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. It utilizes electrons from NADH and FADH₂ through a series of oxidation-reduction reactions, creating a hydrogen ion concentration gradient in the intermembrane space. Oxygen acts as the final electron acceptor, forming water as a byproduct. This process is essential for generating ATP via oxidative phosphorylation, highlighting the interconnectedness of cellular respiration stages and the importance of the ETC in energy production.

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. The electron transport chain, or the ETC, is part of the fourth step of aerobic cellular respiration and consists of mitochondrial inner membrane proteins. These are proteins that are found in the inner mitochondrial membrane. If we take a look at our image down below, notice that this series of proteins embedded in the membrane represents the electron transport chain.

It's important to note that in this image, we're still looking at the mitochondria. The membrane you see here represents the inner mitochondrial membrane, and the membrane you see above represents the outer mitochondrial membrane. Of course, that means that the space below, within the inner mitochondrial membrane, is the mitochondrial matrix. Then we have the inner mitochondrial membrane and the space between the inner and outer mitochondrial membranes, which represents the intermembrane space. On the outside of the outer mitochondrial membrane, which you see above, represents the outside of the mitochondria but still inside the cell. This is the cytoplasm of the cell. We're examining the mitochondria here in the electron transport chain.

The electron transport chain is responsible for harnessing the energy of electrons, as its name implies. These electrons come from the electron carriers NADH and FADH₂, which have been generated throughout this process of aerobic cellular respiration. The energy of the electrons from NADH and FADH₂ is harnessed in a series of redox reactions or oxidation-reduction reactions.

Ultimately, the energy from these redox reactions is used to generate a hydrogen ion concentration gradient by pumping hydrogen ions into the intermembrane space between the inner and outer mitochondrial membranes of the mitochondria. Throughout our process of aerobic cellular respiration, glycolysis, pyruvate oxidation, and the Krebs cycle, we've generated a lot of electron carriers. A lot of NADHs and some FADH₂s as well. They take their electrons to the electron transport chain. Notice that the NADH is dropping off its electrons at the electron transport chain and becoming NAD⁺, the empty electron taxi cab, if you will. The FADH₂s are also dropping off their electrons at the electron transport chain but at a different position, and they become FAD. These electrons undergo a series of redox reactions where some proteins are losing electrons and others are gaining them, continually making their way through the electron transport chain.

The energy from those redox reactions is used to create a hydrogen ion concentration gradient where these hydrogen ions are being continuously pumped into the intermembrane space so that there is a high concentration of hydrogen ions in the intermembrane space. The electrons that are dropped off and move through the electron transport chain end up on what's known as the final electron acceptor. The final electron acceptor, as its name implies, is the final molecule that's going to accept the electron transport chain's electrons. During aerobic cellular respiration, the final electron acceptor is the molecule oxygen gas or O₂.

When oxygen gas serves as the final electron acceptor during aerobic cellular respiration, it ultimately interacts with some hydrogen ions to form water. Water is a byproduct of aerobic cellular respiration. If you go back and look at the overall chemical equation of aerobic cellular respiration, you'll see that water is a byproduct because oxygen is acting as the final electron acceptor, reacting with hydrogen ions to form water. This here really concludes our lesson on the electron transport chain, but what we're going to learn here is that the electron transport chain is really just part of the fourth step of aerobic cellular respiration. It builds the hydrogen ion concentration gradient, but then it's chemiosmosis that utilizes that hydrogen ion concentration gradient.

The electron transport chain goes hand in hand with chemiosmosis, which we're going to talk about in another video as we move forward in our course. But for now, this here concludes our introduction to the electron transport chain and how it's used to generate a hydrogen ion concentration gradient and how it uses oxygen gas as the final electron acceptor, and that oxygen gas will form water. We'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.

Remembering the ETC

So 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. In this cartoon, the electron transport chain is represented as an airport. Here, the 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 here. And then, of course, the space between the inner and outer membranes of the mitochondria will represent the intermembrane space, which, in this cartoon, you can think of as the international airspace.

And then, of course, down below, we have the matrix of the mitochondria, the innermost region of the mitochondria, now called here the drop-off matrix. You might recall that the NADH and FADH₂ electron carriers are these electron taxi cabs. Notice these little electron taxi cabs down below representing the NADH and FADH₂, highlighted in their reduced forms because they have electron passengers. They carry 2 electrons.

Notice that these are the full versions of the electron taxi cabs, and these electron carriers pick up and drop off electrons at this international airport, representing the electron transport chain. The NADH drops 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, which unfortunately, turn into lost luggage or lost packages. The 'p' in packages can hopefully remind you of the 'p' in protons.

All of these packages or luggage represent protons; thus, we have H⁺ inside them. There is a buildup of protons in the intermembrane space as the electrons are being dropped off in the electron transport chain. These electrons that have been dropped off at the electron transport chain will need to move through the electron transport chain. When you get to an airport, you have to go through customs, then security, and wait in line to get on the actual airplane.

These electrons make their way through the electron transport chain to the airplane, and once they're on the airplane, they go to their final destination. The final destination, representing the final electron acceptor, is the "big O" or Orlando here in our cartoon. Orlando represents oxygen, which is O₂. In Orlando, with many amusement parks and waterparks, you can think of a water slide here to remind you of the reaction of electrons with protons to form water. A little bit of water will be produced. Hopefully, this little cartoon can help you remember some of the steps and critical stages of the electron transport chain.

So, that being said, we'll be able to apply some concepts as we move forward and continue to learn more as well. See you all in our next video.

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

• 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.

Here’s what students ask on this topic:

What is the electron transport chain and where is it located?

The electron transport chain (ETC) is a series of protein complexes and other molecules embedded in the inner mitochondrial membrane. It plays a crucial role in aerobic cellular respiration, specifically in the fourth step. The ETC utilizes electrons from NADH and FADH₂ to create a hydrogen ion concentration gradient across the inner mitochondrial membrane. This gradient is essential for ATP production via oxidative phosphorylation. The final electron acceptor in the ETC is oxygen, which combines with hydrogen ions to form water as a byproduct.

How do NADH and FADH₂ contribute to the electron transport chain?

NADH and FADH₂ are electron carriers generated during earlier stages of aerobic cellular respiration, such as glycolysis, pyruvate oxidation, and the Krebs cycle. They transport high-energy electrons to the electron transport chain (ETC). NADH donates its electrons to the ETC at an earlier point than FADH₂. These electrons move through a series of redox reactions within the ETC, releasing energy that is used to pump hydrogen ions into the intermembrane space, creating a concentration gradient essential for ATP synthesis.

What is the role of oxygen in the electron transport chain?

Oxygen serves as the final electron acceptor in the electron transport chain (ETC). As electrons move through the ETC, they eventually reach oxygen, which combines with hydrogen ions to form water. This reaction is crucial because it ensures the continuous flow of electrons through the ETC, preventing a backup of electrons and allowing the process of ATP production to proceed efficiently. Without oxygen, the ETC would halt, and ATP synthesis would be severely impaired.

What is the significance of the hydrogen ion concentration gradient in the electron transport chain?

The hydrogen ion concentration gradient created by the electron transport chain (ETC) is essential for ATP production. As electrons move through the ETC, energy is released and used to pump hydrogen ions from the mitochondrial matrix into the intermembrane space. This creates a high concentration of hydrogen ions in the intermembrane space. The gradient represents potential energy, which is harnessed by ATP synthase to convert ADP and inorganic phosphate into ATP during chemiosmosis. This process is known as oxidative phosphorylation and is vital for cellular energy production.

What are redox reactions, and how do they function in the electron transport chain?

Redox reactions, or oxidation-reduction reactions, involve the transfer of electrons between molecules. In the electron transport chain (ETC), redox reactions occur as electrons are passed from one protein complex to another. During these reactions, one molecule is oxidized (loses electrons) while another is reduced (gains electrons). These redox reactions release energy, which is used to pump hydrogen ions into the intermembrane space, creating a concentration gradient. This gradient is essential for ATP production via oxidative phosphorylation.