all right welcome back to our second video for chapter 7 here we're going to look at what happens after glycolysis including the oxidation of pyrovate the citric acid cycle and oxida phosphorilation so what happens after glycolysis really depends on if we have oxygen present or not if we have oxygen available and here we're going to focus on eukariotic cells because we are ukar humans then what happens next is the two pyrovate molecules we generated at the end of glycolysis will move into the mitochondria and become oxidized and this process of oxidizing pyrovate creates something called acetyl COA that will be going into the citric acid cycle the step after the oxidation of pyate so during this process let's look let's look at what happens I'm going to look at just one pyrovate molecule I know I generate two from glycolysis but let's look at one at a time so the first step it looks like is I'm going to remove a carboxy group from pyate and that's going to be released in the form of carbon dioxide it looks like when pyate is oxidized to acetyl COA this is a redox reaction so whenever something is oxidized the other thing has to be reduced something has to be reduced because the electrons have to go somewhere and it looks like it's nad+ that becomes reduced and generates my high energy electron carrier nadh so if I look at the inputs and outputs I have two pyate because I had two of them formed at the end of glycolysis I need two of those NAD plus molecules and I need two co-enzyme A's my outputs include two carbon dioxides each one is from each of those pyrates two nadh and then two acetyl coas that will enter the citric acid cycle next so after the production of acety COA from the oxidation of pyate reactions we move acety COA into the citric acid cycle and again just like in glycolysis you do not have to memorize every single reaction that's happening here we're going to look at and focus on what goes in what comes out where the reactions are happening and notable characteristics so if I look at the citric acid cycle and by the way this is often also known as the crab cycle named after the guy who discovered this in the 30s 1930s I should say and then sometimes it's also called the tricarboxylic acid cycle although that name is pretty old I don't really hear that as often most of the time people call this the citric acid cycle the reason for this is because the first product of the re of the cycle is citrate also known as citric acid so let's see what happens in that very first step of the citric acid cycle we take acetyl COA from the previous step and that was two carbons so each acetyl KOA has a two carbons in it from the glucose remember we lost we had pyate and we lost one of the carbons in the form of CO2 per pyrovate molecule the acety is combined to a four carbon molecule called oxaloacetate so this one has four carbons this one has two carbons to form citrate six citrate is also a six carbon molecule then as we go through the whole citric acid cycle we're going to be oxidizing citrate and those two carbons we put in in the form of acetyl COA will both be oxidized and released in the form of CO2 along the way it looks like we have some electron transfers so some redox reactions in order to generate three nadh sorry NAD and one fadh2 molecules so we generate some of these high energy electron carriers because there are some redo reactions happening along the way it looks like we also produce some GTP which is synonymous with ATP and which which one we make really depends on which cell we're kind of looking at what kind of cell we're looking at and then as we go through the cycle because we released two carbon dioxides what we have left over is again oxaloacetate the molecule we started with at the beginning so this this citric acid cycle keeps going on it runs continuously because you're recycling your initial reactant so the citric acid cycle only happens when we have oxygen available and in UK carots it happens in the mitochondria specifically in The Matrix of the mitochondria do you guys remember mitochondria are double membrane organel they have an outer fosol lipid membrane but they also have an inner fosol lipid membrane that is folded up to increase surface area and this inner membrane was called the Christi the liquid inside if I just put an X where this liquid is is called the mitochondrial Matrix and this is where the citric acid cycle primarily happens if I look at the pathway if I just look at all these reactions over here even though the citric acid cycle requires oxygen there's no direct use of oxygen here so why do we only go through this pathway when we have oxygen it's because all of these high energy electron carriers that we're producing those three nadh and then that single fadh2 or is that third there it is 3 nadh and 1 fadh2 those are going to be shuttled to the next step where oxygen will be used directly and let's see I make only a little bit of ATP or GTP in this in this reaction depending on the cell type I have so there's not much ATP or GTP made directly and again there's no Oxygen consumed directly so let's this into everything that's happened so far we had glycolysis in which we started with glucose a six carbon molecule at the end of glycolysis I'll just put gly we had two three carbon molecules these were called pyrovate or pyic acid and then I had that oxidation of pyrovate so each of these pyrates will get oxidized forming acetyl COA which is a two carbon molecule where did that third carbon go remember I lost it in the form of CO2 to all right so I breathe that out if I'm human so I blow that out I've got two carbons left each of these carbons or two carbon molecules enters the citric acid cycle and interestingly enough it looks like per turn of the citric acid cycle which is per acetyl COA I lose two more carbon dioxides so by the end of the citric acid cycle I have already oxidized all of the carbons from my six carbon glucose all right so let's look at all the outputs so far from glycolysis the oxidation of pyate and the citric acid cycle I know that I generated a net of 2 ATP from glycolysis and then I saw two more from the citric acid cycle remember we're going to consider GTP as equivalent to ATP for now and the reason there's two even though I only saw one in that previous diagram of the citric acid cycle I saw one is because remember there's two acetel coas two two carbon molecules because of the two pyrates that were generated from glycolysis so I have a net of 4 ATP so far at this point meaning at the end of the citric acid cycle I have oxidized all of the carbons from glucose as I just mentioned and then I generated a bunch of these high energy electron carriers nadh some of them from glycolysis some of them from the oxidation of pyate and many of them from citric acid cycle I also made another type of high energy electron carrier fadh2 also from the citric acid cycle so as I mentioned glucose is already completely oxidized by the end of the citric acid cycle and I have a lot of potential energy stored in the form of these high energy electron carriers so is most of the energy from glucose stored where is it in ATP in CO2 these electron carrier molecules we're going to say that it's in the electron carrier molecules remember I called these the tickets from those arcade type games so we're going to trade in our tickets for ATP in the very last step of cellular respiration our final pathway when we have oxygen available after the citric acid cycle is oxidative phosphorilation and this is exciting this is where we get to trade in our high energy electron carriers or tickets for our energy currency ATP so most of the ATP produced during cellular respiration occurs here this is the only pathway where we use oxygen directly and we're going to see that in this pathway we have something called the electron transport chain which I often abbreviate et C for short and chemiosmosis which I mentioned earlier is the most common method by which we produce ATP what we're going to see is the electron transport chain component of oxidative phosphorilation is going to create a proton concentration gradient it's going to be an electrochemical gradient and that is going to provide energy to power CH osmosis the production of ATP through chem osmosis and this is going to be happening in the inner membrane of the mitochondria so we're going to see a couple of regions involved but the proteins involved or the enzymes involved in this process will be embedded in the inner membrane of the mitochondria the Christi so let's look at that first part of oxidative phosphorilation the electron transport chain the Etc remember we're looking at the mitochondria and that inner membrane of the mitochondria the Christie and these are where the proteins are embedded in that inner mitochondrial membrane so this picture right here is basically here intermembrane space is the space between the two membranes and the mitochondrial Matrix is over here so if I look carefully it looks like what's happening is we have a bunch of electron Transporters embedded in the membrane and these are the blue proteins shown here and we are going to be collecting electrons from those high energy electron carriers we produced earlier so nadh will donate electrons to the electron transport chain in order to regenerate nad+ for glycolysis and crab cycle or citric acid cycle fadh will be doing the same thing it's going to oxidize Itself by donating electrons to this electron transport chain as these proteins these electron Transporters get reduced become reduced by receiving the electrons from these high energy electron carriers they gain energy to push protons from The Matrix into the inter membering space and as this happens we're going to build up a nice proton gradient in this inter excuse the inter membrane space ultimately we're going to let the protons back down into the Matrix which will be a very spontaneous or favorable process releasing energy to form ATP and we're going to see later that oxygen is required because the electrons that were donated to this electron transport chain have to go somewhere at the end so there's no backup in the system the final electronic scepter in this system is oxygen so oxygen will receive the electrons that were donated from nadh and fadh2 to form water so how do electrons move across the electron transport chain what causes them to move if we look carefully at the diagram here there are four complexes four very large protein complexes embedded in that inner membrane of the mitochondria and they are complex one 2 3 and four don't have to worry so don't worry about what they're made of and all the names of the enzymes just know that there are four complexes that are embedded in the inner membrane of the mitochondria the reason electrons will be transferred from one complex to the next is because each subsequent component of the chain of the electron transport chain is more electr negative than the previous one so it'll almost like suck the electron to itself some of these components are mobile they can actually move around so one of these includes something called ubiquinone or q q can grab the electrons from one complex one and complex 2 and transfer it to complex 3 complex 3 cannot move but we have something called so that was ubiquinone or Q complex 3 has something called cytochrome C that can also move around so it'll take the electrons from complex 3 and transfer them to complex 4 here I told you earlier that the electrons have to go somewhere so that the chain is not backed up and they go to the final electron acceptor oxygen which is when it's reduced forms water so it'll pick up some protons as well to form water if I look at the nadh and fadh2 they enter at different steps in the electron transport chain NAD H enters and donates its electrons to complex number one whereas fadh2 enters later on and donates its electrons to complex number two so the amount of ATP each of these high energy electrons carriers can be traded for varies nadh can be traded for more ATP compared to fadh2 because the number of ATP you can generate depends on the concentration gradient you generate since nadh donates its electrons to the first complex what happens is when the complex receives the electron it changes the shape of the protein the complex so that protons are pumped through and several of these protons are pumped through and then the electrons from nadh are going to keep going down this chain every time it goes down more protons are pumped through into the inter membran space whereas since fadh2 let me use a different color fadh2 enters later on in the chain it skips that first complex so fewer protons are pumped through into the intermembrane space as a result of fadh2 so this is equivalent to fewer atps some textbooks will tell you that nadh can generate about 3 ATP others will say it's about 2 .5 so between 2.5 and 3 ATP per nadh for fadh2 some textbooks will say 2 ATP because they're rounding up others will say 1.5 ATP per fadh2 molecule all right so what's happening in the second part of oxidative phosphorilation is chemiosmosis the more common method by which we produce ATP so we generated that nice proton GR radiant where there are a lot more protons in the intermembrane space compared to fewer inside the mitochondrial Matrix and what wants to happen now is these protons really want to come back in because they want to go from high to low concentration they cannot do so by crossing the membrane because these are charged and remember the hydrophobic layer these fatty tails of the phospholipid Bay will not allow them to pass so the only way they can get back in is through an enzyme called ATP synthes this big blue protein here as protons are allowed back in going from high to low concentration they this is a favorable reaction so that's going to be exergonic it's going to release energy and that energy is going to be used to power the endergonic reaction of the production of ATP so again this protein is critical for the production of ATP through this process CH osmosis we're powering or using the electrochemical gradient generated from the electron transport chain to produce ATP so if I look at the mitochondria remember the inside is the Matrix here we have our intermembrane space this was the inner membrane here's my electron transport chain and where did those nadh and fadh come from again fadh2 I should say remember most of them came from the citric acid cycle some of them came from that oxidation of pyate and we also had some from glycolysis they all eventually donate their electrons to the electron transport chain oops Etc we are using these the energy from these electrons to produce our proton gradient where there's going to be a lot more protons in the intermembrane space and when we allow them to go back down or with their gradient that is exergonic it releases energy and we use that energy to we couple that really with an endergonic reaction to form ATP and again the second half is called CH osmosis and this is just for fun but there were two scientists that won the Nobel Prize in 1997 for the discovery of ATP synthes and one of them was a professor at UCLA when I was there I remember I was there in '97 and we had our chemistry building I forgot what the old name of the chemistry building used to be but there was a big celebration for Paul Boyer and after the Nobel Prize was awarded we renamed the chemistry building to the Boer building and now I believe several buildings at UCLA are named after him so overall if we consider all of the ATP that we produced through the method of cellular respiration it's between approximately 30 to 36 uh ATP molecules per glucose so this really varies depending on what kind of cell or species we're looking at and it also depends on how efficiently nadh is shuttled from the cytoplasm of the cell remember that's where glycolysis happens into the mitochondria where the electron transport chain is found overall we'll just remember somewhere in the 30s that's how many ATP are produced per glucose molecule although we do lose some energy in the form of heat cellular respiration overall is pretty efficient we actually can capture about 34% of the oxidation of glucose that process in the form of ATP and to compare this to like a car probably not a electric car or a hybrid car but a gasoline powered car the efficiency of our cars is about 10% or sometimes less so you imagine you get like 10 gallons of gas and it's so expensive only 1 gallon is actually powering the movement of your car the other nine gallons that energy is lost in the form of heat all right that takes us to the end of our second video for chapter 7 in our third and final video we're going to look at what happens if we don't have oxygen what happens after glycolisis if there is no oxygen