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 while releasing 4 CO2. Finally, oxidative phosphorylation produces 26-34 ATP through the electron transport chain, resulting in a total of 30-38 ATP from one glucose molecule, showcasing the efficiency of aerobic respiration.

Review of Aerobic Cellular Respiration

In this video, we're going to do a review of aerobic cellular respiration. And so 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 recapping the most important takeaways. And 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 that being said, recall that there are 4 stages of aerobic cellular respiration, and down below what we have is an image recapping all four stages of aerobic cellular respiration. And so in aerobic cellular respiration recall that the vast majority of aerobic cellular respiration occurs in the mitochondria and the mitochondria is this big pink thing that's in the background. And so the vast majority of cellular respiration does occur inside of the mitochondria. However, not all of cellular respiration occurs inside the mitochondria because the very first step of aerobic cellular respiration, which is glycolysis, actually occurs just outside of the mitochondria in the area of the cell known as the cytoplasm. And so glycolysis again has the root glyco, which means sugar, and the root lysis, which means to break down.

And so glycolysis is going to break down a sugar, more specifically it's going to break down the sugar, the monosaccharide glucose which has a total of 6 carbon atoms represented by these 6 black circles. And so ultimately these 6 carbon atoms of glucose are all going to be converted into carbon dioxide and exhaled out of our bodies. And so that's important to keep in mind about these 6 carbon atoms of glucose. And so glycolysis is going to take glucose and break it up into 2 pyruvates. And additionally, it also is going to produce 2 NADH molecules which are electron carriers, full taxi cabs if you will, electron taxi cabs.

And also glycolysis is going to produce a net of 2 ATP2 molecules produced via substrate level phosphorylation. Now after these 2 pyruvates have been produced via glycolysis, those 2 pyruvates are going to be transported into the mitochondrial matrix, which is where pyruvate oxidation is going to occur. And so pyruvate oxidation is going to take these 2 pyruvates and it's going to oxidize those 2 pyruvates creating 2 more NADHs, 2 acetyl CoAs, and it's going to release 2 carbon dioxides or 2 CO2 molecules. And so what you'll notice is that in the 2, the 2 pyruvates, each of them have 3 carbon atoms. One of the carbon atoms on each pyruvate is going to be released as CO2, and the other 2 carbon atoms are going to become part of the Acetyl CoA molecule.

Now after these 2 acetyl CoA molecules have been produced, they are going to transition into the citric acid cycle or the Krebs cycle. And the Krebs cycle is ultimately going to produce, through both of the Acetyl CoA coming through, it's going to end up producing a total of 2 ATP2 molecules, a total of 2 FADH2 molecules, and a total of 6 NADH molecules. And it's also going to release these 4 carbon atoms between both Acetyl CoAs as, 4 CO2 molecules. And so these are the products of, the citric acid cycle or the Krebs cycle. And so ultimately, all 6 of the carbon atoms that originally came in as glucose were released as 6 carbon dioxide.

And so notice that a total of 6 carbon dioxide are being released and exhaled. And so, all of the carbon atoms we followed, their path in this process for them to all get released. And so we're not going to follow those carbon atoms any further. Instead, what we're going to do is follow these electron carriers that have been produced throughout this process. And so notice that, cumulatively there are a total of 10 NADH molecules that have been generated and there's also a total of 2 FADH2 that have been created.

So here is the total of these 3 processes, how many electron carriers they produced. And so once again, all of these electron carriers are going to make their way to the electron transport chain, and, after the electron transport chain builds up a hydrogen ion concentration gradient, chemiosmosis is going to allow for the production of lots and lots of ATP through oxidative phosphorylation. And so there's some 26 to 34 ATP2 molecules produced in this final stage of aerobic cellular respiration. And so 26 to 34 is the vast majority of the ATP because recall that the first three stages combined only produce a total of 4 ATP via substrate level phosphorylation. And so also in the electron transport chain, what's going to happen is there are going to be 6 oxygen gas molecules that are going to act as the final electron acceptor in the electron transport chain, and those 6 oxygen gas molecules are going to react to form 6 water molecules, and so we have those here as well.

And so when we're looking at the grand total of how many ATP molecules, aerobic cellular respiration produced, we need to consider the total amount of ATP produced by oxidative phosphorylation, which is some 26 to 34, and we also need to consider the ATPs produced via substrate level phosphorylation during the Krebs cycle or citric acid cycle and during glycolysis as well. And so basically what we have is 26 + 4 is going to give us a total of 30 ATPs at the minimum. And then of course 34 ATP plus, these 2 here is going to give us a total of 38 ATP. And so the grand total amount of ATP between all of aerobic cellular respiration is somewhere between 30 to 38 ATP. And that is all from just one single glucose molecule that enters the cell, leads to some 30 to 38 ATPs.

And so that's pretty efficient. From one glucose, you get 30 to 38 ATPs that is incredibly efficient. And so this here concludes our review of aerobic cellular respiration, and we'll be able to get some practice applying these concepts as we move forward. So I'll 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.

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. Notice below in this table, we have the four stages of aerobic cellular respiration across the top. These are glycolysis, pyruvate oxidation, the Krebs cycle or the citric acid cycle, and oxidative phosphorylation, which includes the electron transport chain and chemiosmosis. Over here, we have 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.

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 is actually going to be 0. Glycolysis is going to produce a net of 2 ATPs, 0 FADH₂s but it does produce 2 NADHs. The ending molecule is really going to be 2 pyruvate molecules.

Now moving on to pyruvate oxidation, the start molecule for pyruvate oxidation is going to be the pyruvates that were generated in glycolysis, so we can go ahead and put in 2 pyruvates here. In terms of carbon dioxide, each of these pyruvates is going to lose a carbon as a carbon dioxide molecule, so there's going to be a total of 2 CO₂ molecules produced. There are 0 ATPs and 0 FADH₂s made, but there are 2 NADH molecules made in pyruvate oxidation. Because pyruvate oxidation is the second stage, it produces, it takes 2 pyruvates and converts them into 2 carbon dioxide, 2 NADHs, and 2 Acetyl CoA molecules, which is the ending molecule of pyruvate oxidation.

Next, we have the Krebs Cycle or the Citric Acid Cycle, and 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 CoAs. Each of these acetyl CoAs has to undergo the Krebs cycle. 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. The ending molecule is tough to specify because the cycle is a cycle that begins and ends at the same place. Ultimately, the cycle ends with oxaloacetate regeneration.

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. This oxaloacetate just continues to be part of another Krebs Cycle revolution or another Krebs Cycle reaction. All of the 6 carbon atoms of glucose were ultimately converted into carbon dioxide.

Now, we're going to follow these electron carriers to the final step, which is going to be the electron transport chain in chemiosmosis, performing oxidative phosphorylation. During oxidative phosphorylation, the starting molecules are going to be the electron carriers such as, for example, NADH and FADH₂s. These NADH and FADH₂ electron carriers are going to drop off their electrons and ultimately, in terms of carbon dioxide, there are going to be 0 carbon dioxides produced. In terms of ATP molecules, there's going to be somewhere between 26 to 34 ATP molecules that are produced during oxidative phosphorylation.

The vast majority of ATP comes from the final stage here with oxidative phosphorylation. They don't produce FADH₂s and NADHs; instead, they consume those by taking their electrons. In terms of the ending molecule, what we could say is that it is going to be water, H₂O. Recall that oxygen gas acts as the final electron acceptor and that oxygen gas reacts with hydrogen ions to form water.

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. In terms of the totals for carbon dioxide, there are a total of 6 carbon dioxides produced. The original 6 carbon atoms found in glucose were all ultimately converted into 6 CO₂ molecules, which are ultimately exhaled from our bodies. In terms of the total amount of ATP, there are somewhere between 30 to 38 total ATPs produced in aerobic cellular respiration. In terms of FADH₂s, the total is going to be 2. In terms of NADHs, there's going to be a total of 10 NADHs produced.

This here concludes and fills out our entire table, which is just reviewing the total products for each stage of aerobic cellular respiration. Now that we've filled out this table, we can move on and apply some of the concepts we've reviewed in some practice problems. 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^–).

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.

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 while releasing 4 CO₂.

4. Oxidative Phosphorylation: This occurs in the inner mitochondrial membrane and produces 26-34 ATP through the electron transport chain and chemiosmosis.

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

During aerobic cellular respiration, a total of 30-38 ATP molecules are produced from one glucose molecule. This includes:

1. 2 ATP from Glycolysis

2. 2 ATP from the Krebs Cycle

3. 26-34 ATP from Oxidative Phosphorylation

The range in ATP production is due to variations in the efficiency of the electron transport chain and chemiosmosis.

What is the role of NADH and FADH₂ in aerobic cellular respiration?

NADH and FADH₂ are electron carriers that play a crucial role in aerobic cellular respiration. They are produced during Glycolysis, Pyruvate Oxidation, and the Krebs Cycle. These molecules carry high-energy electrons to the electron transport chain in the inner mitochondrial membrane. Here, the electrons are used to create a proton gradient that drives the production of ATP through oxidative phosphorylation. NADH contributes to the production of approximately 3 ATP per molecule, while FADH₂ contributes to about 2 ATP per molecule.

What happens to the carbon atoms in glucose during aerobic cellular respiration?

During aerobic cellular respiration, the 6 carbon atoms in glucose are ultimately converted into carbon dioxide (CO₂) and exhaled from the body. The process is as follows:

1. Glycolysis: Glucose (6 carbons) is broken down into 2 pyruvate molecules (3 carbons each).

2. Pyruvate Oxidation: Each pyruvate loses one carbon as CO₂, resulting in 2 acetyl CoA (2 carbons each) and 2 CO₂.

3. Krebs Cycle: The 2 acetyl CoA molecules are further broken down, releasing 4 CO₂.

In total, 6 CO₂ molecules are produced from one glucose molecule.

Where does oxidative phosphorylation occur and what is its significance in aerobic cellular respiration?

Oxidative phosphorylation occurs in the inner mitochondrial membrane. It is the final stage of aerobic cellular respiration and is significant because it produces the majority of ATP. During this process, electrons from NADH and FADH₂ are transferred through the electron transport chain, creating a proton gradient across the inner mitochondrial membrane. This gradient drives the synthesis of ATP through chemiosmosis, resulting in the production of 26-34 ATP molecules. This stage is crucial for the high efficiency of aerobic respiration.