Electron Transport Chain - Online Tutor, Practice Problems & Exam Prep

The electron transport chain (ETC) is a crucial component of aerobic cellular respiration, located in the inner mitochondrial membrane in eukaryotes and the plasma membrane in prokaryotes. It utilizes electron carriers like NADH and FADH₂ to facilitate redox reactions, generating a hydrogen ion gradient. This gradient is essential for ATP production via chemiosmosis. Oxygen acts as the final electron acceptor, forming water as a byproduct. Understanding the ETC is vital for grasping energy production in cells and the overall process of cellular respiration.

Electron Transport Chain

In this video, we're going to begin our lesson on the electron transport chain. The electron transport chain is commonly abbreviated as just the ETC. It is part of the fourth step of aerobic cellular respiration and consists of mitochondrial inner membrane proteins. These proteins are found in the inner mitochondrial membrane. If we take a look at our image below, notice that these series of proteins embedded in the membrane represent the electron transport chain. It's important to note that we are still looking at the mitochondria. This membrane that you see here represents the inner mitochondrial membrane, and this membrane that you see above represents the outer mitochondrial membrane. This space that's down below within the inner mitochondrial membrane is the mitochondrial matrix. The space that's in between the inner and the outer mitochondrial membranes is the intermembrane space. On the outside of the outer mitochondrial membrane, this blue space up above, represents the outside of the mitochondria but still inside of the cell, or the cytoplasm of the cell.

The electron transport chain, or ETC, harnesses the energy of electrons, as its name implies. These electrons come from the electron carriers NADH and FADH₂, which have been generated throughout the process of aerobic cellular respiration. The energy of the electrons from NADH and FADH₂ is harnessed in a series of redox reactions, and ultimately this energy is used to generate a hydrogen ion concentration gradient by pumping hydrogen ions into the intermembrane space. Through the process of aerobic cellular respiration, glycolysis, pyruvate oxidation, and the Krebs cycle, we've generated a lot of electron carriers. NADH and FADH₂ take their electrons to the electron transport chain, where NADH drops off its electrons and becomes NAD⁺, and FADH₂ does the same at a different position, becoming FAD. These electrons undergo a series of redox reactions, where some proteins lose electrons and others gain them, continually moving through the electron transport chain through these reactions.

The electrons end up on what's known as the final electron acceptor. The final electron acceptor, during aerobic cellular respiration, is molecular oxygen gas, or O₂. Oxygen, serving as the final electron acceptor, ultimately interacts with some hydrogen ions to form water, H₂O. Water is a byproduct of aerobic cellular respiration because oxygen acts as the final electron acceptor, reacting with hydrogen ions to form water. This concludes our lesson on the electron transport chain, which is primarily part of the fourth step of aerobic cellular respiration, involving the construction of the hydrogen ion concentration gradient. The ETC goes hand in hand with chemiosmosis, which we will discuss in another video. But for now, this concludes our introduction to the electron transport chain and how it uses oxygen gas as the final electron acceptor to form water. We will be able to get some practice applying these concepts as we move forward in our course. So, I'll see you all in our next video.

Remembering the ETC

Before we move on and talk about chemiosmosis, in this video we're going to share with you a very interesting diagram of this cartoon that can hopefully help you with remembering the electron transport chain or the ETC. And so here in this cartoon, the electron transport chain is represented as an airport. You can see that here this highlighted region represents the inner mitochondrial membrane which is again this airport. Notice that up above, what we have is the outer mitochondrial membrane and you can see we're labeling the cytoplasm as this region at the very top. And then, of course, the space between the inner and outer membranes of the mitochondria is going to represent the intermembrane space, which in this cartoon you can think of as the international airspace. Down below, what we have is the matrix of the mitochondria, which is the innermost region of the mitochondria, so we're calling it the drop-off matrix.

You might recall that the NADH and FADH₂ electron carriers can be thought of as these electron taxicabs. Notice that we have these little electron taxicabs down below representing the NADH and FADH₂. These highlighted versions of the taxicabs are in their reduced forms because they have electron passengers. They carry 2 electrons. These electron carriers, we know, can pick up and drop off electrons; thus, these carriers are dropping off electrons at this international airport, representing the electron transport chain. The NADH drop off their electrons at an earlier region than the FADH₂s which drop off their electrons at a different region of this airport, or a different region of the electron transport chain.

Now, these electron passengers are going to have luggage, or packages that they carry with them, and unfortunately, it turns out that the luggage or the packages that these electrons have are going to be turned into lost luggage or lost packages. The "p" in packages can hopefully remind you of the "p" in protons. So, this means that all of these packages or luggage is going to represent protons, which is why we have H⁺ inside of them. There's going to be a buildup of protons in the intermembrane space as these electrons are being dropped off at the Electron Transport Chain.

These electrons that have been dropped off at this Electron Transport chain or at this airport are going to need to move through the electron transport chain or move through the airport. We know that when you get to an airport, there are different steps: you have to go through customs, then you have to get through security, and then you have to wait in line to get on the actual airplane. These electrons are going to make their way through the electron transport chain to get to this airplane, and once they're on the airplane, we know that they're going to go to their final destination and the final destination represents the final electron acceptor, which we know is going to be the big "O" and the big "O" is Orlando here in our cartoon, and of course, the big "O", or Orlando, represents our final electronic acceptor, which we know is oxygen which is O₂. In Orlando, there are many different types of amusement parks and water parks, and you can think of a water park in all of these water slides, and we know that once these electrons have gone to their final electron acceptor, oxygen, that they are going to react with protons to form water, so you can think of a water slide here to remind you of that idea, and we know that a little bit of water will be produced.

Hopefully, this little cartoon here can help you with remembering some of the steps and critical steps of the electron transport chain. That being said, we'll be able to apply some concepts as we move forward and continue to learn more as well. So see you all in our next video.

In the electron transport chain, the final electron acceptor is:

a) H₂O.

b) CO₂.

c) H₂O.

d) O₂.

e) NAD⁺.

• A. H₂O.
• B. CO₂.
• C. O₂.
• D. NAD⁺.

Which of the following events takes place in the electron transport chain?

a) The breakdown of glucose into six carbon dioxide molecules.

b) The breakdown of NADH and FADH₂ to carbon dioxide.

c) Harnessing energy from high-energy electrons derived from glycolysis, pyruvate oxidation, and the Krebs cycle.

d) Substrate-level phosphorylation.

• A. The breakdown of glucose into six carbon dioxide molecules.
• B. The breakdown of NADH and FADH2 to carbon dioxide.
• C. Harnessing energy from high-energy electrons derived from glycolysis, pyruvate oxidation, and the Krebs cycle.
• D. Substrate-level phosphorylation.

Electron Transport Chain in Prokaryotes

In this video, we're going to briefly cover the electron transport chains in prokaryotes. And so prokaryotic electron transport chains are actually really similar to eukaryotic electron transport chains, except that they are found in a different location within the cell. Instead of being found in the inner mitochondrial membrane, like the eukaryotic electron transport chains are, the prokaryotic electron transport chains are actually found in the cell's plasma membrane. This is because prokaryotic cells do not have mitochondria or membrane-bound organelles.

Below, we're showing you an example image of the electron transport chain in a gram-negative bacteria, E. coli. Notice that the membrane you see here is not the membrane of the inner mitochondrial membrane. Instead, this is the inner membrane of the gram-negative cell. It's literally the plasma membrane, the cell's membrane. It's not the membrane of an organelle. The inside of the cell here represents the cell's cytoplasm, whereas the area above the membrane would represent the periplasm, basically the space between the cell's inner membrane and the peptidoglycan layer found on the outside.

The electron transport chain is actually fairly similar. The proteins might be different, and there might be some slight differences, but overall, the effect is quite similar. Electron carriers drop off electrons, and proteins within the electron transport chain create a hydrogen ion gradient. This hydrogen ion gradient can be used to generate ATP by ATP synthase, which isn't shown in this image. Ultimately, oxygen gas can still be the final electron acceptor and can react to create water. The biggest takeaway here is that the location of the electron transport chain in prokaryotes is different from that in eukaryotes. Prokaryotic electron transport chains are found in the cell's plasma membrane, whereas eukaryotic electron transport chains are found in the mitochondria for cellular respiration.

This concludes our brief lesson on this topic. We'll be able to get some practice applying this knowledge as we move forward and learn more. I'll see you all in our next video.

TRUE or FALSE:Electron transport in eukaryotes occurs in the inner mitochondrial membrane.

• A. True.
• B. False.

Here’s what students ask on this topic:

What is the electron transport chain and where is it located in eukaryotic cells?

The electron transport chain (ETC) is a series of protein complexes and other molecules embedded in the inner mitochondrial membrane of eukaryotic cells. It plays a crucial role in aerobic cellular respiration, facilitating the transfer of electrons from electron carriers like NADH and FADH₂ through a series of redox reactions. This process generates a hydrogen ion gradient across the inner mitochondrial membrane, which is essential for ATP production via chemiosmosis. The final electron acceptor in the ETC is oxygen, which combines with hydrogen ions to form water as a byproduct.

How does the electron transport chain contribute to ATP production?

The electron transport chain (ETC) contributes to ATP production by creating a hydrogen ion (H⁺) gradient across the inner mitochondrial membrane. As electrons are transferred through the ETC, energy is released and used to pump H⁺ ions from the mitochondrial matrix into the intermembrane space. This creates a high concentration of H⁺ ions in the intermembrane space. The resulting electrochemical gradient drives H⁺ ions back into the matrix through ATP synthase, a process known as chemiosmosis. The flow of H⁺ ions through ATP synthase provides the energy needed to convert ADP and inorganic phosphate (P_i) into ATP.

What are the roles of NADH and FADH₂ in the electron transport chain?

NADH and FADH₂ are crucial electron carriers in the electron transport chain (ETC). They are produced during earlier stages of aerobic cellular respiration, such as glycolysis, pyruvate oxidation, and the Krebs cycle. NADH and FADH₂ donate electrons to the ETC. NADH transfers its electrons to the first protein complex in the ETC, while FADH₂ donates its electrons to a later point in the chain. The electrons then move through a series of redox reactions, releasing energy that is used to pump hydrogen ions (H⁺) into the intermembrane space, creating a gradient essential for ATP production.

What is the final electron acceptor in the electron transport chain and what is its significance?

The final electron acceptor in the electron transport chain (ETC) is oxygen (O₂). Oxygen's role is crucial because it ensures the continuation of electron flow through the ETC. As electrons reach the end of the chain, they are transferred to oxygen, which then combines with hydrogen ions (H⁺) to form water (H₂O). This reaction is essential for maintaining the flow of electrons and preventing a backup in the ETC. Without oxygen as the final electron acceptor, the ETC would halt, stopping ATP production and leading to cellular energy deficiency.

How does the electron transport chain differ between prokaryotes and eukaryotes?

While the fundamental process of the electron transport chain (ETC) is similar in both prokaryotes and eukaryotes, the primary difference lies in its location. In eukaryotes, the ETC is located in the inner mitochondrial membrane. In contrast, prokaryotes, which lack mitochondria, have their ETC embedded in the plasma membrane. Despite this difference, both types of cells use the ETC to create a hydrogen ion gradient that drives ATP production via chemiosmosis. Additionally, the specific proteins and complexes involved in the ETC may vary between prokaryotes and eukaryotes.