The Krebs Cycle (it's a never ending one too)

labeled for reuse link

We've finally arrived. Well technically we were already in the matrix during the link reaction. But anyway. We're back!

As is implied by the name this is a cycle. And what does that mean? Well, it repeats itself... I'm hoping you have a pretty clear idea of what a cycle is... If not, well I can't really help you. 

Alrighty then, moving around this cycle is a 4 carbon molecule called, oxaloacetate (I'll be quite surprised if that's spelled correctly...). So one of the two Acetyl CoA molecules we made during the link reaction will enter the Krebs cycle. There it will combine with an oxaloacetate molecule to form a 6 carbon compound called, citrate.

Citrate will then be oxidized and decarboxylated. The decarboxylation will create a CO2 molecule, and a resulting 5 carbon compound. The oxidation will cause the reduction of another NAD+ molecule to form NADH. 

This will happen one more time, to create a 4 carbon compound, another NADH, and another carbon dioxide molecule. 

The 4 carbon compound will now undergo further modification and oxidation. This will result in another NADH molecule, the reduction of coenzyme FAD to form FADH2, and the reduction of ADP to form ATP. 

All these steps help us bring this 4 carbon compound back to the original oxaloacetate. 

The cycle then begins again. 

Also keep in mind that this cycle will run twice for every one glucose molecule, because we produce two molecules of Acetyl CoA. 

So with this in mind, these are the products of the Krebs Cycle: 

2 ATP molecules

6 molecules of electron carrier NADH

2 molecules of electron carrier FADH2

4 molecules of CO2 

In total we have a net gain of 4 ATP molecules, out of the 36 total. 

We have 10 NADH molecules (2 from glycolysis, 2 from the link reaction, and 6 from the Krebs cycle) 

And finally we have 2 FADH2 molecules. 

Hope this was informative. Sorry if it wasn't. Next step, the electron transport chain and chemiosmosis.

PS: You'll get the featured image if you know german :)