[Music] hello everyone this is andy from med school eu and today we're going to continue on with the topic of bioenergetics and more specifically we're going to take a look at aerobic respiration so in the previous video we went through the process of glycolysis which is the first stage of cellular respiration and we're going to have to decide where the products of glycolysis go so what is the path of glycolysis products and where do they turn and where does the cellular respiration continue uh with certain conditions so what we have is we have our mitochondria of course the double membrane system here and this is our pyruvate that we've made through the process of glycolysis so we're gonna label this as pyruvate pyruvate it's the three carbon molecule and it's of course it's made in the cytosol or the cytoplasm where the process of glycolysis occurs and the product of glycolysis is two pyruvate molecules so there's two pyruvate molecules however in this just for the purpose of this slide we're always going to take a look at one uh just to see exactly what happens to it now what is the path of pyruvate from the cytosol here's the mitochondria inside the cell and where does this pyruvate go well it could go into the mitochondria inside past the two membranes or it could stay in the cytosol and not enter the mitochondria now what distinguishes the two processes is that the presence of oxygen so if we have here let's let's pick another color if we have high oxygen available for the cell so the cell is able to consume oxygen and is able to get oxygen diffused inside its cellular membrane and there's just oxygen molecules flowing around that gives pyruvate products of glycolysis the ability to penetrate the outer and the inner membrane of mitochondria and go into the mitochondrial matrix and of course this is where cellular respiration happens with the krebs cycle which we will go over in this lecture however now if if oxygen is not available or it's in low concentration for the cell and the best example of having low oxygen presence for the cell is when you're exercising so when you're doing extremely extraneous exercise for example you're doing bicep curls and during the set of bicep curls you're not you're not pausing so you're not your muscle does not stop exercising and you keep going for let's say 30 seconds 40 seconds now during that time the oxygen supply of the cell is being depleted because it's being used in order to to provide energy for the cell so that it could continue to contract and once it gets completely depleted we're no longer using the krebs cycle and all of and all the rest of the cellular respiration methods we are going to go through something called fermentation fermentation and typically only after you stop your set so you put the dumbbells down and and you rest your muscle this is when oxygen actually gets into the the muscle cell and the oxygen levels rise and then of course the pyruvate is able to break out of this fermentation and enter into the krebs cycle or enter into mitochondria to continue on and produce a lot more atp however if it's not available like during a set or during strenuous exercise where you're you're doing at a maximum rep capacity so it's not something like running because running is sub-maximal so you're not exerting all your force for running when you're running you're exerting maybe 30 maybe 40 of your maximum force that you can put off with your legs and therefore this is why we're able to run for so long because we get a continuous supply of oxygen to those muscles to those cells and they're able to go through the process of cellular respiration producing lots and lots of atp and this is why we can run things like marathons without pausing and we can run even longer distances without pausing however if you are doing something like your maximum squat if you're doing your maximum bicep curls then you're probably going to stop at one or two and you're not going to be able to do a third curl because your muscles are simply too tired you've built up too much lactic acid as a result of fermentation so the next step in terms of the cellular respiration we have pyruvate oxidation so our molecule of pyruvate of course this is pyruvate that is in the cytoplasm it enters the outer membrane by simple diffusion it enters the inner membrane of the mitochondrion by transport proteins it uses a symport it uses a symport transport protein where ions are used in order to transport the molecule of pyruvate inside into the matrix of the mitochondria and this is a secondary membrane transfer secondary active membrane transport and that's that's going to go into matrix of mitochondria so keep that in mind that it goes through the secondary active membrane transport through a process called symport that we've talked about in previous lectures in terms of transport across membranes now here we're gonna discuss the process of pyruvate oxidation what this means is pyruvate is is going to be oxidized so the loss of electrons is going to occur to pyruvate in order to create another molecule called acetyl coa so let's label this molecule as acetyl coa and let's go through the process what actually happens so it is combined with an enzyme called pyruvate dehydrogenase complex and what this pyruvate dehydrogenase does is it takes pyruvate through an oxidation reaction where it oxidizes pyruvate and reduces nad plus into nadh in order to produce acetyl coa two carbon molecule of acetyl coa and it releases carbon dioxide so remember there's two molecules of pyruvate means there's going to be two acetyl coas entering the matrix or inside the matrix and there's going to be two co2s released here so keep that in mind so the coash is simply just another molecule that's being added to the the carbon here as as it is added right there and we call it acetyl co a coenzyme a now of course nad plus goes through reduction into nadh whenever we add a hydrogen we go through reduction now of course the the pyruvate goes through oxidation reaction where it's losing electrons and we end up with acetyl-coa molecule and this is what enters then goes into something called a krebs cycle krebs cycle and all of this all of this process this pyruvate oxidation and the krebs cycle it all occurs in mitochondrial mitochondrial matrix so our acetyl-coa molecules have entered the citric acid cycle or we call it krebs cycle and let's discuss what happens at each of the steps so step number one we have the two carbon acetyl-coa so we're going to take a look at this whole cycle in terms of just the one acetyl-coa molecule but remember we have two acetyl-coas entering per glucose molecule so glucose goes through glycolysis which produces two pyruvate no two pyruvate are converted to two acetyl-coa molecules and of course these two acetyl-coa will enter into the krebs cycle however for the purposes of this video we're simply just going to look at one and go through the process however you you must know and you you should imagine that the acetyl-coa would go through this twice so what what happens in our first step is that the acetyl-coa is being has been carried into the krebs cycle with the co-a molecule and the two carbons the two carbons from acetyl are going to be transferred onto oxaloacetate so oxaloacetate is a four carbon molecule that is uh the the byproduct of the citric acid cycle every cycle finishes with oxaloacetate and oxaloacetate will combine with the two carbon acetyl to make a molecule called citrate now citrate has six carbons we combine the four carbons with two making six carbons and the co-a is disassembled from the acetyl group and the co-a simply remains in the matrix for the next acetyl or for the next pyruvate to come in and be able to attach through now this whole attachment and this this entire synthesis of citrate is going to go through an enzyme called citrate synthase and keep in mind that every single enzyme that is mentioned almost every enzyme that is mentioned in this cycle will have the first the first name of it will be the name of either the reactants or the product in this case it is the product since it's citrate and it's synthase synthase meaning it is it assists in the synthesis of citrate and the synthesis will simply be the addition of oxaloacetate to the acetyl group making it six carbons the next step our citrate molecule is going to be uh is going to become isocitrate which is another six carbon molecule and this citrate is simply rearranged into its isomer so the isocitrate is an isomer isomer meaning that it is the same chemical formula but the bonds are arranged differently and this is done through an enzyme called econotaze now moving on to the next step this is where things begin to get very interesting in terms of the the krebs cycle is what we have our isocitrate six carbon molecule is going to be converted into alpha ketoglutarate which is a five carbon molecule now keep in mind each time that we go down a carbon we lose a carbon from our cycle it is lost in the form of co2 so here we we have the production of co2 as you know the byproduct of cellular respiration is is carbon dioxide and this is where it comes from we we get these carbon dioxides from oxidizing molecules in the krebs cycle and this is the first part of it here so isocitrate as being is is going to be oxidized into alpha-ketoglutarate and because this is an oxidation reaction dehydrogenase remember performs oxidation reactions because this is a oxidation reaction there must be a a reduction reaction making a redox correct so the redox reaction will be that nad plus is going to be reduced into nadh and a proton so this is where we produce our first electron carrier within the krebs cycle and this is all done through isocitrate dehydrogenase moving on to the next step the alpha-ketoglutarate is going to be further oxidized into suicide so another coa molecule will come in and be attached to a four-carbon molecule called suicidal now keep in mind each time we lose a carbon from our oxidation reaction we're going to get the carbon dioxide out of it so again we produce a carbon dioxide here now because this is an oxidation because we use another dehydrogenase alpha ketoglutarate dehydrogenase specifically we have a reduction reaction of nad plus into nadh and a proton and again we produce another electron carrier for our further reactions moving on into the next step so just pay attention to this side of the equation what we have is from susan alkaway the co-a the coenzyme a is going to dissociate it's going to break off and we're going to end up with just a molecule of susana which is another four carbon molecule we did not lose any carbons therefore we did not lose any we did not produce any carbon dioxide now the interesting thing is that the release of coe from susan alkaway produces susanate and the energy released converts gdp to gtp so because we are releasing this koa molecule from susan alkaway because of the release here it produces energy and this energy is basically harvested by gdp and an inorganic phosphate combining these producing a molecule of gtp and gtp is another molecule of energy however this gtp is then further converted into atp and this is the only atp made directly by the citric acid cycle so we we're going to see that these electron carriers nadh will make lots and lots of atp molecules later on however for now we must know that the citric acid cycle does produce atp directly and here's the method so we must know this is direct production of atp and this is the only direct production of atp in the citric acid cycle as it produces one atp per acetyl coa molecule so if there's two acetyl coas overall each glucose molecule will produce two atp molecules moving on to the next step we have another oxidation with the dehydrogenase we're going to associate dehydrogenase so the susanate is going to go through an oxidation reaction and it's going to lose electrons which then the fad will become fadh2 and this is another electron carrier molecule just like nadh that we're going to use in our next step and here we don't have a loss of carbon even though we go through oxidation however what what is removed is two protons and two electrons from the susanate and because we have a removal of electrons we're going to have removal of protons and these two protons will be added on along with the electrons to the fad molecule having it reduced and therefore the susunit because it lost electrons becomes fumarate still with four carbons but it is oxidized because it has lost electrons the next step is a hydration reaction because we have the addition of water into the molecule into the equation and what we have is the fumarate is going to be converted into malate and this is just another isomer of a fumarate it's just going to isomerize it through an enzyme called fumarase and we'll convert it into malate molecule again the four carbons still remain and finally the in the last step the malate is going to go through malay dehydrogenase and this dehydrogenase again is going to oxidize the malate and take away an electron and a proton making it oxaloacetate with four carbons and the nad plus will become nadh the reduced form so overall here what we have is that one acetyl-coa molecule will produce one two three nadh one nada fadh2 and one atp now if we put through two molecules of acetyl coa then of course everything will be multiplied by two in the citric acid cycle so this will conclude the video for today i decided to split the lecture on aerobic respiration into two parts so in the next part in part two we're going to take a look at how our molecules of nadh and fadh2 our electron carriers are going to be oxidized and used in the electron transport chain in order to produce lots and lots of atp through the process of oxidative phosphorylation and chemiosmosis [Music] you