no such thing as "anaerobic respiration": in animals, respiration always uses oxygen as the terminal electron acceptor. Mitochondrial beta-oxidation is coupled to the respiratory chain, and therefore requires oxygen. Peroxisomal oxidation is not directly coupled to respiration, but the process still requires oxygen, which in this case is reduced directly by the fatty acid oxidases. So there is no truly anaerobic form of fatty acid oxidation.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.