Understanding the Electron Transport Chain

Hello friends in this video we will be discussing about electron transport chain and oxidative phosphorylation. First of all let's recap the things. We have been discussing about cellular respiration. In the previous videos we discussed about glycolysis and citric acid cycle. We saw the oxidation of glucose molecule to pyruvate constitutes as the glycolysis. And in that we also get reduction of NAD plus molecule into NADH. Although ATPs are also getting produced here, but we'll be more focused towards electron carrying molecules, NADH and FADH too. Because this is what the ETC is all about. Then pyruvate is first converted into acetyl-CoA, which is further oxidized in cycle of reactions called a citric acid cycle or simply Krebs cycle. So eventually what we get from these biochemical reactions? Besides direct production of ATP molecules, we also get reduction of NAD plus and FADH molecules. In glycolysis, the NAD plus is reduced to NADH thus gaining the electrons here. And furthermore, in the conversion process of pyruvate to acetyl-CoA, we get the reduction of NAD plus to NADH also. And finally, in the citric acid cycle or Krebber cycle, NAD plus and FADH molecules are reduced to NADH and FADH2 respectively. So you can see in the end we get these two electron carrying molecules in the name of NADH and FADH2 and are called electron carriers and these electron carriers are subjected to oxidation in electron transport chain while these are oxidized back to its original form that's NAD plus and FADH and in that they lose their high energy electrons and energy in these electrons is used to pump the protons from matrix to the intermembrane space. When electrons transit from one complex molecule to the other in the electron transport chain of inner mitochondrial membrane, they lose their energy and this energy is used to pump the protons into the intermembrane space. So this is how the electron transport chain works in the mitochondria. Now let's see in detail how electron transport chain drives in the inner mitochondrial membrane. First of all we will see the electron transport chain for NADH electrons. How the electrons from NADH are driven into the electron transport chain? You know the electron transport chain drives in inner mitochondrial membrane with which we get matrix side and inter membrane space as shown in the diagram. And for NADH electrons to be transported into the chain we have four protein complex molecules present in the membrane. First we have NADH-ubicoinone oxidoreductase also called as complex 1 molecule. Then we have cytochrome C reductase also called as complex 3 molecule. After that we have cytochrome C oxidase also called as complex 4 molecule. Here in this case complex 2 is missing because this complex 2 is not used in NADH electrons rather it is used for FADH2 electrons. That's why complex 2 is not present here. And not only these three molecules are present for NADH electrons to be carried into the chain but here also we have a mobile electron carrier protein which is known by the name of cytochrome c complex which transports one electron at a time from complex 3 to complex 4 as shown in the diagram. It takes the electrons from complex 3 and delivers it to the complex 4. Now what's the work to be done by the electrons that will be delivered into this transport process? So, we know in the matrix we have a high concentration of protons and these protons need to be transported out of the matrix to create an electrochemical proton gradient so that we can produce the ATPs from proton motive force. So let's start the electron transport chain now. Here first of all NADH is oxidized back to NAD plus and H positive with the help of complex one that's NADH reductase enzyme. The total of two electrons are lost by NADH molecule. And with which phlavin mononucleotide is first reduced which further gives electron to the iron sulfur cluster and finally the two electrons are received by ubiquinone molecule which is further reduced to ubiquinol and in between these processes four protons are pumped into the intermembrane space as shown in the diagrams. And after that ubiquinol loses these accepted electrons and in that process the additional two protons are pumped into the ender membrane space and finally the ubiquinol is again oxidized back into the ubiquinone and the two electrons are accepted by the iron sulfur cholesterol first with which another two protons are pumped into the inter membrane space thus a total of four protons got pumped at complex three site now from here two electrons which are with the fps protein are first accepted by cytochrome first and from here cytochrome c complex a mobile carrier accepts a single electron at a time and carries it to the complex four So, it must be kept in mind that two electrons are not carried simultaneously by cytochrome C complex. Rather, only a single electron is carried. And after a delivery of one electron to the complex IV, it jumps back to the complex III and carries another electron. Then within this complex IV, the electrons are transported again one at a time, first to a pair of copper ions called CuA2, then to cytochrome A and other cytochrome molecules. And finally the electrons are accepted by oxygen molecule, the ultimate electron acceptor yielding us water molecule in the end. And in that last phase another two protons are pumped into the intermembrane space. So this completes our electron transport chain for the NADH electrons. So looking at the diagram we can see a total of four protons are pumped at complex one site. the another four protons at complex three site and finally the last two protons are pumped at complex four site so we can say from one nadh molecule the etc or we can say electron transport chain pumps the total of 10 protons into the inter membrane space now let's see the electron transport chain for the electrons of fadh2 molecules in this process of electron transport chain the complex one is skippered And here we have complex II succinate COQ reductase in action. First of all we see succinate dehydrogenase enzyme oxidizes a molecule of succinate to fumarate. And remember this step is from citric acid cycle. So why we have shown it here? It's because the succinate dehydrogenase enzyme is an integral component of succinate COQ reductase complex. That's why I have shown it here. The two electrons released in the conversion of succinate to fumarate in citric acid cycle or transport first to FAD which gets converted into FADH2. Then this FADH2 molecule loses two electrons to an iron sulfur cluster and finally to COQ which gets reduced to COQH2 and in that process four protons are pumped into the intermembrane space from matrix as you can see in this diagram and eventually we also get COQ back into the Q cycle. Now from here all the reactions are same as we have seen for NADH electrons. So we notice it here is that a complex one is not available in action here or we can say complex one molecule is not getting involved here. You know in ETC of NADH molecule it pumped four protons. So that means four protons will not be pumped here for FADH2 electrons because it's missing here. So a total of six protons are getting pumped by FADH2 oxidation. Four at complex three and two at complex 4. So this concludes our ETC for both NADH and FADH molecule. Now at the end if we calculate how many protons are getting pumped by the electron transport chain we see one NADH pumps 10 protons to the intermembrane space while as FADH2 molecule pumps 6 protons only a short of 4 protons from the NADH. So we needed electrochemical proton gradient across the membrane and now we have it. So the next process will be the oxidative phosphorylation where we will briefly see how protons will generate the ATP production. In the oxidative phosphorylation we see the involvement of another important complex molecule known by the name of ATP synthase or complex V. Considering the proton gradient across the inner mitochondrial membrane, the ATP synthase molecule has got ion channel present in it. And it's through this ion channel the protons flow back to the matrix. that is the chemiosmosis movement of ions across semi-permeable membrane down their electrochemical gradient and the rotation of f1 subunit driven by the proton movement through f0 powers atp synthesis so this is how the oxidative phosphorylation is coupled with the electron transport chain Now, a thing to remember, one ATP molecule is getting generated by the flow of four protons through the ATP synthase from intermembrane space to the matrix. So, if we recall, one NADH pumps ten protons to the intermembrane space and when these ten protons will flow back to the matrix, that time, this will be equal to the 2.5 ATPs from oxidative phosphorylation as four protons gives us one ATP. And for FADH2 molecule, which pumps six protons, that equals to the 1.5 ATP is from oxidative phosphorylation. So this is how the NADH and FADH2 differs in the ATP production. I hope you like the video. If you like it, give it a thumbs up and make sure to subscribe this channel. Thanks.

And in that we also get reduction of NAD plus molecule into NADH. Although ATPs are also getting produced here, but we'll be more focused towards electron carrying molecules, NADH and FADH too. Because this is what the ETC is all about.

Then pyruvate is first converted into acetyl-CoA, which is further oxidized in cycle of reactions called a citric acid cycle or simply Krebs cycle. So eventually what we get from these biochemical reactions? Besides direct production of ATP molecules, we also get reduction of NAD plus and FADH molecules. In glycolysis, the NAD plus is reduced to NADH thus gaining the electrons here.

And furthermore, in the conversion process of pyruvate to acetyl-CoA, we get the reduction of NAD plus to NADH also. And finally, in the citric acid cycle or Krebber cycle, NAD plus and FADH molecules are reduced to NADH and FADH2 respectively. So you can see in the end we get these two electron carrying molecules in the name of NADH and FADH2 and are called electron carriers and these electron carriers are subjected to oxidation in electron transport chain while these are oxidized back to its original form that's NAD plus and FADH and in that they lose their high energy electrons and energy in these electrons is used to pump the protons from matrix to the intermembrane space.

When electrons transit from one complex molecule to the other in the electron transport chain of inner mitochondrial membrane, they lose their energy and this energy is used to pump the protons into the intermembrane space. So this is how the electron transport chain works in the mitochondria. Now let's see in detail how electron transport chain drives in the inner mitochondrial membrane.

First of all we will see the electron transport chain for NADH electrons. How the electrons from NADH are driven into the electron transport chain? You know the electron transport chain drives in inner mitochondrial membrane with which we get matrix side and inter membrane space as shown in the diagram.

And for NADH electrons to be transported into the chain we have four protein complex molecules present in the membrane. First we have NADH-ubicoinone oxidoreductase also called as complex 1 molecule. Then we have cytochrome C reductase also called as complex 3 molecule.

After that we have cytochrome C oxidase also called as complex 4 molecule. Here in this case complex 2 is missing because this complex 2 is not used in NADH electrons rather it is used for FADH2 electrons. That's why complex 2 is not present here.

And not only these three molecules are present for NADH electrons to be carried into the chain but here also we have a mobile electron carrier protein which is known by the name of cytochrome c complex which transports one electron at a time from complex 3 to complex 4 as shown in the diagram. It takes the electrons from complex 3 and delivers it to the complex 4. Now what's the work to be done by the electrons that will be delivered into this transport process? So, we know in the matrix we have a high concentration of protons and these protons need to be transported out of the matrix to create an electrochemical proton gradient so that we can produce the ATPs from proton motive force. So let's start the electron transport chain now.

Here first of all NADH is oxidized back to NAD plus and H positive with the help of complex one that's NADH reductase enzyme. The total of two electrons are lost by NADH molecule. And with which phlavin mononucleotide is first reduced which further gives electron to the iron sulfur cluster and finally the two electrons are received by ubiquinone molecule which is further reduced to ubiquinol and in between these processes four protons are pumped into the intermembrane space as shown in the diagrams. And after that ubiquinol loses these accepted electrons and in that process the additional two protons are pumped into the ender membrane space and finally the ubiquinol is again oxidized back into the ubiquinone and the two electrons are accepted by the iron sulfur cholesterol first with which another two protons are pumped into the inter membrane space thus a total of four protons got pumped at complex three site now from here two electrons which are with the fps protein are first accepted by cytochrome first and from here cytochrome c complex a mobile carrier accepts a single electron at a time and carries it to the complex four So, it must be kept in mind that two electrons are not carried simultaneously by cytochrome C complex.

Rather, only a single electron is carried. And after a delivery of one electron to the complex IV, it jumps back to the complex III and carries another electron. Then within this complex IV, the electrons are transported again one at a time, first to a pair of copper ions called CuA2, then to cytochrome A and other cytochrome molecules.

And finally the electrons are accepted by oxygen molecule, the ultimate electron acceptor yielding us water molecule in the end. And in that last phase another two protons are pumped into the intermembrane space. So this completes our electron transport chain for the NADH electrons. So looking at the diagram we can see a total of four protons are pumped at complex one site. the another four protons at complex three site and finally the last two protons are pumped at complex four site so we can say from one nadh molecule the etc or we can say electron transport chain pumps the total of 10 protons into the inter membrane space now let's see the electron transport chain for the electrons of fadh2 molecules in this process of electron transport chain the complex one is skippered And here we have complex II succinate COQ reductase in action.

First of all we see succinate dehydrogenase enzyme oxidizes a molecule of succinate to fumarate. And remember this step is from citric acid cycle. So why we have shown it here?

It's because the succinate dehydrogenase enzyme is an integral component of succinate COQ reductase complex. That's why I have shown it here. The two electrons released in the conversion of succinate to fumarate in citric acid cycle or transport first to FAD which gets converted into FADH2. Then this FADH2 molecule loses two electrons to an iron sulfur cluster and finally to COQ which gets reduced to COQH2 and in that process four protons are pumped into the intermembrane space from matrix as you can see in this diagram and eventually we also get COQ back into the Q cycle.

Now from here all the reactions are same as we have seen for NADH electrons. So we notice it here is that a complex one is not available in action here or we can say complex one molecule is not getting involved here. You know in ETC of NADH molecule it pumped four protons. So that means four protons will not be pumped here for FADH2 electrons because it's missing here. So a total of six protons are getting pumped by FADH2 oxidation.

Four at complex three and two at complex 4. So this concludes our ETC for both NADH and FADH molecule. Now at the end if we calculate how many protons are getting pumped by the electron transport chain we see one NADH pumps 10 protons to the intermembrane space while as FADH2 molecule pumps 6 protons only a short of 4 protons from the NADH. So we needed electrochemical proton gradient across the membrane and now we have it. So the next process will be the oxidative phosphorylation where we will briefly see how protons will generate the ATP production.

In the oxidative phosphorylation we see the involvement of another important complex molecule known by the name of ATP synthase or complex V. Considering the proton gradient across the inner mitochondrial membrane, the ATP synthase molecule has got ion channel present in it. And it's through this ion channel the protons flow back to the matrix. that is the chemiosmosis movement of ions across semi-permeable membrane down their electrochemical gradient and the rotation of f1 subunit driven by the proton movement through f0 powers atp synthesis so this is how the oxidative phosphorylation is coupled with the electron transport chain Now, a thing to remember, one ATP molecule is getting generated by the flow of four protons through the ATP synthase from intermembrane space to the matrix. So, if we recall, one NADH pumps ten protons to the intermembrane space and when these ten protons will flow back to the matrix, that time, this will be equal to the 2.5 ATPs from oxidative phosphorylation as four protons gives us one ATP.

And for FADH2 molecule, which pumps six protons, that equals to the 1.5 ATP is from oxidative phosphorylation. So this is how the NADH and FADH2 differs in the ATP production. I hope you like the video.

If you like it, give it a thumbs up and make sure to subscribe this channel. Thanks.

Transcript for:Understanding the Electron Transport Chain

Transcript for:
Understanding the Electron Transport Chain