0:00 In this video, we're going to talk about ox area phosphorylation. 0:23 Also known as the electron transport chain. 0:27 Before I begin, please know that the actual 0:31 phosphorylation process, the electron transport chain, is not fully understood 0:36 and new stuff 0:37 keeps coming up in the science world. 0:40 So yeah, just remember that. 0:43 So some things might be left blank, but know that this is the overall sort of 0:49 picture in 0:50 a way. 0:51 So we begin here, inside the cell. 0:53 Here are the two mitochondrial membranes. 0:55 Here's a cytoplasm. 0:56 The intermembrane space and the matrix inside the mitochondria. 1:00 And so if this were the mitochondrial membrane, the other would be the intermem 1:06 brane. 1:07 Now the electron transport chain consists of four important structural proteins 1:14 known 1:15 as the four complexes, complex one, complex two, complex three, and complex 1:20 four. 1:21 Also in the oxidative phosphorylation process, we cannot miss out the one 1:26 important enzyme 1:27 which creates the ATP known as ATP synthase over here. 1:32 ATP synthase is sometimes known as the complex five, but for now we'll just 1:38 call it ATP synthase. 1:39 Now the electron transporters, the four complexes each have names. 1:46 Complex one is known as NADH dehydrogenase. 1:50 Complex two, succidate dehydrogenase, complex three, cytochrome C-oxy reductase 1:55 , and complex 1:56 four is known as cytochrome oxidase. 2:00 And lastly, complex five is known mainly as ATP synthase. 2:05 Okay, now the two important substances to begin the oxidative phosphorylation 2:11 process 2:12 are the electron carriers from glycolysis, from the preparatorysep and the Kre 2:18 ms cycle. 2:19 The total amount of electron carriers from each of these processes, we have our 2:24 10 NADHs 2:26 and two FADH2s. 2:28 So 10 NADHs and two FADH2s are the total amount of electron carriers we obtain 2:33 from glycolysis, 2:34 the preparatorysep and Krems cycle. 2:36 All right, knowing this piece of information, we have to understand what 2:39 electron transport 2:40 chain is and what oxidative phosphorylation is. 2:44 Essentially, what electron transport chain is is essentially where an electron 2:48 is being 2:49 transported through this chain. 2:52 This chain is complex one, two, three, and four. 2:55 And so these electrons, where do they come from? 2:58 They come from the electron carriers, the 10 NADHs and the two FADH2s, which 3:02 were obtained 3:03 from glycolysis, preparatorysep and Krems cycle. 3:07 So the electrons are obtained from these electron carriers, and then they 3:11 travel through the 3:12 electron transport chain, where the electrons, then their final destination, 3:17 will be oxygen, 3:18 which will help reduce oxygen to form H2O. 3:21 So oxygen is known as a final electron acceptor. 3:25 And then during this process as well as when the electrons are moving through 3:29 this electron 3:29 transport chain, hydrogen ions are being pumped out. 3:33 And with these hydrogen ions, ATP is made. 3:37 So that was just a brief overview. 3:39 Now let's begin with NADH, the electron carrier NADH and let's look at only one 3:45 NADH and its 3:46 influence and what happens to it and its electrons through oxidative phosphory 3:51 lation. 3:52 And we begin with NADH through complex one. 3:55 Some important structures within complex one is a flavon mononucleotide, FMN, 3:59 and also 4:00 a series of iron centers, as well as an iron sulfur center, N2 over here. 4:07 Before we continue with complex one, another important protein structure, which 4:10 floats 4:11 in an inner mitochondrial membrane, is ubiquinin, or also known as coenzyme Q10 4:18 . 4:18 And it, its purpose is to carry electrons as well through these different 4:23 complexes, 4:24 because it is a mobile protein, whereas the complexes are stationary. 4:29 So let's go back to complex one, NADH dehydrogenase. 4:33 Let us follow the electrons and the fate of one NADH plus H molecule, which is 4:39 an electron 4:40 carrier. 4:41 So NADH dehydrogenase will oxidize NADH plus H to form NAD. 4:47 And through this process, it will obtain two electrons. 4:50 The two electrons will be firstly given to flavon mononucleotide, FMN here, and 4:57 then 4:58 the two electrons will pass through a series of iron centers, like so, where it 5:02 will stop 5:03 at the iron sulfur center. 5:05 And next what happens is that the two electrons will create a proton gradient. 5:09 It will bring in two hydrogen ions from the matrix, and then we'll bind to 5:15 ubiquinin. 5:16 And as it binds to ubiquinin, it will reduce ubiquinin to make ubiquinol. 5:21 And so ubiquinol has two hydrogens, so we write it up as QH2. 5:26 And also during this process, the electrons, as it travels through, will pump 5:32 up, will 5:32 pump four hydrogen ions from the matrix into the intermembrane space, like so. 5:39 Now ubiquinol is essentially carrying the two electrons, but it's not as 5:45 electrons, 5:46 it's just as hydrogen. 5:47 So ubiquinol will travel through the inner mitochondrial membrane with the two 5:51 electrons, 5:52 right? 5:53 And it will travel through. 5:54 It will associate with complex two, but it will associate with complex three. 6:00 Now, let's look at complex three. 6:03 Complex three has a few important subunits. 6:07 Three important structures within it. 6:11 One is called cytochrome B, the other is called resky iron sulfur proteins, and 6:16 the 6:16 other one is called cytochrome C1. 6:19 The most important structure, however, is cytochrome C, which is a mobile 6:24 protein in 6:25 the intermembrane space, and is attached to the complex three. 6:31 Complex three cytochrome C-oxy reductase will essentially oxidize ubiquinol to 6:35 ubiquinin, 6:36 and it will essentially steal the two electrons from it. 6:40 And it will pass the two electrons to cytochrome C. 6:43 So now the cytochrome C has two electrons, as to say. 6:46 And also during this process, as the electrons are passing through, complex 6:52 three will also 6:53 pump four hydrogen ions from the matrix into the intermembrane space. 6:59 Next cytochrome C will travel through the intermembrane space and attach to, 7:03 and bind 7:03 to essentially complex four, the cytochrome oxidase, and it will attach to one 7:12 of the subunits 7:13 of complex four. 7:15 Complex four consists of three main subunits, one, two, and three, simple 7:19 enough. 7:20 And as it gives the two electrons to complex four, complex four cytochrome oxid 7:27 ase will 7:28 then, with the two electrons, reduce oxygen, half an oxygen, which is 7:34 essentially one oxygen 7:35 molecule, with two hydrogen ions to form one water molecule. 7:42 And also during this process, cytochrome oxidase, complex four, will pump two 7:47 hydrogen ions 7:48 from the matrix into the intermembrane space. 7:53 Now I hope you understand why this is called an electron transport chain, 7:56 because the electron 7:57 is transported between all these complexes, where it will arrive at oxygen 8:04 finally. 8:05 And so we say oxygen is the final electron acceptor. 8:10 And remember, these electrons only came from one NADH. 8:15 And so now if we calculate all the protons pumped from one NADH, we have got 8:21 four from 8:22 complex one, four another four hydrogen ions pumped up from complex three, and 8:30 another 8:31 two from complex four, giving us a total of ten hydrogen ions, ten protons 8:37 being pumped 8:38 from the matrix into the intermembrane space from through one NADH molecule. 8:45 And also this creates one water from complex four. 8:50 And so what do we do with these ten hydrogen ions which are in the intermembr 8:54 ane space? 8:55 Well, it will get fed, we can say, it will go through the ATP synthase, complex 9:00 five, 9:00 to produce ATP. 9:02 So let's have a look at ATP synthase. 9:04 ATP synthase consists of many, many subunits. 9:08 It consists mainly of two complexes. 9:11 It has F0 complex and F1. 9:15 Let's look at the F1. 9:16 F1 consists of alpha and beta subunits, a gamma subunit and also a epsilon sub 9:24 unit here. 9:26 And the alpha and beta subunits is what actually produces the ATP. 9:30 That's what ADP and organic phosphate binds to. 9:34 F0 consists of ten C subunits, an A subunit, two B subunits, and a delta sub 9:40 unit down here. 9:43 Now all these different subunits we don't actually have to memorize, we just 9:45 have to 9:46 know their functions. 9:48 So ATP synthase will make ATP when hydrogen ions pass through this complex. 9:57 And it's actually four hydrogen ions that have to pass through to make one ATP. 10:03 Now to make ATP, there are actually many ADPs, adenosine disphosphate and in 10:09 organic phosphates 10:10 inside the matrix. 10:14 And so when four hydrogen ions pass through the A subunit of F0, this will 10:20 cause the C 10:21 subunits of the F0 to rotate. 10:24 When it rotates, it will essentially phosphorylate ADP to form ATP. 10:32 So four hydrogen ions passing through will create one ATP here. 10:37 Therefore, because we have ten hydrogen ions in the intermembrane space from 10:41 one NADH, 10:43 this means when ten hydrogen ions pass through the ATP synthase, it will 10:48 produce a total of 10:49 2.58 ATP. 10:52 Just think about it. 10:53 So one NADH will finally make 2.58 ATP from ten hydrogen ions.
