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

The electron transport chain (ETC) is a crucial component of aerobic respiration, located in the inner mitochondrial membrane. It utilizes electrons from NADH and FADH₂ through redox reactions to create 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, linking the ETC to chemiosmosis, where the proton gradient drives ATP synthesis. Understanding these mechanisms is vital for grasping cellular energy production.

Electron Transport Chain

In this video, we're going to begin our lesson on the electron transport chain. And so the electron transport chain is commonly abbreviated as just the ETC. And so the electron transport chain or the ETC is part of the fourth step of aerobic cellular respiration. And really, the electron transport chain, or the ETC, consists of mitochondrial inner membrane proteins, and so these are going to be proteins that are found in the inner mitochondrial membrane. If we take a look at our image down below, notice that these series of proteins that you see 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. This membrane that you see here represents the inner mitochondrial membrane, and this membrane that you see up above represents the outer mitochondrial membrane. Of course, that means that this space that's down below here within the inner mitochondrial membrane is going to be the mitochondrial matrix. Then we have the inner mitochondrial membrane and then the space that's in between the inner and the outer mitochondrial membranes, which is basically this space right here. This space represents the intermembrane space. And then, of course, on the outside of the outer mitochondrial membrane, which is basically this blue space that you see up above here, this represents the outside of the mitochondria, but still inside of the cell. So it's going to be the cytoplasm of the cell. And so really, we're looking at the mitochondria here in the electron transport chain.

Now, it's important to note that the electron transport chain or the ETC is going to be responsible for harnessing the energy of electrons, as its name implies. And these electrons are going to come from the electron carriers NADH and FADH₂, which have been generated throughout this process of aerobic cellular respiration. And so the energy of the electrons from NADH and FADH₂ is going to be harnessed in a series of redox reactions or oxidation-reduction reactions. And ultimately, the energy of the electrons from these redox reactions is going to be 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. So, let's take a look at our image down below to clear some of this up. So, throughout our process of aerobic cellular respiration and glycolysis, pyruvate oxidation, and the Krebs cycle, we've generated a lot of electron carriers. A lot of NADHs and some FADH₂s as well. And these electron carriers are going to take their electrons to the electron transport chain that we have here. And so notice that the NADH is dropping off its electrons here at the electron transport chain and becoming NAD⁺, the empty electron taxi cab if you will. And the FADH₂s are also dropping off their electrons at the electron transport chain, but just at a different position and they become FADs. And so, what you'll notice is that these electrons are getting dropped off at the electron transport chain and they undergo a series of redox reactions or oxidation reduction reactions where some proteins are going to be gaining electrons and they're going to be losing electrons and others will be gaining them and they'll continually make their way through the electron transport chain through a series of redox reactions. So the electrons are moving through. They get dropped off, the electrons get dropped off, and then the electrons move their way through the electron transport chain through a series of redox reactions. And the energy from those redox reactions is going to be 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.

Now notice here that the electrons that are being dropped off and moving through the electron transport chain those electrons end up on what's known as the final electron acceptor. And so notice up above in our text we're defining the final electron acceptor. And so the final electron acceptor, as its name implies, is the final molecule that's going to accept the electron transport chain's electrons. And so during aerobic molecule oxygen gas or O₂. And so when oxygen is serving as the final electron acceptor during aerobic cellular respiration, it's ultimately going to interact with some hydrogen ions to form water. And water is going to be a byproduct of aerobic cellular respiration. And when you go back and look at the overall chemical equation of aerobic cellular respiration, you'll see that water is going to be a byproduct, and that's because oxygen is acting as the final electron acceptor reacting with hydrogen ions to form water. And so let's take a look at our image down below to clear some of this up, and once again notice that all these electrons that are being dropped off at the electron transport chain are going to go and make their way through the electron transport chain, and they end up on the final electron acceptor which is going to be oxygen gas. And so notice that we have O₂ or oxygen gas here, which is the final electron acceptor. And then this final electron acceptor, oxygen gas, is going to react with some hydrogen ions to produce water. And once again, over here we have H₂O, which is water. This is why water is said to be a byproduct of aerobic cellular respiration.

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 because, really, it is step 4a and there is a step 4b. And that's because the electron transport chain builds the hydrogen ion concentration gradient but then it's chemiosmosis. And so 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 the final electron acceptor, I mean oxygen gas, as the final electron acceptor, and that oxygen gas will form water. So, 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. And so here in this cartoon, the electron transport chain is represented as an airport. And so you can see that this highlighted region represents the inner mitochondrial membrane which is again this airport. And so 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 is going to represent the intermembrane space which here in this cartoon you can think of as the international airspace. And then, of course, down below what we have is the matrix of the mitochondria which is the innermost region of the mitochondria and so we're calling it here the drop-off matrix. And so you might recall that the NADH and _FADH2 electron carriers can be thought of as these electron taxicabs. And so notice that we have these little electron taxicabs down below representing the NADH and _FADH2. And so notice that these highlighted versions of these taxicabs are in their reduced forms because they have electron passengers. They carry ₂ electrons. And so notice that this is the full version of the electron taxicab and these electron carriers, we know that they can pick up and drop off electrons and so here these electron carriers are dropping off electrons at this international airport which is again representing the electron transport chain. So, the electron carriers are dropping off electrons at the electron transport chain. The NADH drop off their electrons at an earlier region than the _FADH twos 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 get turned into lost luggage or lost packages. And so the 'p' in packages can hopefully remind you of the 'p' in protons. And so what this means is that all of these packages or luggage is going to represent protons, which is why we have h+ inside of them. And so we know that there's going to be a buildup of protons in the intermembrane space as these electrons are being dropped off in the electron transport chain. And so 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. And we know that when you get to an airport there are different steps. You have to go through customs and then you have to get through security and then you have to wait in line to get on the actual airplane. And so these electrons are going to make their way through the electron transport chain to get to this airplane here 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 electron acceptor which we know is oxygen which is O₂. And so Orlando here represents O₂ and we know that in Orlando there are many different types of amusement parks and water parks and so 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 and so you can think of a water slide here to remind you of that idea and so we know that a little bit of water will be produced. And so hopefully, this little cartoon here can help you with remembering some of the steps and critical steps 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. 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.

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 respiration by transferring electrons from NADH and FADH₂ to oxygen through a series of redox reactions. This process creates a hydrogen ion (proton) gradient across the inner mitochondrial membrane, which is essential for ATP production via oxidative phosphorylation. The ETC is located in the inner mitochondrial membrane, with the intermembrane space and the mitochondrial matrix on either side.

How does the electron transport chain contribute to ATP production?

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

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 donate electrons to the ETC, which are then transferred through a series of protein complexes and other molecules. NADH donates its electrons to Complex I, while FADH₂ donates its electrons to Complex II. The transfer of electrons through the ETC releases energy, which is used to pump protons into the intermembrane space, creating a proton gradient. This gradient is essential for ATP production via oxidative phosphorylation.

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

Oxygen (O₂) is the final electron acceptor in the electron transport chain (ETC). Its role is crucial because it accepts the electrons at the end of the ETC, allowing the chain to continue functioning. When oxygen accepts electrons, it combines with hydrogen ions (protons) to form water (H₂O) as a byproduct. This reaction is essential for maintaining the flow of electrons through the ETC, which in turn sustains the proton gradient necessary for ATP production via oxidative phosphorylation.

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

The hydrogen ion (proton) 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 protons from the mitochondrial matrix into the intermembrane space, creating a high concentration of protons in the intermembrane space. This gradient represents potential energy, which is harnessed by ATP synthase. Protons flow back into the matrix through ATP synthase, driving the synthesis of ATP from ADP and inorganic phosphate (P_i). This process is known as chemiosmosis.