Overview of Cellular Respiration Process

Hi, it's Kim, and today I am talking to you about cell respiration, also called cellular respiration. I am going to write cellular respiration once, and after that I am going to only write and say cell respiration because it's easier. Okay, cellular respiration is one of the two major energy processes that we are talking about. The other one is photosynthesis. I want to start by making it really clear that it's not an either or thing. A lot of students get confused and think that living organisms either carry out photosynthesis or cellular respiration, but cellular respiration is carried out by all living organisms. And what do I mean by that? I mean, all living organisms. So that includes bacteria. and archaea, which of course are the prokaryotes. And then it includes all the eukaryotes, so protists, fungi, plants, and animals. This is how living organisms take the energy from their food and convert it to the form that cells need to carry out. chemical reactions, and that is ATP. So in the shortest possible version of answering the question, what is cellular respiration? It is the process used by all living organisms. to make ATP from the energy in food molecules, with glucose being the preferred food molecule for that. All living organisms must do this. Chemical reactions in living cells cannot directly use the energy available in food molecules. It has to get converted to another form. So it'd be just as if you visited a country that didn't accept U.S. currency and you had to exchange that money for a different form of money. It's the exact same process in a way because you're just taking one form of energy and you're exchanging it for another form of energy. Energy is lost in the process. It's not 100% transfer. So just like you pay an exchange fee sometimes to exchange that money, we're going to pay an exchange fee to make that ATP. Also important to realize what it means when we say make ATP. And we talked about that in the energy lecture, but I'm going to remind you of that again in a minute. Who on this list carries out photosynthesis? Not all living organisms, right? So photosynthesis. Obviously, plants carry out photosynthesis. Some protists carry out photosynthesis. In fact, when we talk about photosynthesis in detail in a separate lecture, you're going to see that photosynthetic protists are the base of the food chain in aquatic systems. Incredibly important. There are not multicellular plants in the ocean. And then some bacteria can carry out photosynthesis. So not all organisms carry out photosynthesis, but all living organisms carry out cell respiration. Let's look at the connection between those chemical processes. So the incoming ingredients for photosynthesis are water and carbon dioxide. And then the other important ingredient is light energy from the sun. And through the most important chemical reaction on Earth, all life on Earth depends on this chemical reaction called photosynthesis. These organisms are able to take light energy from the sun and convert it to chemical energy. that the entire food chain can use, including themselves. We typically use glucose as the carbohydrate that is produced when we talk about this, but plants and protists and bacteria can produce other sugars through photosynthesis as well. And you'll see that when we talk about it in detail. And also oxygen is produced during photosynthesis. These are then the ingredients that are needed for cellular respiration. In cell respiration, living organisms take the energy in that food and convert it to ATP and in the process produce water and carbon dioxide. If you recall the general equation for cell respiration and the general equation for photosynthesis that we've already talked about several times, those are the reverse of each other. So remember that general equation for cellular respiration, glucose and oxygen becoming CO2 and water. The opposite of that was photosynthesis. So remember, photosynthesis was carbon dioxide and water becoming glucose and oxygen. So that's the connection between those two processes. Again, not all organisms carry photosynthesis, but all living organisms carry out cellular respiration. Why do these photosynthetic organisms do this? They're not just being nice. They're not being charitable and doing this for the rest of the food chain. They're doing this because they don't eat. They can't eat. So they have to produce their own energy. They then provide the energy for the rest of the food chain because we aren't able to take light energy from the sun and convert it to food. We either have to eat a photosynthetic organism or eat somebody who ate a photosynthetic organism. So this is a very, very important connection to realize. Okay, I also want to remind you what it means when we say make ATP during cellular respiration. Making ATP in cellular respiration means... phosphorylating ADP to ATP. What do we mean by that? Remember phosphorylation means transfer of a phosphate group from one molecule to another. In this case, that phosphate group is getting added to ADP to make ATP. I'm going to show you that in just a little bit more detail. So just a reminder of the structure. Remember ADP and ATP are both nucleic acids. So the basic structure, it starts off looking a lot like an RNA nucleotide. It's the ribosugar. The base is adenine. And I'm just going to draw a very simplified version with an A with a circle around it. And then... If this was an RNA nucleotide, it would just have one phosphate group. But I'm going to draw ATP first, adenosine triphosphate. So ATP means adenosine triphosphate, three phosphate groups. So one's already drawn. There's number two. And then number three, we draw with a squiggly line, which... indicates that that is a high energy bond. And when it's broken, a lot of energy is released. I'm not going to go into the reasons for that being a high energy bond. If you take a higher level biology class, you might go into the reasons for that. But it's important to realize that breaking that bond and transferring that phosphate group, that equals energy. OK, because it's exergonic. Remember, exergonic reactions release energy. And now that phosphate group is going to go to another molecule and give that. molecule energy to go do what it needs to do. So either combine with something else or break apart whatever is needed that transfer that phosphate group breaking that high energy bond and releasing that energy is going to provide the energy to carry out another reaction. But what we're left with as a result is a molecule that now just has two phosphate groups. Because that third one was transferred. So we now just have adenosine diphosphate, ADP. So again, transfer of that phosphate group, breaking that bond. And transferring that phosphate group to another molecule, energy was released when that bond was broken. And that energy that was released is now being transferred in the form of that phosphate group. So when that phosphate group gets transferred, that provides energy to something else to carry out a chemical reaction. That is an energy transfer. Remember that exergonic reactions are coupled with... endergonic reactions. Endergonic reactions require energy input. Another important endergonic reaction is adding that phosphate group back onto ADP to regenerate ATP. That is going to be endergonic. So ADP becoming ATP again is going to require a phosphate group to get added back on. And that is endergonic. Okay. Which means energy is required and that's, what's going to happen during cellular respiration. So again, in cell respiration, when we say we're making ATP, we're not making ATP from scratch. We're re-phosphorylating ADP to make ATP. Where does that energy come from during cell respiration? It's going to come from two potential energy sources. So energy for phosphorylating ADP during, and I'm going to now start calling it cell respiration. It's simpler for all of us. It's going to come from two sources. One is going to be the potential energy that's stored in the covalent bonds of our food molecules, in particular glucose. That's going to be one important source of energy that is going to be used to phosphorylate ADP back into ATP. And the second is going to be the potential energy in a very important concentration gradient that is going to be established during cellular respiration. Remember that concentration gradients and covalent bonds are both excellent sources of potential energy in the cell. And both of those are going to be sources of energy for adding that phosphate group onto ADP to produce ATP. There are going to be two methods. or phosphorylating ADP to form ATP. And it's important to know these two terms. One is called substrate level phosphorylation. And the other is called oxidative phosphorylation. When I summarize the four major steps of cell respiration, I am going to point out which method of producing ATP is being used during that stage that's producing ATP. So I'll be using these terms again. I'm not going to explain them further at this point, but I will when we get to those stages where those two methods are being used. So just for now, realize two energy sources for phosphorylation and then two methods of carrying out phosphorylation. So that's the difference between those two pieces of information. So the energy for carrying it out is going to come from covalent bonds and... a concentration gradient. The methods are going to be either substrate level phosphorylation or oxidative phosphorylation. I know those sound like big terms, but when we break them down, they're not going to seem as complex. Okay. Also involved in this story are some really important electron carriers, and I will be talking about them as we go along as well. So those are going to be some key players in the story. Now for the quick overview of cellular respiration, I'm going to tell you the four major stages. I also want you to realize that I am giving you a very simplified version. I don't want you to know all the details of each step of each of these four major stages. Some books will tell you there are three stages because they don't count pyruvate oxidation as a stage. I am counting it as a stage, as do many other textbooks. I will also show you some pictures at the end that will summarize all of this a little better than my drawings. But for now, I want you to draw. So I'm going to draw so that you'll draw. Okay, four major stages of cell respiration. Again. Cellular respiration is just too much for us to say every time. For now, I'm just going to list them with no further explanation. Glycolysis, pyruvate oxidation. Citric acid cycle, also called the Krebs cycle. And finally, oxidative phosphorylation. Oxidative phosphorylation is going to have two major parts. One is the electron transport chain. And then the other is chemiosmosis. This is a very complex metabolic pathway. Remember during the energy lecture, I talked about metabolic pathways and the fact that they are multi-step. The product of one stage becomes the reactant of the next stage. And we finally will end up with an end product. There are also enzymes involved at each stage. I'm not going to ask you to know the intermediates. I'm also not going to ask you to know the enzymes, but I just want you to realize this is a very complex process and I am just giving you the very basic version. You don't, for this 100 level class, need to know more than this. You can always plug details in later. So if you go on to take a higher level bio class, whether it be microbiology, Physiology, Bio 200 for Biomajors. You will hit cell respiration again in more detail. I believe if you can understand the basic version, you can plug details in later. So I know that it's complex. I know that these terms are a little overwhelming. I am going to give you a chart at the end that I think does a really good job of summarizing everything. So if you don't get it the first time around, please just watch this video. a second time, a third time. And again, I don't need you to know all of the details. I need you just to know what I'm telling you. Also important to realize there is a cell respiration worksheet. And if you can answer all the questions on the worksheet, then you'll be able to answer all of the questions on the exam. So that's important to realize too. Okay. Where is this all happening? Okay. This is happening in our cells. So important to realize that I'm going to draw just a giant cell here. I'm going to draw the nucleus pretty small DNA. So remember that for glucose to get into our cells, it requires insulin, but I'm not even going to get into that level of detail. Let's assume that this glucose got into our cells and now here it is in the cytoplasm of the cell. So for the purposes of this lecture, We can really assume that this region between the nuclear envelope and the plasma membrane, this whole region is called the cytoplasm. The liquid portion of that is sometimes called the cytosol. So that would be the liquid portion. So if you read a textbook, I'm pointing this out because if you read a textbook about cell respiration, some textbooks will say that this first stage takes place in the cytoplasm. Some will say cytosol. I just want you to realize those are really saying the same thing. It's in the same region of the cell. So glucose enters the cell and then it's going to immediately go into the first stage of cell respiration, which is called glycolysis. Glycolysis, that means sugar splitting. If there's enough oxygen present, then the breakdown of the products of glycolysis will continue. If not, it's going to go through something called fermentation. And we're going to talk briefly about fermentation also. But First, we're going to talk about what's referred to as aerobic respiration. So aerobic means with oxygen. The other possible type of respiration is called anaerobic respiration. And I'm sure you've heard these terms before related to exercise. This means without enough oxygen. So and means without. We're going to start by talking about aerobic respiration. Then we will talk briefly about anaerobic respiration. The other term for this is fermentation. Fermentation produces some amazing products that we use. And we'll talk about that as well. But for this first round, I'm going to be talking about aerobic respiration, what happens when there's enough oxygen present. But it's important to realize that this first stage, glycolysis can happen with or without oxygen. So glycolysis, the first stage of cellular respiration. So I'm just going to put a number one here to indicate this is the first stage. And it means sugar splitting. So glyco, glycogen, remember, is a chain of glucose. Glyco is a term that just refers to a sugar. To lyse is to break or split. This, you can call this sugar breaking, sugar splitting. And this is happening in the cytoplasm of the cell. when glucose first enters the cell. And that's what we start with in glycolysis. The cell starts with glucose and glycolysis is pretty complex. It's 10 steps. I don't want you to know those 10 steps, but I want you to realize that the product of the first step then becomes the reactant of the second step. And then the product of that step becomes the reactant of the next step. There are enzymes involved at each stage. And throughout those 10 steps, we need to use 2-ATP as an energy source to get things started. So there is an energy investment phase in which 2-ATP are used. But we make 4-ATP throughout glycolysis. And at the end of these 10 steps, We have a product in which we started with a six carbon glucose. And we now after 10 steps have split it into two, three carbon molecules called pyruvate. And those are each three carbon molecules. We also do something really important during glycolysis, and that is that the electron carriers are going to start picking up hydrogens from that original glucose molecule. So just to quickly remind you of the general equation for cellular respiration. 36 ATP, that's a very general number. Okay, some books will say 36 to 38. Realize that this is just on average, but it is the number that I'm going to use today. It's the number that most textbooks use just for accounting purposes. Okay, but realize that's just an average. Every cell does it a little differently. Every person does it a little differently. It might not be the exact same every time, but on average, we make 36 ATP for every one glucose. Important to realize oxygen is required for the aerobic respiration that we're going to be talking about. Carbon dioxide and water are products. We're going to be keeping track of CO2 as we go along. We're also going to be keeping track of what happens to glucose as it's being broken apart. And of particular interest are these 12 hydrogens. Those hydrogens are going to get picked up by electron carriers and eventually stripped away from those electron carriers. to set up the concentration gradient that's going to be used to produce most of the ATP during cell respiration. So it's important to follow those 12 hydrogens throughout the process. In glycolysis, two of those hydrogens are picked up by the electron carrier NAD+, to make two NADH. So during glycolysis, the first two of those hydrogens are picked up and this electron carrier is now going to shuttle those hydrogens and their accompanying electrons to a very important stage at the very end. But again, it's important for us to track those 12 hydrogens because those are going to be a major energy source at the very end when that concentration gradient is set up. So summary of glycolysis. What do we start with? We start with glucose. What do we end with? We end with two pyruvate molecules. How many ATP were made? Four were made, but two were used. So that's a net of two ATP that were generated during glycolysis. Where is this taking place? It's taking place in the cytoplasm of the cell. And this is, by the way, the only stage that can take place with or without oxygen. I know we're just talking about what happens with oxygen right now, but glycolysis can happen with or without oxygen. It's the only stage that can happen without oxygen. All of the other stages are going to require oxygen to take place. Also important to realize we picked up the first two of the 12 hydrogen and made two NADH. NAD plus is an electron carrier. And when it picks up electrons, it becomes NADH. Remember, gain of hydrogen equals gain of electrons. And Leo the lion says ger. So gain of electrons is reduction. So this is reduction. Okay, we would say that NAD plus is reduced. And that reaction is called reduction to become NADH. In a few minutes, when we talk about those hydrogens being stripped away, remember loss of electrons is oxidation. So NADH is going to get oxidized when those electrons and the hydrogens get stripped away. So that's the summary of glycolysis. I'm going to summarize this in a table at the end. Just as in these 10 steps. The product of one stage becomes the reactant of the next stage. That happens here also. So now we ended with these two pyruvate. These two pyruvate are now what we're going to use to start the next stage called pyruvate oxidation. Okay. So second stage of cellular respiration is called pyruvate oxidation. Okay. Start with... two molecules of pyruvate that were the products of glycolysis. These are each three carbon molecules. Three carbon molecules cannot enter citric acid cycle. A carbon needs to get shaved off from each of those. This used to be called the grooming stage. It used to be called the transition stage. It's had a number of different names. It even still has a number of different names. For this class, we're calling it pyruvate oxidation. So we start with two pyruvate. And what's going to happen is for each of those pyruvate molecules, a carbon is going to be lost as CO2. So two CO2 are going to get released, one per pyruvate. Also, two hydrogens are going to get picked up by NAD plus to form 2-NADH. And what we're left with at the end is two molecules of what's called acetyl coenzyme A. It's written co-A for short. Those are two carbon molecules. A coenzyme gets attached in the process too. You don't need to know that level of detail. Two carbon dioxides are released. That is important to know. That's two of our carbons from our C6H12O6. We picked up two more hydrogens. So now we've picked up four total of those 12 hydrogens. Remember C6H12. 06, 12 hydrogens. We picked up two in glycolysis. We've now picked up two more in the transition phase. No ATP is made in pyruvate oxidation. Why is this stage necessary? This stage is necessary because we can't break, we can't complete the breakdown of glucose. without the citric acid cycle. Citric acid cycle requires a two carbon molecule called acetyl coenzyme A. So this transition phase also called pyruvate oxidation is necessary. Okay. Important to realize that even though ATP is not made, it's an important transitional phase. And that's why it used to be called the transition phase. It's a transitional phase between glycolysis and citric acid cycle. So that's why some textbooks don't call it a separate stage. cell respiration. But for this class, we do call it a separate stage. Also important to realize where this is happening. And it only happens if oxygen is present. So pyruvate oxidation requires oxygen. And where is it taking place? It takes place in the matrix of the mitochondria. So I'm going to draw a mitochondrion to remind you of where the matrix is. And the structure of this mitochondrion is going to be really important as we go through these next stages of cellular respiration. So I'm going to go back to the cell for a minute. Here's the cell again, nucleus out here in the cytoplasm. Glucose came into the cell. It went through. glycolysis, glycolysis, sugar splitting, and it produced 2-pyruvate out here in the cytoplasm. Now, if oxygen is present, so I'm just going to say if O2, those 2-pyruvate are going to go into the mitochondrion and complete the breakdown of glucose. Okay. If no O2, then fermentation is going to happen. Anaerobic respiration. But we're going to talk about that separately. Now we're just going to talk about if O2 is present. If O2 is present, then those two pyruvate go into the mitochondrion and that's where pyruvate oxidation, citric acid cycle, and oxidative phosphorylation are all going to take places in the mitochondrion. So looking at that mitochondrion blown up bigger and recalling the structure of this, the inside region here is called the matrix. This is the outer membrane. This is the inner membrane. This space between the two membranes, this space here is called the intermembrane space. It's a space between the two membranes. This is important because different stages of cell respiration are going to take place in different regions of that mitochondrion. Okay, so remember one mitochondrion. That's the single mitochondria is the plural. So we're just talking about one of them right now. Pyruvate oxidation and citric acid cycle are both going to happen in the matrix. Oxidative phosphorylation is going to happen in several different regions. And we'll talk about that. Also important to realize when we say membrane, membrane always means mostly a phospholipid bilayer with some important. proteins embedded. So membrane is a phospholipid bilayer. So if we blew up that outer membrane, if we blew up that inner membrane, you would see mostly phospholipids forming a bilayer like this with those heads pointing outward and the tails pointing inward. And then there are going to be some really important proteins embedded in that membrane as well. and then more phospholipids. That's going to be an important part of the story as well, is just the structure of that membrane. So that's true, the outer membrane and the inner membrane. The inner membrane of the mitochondrion in particular is going to be an important part of this story in helping set up a very important concentration gradient to generate most of our ATP. Okay, so glycolysis happened out in the cytoplasm. to produce those two pyruvate. And then if there's enough oxygen present, those two pyruvate go into the matrix of the mitochondrion. And that is where pyruvate oxidation and citric acid cycle are going to take place is in the matrix of the mitochondrion. So now we've produced two acetyl coenzyme A in the matrix. And now the third stage of cellular respiration is going to happen. And that's called the citric acid cycle. Okay, and in the citric acid cycle, we start with what we ended with last time. So in the previous step, we ended with a two acetyl coenzyme A called acetyl-CoA. And I'm going to go through. multiple steps. You don't even need to know the number. I know I told you 10 on glycolysis. I kind of regret doing that now because I don't want you to fixate on how many steps it is. We're going to go through multiple steps. And during the citric acid cycle, the breakdown of glucose becomes complete as four CO2 are going to get released and eight Hydrogens are going to get picked up with electron carriers, mostly by NAD+, but there's going to be another electron carrier that's used also. Six NADH are going to get produced and two FADH2 are going to get produced. when an electron carrier called FADH picks up two electrons. Remember there are two acetyl-CoA coming through citric acid cycle, so really it's three NADH and one FADH2 for each of those two, so I'm just combining the sum total of what happens in citric acid cycle. Two ATP are going to get produced and as I said a minute ago, four CO2 are released. And at the end of the citric acid cycle, nothing is left of glucose. Just all of the 12 hydrogens being carried by the electron carriers. And just to remind you, we made two NADH in glycolysis, two NADH in pyruvate oxidation, six NADH and two FADH2. And the citric acid cycle, 6, 8, 10, 12, that's 12 hydrogens. Remember C6H12O6. So that's our 12 hydrogens. This carbon and oxygen were released as CO2 along with part of the oxygen. So remember the reactants include not only glucose, but six oxygens. So. Remember the way this works, six O2s, that's 12 oxygens. Okay, that's six oxygens. So that's 18 oxygens total. If we release six CO2. Number two during pyruvate oxidation and four in citric acid cycle. That's the six. That's six carbons and 12 oxygens. So minus 12 oxygens, there's six oxygens left. So at the end of the citric acid cycle, all the hydrogens have been picked up by electron carriers. Carbon and oxygen have been released as CO2. So there's our six carbons. Six carbons released to CO2. 12 of the oxygens have been released to CO2. All the hydrogens are being carried by electron carriers. So there's nothing left of glucose at the end of the citric acid cycle. But we've only made 4 ATP. We need to make 36 total. But glucose is gone. So all of that potential energy in the covalent bonds of glucose, remember that was one of our energy sources. That's all been used up. That only allowed us to make four ATP. So two ATP in glycolysis and two ATP in citric acid cycle. I'm just abbreviating it for now. That means 32 more need to get made, but glucose is gone. Okay, so how were these made? These were made. By a process called substrate level phosphorylation. So all four of these are all made. Okay, so all four were made. Remember, we actually made four in glycolysis, but we used two. So we actually made six total, but we've used two. So all four of those net were made by the process called substrate level phosphorylation. What does that mean? Let's break this down. Substrate level. Think back to enzymes. Remember that an enzyme has a very specific shape, and I'm just going to draw a pretend shape here. Remember that this part where the reactant binds is called the actin. side of the enzyme. And when a reactant binds to an enzyme, it's called the substrate. So the substrate is the reactant in an enzyme catalyzed reaction. And in this case, this substrate has a phosphate group attached to it, and it's going to transfer that phosphate group to ADP. So this is ADP. And this enzyme is going to facilitate transfer of that phosphate group. Remember, transfer of a phosphate group is called phosphorylation. And in this case, transfer of a phosphate group from a molecule to ADP. to make ATP. And that is called substrate level because it's taking that substrate, the reactant and transferring that phosphate group, phosphorylation, transfer the phosphate group to ADP to make ATP. If you really want to look at the steps of glycolysis and the citric acid cycle, you can see which specific enzyme is involved in doing that and which exact reactant or substrate is used to basically donate that phosphate group and transfer it to ADP to make ATP. That's how we made those first four ATP, two in glycolysis and two in citric acid cycle. I want to just quickly draw a chart to summarize everything that's happened so far before we get to oxidative phosphorylation at the end, which is how we're going to make 32 more ATP. But I think that this chart will help really summarize it. I just, I want to make sure I don't leave off anything. So I'm going to try to write small here and I actually want my grid lines. So this is going to be our stage. Start with and with. I'm going to skip the where because it can't really fit on this, but I'm going to mention the where. I just I'm not going to put it on the chart because it doesn't really fit in that place. Method of ATP production, electron carriers. I'm just going to call them E carriers and CO2. Okay, I only have four stages, but I have a feeling I'm going to have to write like below the line. Sorry, I know this is really messy, but I promise this will help. It will help summarize everything. Okay, first stage, glycolysis. We start with glucose. Glucose enters the cytoplasm of the cell. So I'm going to say glycolysis. In the cytoplasm. Again, we could say cytosol. Go through a lot of steps. Don't need to know the numbers. Just forget that I ever even told you that it was 10. Okay. And with two molecules of pyruvate. Number of ATP produced, two net. Remember we used two and made four, but it's two net made by substrate level phosphorylation. which I'm just going to abbreviate SLP, electron carriers, 2 NADH were made. The first two of those 12 hydrogens were picked up. I'm going to write that a little neater. 2 NADH and no CO2. were released in glycolysis. And remember, this is the only stage that can happen with or without oxygen. If enough oxygen is present, then we go into the second stage, which is called pyruvate oxidation. And that happens in the mito matrix. which is of course mitochondria. And I don't know how that just happened. Yeah. My hand, when it touches the screen, does all kinds of crazy stuff. Okay. Again, we start with what we ended with in the last stage. So we ended with two pyruvate. That means here we start with two pyruvate. Sorry. It's so small there. And that's a two. End with two. Acetyl Coenzyme A. I'm just going to make that two a little better there. Number of ATP made, zero. So this is not applicable. Number of electron carriers, two NADH and two CO2 were released. That's how we made those two acetyl-CoA, by shaving off carbon from each of those two pyruvates. Remember, the pyruvates were three carbon molecules. The acetyl-CoA are two carbon molecules. And now we go into the citric acid cycle, which also happens in the mitochondrial matrix. So oxygen is required. So citric acid cycle. In the mito matrix. Start with two acetyl-CoA. End with nada. Okay, we completed the breakdown of glucose. So there's nothing left. of glucose. Okay. Just those electron carriers, just the 12 hydrogens. That's all that's left. So that's where all the potential energy now is. We've only made four ATP because remember, we make two more ATP by substrate level phosphorylation, six NADH. and two FADH2s and four CO2 are released. So there's all six of our CO2. Here's our 12 electron carriers, six, eight, 10, 12. So now all of the potential energy is in those electron carriers because glucose has broken down. It's been released as CO2. The hydrogens are being carried by the electron carriers at the end of the citric acid cycle. That's where all the potential energy is now is in those electron carriers. That's a really important point. And there is a question on the worksheet about that to point out how important that is. Okay, so at the end of the citric acid cycle, all the potential energy is now in those 12 electron carriers. Again, I apologize for how messy this chart is, but I do think it's really important. important to kind of summarize everything in your brain. And this is a good way to really summarize it. Now we need to make 32 more ATP, and that's going to happen in the last stage called oxidative phosphorylation. And oxidative phosphorylation doesn't really fit into this chart. Okay, this is just going to be a stage in which a lot of ATP are generated because of this concentration gradient that's going to get set up. So oxidative. phosphorylation. If we had to fit it in the chart, we would say we start with the 12 electron carriers. Where is this happening? I'm going to say the entire mitochondrion is really being used, everything except the outer membrane. is being used. Number of ATP made is going to be on average 32 ATP. And they're made by a very important enzyme that is embedded in the inner membrane of the mitochondrion. So let's look at the structure of that mitochondrion again. Oops, sorry. In living systems, whenever something is folded, it increases the surface area. Imagine that you cut this outer membrane and you took this as a, just imagine it being a string. Okay. We know it's phospholipids with some proteins embedded in it, but imagine you stretch it out. That's going to be a lot shorter in length than this. If we did the same here, this is a lot longer. It's folded, right? Folds, increased surface area. So anything that's happening, you've got to know there's something really important happening in that membrane. Embedded in this membrane are some really important protein complexes. that make up something called the electron transport chain. Okay, so these are proteins that are embedded in that inner membrane. So remember this is the matrix, this is the inner membrane, this is the outer membrane, and this is the intermembrane space in between here. So we have all 12 of those electron carriers here. We have the 10 NADH, And the two FADH2s that were generated in those first three stages, when those electron carriers were reduced, they were reduced when they picked up the hydrogens, gain of electrons is reduction, GRR. They're now going to lose those electrons. They're going to become oxidized. That's why this is called oxidative phosphorylation. Those 12 electron carriers are going to be oxidized because what happens is when they come in contact with these proteins in the inner membrane of the mitochondrion, those hydrogens are going to get stripped away and pumped out into this space, this intermembrane space. They are charged. This is a really important thing to realize. The electrons... are being stripped away and they're getting bounced through these proteins in something called the electron transport chain. And those electrons are generating energy as they fall down this energy ladder. They're generating energy to pump those hydrogens against a concentration gradient out into this space. So there are a lot of important concepts involved here. One is, you know, that the energy generated by those electrons falling down an energy ladder is giving energy to pump. pump those hydrogens against a concentration gradient, and they're building up out here. They can't just come across the phospholipid bilayer because remember that charged ions cannot move across those nonpolar tails. Remember, charged ions or molecules cannot simply diffuse by simple diffusion. across phospholipids. So what happens is those 12 hydrogens are going to build up in this intermembrane space and that now represents a concentration gradient. Hydrogens are stripped from the electron carriers by proteins in the inner membrane of the mitochondrion. and they are pumped into the inter membrane space where they build up and they create a concentration gradient. So a concentration gradient is established. All of those hydrogens are now representing a ton of potential energy. When they come back across the membrane, they're not going to come across the phospholipids. They can only come across one way. They can only come back across the membrane. Remember that to reach equilibrium, they need to come back. So they're high out here and they're low over here, but they can't just cross that phospholipid bilayer. So now through facilitated diffusion, they're going to come across a very important protein. So they can only come back across the membrane by what's called facilitated diffusion through. a very important protein, one of the most important proteins in your body, and it's called ATP synthase. Remember enzymes are cool because the name tells you what they do and they end in ASE. So this ASE tells us that it's an enzyme. It's going to synthesize ATP. When those hydrogens come back across through that enzyme, it's going to phosphorylate ATP to form ATP. And I'm going to show you a picture of that happening. But first I want to go back to my picture here. Here's ATP synthase. Here's ATP synthase. They're going to be scattered throughout this membrane. And that's the only way that hydrogens can come back across. Okay, so here's the ATP synthase. And the hydrogens can only come back across through that enzyme. They can't come across that phospholipid bilayer because they are charged. And when they come back across, it's going to phosphorylate ADP to form ATP. So if this is ADP and it's just sitting there waiting, as those hydrogens come across, it generates... energy to phosphorylate, to stick phosphates back on that ADP to form ATP. And I'm going to show you a picture of that happening in a minute. But for now, I'm going to blow up that membrane. I'm going to draw a blow up of that inner membrane. So if we look at the mitochondrion again, sloppy version, I'm going to just take a piece of that and blow it up. So I'm blowing up that inner membrane and it's phospholipids, which hydrogens cannot come across. It's some important protein complexes. And you don't need to know about these in detail. Here's another one. And what happens is when those electron carriers come in contact with those protein complexes, those protein complexes are going to strip the hydrogens away and pump them out into the space. Oops, sorry, I didn't mean to do that. And then this is going to be our ATP synthase. And it's kind of like a rotor. More phospholipids. Okay, and on this side, we have a bunch of ADP, and we have a bunch of phosphate groups. Okay, NADH comes in contact with this protein. The hydrogen is going to get stripped away and pumped out into this space. And what we're left with is NAD+. Loss of electrons is oxidation. So that NADH became oxidized to form NAD+. And that hydrogen gets pumped out into this space. Okay, that's going to keep happening. And these hydrogens build up out here. They can't just come across that phospholipid bilayer because they're charged, but they can come across through the ATP synthase. And when they do, this rotor spins and it sticks phosphate groups onto ADP to form ATP. And 32 ATP on average are going to get generated through this process. Important terms here. The protein complex is stripping away those hydrogens and pumping them out into that space is called the electron transport chain. And when the hydrogens come back across and generate the ATP by phosphorylating ADP with the energy of them coming back across, it's like water behind a dam coming through a hydroelectric plant and generating electricity. That potential energy is coming from that concentration gradient. That part is called chemiosmosis. Those hydrogens coming back across. Those two together make up what's called oxidative phosphorylation. Sorry, it wouldn't all fit on that one line. Oxidative. phosphorylation. I'm sorry, there's some really loud construction noise going on outside of my neighbor's house right now. Those are the two stages of oxidative phosphorylation. Electron transport chain, the hydrogens are stripped away. Those electron carriers become oxidized. The hydrogen is pumped out into the space. Chemiosmosis is when those hydrogens come back across and phosphorylate ADP to form ATP. I'm going to show you a better picture of that in a minute. That's how 32 ATP are generated at the end. OK, so if we tried to fit that into the chart up above, here's our chart. Again, we just start with the 12 electron carriers and we make 32 ATP really by chemiosmosis. I mean, the chemiosmosis part is where they get made. I mean. They say that they're made by oxidative phosphorylation, but they're made during the chemiosmosis part of that. I would never ask you a question to make that distinction. I would just ask you how many ATP are generated during oxidative phosphorylation. Realize that it's all because of that magical enzyme called ATP synthase, which I'm also going to show you a picture of. So I'm going to show you a better picture of the electron transport chain, a better picture of ATP synthase. Just want to double check that there wasn't some other picture I wanted to draw for you. Okay. We also need to talk about fermentation and I'm going to do that on the diagrams too. Okay. I would love to ask you right now, if you have any questions, but we are not live, so I can't do that, but I know this is a lot. Okay. It's a lot on the surface. It seems really, really boring, but just realize this is an amazing process. Like how cool is this, that we can take energy from our food and we can package it as ATP and we can use it. anytime, anyplace in the cell. We don't have to have a gas tank that's full. We don't have to be on a glucose drip all day long. We can take that energy from our food and we can convert it to an energy currency that can be used anytime, anyplace in the cell. And remember I've told you before, you make and use your body weight in ATP every day. That's pretty amazing too. If you stop making ATP, you die. rat poison called cyanide is blocking a stage of cell respiration. There are a lot of poisons that block key stages of cell respiration and cause death of that organism, whether it be a plant, an insect, um, different pesticides are used to do that. So, and there are different poisons that are used to do that too. You must make ATP all day, every day. Otherwise, the chemistry of your cells shuts down because remember you can't directly use energy from your food. You have to convert it to ATP and that ATP is then used to drive chemical reactions that require energy in the cell. Okay. I'm going to pull up some pictures. So please just stick with me for a second here while I pull up these images. Okay, these are the photos I want to show you of cellular respiration. These are some better images than what we drew together in the notes. So this is NAD+. It's one of the two electron carriers. Remember, the other one is FADH. That becomes FADH2. And you can see that it is a nucleotide. And when it picks up hydrogens, it's becoming reduced. When it drops off the hydrogen, it's becoming oxidized. So I just wanted to show you that better picture. This is just an overview of cell respiration. It's showing that glycolysis takes place out in the cytosol. Again, this term cytosol and cytoplasm can be used interchangeably. But during this process, we make two ATP net by substrate level phosphorylation. It doesn't show pyruvate oxidation happening, but pyruvate oxidation is going to happen here in the matrix of the mitochondrion. And again, this is only if oxygen is present, that those two pyruvate go into the mitochondrion. Pyruvate oxidation produces the acetyl-CoA that then go through citric acid cycle. And remember at that point, we've completely broken down glucose. All the energy is now in those 12 electron carriers, and we make two more ATP net by substrate level phosphorylation. And then finally, at the end, during oxidative phosphorylation, which includes the electron transport chain and chemiosmosis, on average, 32 ATP are made by oxidative phosphorylation. And remember, it's specifically during the chemiosmosis when those hydrogens come back across that those 12, I'm sorry, 32 ATP are being made. This shows you a picture of substrate level phosphorylation. And I already drew this picture for you, but it shows that substrate. is the reactant that's going to transfer a phosphate group to ADP to make ATP. And remember that we make two ATP in glycolysis by substrate level phosphorylation, and we make two in citric acid cycle by substrate level phosphorylation. This slide got a little wonky, but... This is the first five stages of glycolysis. Remember, it's 10 stages long, but you don't need to know that. You start with glucose. We're going to use some ATP here. We're going to use some ATP here to get things started. And then at the end of the 10, we've made four. So remember, we used to make four. So that's two net ATP. You can see there is an enzyme involved at each stage. So anything that ends in ASE is an enzyme. And you can see that the product in one stage becomes the reactant of the next stage, just like in any other metabolic pathway. So this 3-phosphoglycerate is a product of the prior stage and then becomes the reactant of the next stage. And at the end, we end up with two molecules of pyruvate that are three carbon molecules, one, two, three, and we end up with two of those. Those two then go through pyruvate oxidation. So let me back down here. So if oxygen is present, the two pyruvate go into the mitochondrion and go through pyruvate oxidation where those two acetyl-CoA are produced that then goes through citric acid cycle. If there's not enough oxygen present, we go through fermentation. This is pyruvate oxidation. So for each pyruvate, one carbon dioxide is released. And since we have two pyruvate, sorry, this is really writing fat right now. Two pyruvate are going to make two carbon dioxide, two NADH, and we end up with two acetyl-CoA. That E should not be on the end. Those two acetyl-CoA then go through citric acid cycle. You can see those steps of citric acid cycle here. Again, you don't need to know these eight steps, but you can see we start with the acetyl-CoA and you can see where we pick up the hydrogens with the electron carrier. So remember we have two of these, so everything gets doubled. So if you count all the NADHs, one, two, three, but that gets doubled. So that's six NADH. And then this gets doubled. So two FADH2s and this gets doubled. So it's two ATP. These are the protein complexes that are embedded in the inner membrane of the mitochondrion. And this is ATP synthase. I'm going to come back to that picture in a minute because I want to show you this first. So this shows those protein complexes. stripping away those hydrogens so nadh is becoming oxidized loss of electrons is oxidation the hydrogens get pumped out into the space using the energy generated when those electrons fall down this energy staircase and all those hydrogens build up out there they can't come across these phospholipids because remember they can't cross those nonpolar tails so they're not allowed across there The only way they can come across is through ATP synthase. And when that happens, ADP is phosphorylated to form ATP. And that part is called the chemiosmosis. So I really like this explanation. It says electron transport chain, electron transport and pumping of protons, which are the H plus, which creates an H plus gradient. This is a concentration gradient across the membrane. And then chemiosmosis is ATP synthesis powered by the flow of the H plus back across the membrane. When those come through, that produces enough energy to add that phosphate group onto ADP to make ATP. And on average, we make 32 that way. Oh boy. Sorry. When it gets towards the edge, it just really gets wonky over there. Sorry. So 32 on average ATP get made that way. Also, one thing we haven't talked about yet, the final electron acceptor oxygen. When those hydrogens come back across, they're going to finally join up with oxygen and produce water. So remember that general equation. Sorry, let me write it up here. C6H12O6. plus 6-O-2, 6-C-O-2. Remember two were released in pyruvate oxidation and four were released in the citric acid cycle. Those oxygen now are going to combine with those hydrogens to form the six waters. Okay. This is a good summary slide. I like the summary slide. The only thing it doesn't show you is it doesn't show you pyruvate oxidation in detail, but it shows you that glycolysis takes place out in the cytoplasm. You start with glucose, you end with 2-pyruvate and produce 2-ATP by substrate level phosphorylation. If there's enough oxygen present, you go into the mitochondrial matrix and make 2-acetyl-CoA through pyruvate oxidation, which then go through the citric acid cycle and we make 2 more ATP by substrate level phosphorylation. And then all of those electron carriers go into oxidative phosphorylation because when they hit that inner membrane in the mitochondria, the protein complex is embedded in the inner membrane, strip away those hydrogens, they get pumped into the intermembrane space. They can only come back across through ATP synthase. And here's that amazing, amazing enzyme that is going to phosphorylate ADP to form ATP when those hydrogens come back across. the most amazing membrane, the most amazing enzyme. So this is the number one enzyme in my book. This is an incredible enzyme. Can you even imagine how tiny, like think about how tiny your cells are. And then in the inner membrane of the mitochondrion is this little enzyme. And there are, you know, millions of them in each cell. Okay, what is fermentation? Fermentation happens when there's not enough oxygen present. And there are several different products that can occur, but in us, in animals, it's lactic acid, also called lactate. So you can see that if there aren't enough oxygen present, those two pyruvate, oops, sorry, those two pyruvate, rather than going into the mitochondria and producing more ATP, instead what happens is that NAD plus is going to get regenerated and lactic acid or ethanol are going to form. So certain organisms are going to make alcohol as a product of fermentation. Certain others are going to make um, lactic acid. And this is what we make. We make lactate or lactic acid. Okay. So this is what, when you start doing anaerobic exercise, so you exercise to the point where your muscles are not getting enough oxygen anymore. Lactic acid is what causes your muscles to burn. It's also, it causes the soreness the next day after a really hard workout, best way to move that out of your muscles is to exercise again and move that back into your bloodstream. But so lactate also called lactic acid. That's the product of fermentation. That is anaerobic respiration, respiration without enough oxygen present. So that means if there's not enough oxygen present, how many ATP can you make for every glucose? Only two. So when you're doing anaerobic respiration, you are burning glucose at an accelerated rate. You're exercising, your muscles need ATP. They need that energy. So you start burning glucose at a higher rate. In other words, you're burning calories at a higher rate because you're only producing two ATP for every glucose instead of 36 on average for every glucose. So the most you can produce in fermentation is two ATP for every glucose. We have a lot of products that are made by fermentation. Many of them, you know, so obviously beer and wine. And other alcohols, really, you know, all alcohol we drink is made by alcohol fermentation where ethanol is produced. Even rubbing alcohol, acetone, vinegar. So anything that's made with vinegar, including pickles, soy sauce, kimchi, kombucha, all those fermented products are, you know, fermentation means anaerobic respiration. And that alcohol is getting produced or lactic acid. And there are some other chemicals that can get produced depending on the type of bacteria that are carrying it out. So certain bacteria and certain yeasts can give us different types of fermentation. So yeast produced alcohol fermentation. So that's how we get beer and wine and other forms of alcohol that we drink is from yeast fermentation. So they would be producing ethanol. as a byproduct of that fermentation. Also important to note that you can use other organic molecules to carry out cell respiration. It's just not as efficient. The cells prefer carbohydrates. Those enter glycolysis. Fats and proteins enter cell respiration at a later stage, and there is a cost associated with that. So it's not the healthiest way to carry out cell respiration. The healthiest way is from carbohydrates. but just wanted you to realize you can use fats and proteins, but they come at a cost to the cell. So carbohydrates are the preferred fuel for the body to produce ATP. Okay. That is cell respiration. Please make sure you can answer all of the questions on the study guide or the separate worksheet. So depending on when you're watching this. video, you might have a separate worksheet or you might have those questions just as part of your study guide. If you're not sure which one, be sure to ask.

The other one is photosynthesis. I want to start by making it really clear that it's not an either or thing. A lot of students get confused and think that living organisms either carry out photosynthesis or cellular respiration, but cellular respiration is carried out by all living organisms.

And what do I mean by that? I mean, all living organisms. So that includes bacteria.

and archaea, which of course are the prokaryotes. And then it includes all the eukaryotes, so protists, fungi, plants, and animals. This is how living organisms take the energy from their food and convert it to the form that cells need to carry out. chemical reactions, and that is ATP.

So in the shortest possible version of answering the question, what is cellular respiration? It is the process used by all living organisms. to make ATP from the energy in food molecules, with glucose being the preferred food molecule for that.

All living organisms must do this. Chemical reactions in living cells cannot directly use the energy available in food molecules. It has to get converted to another form.

So it'd be just as if you visited a country that didn't accept U.S. currency and you had to exchange that money for a different form of money. It's the exact same process in a way because you're just taking one form of energy and you're exchanging it for another form of energy. Energy is lost in the process.

It's not 100% transfer. So just like you pay an exchange fee sometimes to exchange that money, we're going to pay an exchange fee to make that ATP. Also important to realize what it means when we say make ATP.

And we talked about that in the energy lecture, but I'm going to remind you of that again in a minute. Who on this list carries out photosynthesis? Not all living organisms, right?

So photosynthesis. Obviously, plants carry out photosynthesis. Some protists carry out photosynthesis. In fact, when we talk about photosynthesis in detail in a separate lecture, you're going to see that photosynthetic protists are the base of the food chain in aquatic systems.

Incredibly important. There are not multicellular plants in the ocean. And then some bacteria can carry out photosynthesis.

So not all organisms carry out photosynthesis, but all living organisms carry out cell respiration. Let's look at the connection between those chemical processes. So the incoming ingredients for photosynthesis are water and carbon dioxide.

And then the other important ingredient is light energy from the sun. And through the most important chemical reaction on Earth, all life on Earth depends on this chemical reaction called photosynthesis. These organisms are able to take light energy from the sun and convert it to chemical energy.

that the entire food chain can use, including themselves. We typically use glucose as the carbohydrate that is produced when we talk about this, but plants and protists and bacteria can produce other sugars through photosynthesis as well. And you'll see that when we talk about it in detail.

And also oxygen is produced during photosynthesis. These are then the ingredients that are needed for cellular respiration. In cell respiration, living organisms take the energy in that food and convert it to ATP and in the process produce water and carbon dioxide. If you recall the general equation for cell respiration and the general equation for photosynthesis that we've already talked about several times, those are the reverse of each other. So remember that general equation for cellular respiration, glucose and oxygen becoming CO2 and water.

The opposite of that was photosynthesis. So remember, photosynthesis was carbon dioxide and water becoming glucose and oxygen. So that's the connection between those two processes. Again, not all organisms carry photosynthesis, but all living organisms carry out cellular respiration.

Why do these photosynthetic organisms do this? They're not just being nice. They're not being charitable and doing this for the rest of the food chain. They're doing this because they don't eat. They can't eat.

So they have to produce their own energy. They then provide the energy for the rest of the food chain because we aren't able to take light energy from the sun and convert it to food. We either have to eat a photosynthetic organism or eat somebody who ate a photosynthetic organism. So this is a very, very important connection to realize.

Okay, I also want to remind you what it means when we say make ATP during cellular respiration. Making ATP in cellular respiration means... phosphorylating ADP to ATP. What do we mean by that? Remember phosphorylation means transfer of a phosphate group from one molecule to another.

In this case, that phosphate group is getting added to ADP to make ATP. I'm going to show you that in just a little bit more detail. So just a reminder of the structure.

Remember ADP and ATP are both nucleic acids. So the basic structure, it starts off looking a lot like an RNA nucleotide. It's the ribosugar.

The base is adenine. And I'm just going to draw a very simplified version with an A with a circle around it. And then... If this was an RNA nucleotide, it would just have one phosphate group. But I'm going to draw ATP first, adenosine triphosphate.

So ATP means adenosine triphosphate, three phosphate groups. So one's already drawn. There's number two.

And then number three, we draw with a squiggly line, which... indicates that that is a high energy bond. And when it's broken, a lot of energy is released. I'm not going to go into the reasons for that being a high energy bond.

If you take a higher level biology class, you might go into the reasons for that. But it's important to realize that breaking that bond and transferring that phosphate group, that equals energy. OK, because it's exergonic. Remember, exergonic reactions release energy. And now that phosphate group is going to go to another molecule and give that.

molecule energy to go do what it needs to do. So either combine with something else or break apart whatever is needed that transfer that phosphate group breaking that high energy bond and releasing that energy is going to provide the energy to carry out another reaction. But what we're left with as a result is a molecule that now just has two phosphate groups. Because that third one was transferred.

So we now just have adenosine diphosphate, ADP. So again, transfer of that phosphate group, breaking that bond. And transferring that phosphate group to another molecule, energy was released when that bond was broken. And that energy that was released is now being transferred in the form of that phosphate group. So when that phosphate group gets transferred, that provides energy to something else to carry out a chemical reaction.

That is an energy transfer. Remember that exergonic reactions are coupled with... endergonic reactions. Endergonic reactions require energy input.

Another important endergonic reaction is adding that phosphate group back onto ADP to regenerate ATP. That is going to be endergonic. So ADP becoming ATP again is going to require a phosphate group to get added back on. And that is endergonic.

Okay. Which means energy is required and that's, what's going to happen during cellular respiration. So again, in cell respiration, when we say we're making ATP, we're not making ATP from scratch. We're re-phosphorylating ADP to make ATP. Where does that energy come from during cell respiration?

It's going to come from two potential energy sources. So energy for phosphorylating ADP during, and I'm going to now start calling it cell respiration. It's simpler for all of us.

It's going to come from two sources. One is going to be the potential energy that's stored in the covalent bonds of our food molecules, in particular glucose. That's going to be one important source of energy that is going to be used to phosphorylate ADP back into ATP. And the second is going to be the potential energy in a very important concentration gradient that is going to be established during cellular respiration. Remember that concentration gradients and covalent bonds are both excellent sources of potential energy in the cell.

And both of those are going to be sources of energy for adding that phosphate group onto ADP to produce ATP. There are going to be two methods. or phosphorylating ADP to form ATP.

And it's important to know these two terms. One is called substrate level phosphorylation. And the other is called oxidative phosphorylation.

When I summarize the four major steps of cell respiration, I am going to point out which method of producing ATP is being used during that stage that's producing ATP. So I'll be using these terms again. I'm not going to explain them further at this point, but I will when we get to those stages where those two methods are being used.

So just for now, realize two energy sources for phosphorylation and then two methods of carrying out phosphorylation. So that's the difference between those two pieces of information. So the energy for carrying it out is going to come from covalent bonds and... a concentration gradient.

The methods are going to be either substrate level phosphorylation or oxidative phosphorylation. I know those sound like big terms, but when we break them down, they're not going to seem as complex. Okay.

Also involved in this story are some really important electron carriers, and I will be talking about them as we go along as well. So those are going to be some key players in the story. Now for the quick overview of cellular respiration, I'm going to tell you the four major stages. I also want you to realize that I am giving you a very simplified version. I don't want you to know all the details of each step of each of these four major stages.

Some books will tell you there are three stages because they don't count pyruvate oxidation as a stage. I am counting it as a stage, as do many other textbooks. I will also show you some pictures at the end that will summarize all of this a little better than my drawings. But for now, I want you to draw. So I'm going to draw so that you'll draw.

Okay, four major stages of cell respiration. Again. Cellular respiration is just too much for us to say every time. For now, I'm just going to list them with no further explanation.

Glycolysis, pyruvate oxidation. Citric acid cycle, also called the Krebs cycle. And finally, oxidative phosphorylation. Oxidative phosphorylation is going to have two major parts. One is the electron transport chain.

And then the other is chemiosmosis. This is a very complex metabolic pathway. Remember during the energy lecture, I talked about metabolic pathways and the fact that they are multi-step.

The product of one stage becomes the reactant of the next stage. And we finally will end up with an end product. There are also enzymes involved at each stage.

I'm not going to ask you to know the intermediates. I'm also not going to ask you to know the enzymes, but I just want you to realize this is a very complex process and I am just giving you the very basic version. You don't, for this 100 level class, need to know more than this. You can always plug details in later. So if you go on to take a higher level bio class, whether it be microbiology, Physiology, Bio 200 for Biomajors.

You will hit cell respiration again in more detail. I believe if you can understand the basic version, you can plug details in later. So I know that it's complex. I know that these terms are a little overwhelming.

I am going to give you a chart at the end that I think does a really good job of summarizing everything. So if you don't get it the first time around, please just watch this video. a second time, a third time. And again, I don't need you to know all of the details. I need you just to know what I'm telling you.

Also important to realize there is a cell respiration worksheet. And if you can answer all the questions on the worksheet, then you'll be able to answer all of the questions on the exam. So that's important to realize too. Okay.

Where is this all happening? Okay. This is happening in our cells.

So important to realize that I'm going to draw just a giant cell here. I'm going to draw the nucleus pretty small DNA. So remember that for glucose to get into our cells, it requires insulin, but I'm not even going to get into that level of detail. Let's assume that this glucose got into our cells and now here it is in the cytoplasm of the cell.

So for the purposes of this lecture, We can really assume that this region between the nuclear envelope and the plasma membrane, this whole region is called the cytoplasm. The liquid portion of that is sometimes called the cytosol. So that would be the liquid portion.

So if you read a textbook, I'm pointing this out because if you read a textbook about cell respiration, some textbooks will say that this first stage takes place in the cytoplasm. Some will say cytosol. I just want you to realize those are really saying the same thing.

It's in the same region of the cell. So glucose enters the cell and then it's going to immediately go into the first stage of cell respiration, which is called glycolysis. Glycolysis, that means sugar splitting. If there's enough oxygen present, then the breakdown of the products of glycolysis will continue. If not, it's going to go through something called fermentation.

And we're going to talk briefly about fermentation also. But First, we're going to talk about what's referred to as aerobic respiration. So aerobic means with oxygen.

The other possible type of respiration is called anaerobic respiration. And I'm sure you've heard these terms before related to exercise. This means without enough oxygen.

So and means without. We're going to start by talking about aerobic respiration. Then we will talk briefly about anaerobic respiration. The other term for this is fermentation.

Fermentation produces some amazing products that we use. And we'll talk about that as well. But for this first round, I'm going to be talking about aerobic respiration, what happens when there's enough oxygen present.

But it's important to realize that this first stage, glycolysis can happen with or without oxygen. So glycolysis, the first stage of cellular respiration. So I'm just going to put a number one here to indicate this is the first stage. And it means sugar splitting.

So glyco, glycogen, remember, is a chain of glucose. Glyco is a term that just refers to a sugar. To lyse is to break or split. This, you can call this sugar breaking, sugar splitting.

And this is happening in the cytoplasm of the cell. when glucose first enters the cell. And that's what we start with in glycolysis. The cell starts with glucose and glycolysis is pretty complex.

It's 10 steps. I don't want you to know those 10 steps, but I want you to realize that the product of the first step then becomes the reactant of the second step. And then the product of that step becomes the reactant of the next step. There are enzymes involved at each stage.

And throughout those 10 steps, we need to use 2-ATP as an energy source to get things started. So there is an energy investment phase in which 2-ATP are used. But we make 4-ATP throughout glycolysis. And at the end of these 10 steps, We have a product in which we started with a six carbon glucose.

And we now after 10 steps have split it into two, three carbon molecules called pyruvate. And those are each three carbon molecules. We also do something really important during glycolysis, and that is that the electron carriers are going to start picking up hydrogens from that original glucose molecule.

So just to quickly remind you of the general equation for cellular respiration. 36 ATP, that's a very general number. Okay, some books will say 36 to 38. Realize that this is just on average, but it is the number that I'm going to use today. It's the number that most textbooks use just for accounting purposes.

Okay, but realize that's just an average. Every cell does it a little differently. Every person does it a little differently.

It might not be the exact same every time, but on average, we make 36 ATP for every one glucose. Important to realize oxygen is required for the aerobic respiration that we're going to be talking about. Carbon dioxide and water are products.

We're going to be keeping track of CO2 as we go along. We're also going to be keeping track of what happens to glucose as it's being broken apart. And of particular interest are these 12 hydrogens. Those hydrogens are going to get picked up by electron carriers and eventually stripped away from those electron carriers. to set up the concentration gradient that's going to be used to produce most of the ATP during cell respiration.

So it's important to follow those 12 hydrogens throughout the process. In glycolysis, two of those hydrogens are picked up by the electron carrier NAD+, to make two NADH. So during glycolysis, the first two of those hydrogens are picked up and this electron carrier is now going to shuttle those hydrogens and their accompanying electrons to a very important stage at the very end.

But again, it's important for us to track those 12 hydrogens because those are going to be a major energy source at the very end when that concentration gradient is set up. So summary of glycolysis. What do we start with?

We start with glucose. What do we end with? We end with two pyruvate molecules.

How many ATP were made? Four were made, but two were used. So that's a net of two ATP that were generated during glycolysis. Where is this taking place?

It's taking place in the cytoplasm of the cell. And this is, by the way, the only stage that can take place with or without oxygen. I know we're just talking about what happens with oxygen right now, but glycolysis can happen with or without oxygen. It's the only stage that can happen without oxygen.

All of the other stages are going to require oxygen to take place. Also important to realize we picked up the first two of the 12 hydrogen and made two NADH. NAD plus is an electron carrier.

And when it picks up electrons, it becomes NADH. Remember, gain of hydrogen equals gain of electrons. And Leo the lion says ger. So gain of electrons is reduction.

So this is reduction. Okay, we would say that NAD plus is reduced. And that reaction is called reduction to become NADH.

In a few minutes, when we talk about those hydrogens being stripped away, remember loss of electrons is oxidation. So NADH is going to get oxidized when those electrons and the hydrogens get stripped away. So that's the summary of glycolysis. I'm going to summarize this in a table at the end. Just as in these 10 steps.

The product of one stage becomes the reactant of the next stage. That happens here also. So now we ended with these two pyruvate. These two pyruvate are now what we're going to use to start the next stage called pyruvate oxidation. Okay.

So second stage of cellular respiration is called pyruvate oxidation. Okay. Start with... two molecules of pyruvate that were the products of glycolysis. These are each three carbon molecules.

Three carbon molecules cannot enter citric acid cycle. A carbon needs to get shaved off from each of those. This used to be called the grooming stage.

It used to be called the transition stage. It's had a number of different names. It even still has a number of different names.

For this class, we're calling it pyruvate oxidation. So we start with two pyruvate. And what's going to happen is for each of those pyruvate molecules, a carbon is going to be lost as CO2. So two CO2 are going to get released, one per pyruvate. Also, two hydrogens are going to get picked up by NAD plus to form 2-NADH.

And what we're left with at the end is two molecules of what's called acetyl coenzyme A. It's written co-A for short. Those are two carbon molecules. A coenzyme gets attached in the process too.

You don't need to know that level of detail. Two carbon dioxides are released. That is important to know. That's two of our carbons from our C6H12O6. We picked up two more hydrogens.

So now we've picked up four total of those 12 hydrogens. Remember C6H12. 06, 12 hydrogens.

We picked up two in glycolysis. We've now picked up two more in the transition phase. No ATP is made in pyruvate oxidation. Why is this stage necessary? This stage is necessary because we can't break, we can't complete the breakdown of glucose.

without the citric acid cycle. Citric acid cycle requires a two carbon molecule called acetyl coenzyme A. So this transition phase also called pyruvate oxidation is necessary.

Okay. Important to realize that even though ATP is not made, it's an important transitional phase. And that's why it used to be called the transition phase. It's a transitional phase between glycolysis and citric acid cycle.

So that's why some textbooks don't call it a separate stage. cell respiration. But for this class, we do call it a separate stage.

Also important to realize where this is happening. And it only happens if oxygen is present. So pyruvate oxidation requires oxygen. And where is it taking place? It takes place in the matrix of the mitochondria.

So I'm going to draw a mitochondrion to remind you of where the matrix is. And the structure of this mitochondrion is going to be really important as we go through these next stages of cellular respiration. So I'm going to go back to the cell for a minute. Here's the cell again, nucleus out here in the cytoplasm.

Glucose came into the cell. It went through. glycolysis, glycolysis, sugar splitting, and it produced 2-pyruvate out here in the cytoplasm.

Now, if oxygen is present, so I'm just going to say if O2, those 2-pyruvate are going to go into the mitochondrion and complete the breakdown of glucose. Okay. If no O2, then fermentation is going to happen. Anaerobic respiration. But we're going to talk about that separately.

Now we're just going to talk about if O2 is present. If O2 is present, then those two pyruvate go into the mitochondrion and that's where pyruvate oxidation, citric acid cycle, and oxidative phosphorylation are all going to take places in the mitochondrion. So looking at that mitochondrion blown up bigger and recalling the structure of this, the inside region here is called the matrix.

This is the outer membrane. This is the inner membrane. This space between the two membranes, this space here is called the intermembrane space.

It's a space between the two membranes. This is important because different stages of cell respiration are going to take place in different regions of that mitochondrion. Okay, so remember one mitochondrion. That's the single mitochondria is the plural. So we're just talking about one of them right now.

Pyruvate oxidation and citric acid cycle are both going to happen in the matrix. Oxidative phosphorylation is going to happen in several different regions. And we'll talk about that.

Also important to realize when we say membrane, membrane always means mostly a phospholipid bilayer with some important. proteins embedded. So membrane is a phospholipid bilayer. So if we blew up that outer membrane, if we blew up that inner membrane, you would see mostly phospholipids forming a bilayer like this with those heads pointing outward and the tails pointing inward.

And then there are going to be some really important proteins embedded in that membrane as well. and then more phospholipids. That's going to be an important part of the story as well, is just the structure of that membrane. So that's true, the outer membrane and the inner membrane. The inner membrane of the mitochondrion in particular is going to be an important part of this story in helping set up a very important concentration gradient to generate most of our ATP.

Okay, so glycolysis happened out in the cytoplasm. to produce those two pyruvate. And then if there's enough oxygen present, those two pyruvate go into the matrix of the mitochondrion. And that is where pyruvate oxidation and citric acid cycle are going to take place is in the matrix of the mitochondrion.

So now we've produced two acetyl coenzyme A in the matrix. And now the third stage of cellular respiration is going to happen. And that's called the citric acid cycle.

Okay, and in the citric acid cycle, we start with what we ended with last time. So in the previous step, we ended with a two acetyl coenzyme A called acetyl-CoA. And I'm going to go through. multiple steps. You don't even need to know the number.

I know I told you 10 on glycolysis. I kind of regret doing that now because I don't want you to fixate on how many steps it is. We're going to go through multiple steps. And during the citric acid cycle, the breakdown of glucose becomes complete as four CO2 are going to get released and eight Hydrogens are going to get picked up with electron carriers, mostly by NAD+, but there's going to be another electron carrier that's used also.

Six NADH are going to get produced and two FADH2 are going to get produced. when an electron carrier called FADH picks up two electrons. Remember there are two acetyl-CoA coming through citric acid cycle, so really it's three NADH and one FADH2 for each of those two, so I'm just combining the sum total of what happens in citric acid cycle.

Two ATP are going to get produced and as I said a minute ago, four CO2 are released. And at the end of the citric acid cycle, nothing is left of glucose. Just all of the 12 hydrogens being carried by the electron carriers. And just to remind you, we made two NADH in glycolysis, two NADH in pyruvate oxidation, six NADH and two FADH2. And the citric acid cycle, 6, 8, 10, 12, that's 12 hydrogens.

Remember C6H12O6. So that's our 12 hydrogens. This carbon and oxygen were released as CO2 along with part of the oxygen.

So remember the reactants include not only glucose, but six oxygens. So. Remember the way this works, six O2s, that's 12 oxygens. Okay, that's six oxygens.

So that's 18 oxygens total. If we release six CO2. Number two during pyruvate oxidation and four in citric acid cycle. That's the six.

That's six carbons and 12 oxygens. So minus 12 oxygens, there's six oxygens left. So at the end of the citric acid cycle, all the hydrogens have been picked up by electron carriers. Carbon and oxygen have been released as CO2. So there's our six carbons.

Six carbons released to CO2. 12 of the oxygens have been released to CO2. All the hydrogens are being carried by electron carriers. So there's nothing left of glucose at the end of the citric acid cycle. But we've only made 4 ATP.

We need to make 36 total. But glucose is gone. So all of that potential energy in the covalent bonds of glucose, remember that was one of our energy sources.

That's all been used up. That only allowed us to make four ATP. So two ATP in glycolysis and two ATP in citric acid cycle.

I'm just abbreviating it for now. That means 32 more need to get made, but glucose is gone. Okay, so how were these made?

These were made. By a process called substrate level phosphorylation. So all four of these are all made.

Okay, so all four were made. Remember, we actually made four in glycolysis, but we used two. So we actually made six total, but we've used two.

So all four of those net were made by the process called substrate level phosphorylation. What does that mean? Let's break this down.

Substrate level. Think back to enzymes. Remember that an enzyme has a very specific shape, and I'm just going to draw a pretend shape here. Remember that this part where the reactant binds is called the actin. side of the enzyme.

And when a reactant binds to an enzyme, it's called the substrate. So the substrate is the reactant in an enzyme catalyzed reaction. And in this case, this substrate has a phosphate group attached to it, and it's going to transfer that phosphate group to ADP.

So this is ADP. And this enzyme is going to facilitate transfer of that phosphate group. Remember, transfer of a phosphate group is called phosphorylation. And in this case, transfer of a phosphate group from a molecule to ADP. to make ATP.

And that is called substrate level because it's taking that substrate, the reactant and transferring that phosphate group, phosphorylation, transfer the phosphate group to ADP to make ATP. If you really want to look at the steps of glycolysis and the citric acid cycle, you can see which specific enzyme is involved in doing that and which exact reactant or substrate is used to basically donate that phosphate group and transfer it to ADP to make ATP. That's how we made those first four ATP, two in glycolysis and two in citric acid cycle.

I want to just quickly draw a chart to summarize everything that's happened so far before we get to oxidative phosphorylation at the end, which is how we're going to make 32 more ATP. But I think that this chart will help really summarize it. I just, I want to make sure I don't leave off anything.

So I'm going to try to write small here and I actually want my grid lines. So this is going to be our stage. Start with and with. I'm going to skip the where because it can't really fit on this, but I'm going to mention the where. I just I'm not going to put it on the chart because it doesn't really fit in that place.

Method of ATP production, electron carriers. I'm just going to call them E carriers and CO2. Okay, I only have four stages, but I have a feeling I'm going to have to write like below the line. Sorry, I know this is really messy, but I promise this will help.

It will help summarize everything. Okay, first stage, glycolysis. We start with glucose. Glucose enters the cytoplasm of the cell. So I'm going to say glycolysis.

In the cytoplasm. Again, we could say cytosol. Go through a lot of steps. Don't need to know the numbers. Just forget that I ever even told you that it was 10. Okay.

And with two molecules of pyruvate. Number of ATP produced, two net. Remember we used two and made four, but it's two net made by substrate level phosphorylation. which I'm just going to abbreviate SLP, electron carriers, 2 NADH were made.

The first two of those 12 hydrogens were picked up. I'm going to write that a little neater. 2 NADH and no CO2. were released in glycolysis. And remember, this is the only stage that can happen with or without oxygen.

If enough oxygen is present, then we go into the second stage, which is called pyruvate oxidation. And that happens in the mito matrix. which is of course mitochondria.

And I don't know how that just happened. Yeah. My hand, when it touches the screen, does all kinds of crazy stuff.

Okay. Again, we start with what we ended with in the last stage. So we ended with two pyruvate.

That means here we start with two pyruvate. Sorry. It's so small there. And that's a two. End with two.

Acetyl Coenzyme A. I'm just going to make that two a little better there. Number of ATP made, zero. So this is not applicable. Number of electron carriers, two NADH and two CO2 were released. That's how we made those two acetyl-CoA, by shaving off carbon from each of those two pyruvates.

Remember, the pyruvates were three carbon molecules. The acetyl-CoA are two carbon molecules. And now we go into the citric acid cycle, which also happens in the mitochondrial matrix.

So oxygen is required. So citric acid cycle. In the mito matrix. Start with two acetyl-CoA. End with nada.

Okay, we completed the breakdown of glucose. So there's nothing left. of glucose.

Okay. Just those electron carriers, just the 12 hydrogens. That's all that's left.

So that's where all the potential energy now is. We've only made four ATP because remember, we make two more ATP by substrate level phosphorylation, six NADH. and two FADH2s and four CO2 are released. So there's all six of our CO2. Here's our 12 electron carriers, six, eight, 10, 12. So now all of the potential energy is in those electron carriers because glucose has broken down.

It's been released as CO2. The hydrogens are being carried by the electron carriers at the end of the citric acid cycle. That's where all the potential energy is now is in those electron carriers. That's a really important point.

And there is a question on the worksheet about that to point out how important that is. Okay, so at the end of the citric acid cycle, all the potential energy is now in those 12 electron carriers. Again, I apologize for how messy this chart is, but I do think it's really important. important to kind of summarize everything in your brain. And this is a good way to really summarize it.

Now we need to make 32 more ATP, and that's going to happen in the last stage called oxidative phosphorylation. And oxidative phosphorylation doesn't really fit into this chart. Okay, this is just going to be a stage in which a lot of ATP are generated because of this concentration gradient that's going to get set up. So oxidative. phosphorylation.

If we had to fit it in the chart, we would say we start with the 12 electron carriers. Where is this happening? I'm going to say the entire mitochondrion is really being used, everything except the outer membrane. is being used.

Number of ATP made is going to be on average 32 ATP. And they're made by a very important enzyme that is embedded in the inner membrane of the mitochondrion. So let's look at the structure of that mitochondrion again.

Oops, sorry. In living systems, whenever something is folded, it increases the surface area. Imagine that you cut this outer membrane and you took this as a, just imagine it being a string. Okay.

We know it's phospholipids with some proteins embedded in it, but imagine you stretch it out. That's going to be a lot shorter in length than this. If we did the same here, this is a lot longer.

It's folded, right? Folds, increased surface area. So anything that's happening, you've got to know there's something really important happening in that membrane. Embedded in this membrane are some really important protein complexes. that make up something called the electron transport chain.

Okay, so these are proteins that are embedded in that inner membrane. So remember this is the matrix, this is the inner membrane, this is the outer membrane, and this is the intermembrane space in between here. So we have all 12 of those electron carriers here.

We have the 10 NADH, And the two FADH2s that were generated in those first three stages, when those electron carriers were reduced, they were reduced when they picked up the hydrogens, gain of electrons is reduction, GRR. They're now going to lose those electrons. They're going to become oxidized.

That's why this is called oxidative phosphorylation. Those 12 electron carriers are going to be oxidized because what happens is when they come in contact with these proteins in the inner membrane of the mitochondrion, those hydrogens are going to get stripped away and pumped out into this space, this intermembrane space. They are charged.

This is a really important thing to realize. The electrons... are being stripped away and they're getting bounced through these proteins in something called the electron transport chain. And those electrons are generating energy as they fall down this energy ladder. They're generating energy to pump those hydrogens against a concentration gradient out into this space.

So there are a lot of important concepts involved here. One is, you know, that the energy generated by those electrons falling down an energy ladder is giving energy to pump. pump those hydrogens against a concentration gradient, and they're building up out here. They can't just come across the phospholipid bilayer because remember that charged ions cannot move across those nonpolar tails.

Remember, charged ions or molecules cannot simply diffuse by simple diffusion. across phospholipids. So what happens is those 12 hydrogens are going to build up in this intermembrane space and that now represents a concentration gradient. Hydrogens are stripped from the electron carriers by proteins in the inner membrane of the mitochondrion. and they are pumped into the inter membrane space where they build up and they create a concentration gradient.

So a concentration gradient is established. All of those hydrogens are now representing a ton of potential energy. When they come back across the membrane, they're not going to come across the phospholipids.

They can only come across one way. They can only come back across the membrane. Remember that to reach equilibrium, they need to come back. So they're high out here and they're low over here, but they can't just cross that phospholipid bilayer.

So now through facilitated diffusion, they're going to come across a very important protein. So they can only come back across the membrane by what's called facilitated diffusion through. a very important protein, one of the most important proteins in your body, and it's called ATP synthase.

Remember enzymes are cool because the name tells you what they do and they end in ASE. So this ASE tells us that it's an enzyme. It's going to synthesize ATP. When those hydrogens come back across through that enzyme, it's going to phosphorylate ATP to form ATP. And I'm going to show you a picture of that happening.

But first I want to go back to my picture here. Here's ATP synthase. Here's ATP synthase. They're going to be scattered throughout this membrane. And that's the only way that hydrogens can come back across.

Okay, so here's the ATP synthase. And the hydrogens can only come back across through that enzyme. They can't come across that phospholipid bilayer because they are charged. And when they come back across, it's going to phosphorylate ADP to form ATP.

So if this is ADP and it's just sitting there waiting, as those hydrogens come across, it generates... energy to phosphorylate, to stick phosphates back on that ADP to form ATP. And I'm going to show you a picture of that happening in a minute. But for now, I'm going to blow up that membrane. I'm going to draw a blow up of that inner membrane.

So if we look at the mitochondrion again, sloppy version, I'm going to just take a piece of that and blow it up. So I'm blowing up that inner membrane and it's phospholipids, which hydrogens cannot come across. It's some important protein complexes. And you don't need to know about these in detail.

Here's another one. And what happens is when those electron carriers come in contact with those protein complexes, those protein complexes are going to strip the hydrogens away and pump them out into the space. Oops, sorry, I didn't mean to do that. And then this is going to be our ATP synthase. And it's kind of like a rotor.

More phospholipids. Okay, and on this side, we have a bunch of ADP, and we have a bunch of phosphate groups. Okay, NADH comes in contact with this protein. The hydrogen is going to get stripped away and pumped out into this space. And what we're left with is NAD+.

Loss of electrons is oxidation. So that NADH became oxidized to form NAD+. And that hydrogen gets pumped out into this space.

Okay, that's going to keep happening. And these hydrogens build up out here. They can't just come across that phospholipid bilayer because they're charged, but they can come across through the ATP synthase. And when they do, this rotor spins and it sticks phosphate groups onto ADP to form ATP.

And 32 ATP on average are going to get generated through this process. Important terms here. The protein complex is stripping away those hydrogens and pumping them out into that space is called the electron transport chain.

And when the hydrogens come back across and generate the ATP by phosphorylating ADP with the energy of them coming back across, it's like water behind a dam coming through a hydroelectric plant and generating electricity. That potential energy is coming from that concentration gradient. That part is called chemiosmosis. Those hydrogens coming back across.

Those two together make up what's called oxidative phosphorylation. Sorry, it wouldn't all fit on that one line. Oxidative. phosphorylation. I'm sorry, there's some really loud construction noise going on outside of my neighbor's house right now.

Those are the two stages of oxidative phosphorylation. Electron transport chain, the hydrogens are stripped away. Those electron carriers become oxidized.

The hydrogen is pumped out into the space. Chemiosmosis is when those hydrogens come back across and phosphorylate ADP to form ATP. I'm going to show you a better picture of that in a minute. That's how 32 ATP are generated at the end. OK, so if we tried to fit that into the chart up above, here's our chart.

Again, we just start with the 12 electron carriers and we make 32 ATP really by chemiosmosis. I mean, the chemiosmosis part is where they get made. I mean.

They say that they're made by oxidative phosphorylation, but they're made during the chemiosmosis part of that. I would never ask you a question to make that distinction. I would just ask you how many ATP are generated during oxidative phosphorylation. Realize that it's all because of that magical enzyme called ATP synthase, which I'm also going to show you a picture of. So I'm going to show you a better picture of the electron transport chain, a better picture of ATP synthase.

Just want to double check that there wasn't some other picture I wanted to draw for you. Okay. We also need to talk about fermentation and I'm going to do that on the diagrams too.

Okay. I would love to ask you right now, if you have any questions, but we are not live, so I can't do that, but I know this is a lot. Okay.

It's a lot on the surface. It seems really, really boring, but just realize this is an amazing process. Like how cool is this, that we can take energy from our food and we can package it as ATP and we can use it.

anytime, anyplace in the cell. We don't have to have a gas tank that's full. We don't have to be on a glucose drip all day long.

We can take that energy from our food and we can convert it to an energy currency that can be used anytime, anyplace in the cell. And remember I've told you before, you make and use your body weight in ATP every day. That's pretty amazing too.

If you stop making ATP, you die. rat poison called cyanide is blocking a stage of cell respiration. There are a lot of poisons that block key stages of cell respiration and cause death of that organism, whether it be a plant, an insect, um, different pesticides are used to do that.

So, and there are different poisons that are used to do that too. You must make ATP all day, every day. Otherwise, the chemistry of your cells shuts down because remember you can't directly use energy from your food.

You have to convert it to ATP and that ATP is then used to drive chemical reactions that require energy in the cell. Okay. I'm going to pull up some pictures. So please just stick with me for a second here while I pull up these images. Okay, these are the photos I want to show you of cellular respiration.

These are some better images than what we drew together in the notes. So this is NAD+. It's one of the two electron carriers. Remember, the other one is FADH. That becomes FADH2.

And you can see that it is a nucleotide. And when it picks up hydrogens, it's becoming reduced. When it drops off the hydrogen, it's becoming oxidized.

So I just wanted to show you that better picture. This is just an overview of cell respiration. It's showing that glycolysis takes place out in the cytosol. Again, this term cytosol and cytoplasm can be used interchangeably.

But during this process, we make two ATP net by substrate level phosphorylation. It doesn't show pyruvate oxidation happening, but pyruvate oxidation is going to happen here in the matrix of the mitochondrion. And again, this is only if oxygen is present, that those two pyruvate go into the mitochondrion. Pyruvate oxidation produces the acetyl-CoA that then go through citric acid cycle. And remember at that point, we've completely broken down glucose.

All the energy is now in those 12 electron carriers, and we make two more ATP net by substrate level phosphorylation. And then finally, at the end, during oxidative phosphorylation, which includes the electron transport chain and chemiosmosis, on average, 32 ATP are made by oxidative phosphorylation. And remember, it's specifically during the chemiosmosis when those hydrogens come back across that those 12, I'm sorry, 32 ATP are being made.

This shows you a picture of substrate level phosphorylation. And I already drew this picture for you, but it shows that substrate. is the reactant that's going to transfer a phosphate group to ADP to make ATP.

And remember that we make two ATP in glycolysis by substrate level phosphorylation, and we make two in citric acid cycle by substrate level phosphorylation. This slide got a little wonky, but... This is the first five stages of glycolysis. Remember, it's 10 stages long, but you don't need to know that. You start with glucose.

We're going to use some ATP here. We're going to use some ATP here to get things started. And then at the end of the 10, we've made four.

So remember, we used to make four. So that's two net ATP. You can see there is an enzyme involved at each stage. So anything that ends in ASE is an enzyme.

And you can see that the product in one stage becomes the reactant of the next stage, just like in any other metabolic pathway. So this 3-phosphoglycerate is a product of the prior stage and then becomes the reactant of the next stage. And at the end, we end up with two molecules of pyruvate that are three carbon molecules, one, two, three, and we end up with two of those.

Those two then go through pyruvate oxidation. So let me back down here. So if oxygen is present, the two pyruvate go into the mitochondrion and go through pyruvate oxidation where those two acetyl-CoA are produced that then goes through citric acid cycle.

If there's not enough oxygen present, we go through fermentation. This is pyruvate oxidation. So for each pyruvate, one carbon dioxide is released. And since we have two pyruvate, sorry, this is really writing fat right now. Two pyruvate are going to make two carbon dioxide, two NADH, and we end up with two acetyl-CoA.

That E should not be on the end. Those two acetyl-CoA then go through citric acid cycle. You can see those steps of citric acid cycle here.

Again, you don't need to know these eight steps, but you can see we start with the acetyl-CoA and you can see where we pick up the hydrogens with the electron carrier. So remember we have two of these, so everything gets doubled. So if you count all the NADHs, one, two, three, but that gets doubled. So that's six NADH.

And then this gets doubled. So two FADH2s and this gets doubled. So it's two ATP. These are the protein complexes that are embedded in the inner membrane of the mitochondrion. And this is ATP synthase.

I'm going to come back to that picture in a minute because I want to show you this first. So this shows those protein complexes. stripping away those hydrogens so nadh is becoming oxidized loss of electrons is oxidation the hydrogens get pumped out into the space using the energy generated when those electrons fall down this energy staircase and all those hydrogens build up out there they can't come across these phospholipids because remember they can't cross those nonpolar tails so they're not allowed across there The only way they can come across is through ATP synthase.

And when that happens, ADP is phosphorylated to form ATP. And that part is called the chemiosmosis. So I really like this explanation. It says electron transport chain, electron transport and pumping of protons, which are the H plus, which creates an H plus gradient.

This is a concentration gradient across the membrane. And then chemiosmosis is ATP synthesis powered by the flow of the H plus back across the membrane. When those come through, that produces enough energy to add that phosphate group onto ADP to make ATP.

And on average, we make 32 that way. Oh boy. Sorry.

When it gets towards the edge, it just really gets wonky over there. Sorry. So 32 on average ATP get made that way. Also, one thing we haven't talked about yet, the final electron acceptor oxygen.

When those hydrogens come back across, they're going to finally join up with oxygen and produce water. So remember that general equation. Sorry, let me write it up here.

C6H12O6. plus 6-O-2, 6-C-O-2. Remember two were released in pyruvate oxidation and four were released in the citric acid cycle. Those oxygen now are going to combine with those hydrogens to form the six waters.

Okay. This is a good summary slide. I like the summary slide.

The only thing it doesn't show you is it doesn't show you pyruvate oxidation in detail, but it shows you that glycolysis takes place out in the cytoplasm. You start with glucose, you end with 2-pyruvate and produce 2-ATP by substrate level phosphorylation. If there's enough oxygen present, you go into the mitochondrial matrix and make 2-acetyl-CoA through pyruvate oxidation, which then go through the citric acid cycle and we make 2 more ATP by substrate level phosphorylation. And then all of those electron carriers go into oxidative phosphorylation because when they hit that inner membrane in the mitochondria, the protein complex is embedded in the inner membrane, strip away those hydrogens, they get pumped into the intermembrane space.

They can only come back across through ATP synthase. And here's that amazing, amazing enzyme that is going to phosphorylate ADP to form ATP when those hydrogens come back across. the most amazing membrane, the most amazing enzyme. So this is the number one enzyme in my book.

This is an incredible enzyme. Can you even imagine how tiny, like think about how tiny your cells are. And then in the inner membrane of the mitochondrion is this little enzyme. And there are, you know, millions of them in each cell. Okay, what is fermentation?

Fermentation happens when there's not enough oxygen present. And there are several different products that can occur, but in us, in animals, it's lactic acid, also called lactate. So you can see that if there aren't enough oxygen present, those two pyruvate, oops, sorry, those two pyruvate, rather than going into the mitochondria and producing more ATP, instead what happens is that NAD plus is going to get regenerated and lactic acid or ethanol are going to form. So certain organisms are going to make alcohol as a product of fermentation.

Certain others are going to make um, lactic acid. And this is what we make. We make lactate or lactic acid.

Okay. So this is what, when you start doing anaerobic exercise, so you exercise to the point where your muscles are not getting enough oxygen anymore. Lactic acid is what causes your muscles to burn.

It's also, it causes the soreness the next day after a really hard workout, best way to move that out of your muscles is to exercise again and move that back into your bloodstream. But so lactate also called lactic acid. That's the product of fermentation. That is anaerobic respiration, respiration without enough oxygen present.

So that means if there's not enough oxygen present, how many ATP can you make for every glucose? Only two. So when you're doing anaerobic respiration, you are burning glucose at an accelerated rate.

You're exercising, your muscles need ATP. They need that energy. So you start burning glucose at a higher rate.

In other words, you're burning calories at a higher rate because you're only producing two ATP for every glucose instead of 36 on average for every glucose. So the most you can produce in fermentation is two ATP for every glucose. We have a lot of products that are made by fermentation.

Many of them, you know, so obviously beer and wine. And other alcohols, really, you know, all alcohol we drink is made by alcohol fermentation where ethanol is produced. Even rubbing alcohol, acetone, vinegar.

So anything that's made with vinegar, including pickles, soy sauce, kimchi, kombucha, all those fermented products are, you know, fermentation means anaerobic respiration. And that alcohol is getting produced or lactic acid. And there are some other chemicals that can get produced depending on the type of bacteria that are carrying it out. So certain bacteria and certain yeasts can give us different types of fermentation.

So yeast produced alcohol fermentation. So that's how we get beer and wine and other forms of alcohol that we drink is from yeast fermentation. So they would be producing ethanol.

as a byproduct of that fermentation. Also important to note that you can use other organic molecules to carry out cell respiration. It's just not as efficient.

The cells prefer carbohydrates. Those enter glycolysis. Fats and proteins enter cell respiration at a later stage, and there is a cost associated with that. So it's not the healthiest way to carry out cell respiration. The healthiest way is from carbohydrates.

but just wanted you to realize you can use fats and proteins, but they come at a cost to the cell. So carbohydrates are the preferred fuel for the body to produce ATP. Okay. That is cell respiration.

Please make sure you can answer all of the questions on the study guide or the separate worksheet. So depending on when you're watching this. video, you might have a separate worksheet or you might have those questions just as part of your study guide. If you're not sure which one, be sure to ask.

Transcript for:Overview of Cellular Respiration Process

Transcript for:
Overview of Cellular Respiration Process