Electron Transport - Video Tutorials & Practice Problems
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Overview
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Hi in this video we're gonna 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 gonna find it, what's it going to be doing? So the electron transport chain is a collection of different protein complexes that are particularly good at using energy from activated carriers. Which remember what way back debated carriers do they carry electrons and they use this energy to create a proton gradient that's eventually used for a. T. P synthesis. So, um if you remember back to our previous videos, generally, we talked about oxidative phosphor relation which couples electron um carrying 2 80p synthesis. And so the first stage of oxidative phosphor relation is the electron transport chain. So where does it happen while 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 N. I. D. H. And F. A. D. H. Two. And these donate their electrons to the electron transport chain. And when they do so they become in A. D. Plus and F. A. D. So you're gonna see these terms a lot, you've seen them a lot before in other pathways. But you're gonna see them a lot, especially in electron transport chain. So how are these activated carriers used? Well, the electron transport chain consists of a lot of different steps and in these steps that kind of each one? Um These electrons from these activated carriers actually are donated by the electric, 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 electrons are passed to 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 electronic sector. 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 haven't talked about but will that hydrogen is used to produce a T. P. So, this is the overview of the electron transport chain. Now let's move on
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concept
ETC Steps
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12m
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Hi. So now we're going to get more into the nitty gritty of the different steps of the electron transport chain. So the important part of this is that electrons from these carriers and A. D. H. And F. A. D. H. Two are transferred to different proteins in the electron transfer chain which then can use that energy from those electrons to do something. So let's go through each one of these and explore you know how are they interacting with the electrons and what are they doing with that energy? So the first is the N. A. D. H. D. Hydrogen. And so that takes an electron and it can take in an electron because it has this region called an iron sulfur center which has a lot of iron and sulfur in it. Which makes complete sense. And um these regions of this protein complex can accept and then donate electrons. And so when it does this so when it accepts the electrons and donates it that allows you that allows a complex to sort of take up some of that energy and do something else with it. So N A. D. H. D hydrogen is takes an electron via iron sulfur centers. Once that electrons there it wants to donate it it's taken some of that energy wants to donate it. And so when it donates it it donates to a carrier called ubiquity. No you may also see this as coenzyme Q. Depending on what book you're using um who your professor is. But they're essentially the same thing. And so you become known is a hydrophobic electron carrier found within the lipid bi layer. So not all electron carriers are found in the lipid bi layer, but this one is so that's the important thing. So N A. D. H. D. Hydrogen takes in an electron which binds to an iron sulfur center, eventually gives up that electron to ubiquity known or coenzyme Q. Which is found in the lipid bi layer. And in the process of doing this, it actually does something useful with that energy. And that useful action is moving for hydrogen into the inter membrane space. So this is kind of how we're creating this hydrogen or proton gradient, which is going to be used later on in other steps. So this is again the first thing that's happened now. Second, we're starting with the electron being carried by you pick one. Oh and so that you become known is sort of gives that electron to this complex called second A. D. Hydrogen is. And so what this does. It also came to iron sulfur center. So that's how it takes in that electrons. And it can transfer them so it takes in and binds to them through here and transfers them to F. A. D. And you pick one on. And so this is more of a smaller step. And you may actually not see this one in your book. And the reason is because it doesn't necessarily have that big of a function because it's not moving any hydrogen across the membrane, you may actually not see this one. And if you don't see it, don't worry about it, you don't need to memorize it. But some of you will hear about it. And so I just wanted to present it here. Um but obviously the two that I talked about so far, the most important one is gonna be this one. And all of you will need to know about that. So, let's look at this first step here. So here we have, it's going across the membrane. You first, do you remember what membrane this is right? This is gonna be the inner mitochondria membrane. And so what you see here is you have the first complex in A. D. H. D. Hydrogen Nous. And so N A. D. H comes in, It donates that electron. So here's this electron and then it becomes N A. D. Plus, it pumps four hydrogen protons across the membrane. And eventually this electron is transferred to coenzyme Q. Or ubiquity in unknown. Whichever way you see it from here, that electron is transferred to the second complex. And in the process of that it turns FAD. H two into FAD. And then that's going to be carried on to another step, which we'll talk about in just a second. So these are the first two steps. Now let's get to the 3rd and 4th. So the third one is really important. You're definitely gonna see this one, I need to know about it and this is the cytochrome BC one complex. So what this happens is it takes electrons from Ubiquity All. Um which is the reduced form of what we were talking about earlier. So when it um doesn't have electrons, that's called ubiquity. And when it does, it's called Ubiquity all. But it's the same thing just with them without electrons. And so it takes those electrons from and it transfers them to cytochrome C. And like I said before, different electron carriers are found in different places. So cytochrome C is found in the inter membrane space. Now the cytochrome Bc complex. BC one complex takes in electrons because it has a special group called a Heem group which combine iron and undergo iron oxidation. And that is what allows the complex to accept and donate electrons. So, before we talked about iron sulfur centers, this is the same thing. Just a different group. So this is a team group which can undergo iron oxidation which allows for the acceptance or donating of electrons. It's really important. It can move for hydrogen into the inter membrane space. Um for some reason they give this kind of movement a special name and you may see it's called the Q cycle. Um you may not see it that way if you don't I think that's easier. But if you do see the Q cycle. And you're like, what is that? Well, this this special movement. Um and some of you may actually see this complex um as the CO Q. H two cytochrome c. Reductase complex. Um and I really don't have a good explanation of why they don't just give everything one name. Um but instead they have to give everything six names so that it just confuses you. So whatever way you see your professor present this or whatever way your book presents it just use that way. But realize that all of these things we're talking about the same thing. Um Okay, so that's the third step and that's really important, definitely gonna see that. And then the fourth step is also really important and that is going to be the cytochrome C oxidase. So that eventually takes in those electrons and transfers them to oxygen. And so this is why we need to consume so much oxygen because this um complex actually needs all that oxygen to donate the electron stew. And so the cytochrome c oxidase, it takes an electron's because it has a special region called a copper center. So it has a bunch of copper copper that can accept and donate electrons. It also contains a heem group like the cytochrome bc one complex. And so um this one is unique in the fact that it can accept two electrons. And um so how it does this is it binds 02 really tightly and then it accepts two electrons and can break that bond. So now you have each like single oxygen and then what those pair of electrons um accepted by each single oxygen. So eventually it needs four electrons so that it can transfer those to each oxygen. And so for every reduced oxygen. So every time the oxygen split and associated with an electron it moves eight hydrogen into the inter membrane space. So it's a lot. But the important thing to realize is there's four complexes there. We talked about three different sort of centers that allow them to accept electrons. And the purpose of this is to move hydrogen across the membrane. So let me summarize this these last two and then we'll summarize the whole thing together. So first is here's the third complex complex three cytochrome bC one and you can see that it takes in electrons from the coenzyme Q. Or the big one all whatever you want to talk about, the electrons come in and that allows for the pumping of hydrogen across the membrane. Then eventually these electrons get passed along through other electron carriers to the final one cytochrome C oxidase. And those electrons come in here and again pump um hydrogen. Now the important part here is that it donates these electrons to oxygen at the end and for every oxygen, reduced oxygen there's eight hydrogen that are pumped into the membrane and two waters created. So if we're to review this now, I get that it's really, really complicated and really kind of annoying to memorize. So let me just review this so that we can get, you know, what's the most important, What do I exactly need to know? The first thing is that there are four complexes. So you need to know the four complexes and the order that they actually work in, that's going to be important. You're going to need to know which complexes actually pump hydrogen protons across the membrane into the, into the inter membrane space. Remember that? That's gonna be really important. It's also going to be important to know where this occurs if you remember, is the inner middle membrane. It's gonna be really, really, really important to understand the entire process of this last one where it takes has two oxygen's which then gets split each oxygen. So we have 02, it gets split into O and O. Each oxygen take in two electrons. And so each one of these ends up forming H 20. So you get to H20. And in that process eight protons will get transferred across the membrane. Um so it'll be four for this one, will be eight for this one and eight for this one as well. That's really important. And then also um you do need to know some of the activated carriers. So, for instance, this coenzyme Q. It's gonna be a really important thing you're gonna wanna know. Um It's also called Qanon um when it has electrons is called ubiquity all. Um and that's responsible for taking these electrons throughout. Pretty much this whole entire thing until you get to the cytochrome C. Which takes over as the activated carrier then. And then also you need to know different ways that how where the electrons are coming from. So in this first one the electrons are coming from the N A D. H. Then the electrons are coming from the coenzyme Q. Then the electrons are again continuing to go this way they're transferred to the cytochrome C oxidase and then they get transferred that way. So I get it's it's a lot for complexes different ways of interacting um with electrons and how they're transferred. But feel free review this a lot. Make sure you understand every single one of these steps and what is happening in between them. So with that let's now move on.
3
concept
Reduction Potentials
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4m
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Hi. So in this video we're gonna be talking about reduction potentials. And so um 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? So every single complex in the electron transport chain has a redox potential which you may see presented as um as you know this notation here. And so what this measures is the affinity of electrons. So how tightly the electrons are gonna bind to that complex and it does so in false. So high electron transfer 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 um reaction here where in A. D. H. Then loses an electron essentially. So uh it becomes um oxidized, It has this strong or this uh negative um redox potential of negative 3 20 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 are accepting electrons or oxygen becoming reduced to H- 208-16. So that's gonna 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, um so this is gonna be the redox potential and mila volts. But notice up here, we're starting with low to high, this is negative and this is positive and then this is gonna 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 N A. D. H. Comes in, it loses that electron um to the N A. D. H. D. Hydrogen so that it's gonna 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, um 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 in the one previous. So every time everyone is going down it's gonna 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 decided from BC one complex once that electron more than the ubiquitous own, saying for cytochrome c, cytochrome C oxidase and eventually when with 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.
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Problem
Problem
Which of the following is not a complex of the electron transport chain?
A
NADH dehydrogenase
B
Succinate dehydrogenase
C
Cytochrome C oxidase
D
ATP dephosphorylase
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Problem
Problem
Which of the following is the correct order of electrons through the electron chain?
