And before we talk in detail about the electron transport chain, I just want us to review for a second generally the structure of a mitochondria. So remember that the mitochondria has an outer membrane, and then it has an inner membrane, which is folded in this way to form these invaginations that are called cristae. And so we have the outer membrane here. Then we have the inner membrane. And the very interior part of the mitochondria is called The Matrix. And this part between the two membranes is called the Inter membrane space or intermembrane compartment. And what we're interested in, what we're going to be looking at today, going to look at this in remembering the electron transport chain, the members of the electron transport chain are actually embedded in this inner membrane. So it's important for us to keep track of which side is the matrix side and which side is the inter membrane space. So here is our inner membrane. This side is the Matrix, and this site is the inter membrane space.

And so the Krebs cycle, which we just completed, and we've produced all of this NADH and FADH2, has occurred in The Matrix. So we have these molecules NADH and FADH that we've generated from the Krebs Cycle, prep step, and glycolysis, and so if you recall from our tally that we just left off, we have a total of 10 NADH 2 FADH2. So each of these molecules is going to then enter the electron transport chain and drop off the electrons that they're carrying. Remember, where did these electrons come from? They originated in the bonds of glucose. So these are just carriers that have accepted these molecules as glucose was slowly oxidized or as the bonds of glucose were broken, and these electrons now are being dropped off. So NADH will drop off electrons back into the electron transport chain. This whole process is just the passing of electrons from one member of the electron transport chain to the next. So

the first member passes the electrons. And at that point, this member passes the electrons, and they go through a series of electron carrier molecules until the final electronic acceptor. You'll see, is actually oxygen gas. So ultimately, these electrons get added to oxygen gas, and when oxygen gas accepts these electrons along with hydrogen, we end up with water. So this is the point when we looked at the overall reaction, we said glucose plus oxygen yields water and carbon dioxide. Now we're seeing, OK, where is the oxygen playing into this right here. Without oxygen to accept those final electrons, NADH and FADH2 would not be able to drop off the electrons because they couldn't be passed down if there's no final electron acceptor to accept these electrons. So let's look at the details of what's happening here that are important for us to know. Well, I want you to see us as these electrons are being passed from one member of the chain to the next, some of

the energy as those electrons lose a little bit of energy, as they're passed from one carrier to the next. Some of that energy is used to pump a proton (A proton as a positively charged hydrogen ion) from one side of the inner the inner membrane to the other. Notice here is the pumping of a proton. [proton moved through carrier to intermembrane space] Here's the pumping of a proton. [proton moved through carrier to intermembrane space] Now, a proton, because it's charged, cannot pass through the membrane without some kind of a channel or pore because remember, the phospholipid bilayer doesn't allow charged particles to cross. So what's occurring is we're generating a gradient, a concentration gradient. Protons. We have a buildup of protons on one side of the membrane. What does the diffusion say? Diffusion says these want to equalize, right. These protons want to move from where they're most

concentrated to where they're least concentrated. However, they can't directly cross the membrane because of that phospholipid bilayer. So what's important for us to see is this concentration gradient is going to be used to drive the production of ATP. So I want to make sure we understand it's the electrons that have that originated from glucose that are being carried by these electron carrier molecules. It's the passage of these electrons through the electron transport chain that is creating this concentration gradient or this proton gradient. OK, so let's call this a proton. Remember proton, just a positively charged hydrogen. Now, the other thing for us to understand before we talk about what happens with that proton gradient, is a special enzyme I'm showing you here called ATP Synthase. Now, notice that it's also a protein that's embedded in the inner mitochondrial membrane, as you'll see here inside the mitochondria. And what it has is it has a pore

or a channel that allows those protons to cross from the side of the gradient where they're most concentrated to the side where they're at least concentrated. So notice that. Remember, they were built up here on the inner membrane space side. And so they will travel through this pore or channel out to the Matrix side of the intermembrane, and what that does as those flow through this enzyme called ATP synthase, it essentially acts to allow this enzyme to add phosphate onto ADP to generate ATP. So the way that I like to think about how is the movement of these protons actually causing ATP to be generated? Think about the turnstiles that you go through. If you're entering an arena or a big and when you go through, you know, you turn it or a revolving door. When you walk in, you walk through, you turn it, and then that generates the force that allows this enzyme to add a phosphate onto ADP to generate ATP. So this is what we call.

Oxidative phosphorylation, OK, or it can be called chemiosmotic phosphorylation also. Remember, phosphorylation just means the addition of a phosphate molecule, and that's what we see happening here when the phosphate is added on to ADP to get ATP. Oxidative and chemiosmotic just refer to how is that. What is the driving force for that? Now what we see is oxidative, meaning it must be in the presence of oxygen. And we know that that's true because if it wasn't for oxygen here, the electron transport chain could not function because oxygen is required as the final acceptor of those electrons. Now, chemi- Osmotic refers to this gradient that's been generated. So this proton gradient is what's driving the production of ATP from ADP. So if we look at it. Overall. OK, we see that here is our electron transport chain, here's the ATP synthase, these are these are all embedded in the inner

mitochondrial membrane, and there's more than just one, right. These are found throughout this folded inner mitochondrial membrane. And this is just showing you that the citric acid cycle was occurring in the Matrix. That's the portion of the mitochondria. And so therefore, this the matrix side is where we have these electron carriers because these were generated by the citric acid cycle. That's just a side note, the NADH that was produced in the glycolysis in the cytoplasm is shuttled by the cell into the mitochondrial matrix so that they can also drop their electrons off to the electron transport chain. So the electrons are passed through the electron transport chain, which generates our proton gradient. We must have oxygen to be the final acceptor of those electrons, which generates water. It's the gradient then that drives the production of ATP as those protons flow back through because of the buildup on the side of the inner membrane space. And this whole process is

called oxidative phosphorylation, or chemiosmotic phosphorylation. Now, the final thing I want us to talk about today. I mentioned to you that we followed one molecule of glucose. And we saw how it was completely broken down or oxidized into carbon dioxide. And now we've seen how the ATP is actually generated from the breakdown of glucose. Now, the other nutrients that we're ingesting, like proteins and fatty acids. OK, so remember, proteins in your digestive system would be broken down into the individual amino acids. OK, so carbohydrates that you eat and fatty acids which come from the fats that you eat. They all enter this process of cellular respiration in one form or the other. So some of them are directly into the first step of what Glycolysis. Some enter into that prep step where pyruvate has to be converted into an acetyl group. Some enter directly into the Krebs cycle or the citric acid cycle. But all of

these are energy-generating. All of these are going to be used by the cell to produce ATP. OK, and finally. Let's just talk about how much, on average, different cells are going to generate different amounts of ATP per glucose molecule, but in general we can just sort of do a little record-keeping here. So from glycolysis and the Krebs cycle, we already had generated four molecules of ATP. OK, and then what I want us to look at is for every molecule of NADH going through the electron transport chain, we get about three molecules of ATP. So 10 times three ATP. It's going to generate 30 ATP. And for every FADH2 molecule we get about two ATP. So 2 x 2 = 4. We'll move this 4 over here. That's from glycolysis and Krebs cycle, if you add all those up. That's thirty-eight molecules of ATP, however.

we have to subtract about two for the shuttling of the NADH that was produced outside of the mitochondria. In the cytoplasm, that has to be shuttled in so it can drop off the electrons into the electron transport chain. So let's say a total of about thirty-six ATP, give or take, depending on the cell and the conditions.

Electron Transport Chain

Electron Transport Chain