0:00 So let's draw up a table of oxidative phosphorylation and the ATP yield. 0:05 So let's look at all the processes beforehand which provided the electron 0:11 carriers, beginning 0:12 with glycolysis. 0:14 So glycolysis, if you remember, produced two NADHs. 0:20 So now, if NADH, the electron carrier is in complex one, complex one will pump 0:26 out a total 0:27 of eight hydrogen ions from the matrix into the intermembrane space. 0:35 Because for one NADH, it's four, remember. 0:38 And then for complex two, nothing is pumped out. 0:41 Complex three, four hydrogen ions get pumped into the intermembrane space for 0:47 each NADH. 0:48 So because it's two, it gives us eight hydrogen ions. 0:51 And then for complex four, two hydrogen ions are pumped each for each NADH. 0:57 So four hydrogen ions. 0:58 So the total hydrogen ions pumped by two NADH molecules from all the complexes 1:06 equates 1:07 to 20 hydrogen ions. 1:09 So now we have 20 hydrogen ions in the intermembrane space from two NADHs, the 1:16 electron carriers. 1:17 And so if we put this through the ATP synthase where four hydrogen ions will 1:22 give us one ATP, 1:24 this would mean that 20 hydrogen ions will produce five ATP. 1:32 Similarly with the preparatory step, which gave us two NADHs, this means that 1:36 it's exactly 1:38 the same. 1:39 Complex one will pump out eight hydrogen ions into membrane space. 1:41 Complex three, eight hydrogen ions, complex four, four hydrogen ions, giving a 1:44 total again 1:45 of 20 hydrogen ions. 1:47 And so the total amount of ATP produced from 20 hydrogen ions is five ATP. 1:54 Because 20 divided by four is five. 2:00 Looking at the Krebs cycle, the Krebs cycle, if you remember, produced six NADH 2:04 s. 2:05 And so if six NADHs goes through complex one, this means that it would be six 2:11 times four. 2:12 Because for each NADH, four hydrogen ions are being pumped from the matrix into 2:16 the intermembrane 2:17 space, which means that six times four is 24 hydrogen ions, which means complex 2:21 three 2:21 also four hydrogen ions are pumped for each NADH, so 24 hydrogen ions in total. 2:27 And complex four, finally, two hydrogen ions for each NADH, so six times two is 2:32 12 hydrogen 2:33 ions, giving a total of 60 hydrogen ions, which are pumped from the matrix into 2:38 the intermembrane 2:38 space. 2:39 And so how much ATP would this create, just 60 divided by four, because four 2:44 hydrogen 2:44 ions makes one ATP, giving us 15 ATP in total. 2:50 The Krebs cycle, however, also produces two FADH2s, right? 2:55 So what about this? 2:57 Because we learned about NADH only in this diagram. 3:00 We didn't learn about FADH, so where does FADH come into the picture? 3:05 Well, it doesn't start at complex one, surprisingly. 3:10 FADH passes the electrons from complex two, which is succinate dehydrogenase. 3:17 So now I will rub out all these hydrogen ions, which were pumped out by one NAD 3:23 H. 3:24 And so now we will not look at NADH's electrons moving through the electron 3:30 chain, transport 3:31 chains, but we will look at FADH and how its electrons moves and how many ATP 3:37 it will produce. 3:40 So where does FADH2 come from? 3:42 If you remember from the Krebs cycle, the conversion from succinate to fumarate 3:47 requires the enzyme 3:48 succinate dehydrogenase, which is our complex two. 3:52 And so through this conversion, FAD, which is part of complex two, will be 3:58 reduced to 3:59 FADH2. 4:00 And FADH2 provides the electrons to be transported through the electron 4:06 transport chain. 4:07 Now let's just look at the actual complex two. 4:10 Complex two actually is comprised of four main parts, subunits, A, B, C, and D. 4:17 We don't really need to know much about these, but essentially in the center 4:22 somewhere we 4:22 have another series of iron centers, which the electrons from NADH2 will go 4:31 through these 4:33 iron centers and finally to ubiquinin. 4:38 So the two electrons will go to ubiquinin and ubiquinin will turn to ubiquinol. 4:43 Now ubiquinol will then travel to complex three, cytochrome C-oxy reductase, 4:49 where 4:49 it will pass on the electrons to cytochrome C. During this process, complex 4:55 three will 4:55 also pump 400 ions from the matrix into the intermembrane space. 4:59 Cytochrome C with the electrons will then travel to complex four, cytochrome 5:03 oxidase. 5:03 Where at complex four it will cause an additional two hydrogen ions to be 5:09 pumped out from the 5:10 matrix into the intermembrane space. 5:13 So as you can see, the transporting of electrons from FADH and NADH are very 5:20 similar. 5:21 However, FADH does not go through complex one. 5:25 NADH pumps ten hydrogen ions in total through the electron transport chain. 5:31 However, FADH only pumped six hydrogen ions from the matrix into the intermembr 5:37 ane space. 5:38 Therefore, if six hydrogen ions were to go through the ATP synthase pump, it 5:43 will only 5:44 produce 1.5 ATP because four hydrogen ions makes one ATP. 5:51 And so as you can see, FADH will only produce one less ATP than NADH would 5:58 because FADH does 5:59 not pass through complex one. 6:01 And so if we go back to our previous table of our ATP yield, we look at the two 6:06 FADHs 6:07 and look at how many hydrogen ions it will pump. 6:09 At complex one, it does not go through it, so it doesn't pump any hydrogen ions 6:13 . 6:13 Complex two, it doesn't pump any hydrogen ions. 6:16 Complex three, it will pump out four hydrogen ions each, giving a total of 6:22 eight hydrogen 6:23 ions. 6:25 And so also at complex four, one FADH will pump out two hydrogen ions. 6:30 So two FADHs will pump out a total of four hydrogen ions. 6:33 So the total hydrogen ions pumped from the matrix into the intermembrane space 6:38 by two 6:38 FADHs is twelve hydrogen ions. 6:42 So how much ATP can twelve hydrogen ions produce? 6:45 Well, we go twelve divided by four, which will give us three ATP produced by 6:52 two FADHs. 6:53 Now, to make things much a bit more confusing, in glycolysis, because the two 7:03 NADHs are coming 7:04 from the cytoplasm, not from inside the matrix, and so the two NADHs from glyco 7:09 lysis have to 7:10 have some form of mechanism to move from the cytoplasm inside the matrix, right 7:15 ? 7:15 One of its way is through shuttles. 7:17 There are two types of shuttles, one of them will cause the electron transport 7:24 chain to 7:24 not pump as much hydrogen ions from the matrix into the intermembrane space. 7:31 And because this particular shuttle, the two NADHs from glycolysis will miss 7:36 going through 7:37 complex one. 7:38 And so therefore the amount of hydrogen ions pumped from complex one can vary 7:43 from zero 7:43 four to eight hydrogen ions. 7:45 So the total amount of hydrogen ions pumped will technically be either twelve, 7:51 between 7:51 twelve and twenty hydrogen ions. 7:53 So the amount of ATP produced can vary from three to five ATP, four to NADHs 8:00 from glycolysis. 8:01 I hope that makes sense. 8:04 And so why is this again? 8:06 It is because these two NADHs are coming from the cytoplasm and it's some form 8:10 of mechanism 8:11 to go inside the mitochondria. 8:14 One of its mechanism will cause it to miss going through complex one of the 8:18 electron 8:19 transport chain. 8:20 And so this will cause not as much hydrogen ions being pumped. 8:26 So let's look at this particular shuttle. 8:29 And the shuttle is known as the glycerol three phosphate shuttle. 8:33 It is called glycerol three phosphate shuttle because it involves two enzymes 8:38 known as glycerol 8:39 three phosphate dehydrogenase. 8:41 And the two enzymes are actually different in that one of them is situated in 8:46 the mitochondrial 8:47 inner membrane such as here. 8:49 And the other one is in the cytosol, in the cytoplasm. 8:53 And so what happens is NADH will come from glycolysis. 8:57 We're only looking at one NADH. 8:59 NADH is brought into the electron transport chain when it reduces dihydroxyacet 9:05 one phosphate 9:06 into glycerol three phosphate with the enzyme cytosolic glycerol three 9:11 phosphate dehydrogenase. 9:14 And so now we have glycerol three phosphate with the two electrons you can say. 9:19 Now glycerol three phosphate will then be oxidized by the same enzyme except in 9:24 the 9:24 mitochondria, glycerol three phosphate dehydrogenase, the mitochondrial one. 9:29 And during this process, FAD is reduced to FADH2. 9:34 And FADH2 is what provides the electrons to ubiquinin, converting it to ubiquin 9:41 ol. 9:41 Ubiquinol then moves the electrons to complex three. 9:44 Well complex C will then pump out 400 ions per NADH now FADH2. 9:50 And then the electrons will move to cytoplasm C of complex three. 9:55 Cytoplasm C will then move to complex four where it will cause complex four to 9:59 pump out 9:59 200 ions per NADH now FADH. 10:03 And so as you can see, through this glycerol three phosphate shuttle mechanism, 10:08 we are 10:08 passing complex one and complex two. 10:11 So we're passing an addition of 400 ions pumped by complex one. 10:15 And another amazing thing is that we've begun with NADH from glycolysis but we 10:19 end up with 10:20 FADH2 which will provide the electrons to ubiquinin. 10:25 And as we know, FADH will actually produce one less ATP than NADH would. 10:31 And this all makes sense when you think about it. 10:33 So now if we go back to the graph, we can see that the total ATP from oxidative 10:38 phosphorylation 10:39 produced from essentially one glucose molecule, we can say, it equates to 26 to 10:47 28 ATP depending. 10:49 Remember if we use the glycerol three phosphate shuttle. 10:53 I hope this all made sense to you and I hope you enjoyed this video. 10:56 Remember I made some mistakes and another thing is that this electron transport 11:00 chain 11:00 oxidative phosphorylation is not actually fully understood yet so it might 11:03 sound all 11:04 weird. 11:05 I thank you for watching, please like, subscribe and...
