Hi. In this video, we're going to be talking about the electron transport chain. So first, I want to just do an overview of what the electron transport chain is, where you're going to find it, what it's going to be doing. The electron transport chain is a collection of different protein complexes that are particularly good at using energy from activated carriers, which, remember, what do activated carriers do? They carry electrons, and they use this energy to create a proton gradient that's eventually used for ATP synthesis. So, if you remember, back to our previous videos, generally, we talked about oxidative phosphorylation, which couples electron carrying to ATP synthesis. And so, the first stage of oxidative phosphorylation is the electron transport chain. So where does it happen? Well, the electron transport chain is going to be embedded in the inner mitochondrial membrane. And the activated carriers that are super important that carry the electrons, are NADH and FADH2. And, these donate their electrons to the electron transport chain, and when they do so, they become NAD+ and FAD. So you're going to see these terms a lot. You've seen them a lot before in other pathways, but you're going to see them a lot especially in the electron transport chain. So how are these little activated carriers used? The electron transport chain consists of a lot of different steps. And in these steps, it kind of at each one, these electrons from these activated carriers actually are donated by the activated carriers to the electron transport chain at different steps. And those high-energy electrons then can flow through or go through different protein complexes, which then can capture the energy and transfer that to something useful for the cell. So, eventually, all these different, you know, electrons are passed through the electron transport chain that are used their energy is used to do something productive. But eventually, it has to get to the last one. And so the last electron acceptor, so the last thing that accepts an electron from an activated carrier, is oxygen, and that is actually going to be used to form water. So if we're looking at an overview here of the electron transport chain, you can see there, so we have the outer membrane and we have our inner membrane. So you can see that it is embedded in this inner membrane here. And there's a variety of different protein complexes, but eventually these, activated carriers come in, donate their electrons. That electron is then used to pump hydrogen across the membrane. And eventually, in the second step, which we have talked about, but will, the hydrogen is used to produce ATP. So this is the overview of the Electron Transport Chain, now let's move on.
Electron Transport: Study with Video Lessons, Practice Problems & Examples
Created using AIThe electron transport chain (ETC) is a series of protein complexes located in the inner mitochondrial membrane that facilitate oxidative phosphorylation. Activated carriers, NADH and FADH2, donate electrons, creating a proton gradient essential for ATP synthesis. Key complexes include NADH dehydrogenase, cytochrome bc1, and cytochrome c oxidase, each with distinct roles in electron transfer and proton pumping. The process culminates in oxygen acting as the final electron acceptor, forming water and driving ATP production through chemiosmotic coupling.
Overview
Video transcript
ETC Steps
Video transcript
Hi. So now we're going to get more into the nitty-gritty of the different steps of the electron transport chain. The important part of this is that electrons from these carriers, NADH and FADH2, are transferred to different proteins in the electron transfer chain, which then can use that energy from those electrons to do something. Let's go through each one of these and explore how they are interacting with the electrons and what they are doing with that energy. The first is the NADH dehydrogenase, which takes in an electron because it has a region called an iron-sulfur center, which contains a lot of iron and sulfur. These regions of this protein complex can accept and then donate electrons. When it accepts the electrons and donates them, that allows the complex to take up some of that energy and do something else with it. So NADH dehydrogenase takes in electrons via iron-sulfur centers. Once that electron is there, it wants to donate it. It's taken some of that energy. It wants to donate it. When it donates it, it donates to a carrier called ubiquinone. You may also see this as coenzyme Q, depending on what book you're using or who your professor is, but they're essentially the same thing. Ubiquinone is a hydrophobic electron carrier found within the lipid bilayer. Not all electron carriers are found in the lipid bilayer, but this one is. So, NADH dehydrogenase takes in an electron, which binds to an iron-sulfur center, eventually, gives up that electron to ubiquinone or coenzyme Q, which is found in the lipid bilayer. In the process of doing this, it actually does something useful with that energy, and that useful action is moving 4 hydrogens into the intermembrane space. This is how we're creating this hydrogen or proton gradient, which is going to be used later in other steps. This is, again, the first thing that has happened.
Now second, we're starting with the electron being carried by ubiquinone. That ubiquinone gives that electron to this complex called succinate dehydrogenase. It also contains an iron-sulfur center, so that's how it takes in the electrons and can transfer them. It takes in and binds to them through here and transfers them to FAD and Ubiquinone. This is more of a smaller step, and you may not see this one in your book because it does not have a significant function as it's not moving any hydrogen across the membrane. If you don't see this one, don't worry about it. You don't need to memorize it, but some of you will hear about it, and I just wanted to present it here.
The third one is the cytochrome b-c1 complex, which is really important. You're definitely going to see this one. It takes electrons from ubiquinol, which is the reduced form of what we were talking about earlier. So, ubiquinone without electrons is called ubiquinone, and with electrons, it's called ubiquinol. The cytochrome b-c1 complex takes in electrons because it has a special group called a heme group which can bind iron and undergo iron oxidation. This allows the complex to accept and donate electrons. It can move 4 hydrogens into the intermembrane space. This kind of movement is sometimes referred to as the Q cycle. This complex is also known as the CoQH2 cytochrome c reductase complex. Different names are used, but they refer to the same thing.
The fourth step involves the cytochrome c oxidase, which takes in those electrons and transfers them to oxygen. This is why we need to consume so much oxygen because this complex needs all that oxygen to donate the electrons to. The cytochrome c oxidase has a special region called a copper center, which contains a bunch of copper that can accept and donate electrons. It also contains a heme group like the cytochrome b-c1 complex. This one is unique in that it can accept 2 electrons, binding O2 tightly, and then it accepts 2 electrons and can break that bond, so now you have each single oxygen. Then, with those pair of electrons accepted by each single oxygen, it needs 4 electrons in total, so that it can transfer those to each oxygen. For every oxygen reduced, 8 hydrogens are pumped into the intermembrane space, and 2 waters are created. This is a lot, but the important thing to realize is there are 4 complexes. We talked about 3 different centers that allow them to accept electrons, and the purpose of this is to move hydrogens across the membrane.
Reduction Potentials
Video transcript
Hi. So, in this video, we're going to be talking about reduction potentials. And so, the reason we're talking about this here is because the electron transport chain is ordered in a specific way because of different reduction potentials. So what do I mean by that? Every single complex in the electron transport chain has a redox potential, which you may see presented as this notation here. And so what this measures is the affinity of electrons; potentials are strong reducing agents. So what does that mean? Well, that means that they are going to accept electrons very easily. Whereas low electron transfer potentials are strong oxidizing agents, so they're going to be able to donate electrons easily. And so the electron transport chain is arranged in order of increasing reduction potentials. So, for instance, this reaction here, where NADH then loses an electron, essentially, and becomes oxidized, it has this strong or this negative redox potential of negative 320 volts. So if we were to say what is this a low or high? Well, this is going to be a low electron transfer potential because it's negative. I mean, it's very clearly very low. Whereas the oxygen, the sort of taking up of electrons or accepting electrons or oxygen becoming reduced to H2O at 816 volts, that's going to be really high electron transfer potential. So if you remember back to the steps of the electron transfer chain, this reaction actually happens first and this reaction actually happens last. So order of increasing redox potential. So if we look here at this graph, so this is going to be the redox potential in millivolts, but notice up here we're starting with low to high. This is negative and this is positive. And then this is going to be the direction of electron flow throughout the electron transport chain. So what happens if we're just to summarize the electron transport chain? We have NADH comes in, it loses that electron to the NADH dehydrogenase, so that's going to be a low redox potential. And then, as we go through each of these steps, you can see that each one of these complexes is increasing in its redox potential until it gets down here to the very last step, which is oxygen, which has this really high redox potential. So, this is why all of the steps have to happen in the way that they do is because the electrons are transferred to the next complex because that complex is going to be more likely to accept those electrons than the one previous. So every time everyone is going down, it's going to be more likely to accept electrons. And so whenever this complex has this electron, it wants to give it to something. So, of course, it's going to give it to something that wants that electron more. And just that just so happens to be this carrier, and the same thing happens on and on. So the cytochrome bc1 complex wants that electron more than the ubiquinone. Same for cytochrome c, cytochrome c oxidase, and eventually, you end with the oxygen, which really really really wants those electrons. So this is why the electron transport chain is ordered in the way that it is. So with that, let's now turn the page.
Which of the following is not a complex of the electron transport chain?
Which of the following is the correct order of electrons through the electron chain?
Here’s what students ask on this topic:
What is the electron transport chain and where does it occur?
The electron transport chain (ETC) is a series of protein complexes located in the inner mitochondrial membrane. It plays a crucial role in oxidative phosphorylation, where activated carriers like NADH and FADH2 donate electrons to the chain. These electrons pass through various complexes, creating a proton gradient across the membrane. This gradient is essential for ATP synthesis. The final electron acceptor in the ETC is oxygen, which combines with electrons and protons to form water. This process is vital for cellular respiration and energy production in eukaryotic cells.
Created using AIWhat are the main protein complexes involved in the electron transport chain?
The main protein complexes involved in the electron transport chain are:
- NADH Dehydrogenase (Complex I): Accepts electrons from NADH and transfers them to ubiquinone, pumping protons across the membrane.
- Succinate Dehydrogenase (Complex II): Transfers electrons from FADH2 to ubiquinone but does not pump protons.
- Cytochrome bc1 Complex (Complex III): Transfers electrons from ubiquinol to cytochrome c, pumping protons across the membrane.
- Cytochrome c Oxidase (Complex IV): Transfers electrons to oxygen, forming water and pumping protons across the membrane.
Created using AIHow does the electron transport chain create a proton gradient?
The electron transport chain creates a proton gradient by transferring electrons through a series of protein complexes embedded in the inner mitochondrial membrane. As electrons move from one complex to the next, energy is released. This energy is used by certain complexes (Complex I, III, and IV) to pump protons (H+) from the mitochondrial matrix into the intermembrane space. This creates a high concentration of protons in the intermembrane space and a low concentration in the matrix, establishing an electrochemical gradient known as the proton motive force. This gradient is essential for ATP synthesis.
Created using AIWhat is the role of oxygen in the electron transport chain?
Oxygen plays a critical role as the final electron acceptor in the electron transport chain. At the end of the chain, electrons are transferred to oxygen by the cytochrome c oxidase complex (Complex IV). Oxygen then combines with these electrons and protons (H+) to form water (H2O). This step is essential because it ensures the continuous flow of electrons through the chain, preventing a backup of electrons and allowing the process of oxidative phosphorylation to proceed efficiently. Without oxygen, the electron transport chain would halt, and ATP production would cease.
Created using AIWhat is the significance of reduction potentials in the electron transport chain?
Reduction potentials are crucial in the electron transport chain because they determine the order in which electrons are transferred between complexes. Each complex has a specific redox potential, which measures its affinity for electrons. Complexes with lower redox potentials (more negative) donate electrons to those with higher redox potentials (more positive). This ordered transfer ensures that electrons flow efficiently from NADH and FADH2 to oxygen. The increasing redox potential from Complex I to Complex IV drives the movement of electrons and the associated proton pumping, ultimately leading to ATP synthesis.
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