 All right, a couple of things. I mentioned in the last section that parts of cellular respiration in eukaryotes take place in the mitochondria. And in fact, let's just make a note of that. Both the modification of pyruvate and the citric acid cycle both happen in the mitochondrial matrix. Let's write that down. Matrix of mitochondria, that's the location. That's where this is happening. And let's do it here, too, because the citric acid cycle, both of them happen there. Now think about this for a second. So in the cytoplasm of Joe the Cell who's just hanging out needing some energy, you have this very complex series of chemical reactions that begin breaking a glucose molecule down. That's happening in the cell cytoplasm. We end up with pyruvate, which diffuses through the cell membrane of the mitochondria and goes into the mitochondrial matrix. Before we go one step further, we need to look at mitochondrial anatomy. And I'm only going to include the anatomy that's relevant for our discussion here. And I am going to pick my colors. Maybe I don't like the colors that I've picked here. Maybe I whatever. I changed my mind. I'm not picking my colors on purpose. I'm going to draw you a mitochondrian. I don't know if you remember this. They're kind of like little bean shaped cellular organelles. And they have this wildly folded inner cell membrane. So two things they have two cell membranes. This is a really unique quality of the mitochondrion. This is the outer cell membrane. And this is the inner cell membrane. Of the mitochondrion. And the space in between the inner and the outer has a name. And that is called the intermembrane space. This is an important location. The cytoplasm of the mitochondrion is in the middle here. And it's called the mitochondrial matrix. So if you imagine this mitochondrion that I just drew for you. Sitting inside a cell, a eukaryotic cell. Glycolysis is happening out here. And pyruvate travels into the matrix of the mitochondria where the next two steps happen. The fact that I labeled the intermembrane space means you probably should keep that in your brain because we're going to use that for the electron transport chain. But in the meantime, let's go back and continue with what are the products that we're going to get out of these two stages of cellular respiration that are happening in the mitochondrial matrix. First of all, those two pyruvate molecules are going to be transformed into two acetyl-CoA molecules. I'm about to tell you one byproduct of this process. We get two CO2. That's making it gassy. We get two molecules of carbon dioxide. Where did the carbons come from, my friends? We took two pyruvates. We turned them into two acetyl-CoA's plus two carbon dioxide's. So my question for you is how many carbons do you think acetyl-CoA has? Push pause and think about that because it's an easy answer. If we got rid of two carbons from the sixth, the pile of six, the two acetyl-CoA molecules each have two carbons. Does that make sense? Each one has two carbons, which means now we have a total of four carbons and two other carbons floated away as carbon dioxide. Cool! Our first carbon dioxide production. Do you think that's it? Do you think that's all the only thing that's important that happens here? Nope. Whoa. We got two carbon dioxide molecules, but we also got two electron cars. And of course we must have wheels. And what are they going to do? They're going to hop on the highway, home kids. They're going to hop on the highway to the electron transport chain. It's going to be exciting when we get there. We're not done. We got two more electron carriers, but now our acetyl-CoA molecules are going to enter the citric acid cycle. And let's see here. I know I have this somewhere. This acetyl-CoA, okay, who does it combine with and what does it get? We could count, I don't know, there's like eight enzymes involved. In this process, in the citric acid cycle. Which means there's eight molecule changes. There's eight reactions in this cycle. And an acetyl-CoA enters and a new molecule is formed that combines with the new acetyl-CoA that enters and then stuff happens. And then a new molecule is formed that combines with acetyl-CoA. That's how the cycle keeps going. As long as you have acetyl-CoA from the glucose, as long as you keep providing that, you're going to keep providing this citric, this cycle. Which, dude, what's the point of the cycle? Let me tell you. First of all, we're going to go this direction. And I'm going to show this coming off of the whole cycle itself, okay? Not, I'm not going to, like, who cares where exactly this came off of? But what's your hint? What are you going to guess is coming off? And how many do you think come off? True story. Four carbon dioxides are blown off in the citric acid cycle. That means that we've gotten rid of all the carbon compounds. This is with both acetyl-CoAs. So both acetyl-CoAs have to go into this cycle in order to get those four carbon dioxide molecules to come off. I'm happily just summarizing this giddy up for you. Do you think that's the end of the story? Well, I'll tell you right now that we get another 2ATP. Not a PT, a TP. Two more. We're up to four, folks. I wonder what we can buy with four ATPs? Do you think we can get ourselves a whole candy bar? I don't know. What else? What else would you hope? You're like, dude, we got two out of glycolysis and two out of the citric acid cycle. We're about to hit the jackpot. What do you think we're going to get out of this? Mm-hmm. This is the big payoff. We're going to get eight more electron carriers with their wheels intact. And what do they do? They hop on the highway to the electron transport chain. Count them up. We have 12 electron carriers now that are heading to the electron transport chain. This matters. We're super interested in this. Let's take, this is it. This is what we have. Let's take this information and complete our, whatever this thing is, let's complete our chart. In the pyruvate to acetyl-CoA, remember that we got two electron cars. My colors are changing. It's purple in the other one. And we got two carbon dioxides. Okay. I don't know if I'm going to keep up with all my colors here. That's it. That's all I'm seeing. Oh, yep. That's all I'm seeing in to keep track of in our pyruvate modification stage. What about in the citric acid cycle? How many electron carries did we end up with? Eight of those puppies. That's a big deal. Did we get any ATP out of the mix? Yeah. We got two ATPs. Did we get any carbon dioxide? Yes, we did. We got four, which means we're done. We have no more carbons to dioxide. And have we gotten water yet? No. So where do you think the water's going to come from? That's going to be a good story when we talk about where the water comes from. Next up, let me make sure this is a true story. Next up is our conversation about the electron transport chain. Get ready because it's super cool.