Okay, but now let's go ahead and move on to the next stage, which is pyruvate oxidation and the citric acid cycle. If oxygen is present, that is when pyruvate will enter the mitochondria and eukaryotic cells. And we'll talk about later if oxygen is not present.
So here we're going to assume that oxygen is present, and that's why we're moving on into the mitochondria for pyruvate oxidation. All right, so what's going to happen? Well, pyruvate will be oxidized into acetyl-CoA. And acetyl-CoA is used to make citrate in the citric acid cycle.
That's why it's important. So the 2-pyruvate that we generated here in glycolysis, I'll just go ahead and put this here. So 2-pyruvate, that's what's now moving on to the pyruvate oxidation. Now, in addition to CO2 and 2- NADH will be produced.
So we'll have 2CO2 and 2NADH also being produced. Okay, so let's go ahead and look at this reaction. Here we go.
So we have pyruvate right here. We have an input of coenzyme A. We can see that conversion of NAD to NADH plus RCO2.
And then we're going to get out acetyl-CoA. And this is what's important as we progress to the next. stage. Okay, so let's move on to the next stage, citric acid cycle.
This is also referred to as a Krebs cycle, so make sure that you know that those are synonymous. This is going to occur in the mitochondrial matrix, and it'll turn the acetyl-CoA that we just produced in pyruvate oxidation into citrate. So that's really what's happening.
happening here in the citric acid cycle. We get to turn that acetyl-CoA into citrate. We'll also see the release of carbon dioxide, and we'll see the synthesis of energy, ATP. Again, not as much as in the ETC, but we'll see ATP synthesized here as well. Now, lastly, electrons transferred.
to NADH and FADH2 will occur here. FADH2 is another coenzyme that has a similar importance to NAD. So here's the overall, or I should say overview of the complete citric acid cycle. However, You do not need to know the intermediates.
You don't need to know the names of any of the intermediates, nothing like that. What we're going to go through here are just some of the important components of what actually happens in the citric acid cycle and how much energy is being produced here. So this is what you need to know in terms of the citric acid cycle, just to summarize the pathway.
So per glucose molecule, we'll have an input of two acetyl-CoA, and then we'll have these outputs. So we have some energy output, we get two ATP. We have our energy carrying or storing molecules, we have NADH and we have FADH2. Again, both coenzymes, similar function, just a different structure.
And then we also have a release of CO2. So really, I want you to know, just know these inputs and outputs. You don't need to know any of the intermediates or what happens between this, just know the inputs and outputs.
Okay, so let's do a quick check here. Where does the citric acid cycle occur? All right, that's right. It occurs in the mitochondrial matrix. And two, what is the net production of ATP in the citric acid cycle?
It's 2ATP. 2ATP. So now let's go ahead and move on to the last step, which is oxidative phosphorylation. So oxidative phosphorylation consists of the electron transport chain Chemiosmosis, which we talked about before, remember back in photosynthesis, I said that gradient of hydrogen ions that can happen and as they go down their concentration gradient through ATP synthase, that's also known as chemiosmosis. We're going to have our ETC, we're going to have chemiosmosis occurring in the electron transport chain.
So here's a complete overview of it. So hopefully this looks very similar to what we saw before in our last ETC in the photosynthesis section. So we can see proteins embedded in our mitochondrial membrane.
We can see these lines here showing that transfer of electrons. We can see our hydrogen ion gradient. Here is our ATP synthase right here.
So this will be producing ATP and it's going to be powered by this downhill diffusion of our hydrogen ions, our gradient. And here's our final electron acceptor of oxygen which I told you we would come back to. So oxygen will combine with our two free hydrogen or two free hydrogen ions. two electrons and then it'll create water.
So our final electron acceptor is right here. Okay but this is just an overview so now we're going to take it a little bit more step by step. So for the ETC, the ETC is located in the inner membrane of the mitochondria and we can see a collection of proteins and these are numbered. So if you look at this image we have protein 1, three, protein four, cytochrome C.
So these are our embedded proteins that are going to help transfer our electrons. Now, as the electrons, it's called fall, as they fall between our proteins, as they go from one protein to the next, our proteins alternate between being reduced and being oxidized. So as each one accepts a protein, they're reduced. And then when they give up their protein, they've been off.
or when they give up their electron, not protein, when they give up their electron, they've become oxidized. Okay, so when they accept an electron, they're reduced, and when they give up their electron, they're oxidized. So they, again, it's just redox reactions.
Remember this right here, this process is redox reactions. So they alternate between these states of being reduced and being oxidized. So that's what's happening here in the ETC, again, very similar to what we've seen before. The cristae here increase the surface area for reactions to occur. So remember inside of our mitochondria we see folds.
And think back to our previous unit, unit two, we talked about surface area and folds and membranes increase the surface area to volume ratio, which allows cells to be more efficient. So we're increasing our surface area here for all these different reactions to occur. Now we don't actually see the production of ATP direct.
at the cristae, meaning the ATP is happening over here at the ATP synthase. So these cristae do not produce ATP directly. It's the ATP synthase that's going to be producing our ATP. So this will help manage the release of energy.
So all of these proteins here in that increased surface area are going to help manage the release of energy by creating, think of it as like small steps. So instead of having this massive drop of our electron, we're taking it little steps at a time so that the electron can, or so that we can accurately harvest that energy from the fall of the electrons. So this fall of electrons here is going to allow us, allow the mitochondria to be able to manage the energy.
Then ATP is synthesized at the ATP synthase. The final electron acceptor like we talked about before is oxygen and each oxygen will pair with two hydrogen ions and two electrons and then it will form water. So if we look here we can see electrons are going to go from protein one, look at the transfer of electrons, all the way through and then instead of going directly to ATP synthase they're going to be taken to oxygen. And that's when they combine with our protons and our electrons.
And that's when we get water. So this whole thing right here is just managing the fall of the electrons so that we can accurately harvest this energy. Okay, if we were to block this oxygen, let's say I were to cross this oxygen out. For example, the poison, what's the name of the poison? Why am I blanking on it?
Cyanide. There we go. Cyanide. If... Someone consumes cyanide.
Cyanide works by blocking oxygen as a final electron acceptor. So cyanide is going to prevent oxygen from actually being able to grab electrons. So why would that kill someone? Well because what will happen is the electrons will start building up because now complex IV can't pass the electrons to oxygen.
So they start building up here. Well, what happens when complex four becomes overrun with electrons? Well, guess what? They'll start building up at complex three. So you start creating this backup of electrons all the way back over here to complex one.
And so you create this backup of electrons never being able to be accepted to oxygen. And when that happens, you can't actually harvest the energy. So what you're unable to do is... basically breathe. And so someone who consumes cyanide cannot breathe because you're not able to utilize the oxygen that you're taking in.
Because in order to utilize that oxygen, you have to have it be able to combine with this and it creates this sensation of suffocation. And so cyanide will block this and then it effectively shuts down the entire ETC, thereby preventing cellular respiration from occurring, which is why this oxygen is so important. And that's also why, like I said, the ATP exam, did I just say the ATP exam? Oh my goodness. ATP is clearly on my mind talking about the ETC.
That's why the AP exam focuses so much on oxygen because of this vital role that it plays here in the ETC. All right. So for the electron transport chain, one major function is to create the proton gradient across the membrane.
So as proteins shuttle electrons along the ETC, just like we saw before in photosynthesis, that's going to help power the pumping of hydrogen ions into the intermembrane space. So again, that fall of the electron from each protein embedded in the membrane to the next through those redox reactions allows the cell to harness energy to pump hydrogen ions, in this case, into the intermembrane space. to create that hydrogen ion gradient. So this will use the exergonic flow of electrons from NADH and FADH2. Again, those are our energy storing molecules.
All right, next, this gradient will then power chemiosmosis. And remember, chemiosmosis is simply that gradient creating or the cell using that gradient of protons to produce ATP. So those protons we know will flow through ATP synthase, and that's what's going to generate ATP. Now this will use the hydrogen ions, like I said, to power cellular work.
That's simply the definition of chemiosmosis. So the definition of this is just using hydrogen ions to power cellular work. All right, so let's go ahead and look at that here. As our complexes, as you can see, are pumping hydrogen ions out.
So as our electron falls from complex to complex through those redox reactions, we'll see the pumping of hydrogen ions into the intermembrane space. And then we can see their downhill flow. Oops, sorry, I always lose my cursor because I can't see it on mine.
And there it is. We'll see that downhill flow of hydrogen ions through ATP synthase. All right, so here we go, kineosmosis.
Here is where it occurs at the ATP synthase. So again, this is the enzyme that makes ATP from ADP plus our inorganic phosphate, and it's using energy from the hydrogen ion gradient across the membrane. And so we can see those hydrogen ions are flowing down their concentration gradient through ATP synthase, and that's powering this conversion of ADP to ATP.
Now in terms of chemiosmosis, like I said, those hydrogen ions flow down their constant filtration gradient through ATP synthase. And ATP synthase actually acts like a rotor. So when hydrogen ions bind, the rotor can spin. And that's what's powering that conversion of ADP to ATP. So this activates catalytic sites, like I said, to turn ADP plus our inorganic phosphate into our energy source ATP.
Okay, so just like what we saw before, though, so nothing here has changed between photosynthesis and between the ATP synthase and photosynthesis and this ATP synthase, nothing has changed. It's just the location. So now we're powering cellular work in the mitochondria.
Now this process is the major ATP producer of the cell. So and in cellular respiration. So this will produce about 26 to 28 ATP per glucose, which is a massive amount of ATP.
So most of a cell's energy is going to be produced here. All right, so let's do a quick check. Number one, how is a proton gradient formed across the inner mitochondrial membrane?
All right, well, the exergonic flow of electrons from NADH and FADH2 will power the complexes in the ETC to pump those hydrogen ions into the intermembrane space. So NADH and FADH2, remember, those are storing energy, and they're going to help power the complexes or those proteins in the electron transport chain to pump H plus into the intermembrane space. All right, problem number two, what is the final electron acceptor in the ETC? It's oxygen, and that's why oxygen is so important, because if we didn't have it, the ETC would shut down.
And number three, how does ATP synthase obtain energy to convert ADP plus P to ATP? It uses the proton gradient. So the hydrogen ion gradient, as it flows down its concentration, is powering ATP synthase. Okay, go ahead and fill out the chart on your next page and then we'll review it. Okay, so here's the summary chart.
So we have glycolysis, pyruvate oxidation, citric acid cycle, and oxidative phosphorylation. Here's our inputs and our outputs, and that gives us a total, a whopping total of 30 to 32 ATP produced throughout cellular respiration.