Confused About Mitochondria

[Bertje]

Hello everyone!
My question is about exactly what fuel a mitochondria can burn for energy.

Some people say that the mitochondria can directly burn fats and protein with oxygen for energy (when glucose is low for example).

But I always thougth that the mitochondria only can burn glucose with oxygen! And that when glycogen is low, the body starts burning fats and muscle, but it must first change the protein and fatty acids in usable glucose, through glucogenesis if im not wrong... Can somebody please help me out?!

Greetings!

 

[Bertje]

Nobody..?

 

[Dino D]

Did you found out?

 

[Bertje]

No...

 

[BingDing]

It's a good question @Bertje. The short answer is that all three macros can be broken down to acetyl-CoA and that can enter the citric acid cycle to make ATP. The long answer gets complicated pretty fast. The Wiki page on the citric acid cycle is not too confusing. Note that some of the precursor steps (to make the acetyl-CoA) do not have to happen in the mitochondria (at least that's what I think right now).

 

[Bertje]

It's a good question @Bertje. The short answer is that all three macros can be broken down to acetyl-CoA and that can enter the citric acid cycle to make ATP. The long answer gets complicated pretty fast. The Wiki page on the citric acid cycle is not too confusing. Note that some of the precursor steps (to make the acetyl-CoA) do not have to happen in the mitochondria (at least that's what I think right now).

Thanks for the response! Allright I get it, the mitochondrias can make energy from all the 3 macros... only now I have a new question... sorry haha..

If the mitos can make energy from all the 3 macros, then why does something like gluconeogenesis exist? As far as I understand, thats a proces that makes glucose from amino acids, well why does that happen if a mito also can make energy direct from protein, why all the trouble make it first glucose again?

 

[rob]

@contact Gluconeogenesis is needed because certain vital organs, notably the brain, heavily rely on glucose for energy. Since the body cannot always rely on a constant supply of dietary carbs, gluconeogenesis enables it to make glucose from fat and protein. Why, in particular, the brain relies so heavily on glucose for energy and not fats, as per fatty acid oxidation, is still a matter of debate.

 

[redsun]

@contact Gluconeogenesis is needed because certain vital organs, notably the brain, heavily rely on glucose for energy. Since the body cannot always rely on a constant supply of dietary carbs, gluconeogenesis enables it to make glucose from fat and protein. Why, in particular, the brain relies so heavily on glucose for energy and not fats, as per fatty acid oxidation, is still a matter of debate.

There are only some parts of the brain(i think the brain stem?) that absolutely must use glucose, but most of the rest of the brain can utilize ketones if necessary to spare muscle as much as possible. Of course its not necessarily ideal.

 

[rob]

Hi @contact, yes ketones can be used but, as you said, it's not ideal, especially long term. There are different theories as to why glucose is the brain's fuel of choice.

 

[BingDing]

In addition to the brain's use of glucose, our red blood cells do not have any mitochondria and rely on anaerobic glycolysis to make ATP. Anaerobic glycolysis always starts with glucose.

 

[Bertje]

Yes thank you all its clear for me now, I know the brain only can run on glucose so thats why gluconeogenesis must exist