hi everybody welcome to another exciting discussion on cellular respiration fermentation and a little bit of photosynthesis i thought about this for a little bit and i thought it wouldn't harm people to hear a little bit more about what was happening in the citric acid cycle at this point we've already reviewed what occurs in glycolysis the intermediate step and the citric acid cycle but again looking at the citric acid cycle really is not a problem um to see again it's a little bit challenging at first so let's go to it all right so this is the citric acid cycle which i mentioned to you last night the last time has the old-fashioned name of the krebs cycle the citric acid cycle is a little bit more appropriate of a term because it's named after the very first molecule that is created during this process named citrate the old-fashioned name was just named after the person krebs who discovered all this and thankfully he did however now we know it as something a little more neutral in terms of understanding what's going on hmm was that an acid joke like ph neutral anyway so looking at it um we're going to look at the intermediate step we noticed that there were acetyl coas that were coming out from that whole process and remember there were two acetyl coa we'll get back to that in a moment that acetyl coa is coming in through the membranes of the mitochondria and in order to do so there's this co-a which is a coenzyme a which functions kind of like a miniature screwdriver to help getting that little screw on your glasses or your sunglasses once it does its job of getting the rest of the carbons that was previously from pyruvate in then the coa can go off and it can be used once again now from there we notice that there are two carbons from the acetyl portion of acetyl acetyl-coa and already present in the mitochondria is a molecule with four carbons known as oxaloacetate these two combine to make citrate so citrine is a six carbon sugar and of course if it's called an acid what that means is it's going to release or donate hydrogens and so it does right away notice that we've got citrate here we take off one of the carbons making it co2 leaving that's what you're going to be breathing out by the way that's also what you breathed out in the intermediate step so you breathe out the citric citrate carbon dioxide so this carbon dioxide leaves and then the citrate now no longer has six carbons but has five in the process of doing this we've broken off a bond here which then allows for nad plus to become nadh which you all know is better and known better as a reduction because it has gained electrons and hydrogen so this is the reduction therefore the oxidation must be happening between citrate and alpha ketoglutarate notice that the oxidation we've lost those two electrons so it kind of makes sense anyway then from alpha ketoglutarate we have five carbons one of them again is lost in the form of co2 and so we end up going to a four copper molecule called succinate in the process it's the nad plus that gets those electrons and the hydrogen so this right here is the oxidation and oops let me set that again this is the reduction this is the oxidation yeah it happens so notice we've got here four carbons and four carbons from succinate to malate and although it doesn't really look like much is happening the way this is drawn it's the organized organization of the molecule that has changed in terms of the structure however in doing so we've gathered a couple more electrons so that's gaining again so that's a reduction therefore this must be an oxidation also we've added some water here again from malay to oxaloacetate we've got an oxidation that's happening and you know that because here's a reduction in other words every time that you see a reduction you know there's an oxidation every time there's an oxidation you know there's been a reduction so they are coupled reactions now one thing that you want to look at is this could be a nice little simplified version of it now some people like this version because it's got everything on it and some people like this version because it's not so crowded i like a little bit of both i like this one because i know where things are coming from and it's not magic don't like magic in in terms of looking at it biologically on the other hand i like this because it's simplified but it does look a little magical but what we're getting at with the simplified drawing is just essentially what are the products of the reactants of the overall process so we notice that we're coming in here with acetyl coa and we're going to have some things that get produced in the in the process of doing this so that's why we get acetyl coa with the coe uh coenzyme a coming off we've combined the two carbon dioxides see they were here one and two there's the two carbon dioxides we've combined all the nad pluses and nadhs see one two and three and then we've got the atps that were produced out of this which just happened in one step right here and then finally we got the production of fadh2 and that just happened one time so this is a nice simplified way of looking at things if you wanted to know everything that is produced or as a reactant this one will show you all the steps and the idea of the citric acid cycle as being an um a cycle shows you that you have to recreate your starting materials so that way you can continue with the cycle okay so let's take a look at this take a moment identify your react reactants and products go ahead and put this on pause while you do so and then i will start up again all right now that you have gone through your reactants and products think about it why did i put two in front why did i put six and not three well hopefully you remember that all of this is happening times two because originally there were two acetyl coas the two acetyl coas came from the two pyruvate and the two pyruvate came from the one glucose so it's glucose to two pyruvate and glycolysis and then there's two pyruvate two two acetyl coa in the intermediate step and that's why we have two now so if you don't remember that go back take a look at the other stages so you can see where it is that the two comes from okay so that's a citric acid cycle what we're going to do now is look at where we're getting our big bang for our buck and that's going to be happening here in the oxidative phosphorylation portion of this we're going to be looking at why we bothered to get all these electrons over it's about oxidative phosphorylation and yeah we produced a little atp along the way but where are we going to get the big amounts of atp here again big bang for the buck so here we go this is oxidative phosphorylation what we're looking at is of course within the mitochondria notice what we're looking at here is there's two membranes here we're looking at what's happening in the central membrane okay so this is the mitochondrial matrix you know the matrix it's more than a movie so there's the matrix which is actually the central portion of this whole entire thing then there's the inner mitochondrial membrane so that's this pink line that's going around here and then there's the inner membrane space that's the space in between the outer membrane and the inner membrane so you can see where this is kind of happening now a lot of this should look really familiar to you if i point things out i bet you know a lot of this stuff like for example what is this what is this do you remember what they represent what is this what do you think this is and what about this how about this what is this whole thing so let's take a look at it first of all this is a membrane you know it has a phospholipid bilayer and what are the purple things those are proteins right they're going to help with transportation of materials across and when we look at it what are we bringing in we're bringing in electron carriers with their electrons here somehow they're releasing their electrons because now this electron carrier doesn't have any anymore same thing is happening here now when we look over here this red circle usually has meant oxygen in the past and here's water we've seen that as this kind of oblong um blueish spearish kind of thing oval i don't know in any case over here we've got a yellow phosphate and we're making atp now all of these here you can tell because one's been labeled those are hydrogen are we going along or against the gradient when we move them from here to here well we're going from low to high so that means we're going against the gradient normally the gradient is going from high to low as though you're rolling a ball from high to low is very simple it doesn't really even take any extra energy it just needs to start rolling but if you were to go uphill we're pushing that ball up that's going to take more energy okay so clearly we're going against the gradient we're going uphill here and it's not because the picture is drawn from bottom to top this is kind of more like maybe an overview picture if you want to think of it that way so uh it's kind of a little bit like a dam with a lake over here all right so let's start off here um at the beginning of what we know is oxidative phosphorylation oxidative kind of sounds like oxidation which we know how to do with electrons in this case specifically losing electrons that's going to be part of the electron transport chain the etc and then there's phosphorylation which you know has to do with something with the phosphate group really what it means is adding it on to something else and how it's going to happen is through chemi osmosis osmosis meaning movement of water in this case chemi though not water across a membrane that's semi-permeable okay so let's take a look again first half of this whole thing is the electron transport chain and then this little part on the end is chemiosmosis in chemiosmosis we're going to be using atp synthase well what kind of molecule is that what does it sound like don't forget ase means enzyme so this is an enzyme and it's going to synthesize something i wonder what okay now let's take a look at the etc in the etc we're going to bring in nadh which was made in glycolysis in the intermediate step and in the citric acid cycle lovingly known as the cac so we're going to make it in the citric acid cycle glycolysis intermediate step and here we're finally bringing it in to see what's going to happen with it so what's going to happen is nadh is going to be oxidized it's going to lose its electrons to become nad plus okay well where do those electrons go they end up going up here into this protein and that protein shifts shape just a little bit enough to allow for this hydrogen to flow through well the electrons are way up at the top of this protein kind of like that ball and they're going to start rolling downhill so the electrons start to roll downhill and they meet a first little bump and what we end up having is our fadh2 which was created in the citric acid cycle lose its electrons to become fad and it loses those electrons to kind of give a little boost to the electron transport chain as the electrons are moving down from protein to protein the proteins shift shape just enough to allow for hydrogens to move across this continues as the electrons fall and fall and fall and then really what's pulling it down is this uh molecule this molecule is as you know oxygen oxygen we know and i'll write this down it's got a particular nickname to it we put it in the same color as oxygen here oxygen is called the final electron acceptor that's the o2 okay so that's what's happening right there is that this oxygen is pulling these down not unlike gravity in this situation pulling the electrons down towards it and as that happens it becomes even more attractive to hydrogens and then you end up forming water well this is the oxygen that you needed to have to breathe in this is the reason why you breathe in and this water is part of the reason why you urinate out so the co2 that we've seen before you breathe that out the o2 that you breathe in is specifically for this kind of strange if you think about it but that's what's happening okay so that's the final electron acceptor is oxygen here and it's created water now the purpose of this electron transport chain the whole purpose of this whole thing is to create a hydrogen ion gradient so now we have a ton of hydrogen ions here and very few comparatively down here well now that we've created this gradient high and low this allows for the hydrogen to really go nowhere except for through a turbine like we think about in a hydroelectric dam if there's one little hole that's where the water is going to flow through and in this case that turbine is atp synthase as the hydrogen moves through it rotates part of the synthesis and phase the atp synthase which allows for a location of adp to become available as the active site putting adp and p together to make atp and that was our goal here remember the whole goal of cellular respiration was to make atp from glucose strange ending to a long story but that's essentially what we did is we finally took that sugar that we ate and we made it into a very valuable molecule called atp that we can use to do all the things that our cells need to do so and the way it did that at the end was by the transport of electrons which made a hydrogen ion gradient which then allowed for chemiosmosis to happen all right so that's oxidative phosphorylation now here's a picture of putting it all together we've got glycolysis no they notice they put it in the cytosol now with making glucose and two pyruvate they've got all the electron carriers bringing it over to oxidative phosphorylation now the interesting part about this is right here they say substrate level phosphorylation what does substrate level phosphorylation mean what is substrate do you remember that we talked about that before well that means that there's going to be an enzyme that mediates it and if you look back at glycolysis you'll see that picture of the enzyme which helped part of this the same thing is going to happen here in the citric acid cycle and then ultimately in oxidative phosphorylation you end up adding those p's onto the adp's because we've gone through the atp synthase so that has helped with the electron transport now this picture right here is not in your textbook but it's going to be really helpful for part of your test it's kind of a funny thing but oxidative phosphorylation is important about the organism being able to make atp to make energy to do the things that the cell needs and a lot of times it's really a bizarre thing but what stops um organisms from surviving is getting atp about getting energy and so when we look at it poisons actually affect whether or not an organism can do oxidative phosphorylation and actually get atp out of it so looking at it we've got nadh here yielding nad plus but we have this first poison right here wrote known which whoops rhodanone is a poison that affects the first protein here if it affects that first protein it's going to affect the whole etc if it affects the whole atc you're not going to get a hydrogen ion gradient when you don't get a hydrogen ion gradient you actually don't get the protection of atp and so the organism essentially starves from lack of energy similarly cyanide and carbon monoxide affect an organism because the last protein is going to be affecting it so it's affecting the etc and because you can't go down to the final electron acceptor of oxygen you're not going to get that hydrogen diode gradient sorry folks and ultimately you're not going to get chemiosmosis which makes the atp oligomyosin is a poison that's used on fungus so those the problem there is it's actually affecting atp synthase so you might get a gradient but you're never going to get the atp production at least not through this method and then finally dnp is another horrible poison which basically it allows for the mitochondria inner membrane to have blockage i'm sorry it's unblocked so that means the hydrogen can just flow right through and there's no barrier that means that there is no concentration gradient and no atp so really if you understand the function of oxidative phosphorylation you can see how these uh chemicals can affect um organisms survival