The electron transport chain is essentially the main way we make ATP. All of the NADHs and FADH2s we’ve been working on are heading over to the mitochondria, or might already be there, to go through the ETC. Here is how that works!

Inside of the mitochondria, in what is called the mitochondrial matrix, we have our NADH. We already know that we can take off a hydrogen and make it an NADH+ because we’ve seen them start that way in pathways and then get that hydrogen added on. The mitochondrial matrix is inside of the mitochondria and it has all sorts of membranes that project in and make a sort of squiggly maze like looking structure within the mitochondria. These walls are called the inner mitochondrial membrane.

There are protein complexes inside of the inner mitochondrial membrane that are transmembrane, meaning that they reach all the way across, from the mitochondrial matrix to the intermembrane space. The first one of these is called Complex I. NADH comes along and drops of that extra hydrogen here and Complex I pumps it into the intermembrane space. The reason is that that starts to create a concentration gradient for hydrogen, making it want to head back. Complex II does the same job, but actually does it for just FADH2 and not NADH. So, FADH2 is going to skip Complex I and head directly to Complex II. At Complex II, Coenzyme Q takes the electrons we’ve sent up in I and II and transports them to Complex III.

At Complex III, no electrons cross the border but we are going to pump more protons, upping that concentration gradient some more. The electrons get carried on by an enzyme called carrier C.

Alright, now we’re at complex IV. 2 more protons get pumped to the intermembrane space and this process forms water.

Last, ATP synthase, the last complex in our chain, has an ADP and a phosphate attached to it already. It opens up to let they hydrogen flow back with the concentration gradient that we’ve been creating. The latest theories is that ATP synthase sort of spins like that carnival ride that pushes up against the wall. As it spins, it slams the ADP and phosphate together making ATP!

We’ll keep working on our metabolic pathways, so check back again next week!