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Current time:0:00Total duration:15:37

Oxidative phosphorylation and the electron transport chain

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Video transcript

when we looked at glycolysis and the conversion of pyruvate to acetyl co a and then the Krebs or the citric acid cycle we were sometimes directly producing ATP's but we were also doing a lot of reduction of nad to NADH and we later said that that NADH that that can later be oxidized to and that energy from that oxidation that energy that's released from the electrons can be used to actually create ATP and NADH is the main character here but there are other Co enzymes that are involved like coenzyme q and you see that right over here and what i want to talk about in this video is the process by which we actually are able to produce ATP from the oxidation of these coenzymes and that process is what we call oxidative phosphorylation oxidative oxidative phosphorylation now the main player when we're talking about cellular respiration and oxidative phosphorylation is NADH NADH in the process of being oxidized to nad so it gets oxidized to n gets oxidized to nad which has a positive charge I often call it nad plus but let's think about what this has if we just look at if we just look at this reaction from the point of view of NADH being oxidized remember oxidized ID oxidation is losing electrons so nad plus and then you're going to have plus a hydrogen proton plus you're going to have two electrons plus two electrons so this is what's happening when NADH is being oxidized into nad so this is oxidation right over here let me do this in another color so this is oxidation and this process of oxidation if these electrons get the appropriate acceptor molecule it can release a lot of energy and the eventual acceptor of those electrons and I can show the corresponding reduction reaction is we have two electrons to Allah Tron's plus two hydrogen protons or really just two protons a hydrogen nucleus is just a proton doesn't have a neutron for the main isotope of hydrogen so two protons plus half of an oxygen molecule yielding you put all of these two to call of these three all of these things together I should say and you are going to get a water molecule so you can think of it as the oxygen being the final acceptor of the electrons and oxygen likes to be doing oxidant likes to oxidize things that's where the whole word oxidation comes from so here or one another thing is oxygen likes to be reduced it likes to hog electrons so this is oxygen is being reduced oxygen oxygen reduced so if you just directly transferred these electrons from our NADH to the oxygen it would release a lot of energy but it would release so much energy that you wouldn't be able to capture most of it you wouldn't be able to use it to actually do useful work and so the process of oxidative phosphorylation is all about doing this in a series of steps and we do it by transferring these electrons from one electron acceptor to another electron acceptor and every time we do that we release some energy and then that energy can be in a more controlled way be used to actually do work and in this case that work is pumping pumping hydrogen protons across a membrane and then that gradient it forms can actually be used to generate ATP so let's talk through it a little bit more so we're going to go these electrons they're going to be transferred and I won't go into all of the details this is to just give you a high-level overview of it they're going to be transferred to different acceptors which then transfer it to another acceptor so it might go to a coenzyme coenzyme q + cytochrome cytochrome c and that keeps going to different things eventually eventually getting to this state right over here the where those electrons can be accepted by the by the walk by the oxygen to actually form the water and the process every step of the way energy is being released energy energy is being released and this energy as we will see in a second is being used to pump hydrogen protons across a membrane and we're going to use that gradient to actually drive the production of ATP so let's think about that a little bit more so let's zoom in on on a on a mitochondria so this is mitochondria let's say that's our mitochondria and let me draw the inner membrane and then these folds and the inner membrane the singular for them is crista if we're talking the plural is Christy so we have these folds in the inner in the inner membrane right over here so just to be clear what's going on this is the outer membrane outer membrane that is the inner membrane inner membrane the space between the outer and the inner membrane the space right over here that is the inter membrane space inter membrane membrane space and then the space inside the inner inside the inner membrane let me make sure you can read that space properly this this space over here this is the matrix this is the matrix and that is the location of our citric acid cycle or our Krebs cycle and I can symbolize that with this little cycle you know we have a cycle going on here and so that's where the bulk of the NADH is being produced now we also talked about some other Co enzymes in some books or classes you might hear about FA D being reduced to fadh2 which can then be oxidized as part of oxidative phosphorylation other times people say well actually that's going to be attached to an enzyme and then that fadh2 is B is used to reduce coenzyme q to produce Q h2 and then that participates in oxidative phosphorylation so you could think about either one of these I'll focus on Q H to what we'll actually focus on NADH because it's all a similar process fadh2 or Q H 2 enters a little bit later down this process so they don't produce as much as much energy but they still can be you is to help produce ATP but anyway our our citric acid cycle which we shall have shown in previous videos that's occurring in the matrix and now let me do a little zoom in here let me do a zoom in so if I were to zoom in let's say we just in a color that we can see so if I were to zoom in right over there let's show this fold and the inner membrane and it's very and make it let's make it clear that this is like all of these membranes these are all phospholipid bilayers so let me let me draw let me do the same color that I you that I did in the the actual diagram so we have we have all these we have a bilayer of phospholipids and I'm clearly not drawing any of this stuff to scale so almost done all right all right just to make it clear and you have these enzymes that go across the phospholipid bilayer and these enzymes are these protein complexes are actually what facilitate oxidative phosphorylation and these the this this chain of enzymes this chain of proteins is what we call the electron or is what we call the electron transport chain so let me draw that so maybe this is one protein and I'm just drawing them as kind of these abstract abstract and you could refer to the electron transportation as either these proteins we could view as this process of these electrons going from one acceptor to another eventually making its way all the way to the oxygen so that might be one protein this is another protein right over here and I'll just do a couple of them this is really about a high-level overview and what's happening what's happening is as Z and this is just going to be a very high-level simplification of it as you have your let's say initially your NADH comes in so your na dhih H comes in and it donates the protons and the electrons Tron's and then it becomes na d+ so it just became oxidized those electrons will go to an acceptor which then get transferred to another acceptor they get transfer to another acceptor it goes through this electron transport chain and as that energy is released that energy is used to pump hydrogen protons from the matrix so this side right over here the left side right over here this is the matrix this is where our citric acid cycle occurs so we have protons being pumped out so we have these protons being pumped out as we release energy as we go from one electron acceptor to another electron acceptor and so the electrons are going from higher energy states and the releasing energy as they go down this kind of towards more and more electronegative things and they feel more comfortable with the water then they feel then they felt with the NADH and by doing so by these electrons going down that gradient I guess you could say or maybe a better way from going from a higher energy state to a lower energy State we are creating this proton gradient so the concentration of protons on the right side of this membrane and we just to be clear where this is this space right over here this is right over there that's the inter membrane space where the hydrogen proton concentration is building up now this is stored energy because this is a this is electrochemical gradient all this positive charge they want to get away from each other they want to go to this less positive matrix right over here and also just you have a higher concentration of hydrogen's and just natural diffusion they would want to go down their concentration gradient into the matrix there's less of the protons here there's less of the protons on the in the matrix then there are on the interim then there are in the inter membrane space and so there that's the opportunity to now take that energy and produce ATP with them and the way that this happens the way this happens let me extend my membrane a little bit that's a different color so let me extend my membrane a little bit is using using a protein called ATP synthase ATP sent it's actually a protein complex I should say so ATP synthase really an enzyme and ATP synthase goes across it's actually a fascinating fascinating molecule I'll show a better diagram of it in a second but your ATP synthase goes across the membrane it actually has a fairly mechanical structure where it has a bit of a housing and it has an axle in the housing so it looks maybe something like this then it actually has something you could view this as a as the thing that maybe holds it together so it's going across the membrane I'll show a better diagram of it in a second so then of course the membrane continues on membrane continues on and what happens is it allows these hydrogen protons to flow down their electrochemical gradient so these hydrogen protons go down and they actually cause the axle to spin and so maybe I'll draw it this way they actually cause they actually cause the axle to spin as they go as they go down their electrochemical gradient and as this axle spins this actually and it's not the smooth that's not like it's made out of metal or something it's made it's made out of amino acid so it's got this it's all bumpy and and all the rest so it looks something like this and what happens is you have a DPS you have ATP's that get lodged in here so let's say that's an ADP and then a phosphate group and they had actually three different sites where this can happen so that's an ADP and a phosphate group there's another site that I'm not drawing but as this thing rotates it essentially keeps changing the conformation of the protein and jams the phosphate group into the ADP which takes energy and locks them into place to form the ATP and when they form the ATP they no longer they no longer attached to the active site and they let go so you have this this this actually this mechanical motor you can view it as almost like a turbine a water turbine the water goes through it and it that energy is used to generate electricity here hydrogen protons go down their electrochemical gradient that rotary motion is then used to jam phosphate groups onto ADP s to form ATP's and so this is the actual ATP production going on and to get a better a better appreciation for what's going on this is going on in your body right now this is going on in my body otherwise I wouldn't be able to talk this is this is I'm generating my energy this is a more accurate depiction of ATP synthase right over here and based on this diagram this is our this this let me make sure I'm so this right over here I'm having trouble I'm having trouble drawing on on this let me see if I can so this part right over here this area right over there that's our inter membrane space this right over here is our this over here is our matrix this membrane this is a phospholipid bilayer so if I want it I could draw the the bilayer of phospholipids right over here and this is our inner membrane or we could say this is a fold in the inner membrane this could be on our crista and so the hydrogen protons they build up they build up in the inter membrane space because of the electron transport chain and then they flow down and then they flow down their conte the electrochemical gradient turn this rotor and then they cause the creation of the ATP's over here so you have you know ADP ADP plus a phosphate group and then you produce and you produce your ATP so you know this is fascinating this is going on in the cells of your body that's going on as you speak it's not some abstract thing that is somehow separate from your reality this is what is making your reality possible so hopefully you you get a nice appreciation for this I mean we spent a lot of time talking about cellular respiration we spent a lot of time talking about okay we can produce some ATP's directly through glycolysis and through the citric acid cycle but mostly most of the energy is because of the reduction of these coenzymes and especially nad to NADH and then in oxidative phosphorylation and the electron transport chain we can use the oxidation of the NADH to pump hydrogen protons from the matrix to the intermembrane space and then let them get go back through through the ATP synthase which jams the phosphate into the ADP to produce the ATP which is our biological currency you of energy
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