Review of Aerobic Cellular Respiration - Online Tutor, Practice Problems & Exam Prep

Aerobic cellular respiration consists of four stages: glycolysis, pyruvate oxidation, the Krebs cycle, and oxidative phosphorylation. Glycolysis breaks down glucose into 2 pyruvate molecules, producing 2 ATP and 2 NADH. Pyruvate oxidation converts pyruvates into acetyl CoA, yielding 2 NADH and releasing 2 CO₂. The Krebs cycle generates 2 ATP, 6 NADH, and 2 FADH₂, releasing 4 CO₂. Finally, oxidative phosphorylation produces 26-34 ATP, utilizing NADH and FADH₂ while oxygen acts as the final electron acceptor, forming water. Overall, 30-38 ATP are produced from one glucose molecule.

Review of Aerobic Cellular Respiration

In this video, we're going to do a review of aerobic cellular respiration. Really, we're not going to cover any new information in this video. We're only going to review information that we've already covered in our previous lesson videos and recap the most important takeaways. So, if you already feel really good about aerobic cellular respiration, then feel free to skip this video. However, if you're struggling with aerobic cellular respiration even just a little bit, then feel free to stick around because we're going to recap aerobic cellular respiration here.

Now, recall that there are 4 stages of aerobic cellular respiration, and we have an image recapping all four stages. In aerobic cellular respiration, recall that the vast majority occurs in the mitochondria, which is this big pink thing in the background. However, not all of cellular respiration occurs inside the mitochondria. The very first step, glycolysis, actually occurs just outside of the mitochondria in the area of the cell known as the cytoplasm. Glycolysis, with the root 'glyco' meaning sugar and 'lysis' meaning to break down, breaks down the monosaccharide glucose, which has a total of 6 carbon atoms represented by 6 black circles. These 6 carbon atoms of glucose are all eventually converted into carbon dioxide and exhaled from our bodies.

Glycolysis takes glucose and breaks it up into 2 pyruvates. Additionally, it also produces 2 NADH molecules, acting as electron taxis, and glycolysis produces a net of 2 ATPs via substrate-level phosphorylation. After these 2 pyruvates are produced via glycolysis, they are transported into the mitochondrial matrix, where pyruvate oxidation occurs. This process oxidizes the 2 pyruvates, creating 2 more NADHs, 2 acetyl CoAs, and releasing 2 carbon dioxide (CO₂) molecules. In each pyruvate, one of the carbon atoms is released as CO₂, and the other two carbon atoms become part of the acetyl CoA molecule.

After these 2 acetyl CoA molecules are produced, they transition into the citric acid cycle, or the Krebs cycle, which ultimately produces 2 ATP molecules, 2 FADH₂ molecules, and 6 NADH molecules. It also releases 4 carbon atoms between both acetyl CoAs as 4 CO₂ molecules. All 6 of the carbon atoms that originally came in as glucose are released as 6 carbon dioxides, which are all exhaled. Instead of following these carbon atoms further, we'll follow the electron carriers produced throughout this process. Collectively, there are 10 NADH molecules generated and 2 FADH₂s created.

The electron carriers make their way to the electron transport chain. After the electron transport chain builds up a hydrogen ion concentration gradient, chemiosmosis allows for the production of a significant amount of ATP through oxidative phosphorylation, amounting to some 26 to 34 ATP molecules. This stage produces the majority of the ATP because the first three stages combined only produce a total of 4 ATP via substrate-level phosphorylation. Also, during the electron transport chain, 6 oxygen gas molecules act as the final electron acceptor.

Considering the total amount of ATP produced by oxidative phosphorylation, which is some 26 to 34, and the ATPs produced via substrate level phosphorylation during the Krebs Cycle and glycolysis, we have a grand total of ATP from all stages of aerobic cellular respiration between 30 to 38 ATP. This is all from just one single glucose molecule, leading to some 30 to 38 ATPs, which is incredibly efficient. This concludes our review of aerobic cellular respiration, and we'll be able to get some practice applying these concepts as we move forward. See you all in our next video.

Through the first three stages of cellular respiration only 4 ATP molecules have been produced from the initial glucose molecule. In which of the products of these stages is the potential energy to produce more ATP molecules stored?

a) The 6 molecules of CO₂.

b) The H⁺ ions produced.

c) The 10 NADH and 2 FADH₂ molecules.

d) The 4 molecules of ATP.

• A. The 6 molecules of CO₂.
• B. The H⁺ ions produced.
• C. The 10 NADH and 2 FADH₂ molecules.
• D. The 4 molecules of ATP.

Total Products for Each Stage of Aerobic Cellular Respiration

In this video, we're going to continue our review of aerobic cellular respiration by filling in the table with the total products made from a single glucose molecule at each step of aerobic cellular respiration. And so notice down below in this table what we have are the 4 stages of aerobic cellular respiration across the top. And so those are glycolysis, pyruvate oxidation, the Krebs cycle or the citric acid cycle, and oxidative phosphorylation which includes the electron transport chain and chemiosmosis. And so notice over here what we have are the start molecule, the number of carbon dioxide molecules or CO₂, the number of ATP molecules, the number of electron carriers including FADH₂ and NADH, and the ending molecule for the stage. And so when it comes to glycolysis, the start molecule is, of course, going to be a single glucose. So we can go ahead and put in glucose here. In terms of the amount of CO₂ molecules produced during glycolysis, it's actually going to be 0. And then in terms of the ATP molecules, glycolysis is going to produce a net of 2 ATPs. It produces 0 FADH twos, but it does produce 2 NADHs. And the ending molecule is really going to be 2 pyruvate molecules. And so really this is the summary of glycolysis.

So now moving on to pyruvate oxidation here, the start molecule for pyruvate oxidation is, of course, going to be the pyruvates that were generated in glycolysis. And so we can go ahead and put in 2 pyruvates here. We'll put this in red, 2 pyruvates. And so, in terms of carbon dioxide, each of these pyruvates is going to lose a carbon as a carbon dioxide molecule, and so there's going to be a total of 2 CO₂ molecules produced. In terms of ATP, it turns out that there's actually 0 ATPs made in pyruvate oxidation. There are also 0 FADH twos made in pyruvate oxidation, but there are 2 NADH molecules made in pyruvate oxidation. And so because pyruvate oxidation is the second stage, that's helpful to remember that it produces, it takes 2 pyruvates and converts them into 2 carbon dioxide, 2 NADHs, and 2 Acetyl CoA molecules, and that is really the ending molecule of Pyruvate oxidation.

Now moving on, what we have is the Krebs Cycle or the Citric Acid Cycle. And of course, the starting molecule for the Krebs Cycle or the Citric Acid Cycle is going to be the ending molecule for the previous step which is 2 Acetyl CoA, and so we can go ahead and put in 2 Acetyl CoA here as the starting molecules, and each of these acetyl CoA's has to undergo the Krebs cycle. And so there's going to be a cumulative total of 4 carbon dioxide molecules produced, a total of 2 ATP molecules produced, a total of 2 FADH₂ molecules produced, and a total of 6 NADH molecules produced. And of course, the ending molecule is that there is no ending molecule. In fact, we could say that the ending molecule would just be oxaloacetate since that is the molecule that gets regenerated during the Krebs cycle or the citric acid cycle. But really the ending molecule is a tough molecule because the cycle is a cycle that begins and ends with the same place. So ultimately, the cycle ends with oxaloacetate regeneration. And so this oxaloacetate is just going to continue to be part of another Krebs Cycle revolution or another Krebs Cycle reaction. And so notice that all of the 6 carbon atoms of glucose were ultimately converted into carbon dioxide. Notice, there are 6 carbon dioxide that is being produced.

And so now what we're going to do is essentially follow these electron carriers to the final step, which is going to be the electron transport chain in chemiosmosis, which performs oxidative phosphorylation. And so during oxidative phosphorylation, you could say that the starting molecules are going to be the electron carriers, such as for example NADH and FADH twos. And so these NADH and FADH₂ electron carriers are going to drop off their electrons. Ultimately, in terms of carbon dioxide, there are going to be 0 carbon dioxides produced during oxidative phosphorylation. In terms of ATP molecules, there's going to be somewhere between 26 to 34 ATP molecules that are produced during oxidative phosphorylation. So notice the vast majority of ATP comes from the final stage here with oxidative phosphorylation. In terms of FADH twos and NADHs, they don't produce them, so there's going to be 0. Instead, what they do is they consume those NADH and FADH twos by taking their electrons. And then in terms of the ending molecule, what we could say is that it is going to be water, H₂O. And that's because recall that oxygen gas acts as the final electron acceptor and that oxygen gas reacts with hydrogen ions to form water. And so really this here, fills out our entire table, and to get the totals, all we need to do is fill in the rest of these columns here.

And so notice that in terms of the totals for carbon dioxide, there are a total of 6 carbon dioxides that are being produced. And so the original 6 carbon atoms that were found in glucose were all ultimately converted into 6 CO₂ molecules, 6 carbon dioxide molecules. And these 6 carbon dioxide molecules are ultimately exhaled outside of our bodies. Now in terms of the total amount of ATP, what we have is somewhere between 30 to 38 total ATPs produced in aerobic cellular respiration. In terms of FADH₂s, the total are going to be a total of 2. And in terms of NADHs, there's going to be a total of 10 NADHs that were produced. And so this here concludes and fills out our entire table here, which is really just reviewing the total products for each stage of aerobic cellular respiration. And so now that we've filled out this table, we can now move on and apply some of the concepts that we've reviewed and some practice problems. So I'll see you all there.

Water is one of the products of aerobic cellular respiration. What is the source of the oxygen atom utilized to create the water molecules?

a) Carbon dioxide (CO₂).

b) Glucose (C₆H₁₂O₆).

c) Oxygen gas (O₂).

d) Pyruvate (C₃H₃O₃^–).

• A. Carbon dioxide (CO₂).
• B. Glucose (C₆H₁₂O₆).
• C. Oxygen gas (O₂).
• D. Pyruvate (C₃H₃O₃^–).

Approximately how many molecules of ATP are produced from the complete oxidation of one molecule of glucose (C₆H₁₂O₆) through the process of aerobic cellular respiration?

a) 4.

b) 2.

c) 26-34.

d) 30-38.

• A. 4.
• B. 2.
• C. 26-34.
• D. 30-38.

Here’s what students ask on this topic:

What are the four stages of aerobic cellular respiration?

The four stages of aerobic cellular respiration are:

1. Glycolysis: This occurs in the cytoplasm and breaks down glucose into 2 pyruvate molecules, producing 2 ATP and 2 NADH.

2. Pyruvate Oxidation: This occurs in the mitochondrial matrix, converting pyruvates into acetyl CoA, yielding 2 NADH and releasing 2 CO₂.

3. Krebs Cycle (Citric Acid Cycle): This also occurs in the mitochondrial matrix and generates 2 ATP, 6 NADH, and 2 FADH₂, releasing 4 CO₂.

4. Oxidative Phosphorylation: This includes the electron transport chain and chemiosmosis, producing 26-34 ATP, utilizing NADH and FADH₂ while oxygen acts as the final electron acceptor, forming water.

How many ATP molecules are produced in aerobic cellular respiration from one glucose molecule?

Aerobic cellular respiration produces a total of 30-38 ATP molecules from one glucose molecule. This range accounts for the ATP generated through different stages:

1. Glycolysis: 2 ATP

2. Krebs Cycle: 2 ATP

3. Oxidative Phosphorylation: 26-34 ATP

The variation in the total ATP count (30-38) is due to differences in the efficiency of the electron transport chain and the use of NADH and FADH₂ in oxidative phosphorylation.

What is the role of oxygen in aerobic cellular respiration?

Oxygen plays a crucial role in aerobic cellular respiration as the final electron acceptor in the electron transport chain. During oxidative phosphorylation, electrons are transferred through a series of protein complexes in the inner mitochondrial membrane. Oxygen accepts these electrons at the end of the chain, combining with hydrogen ions (H⁺) to form water (H₂O). This process is essential for maintaining the flow of electrons and the production of ATP. Without oxygen, the electron transport chain would halt, and ATP production would be significantly reduced.

What are the main products of the Krebs cycle?

The main products of the Krebs cycle (Citric Acid Cycle) per glucose molecule are:

1. 2 ATP molecules

2. 6 NADH molecules

3. 2 FADH₂ molecules

4. 4 CO₂ molecules

These products are generated through a series of enzymatic reactions that occur in the mitochondrial matrix. The NADH and FADH₂ produced are crucial for the electron transport chain in oxidative phosphorylation, where they contribute to the generation of a significant amount of ATP.

What is the difference between substrate-level phosphorylation and oxidative phosphorylation?

Substrate-level phosphorylation and oxidative phosphorylation are two mechanisms of ATP production:

1. Substrate-level Phosphorylation: This occurs directly in metabolic pathways such as glycolysis and the Krebs cycle. It involves the direct transfer of a phosphate group from a substrate molecule to ADP, forming ATP. For example, glycolysis produces a net of 2 ATP via substrate-level phosphorylation.

2. Oxidative Phosphorylation: This occurs in the mitochondria during the electron transport chain and chemiosmosis. It involves the transfer of electrons from NADH and FADH₂ through protein complexes, creating a proton gradient that drives ATP synthesis via ATP synthase. This process produces 26-34 ATP, making it the primary source of ATP in aerobic respiration.