all right ninja nerds in this video we're going to talk about the KB cycle so you can also call it you know the triricaroxyic acid cycle you can call it the citric acid cycle so there is other names for it it was actually founded and developed by the guy named Hans Krebs that's that's where it came from okay so now when we go through the Kreb cycle we've already gone over in great detail but we've already gone over the glycolysis pathway we have actually gone over all the glut transporters we've gone over the glycolysis pathway of converting what is this molecule right here this is glucose right here we've converted glucose into pyuvate and how many pyuvates have we actually made technically we made two of these right because we split this sixcarbon fragment into two threecarbon fragments so we've actually made two pyuvates and during that process you guys already know that we generated two NADHs and two net ATP and then you know that we've already gone into detail whenever there's oxygen present we can take this pyuvate bring it into the mitochondria and we can transition it right we can get ready to transition to the KB cycle and in that transition step or that preparation step what did we do we added a co-enzyme A into this reaction right and then what else did we do we generated two NADH's and we produced two CO2s by decarboxilation and that was done through this whole pyuvate dehydrogenase complex with the E1 E2 and E3 we already gone we already went over that in great detail and all the mechanisms now we're going into this next thing which is the KB cycle so we formed acceto COA from the transition step right this molecule here is our acetal COA now what we're going to do is we're going to convert this acetto COA we're going to fuse it with this fourcarbon fragment right here this fourcarbon fragment is actually referred to as oxaloacetate so again this guy right here is called I'm going to denote it i'm going to abbreviate it O A oxalloacetate is going to combine with the acetto COA when these two substrates combine they fuse together and the presence of this enzyme and we'll talk about this enzyme in a second but OA is a fourcarbon structure combining with a twocarbon structure and again what is this this red structure coming off of the acettoa that's the co-enzyme A when this acetal COA and when this OA combine with this enzyme they form a sixcarbon molecule look 1 2 3 four five six what is this molecule called this is called citrate you know what's really interesting you know citrate is Krebs starting substrate for making oxaloacetate what did I just do i gave you guys a little quick pneummonic to be able to remember all of this so it's an easier one to be able to do okay so how do I remember i again oxalo acidate and acceto come together in the presence of this enzyme to form citrate and then I like to remember this citrate is Kreb's starting substrate for making oxaloacetate well what is is for is is for iso citrate so let's get all these intermediates out of the way it's an easy way to be able to remember them because that's what we long for all right sometimes they just get it out of the way the memorization right krebs is for alpha keto gluterate i might refer to it as a kg whenever you guys see it like that starting is for sueninal COA suinal COA substrate is for suxenate this is suxenate four is fumemerate and then the last one is making which is going to be malate and the last one is oxaloacetate so again it goes citrate is Kreb's starting substrate for making oxaloacetate just a little quick pneummonic i thought that would help out to just memorize you know the basic intermediates now that we've done that really there's nothing crazy else that we have to know other than just the regulatory steps and what's happening in between okay cool so let's do that now that we know the intermediates let's focus on the enzymes and what's produced and what's happening in each step so acetto coa and OA or oxaloacetate when these two are fusing there's a special enzyme and what is this enzyme doing it's forming citrate it's synthesizing citrate so what would that enzyme be called you call it citrate synthes so there's a citrate synthes enzyme this citrate synthes what is he doing he's taking the oxaloacetate in one part taking the acetto clay in the other part fusing them together and making citrate now the question is this enzyme is extremely very highly regulated so it's going to control this step so acetylco going into citrate with oxaloacetate this is not a reversible step this is a one-way reaction so what does citrate synthes have to be regulated by okay it's going to go on and on what you guys are going to see throughout a series of these biochem videos think about this if our body is having a lot of metabolism so it's occurring a lot a lot of metabolism a lot of KB cycle a lot of electron transport chain activity i'm making a lot of ATP if I'm making a lot of ATP do you think I'm gonna want to keep having the KB cycle going on making more NADHs and FADH2s no because I already have too much of it this is going to inhibit it that's going to aloststerically inhibit this enzyme same thing in the KB cycle you'll see that will generate a lot of what's called NADH that you see here nadhs if there's too many of them it's also basically telling this enzyme there's a lot of energy supply within the cell we don't need anymore shut down don't do this anymore okay then we have another one citrate himself you know whenever there's actually too much citrate citrate can actually come back and inhibit this enzyme so citrate himself can come back and inhibit this enzyme so citrate can say "Okay there's way too much of me." Because generally what's going to happen when you make citrate it'll automatically get converted into isocitrate generally some of this citrate can also get converted into the basic units for fatty acids called malano qua and we'll see that but generally it should be progressing somewhere it shouldn't be building up when it's building up it's letting the citrate synthes know don't make any more of me stop working and then there's another one he's all the way down there though it's called suinal COA so suinal COA is also an alossteric inhibitor he's just a little bit more downstream and he's just telling this enzyme hey before you even think about making citrate there's already too much of me so shut down and stop making more citrate and making more of me making more NADHs more ATP just stop doing that and these are generally the main aloststeric regulators of this citrate synthes now what would be a stimulator we've already talked about this so many times but it's a good good way to keep continuously reviewing atp gets broken down into what guys it gets broken down into ADP and inorganic phosphate if you're breaking down a lot of ATP you're going to build up a lot of ADP and this is going to signify that you are actually not having a lot of ATP within the cell if there's not a lot of ATP in the cell that's not good because ATP is needed for transport mechanisms for metabolic pathways for DNA synthesis so many different things ion channels so ADP would be a very powerful alossteric stimulator of this enzyme it would let this enzyme know hey there's not a lot of ATP you need to continue to keep going through the KB cycle making more NADHs and FADH2s and make more ATP so that would be that guy so generally this is how we're going to aloststerically regulate this googlyide enzyme okay because this googlyide enzyme is involved in this step right here converting the acetto into citrate very very highly regulated step okay so we're done with that one okay so now we got this Betty White enzyme okay this Betty White enzyme with the perm going on is converting citrate which is a sixcarbon molecule into what okay one two three four five six it's still six carbons so what's really happening it's just an isomerization reaction in isomerization reactions all you're doing is you're just shuffling around the hydrogen's and the carbons but there should still be the same number of carbons and hydrogen's and oxygen in this guy as there is carbons hydrogen's and oxygen in this guy so it's just shuffling things around not a crazy crucial step but the enzyme controlling this step as you guys can see is doing what it's able to move in the reverse direction so whenever there is too much isoccitrate you can convert it back into citrate it is possible and it actually does happen and you'll see this whenever we talk about this in fatty acid synthesis but the enzyme that's controlling this is called aonotase ac okay aonotase enzyme so there is you know just because it's not controlling it's not highly regulated and is reversible doesn't mean that this enzyme isn't important you know there's a rat poison um in rat poison there's a chemical that's present called fluo acetate and what happens with this fluo acetate is it's kind of acting like acceto you know acetate is just basically another fancy word for saying it's a twocarbon structure all it has is just a florine attached to it so it's going to get actually converted it's going to act like fluoroacetate so you know how you're going to have acetto coa here you're going to have this fuo acetto coa which gets converted into fuo citrate and that fuocitrate binds onto the aonotase enzyme and what is it eventually going to do it's going to inhibit this enzyme and this enzyme once it's inhibited it can't convert citrate and isoccitrate so you can't you won't be able to generate eventually NADHs FADH2s and ATP and that is a very very bad thing so fluoroacetate can actually cause inhibition of this aonotase enzyme and again it's within rat poison so if you you somehow terribly take on too much rat poison for whatever reason uh it can inhibit this enzyme all right cool now we come into this next one so we're going to convert isoccitrate into alpha ketoglutarate all right cool how many carbons is this guy six carbons how many is this guy one two three four five okay cool five carbons that means I lost a carbon somewhere whenever you guys hear that whenever you see a carbon missing automatically assume that you lost that carbon in the form of CO2 what is that called i know we've talked about it but what is it called whenever you lose a carbon in the form of CO2 what do they call that they call it d caroxilation okay so decarboxilation is the the actual reaction in which you're removing a carbon in the form of CO2 primarily a caroxil carbon well we're losing that okay now in this reaction we have a very very important enzyme this enzyme is called iso citrate de hydrogenase right away bells should start ringing in your head once you hear dehydrogenase automatically know that you are going to be converting NAD positives into NADH's okay automatically once you guys see that automatically think oh I'm going to make NADH's in this step so what happens in this reaction NA positive is reacting in the step to generate Na DH okay that's what's happening in this step i'm taking NAD positive and converting it into NADH cool now you see how this step is one direction it's not birectional so this is not a reversible enzyme it can only be moving in one direction usually any enzyme that forms CO2 is generally usually irreversible isoccitrate dehydrogenase has three pockets on it look it's got this pocket this pocket this pocket what is going to happen here okay again realize that whenever we're actually having high amounts of ATP you guys can automatically think that whenever there's high amounts of ATP this little Snoopy dog has three binding sites okay three binding sites what's going to happen to this little Snoopy dog or the isoccitrate dehydrogenous enzyme if there's too much ATP ATP will inhibit this enzyme and that should already make sense because there's too much energy production we want to slow it down whereas think about the opposite effect if I'm breaking down a lot of AD ATP and generating a lot of ADP that should stimulate this enzyme and that it does my friends okay and for the last one this one's kind of going to be like what the heck where'd that come from calcium is another strong stimulator of this enzyme and this should actually make sense think about this in the muscles in muscles calcium is acting as a nice important type of signaling molecule to activate the the crossbridge formation within the skeletal muscles or even cardiac muscle right he's important for that because we need calcium in order for our muscles to contract but another thing that we need for our muscles to contract is ATP if this enzyme is stimulated he's going to help to generate NADH's which will take those hydrides to the electron transport chain and generate ATP so calcium is helping to stimulate this enzyme till we can make more ATP so we can have more contractions because he knows ATP is needed to detach the meosin from the actin for the crossbridge formation right so calcium is kind of letting this enzyme know make more ATP we're not we don't have enough ATP in the cell we need to make more ATP is an inhibitor because it's saying we have too much stop making more simple nothing crazy about that okay now we're going to move on to this next enzyme this next enzyme is extreme extremely important we really need to remember this enzyme this enzyme right here look at this she's got you know locks here this is called alpha i'm going to do that ketoglutarate KG D hydrogenase enzyme this is an extremely extremely crucial enzyme okay count how many carbons we have again one two three four five for alpha ketoglutarate for sueno COA how many do I have one two three four okay that means I must have lost the carbon oh yeah cool so there must have been decarboxilation i must have lost a carbon in the form of CO2 so there must have been another decarboxilation reaction oh wait zach said whenever I have a dehydrogen automatically think NAD positive to NADH okay so that's not bad this reaction is kaput it's done that's it it's not that bad because all you got to remember is okay five to four loss of CO2 decarboxilation NAD positive to NADH because there's a dehydrogenase enzyme that's it now we have to remember look this she's got three pockets here in her dreads okay what's going to happen same thing now think about this one it's going to be a little tricky nothing crazy you see soxenyl coa he's just sitting here he's going to tell this enzyme if there's too much of him and if this enzyme needs to stop so look look what suininal COA can come over here and do it can come and bind onto this enzyme and it will inhibit this enzyme and tell this enzyme don't keep converting alpha ketoglutate to suininal COA we don't need to do that anymore there's either too much ATP there's too much NADH there's too much energy produced in the cell stop okay now the next ones are the next one's a little weird but it's not crazy you see these NADH's if you start generating too much NADH's that can also tell this enzyme to shut down so this NADH can actually come over here and what can it do look here's our NADH if there's too much NADH's what will it do to this enzyme it will inhibit this enzyme tell this enzyme don't keep converting me alpha ketoglutate into sueninoquake because there's already too much NADHs we need to stop making as much and that will inhibit this enzyme and the last thing is super simple because we already talked about him calcium right calcium is also going to work in this step too so you're going to have NADH who's going to be inhibiting this enzyme sucks in a COA which is going to be inhibiting this enzyme and then what else is going to be working in this step calcium calcium is going to be doing what in this step calcium is going to be stimulating this enzyme here okay so now that should make sense now right because we we generated CO2 by decarboxilation we generated uh some NADH's out of this reaction because we had the alpha ketoglut dehydrogenase but then we need to be able to regulate this enzyme to control how much activity is going on if there's too much succininoa from too much KB cycle activity it's going to inhibit this enzyme to stop this this KB cycle from continuing to occur if there's too much NADHs that are being generated it'll also inhibit this enzyme tell it not to continue to occur because we already have too much NADHS and too much ATP but then again calcium think of the muscles calcium is going to try to do what helps to be able to form that you know allow for the muscle contraction but we need ATP in order for the muscles to contract so without the ATP the muscles won't be able to contract so calcium is helping to activate this enzyme so we can speed up the ATP production all right cool now why did I want to mention this enzyme and say it's extremely important okay in your body alpha ketoglutarate is an integral component of an enzyme called histone demethylase and this histone demethylase basically what histone demethylaces do is let's say here's the DNA here I have a sequence of DNA or something like that right and you know DNA is wrapped around histone proteins and histone proteins are basically very important for being able to control the organization of these DNA the gene expression and stuff like that so these histone proteins are actually going to be having the DNA wrapped around them what histone demethylaces do is you might have methyl groups on these guys here which are basically controlling you know gene modification epigenetics and stuff like that this hyone demethylace will come over and remove those methyl groups alpha ketoglutarate is a co-factor it's a co-actor for this hyone demethylase right in our body we have that enzyme right so what was making the alpha ketoglutarate if you guys remember we were taking what we were having this alpha ketoglutarate which is going to be an important component of this step right here right helping to synthesize you know being a component of the histone demethylace if this alpha ketoglutarate right so remember we had the isoccitrate the isoccitrate was actually being converted what isoccitrate was being converted into alpha ketoglutarate right and that was done by the isoccitrate dehydrogenase enzyme but then alpha ketoglutarate is getting converted converted into what it's getting converted into sueninocoa through what alpha ketoglutarate dehydrogenase in a condition in which there is a mutant form of that alpha ketoglutarate dehydrogenase specifically the one which is having NADPH's involved with it not NADs NADPH's in a condition in which there is some type of mutation in this enzyme with the NADPHs it can actually convert instead of converting it into sueninoa and actually getting a lot of this alpha ketoglutarate you can get another molecule here and it's called two hydroxy glutarate why am I telling you this because two hydroxylutarate will come in and do what it'll bind and prevent this alpha ketoglutarate from being able to bind if alpha ketoglutarate can't bind onto the histone demethylis can you control the gene expression no if gene expression isn't controlled it can lead to tumors It can lead to uncontrolled cell growth primarily super dangerous one you guys have probably heard of it called glycomomas glymomas are basically tumors that are occurring within the gile cells in the brain one of the really really dangerous ones is the astroytoomas or the glyopblastoma multiiform so GBMs which are very very dangerous you usually have an 80% uh metastatic rate and you're usually malignant and can cause you know unfortunate death but again understanding how something so small that you would think you know oh this just metabolism it can have such an amazing effect on your body so again any type of mutation this alpha ketoglutarate dehydrogynase particularly with the NADPH1 instead of the NADH H1 can lead to the formation of a byproduct called two hydroxylutarate which can inhibit the alpha ketoglutarate from binding to the histone demethylase inhibiting this enzyme inhibiting gene expression and leading to uncontrolled cell growth and tumor formation okay now we got that out of the way let's move on to the next one now we got to take this sueninoa and I'm going to convert it into suenate okay what happened here okay somewhere in this reaction oh look at that alpha ketoglutarate going to suinico what did we miss over here we had that COA i should have a COA on this guy what does that mean that means I added a COA onto this step let's add that in there so there must have been a co-enzyme A being added into this step you know this alpha ketoglutate dehydrogenase if you guys remember the pyuvate dehydrogenase complex this enzyme functions in the exact same mechanism so if you guys remember that enzyme you'll remember how this enzyme functions anyway we add the COA in then look what happens we we get rid of the COA so then we lose the COA in this step but it's all for good reason just sometimes we might not like why it does this well what's happening here something really funky is happening when we release the COA it generates a little bit of energy a little bit of potential energy that our body uses to take GDP and an inorganic phosphate and fuse that to form GTP okay it's cool but then you know who comes in adp adp is like "Oh man I'm gonna pit pocket this guy so hard." So what does he do adb comes over here and steals the phosphate from the GTP adp when he gains the phosphate what does he turn into he gains another phosphate so he turns into ATP okay that's cool but what happens to the GTP the GTP unfortunately goes back to GDP okay so it's a cool way of our body being able to generate ATP through what's called substrate level phosphorilation so again what is that called it's called substrate phosphorilation which is completely different as compared to oxidative phosphorilation so substrate phosphorilation doesn't generate as much ATP as compared to oxidative phosphorilation okay so that's happening in this stuff so we're developing ATP and that's coming because of releasing out the co-enzyme A which creates a little bit of energy to take GDP and inorganic phosphate fuse them together to make GTP but then ADP comes over here pit pockets that phosphate from the GTP and makes ATP which converts the GTP back into GDP what enzyme is helping in this step okay this enzyme here converting suenyl COA into suinate it's got a pretty cool enzyme this is called specifically suenyl coa synthetase okay so you have the suenino coa synthetase enzyme and what this enzyme is doing is it's being involved in this step to stimulate the conversion of sueninoa into suxenate now when we get that suenate nothing crazy happens in this next step but let's see what's happening here nonetheless okay look we're taking suenate and we're converting it into fumemerate when we take suenate and convert it into fumemer we have another enzyme look at this look at this freak okay this enzyme right here is special you don't know why look where he's actually anchored he's anchored on the mitochondrial membrane specifically the inner mitochondrial membrane the christe you know this is actually called complex 2 enzyme complex 2 it's a part of the electron transport chain but we like to call it something else we call it suinate dehydrogenase boom light bulb what does that mean automatically you should think FAD in this case to FADH2 but you guys are probably like "Oh dude what you told me it was NAD." any type of co-enzyme usually FAD or NAD is usually involved whenever you hear dehydrogenase okay now because I'm forming FADH2 this is going to be helpful in energy production but you know what else is also helpful for this you know in certain conditions it's called fiochromocyto called fo chromosytoma there's some type of mutation in this enzyme an alteration or mutation this enzyme can cause a situation where you form a neuroblastoma it's usually benign meaning it's not metastatic it doesn't spread But this fiochromosytoone is usually a tumor that develops within the adrenal medulla and it causes an excessive amounts of epinephrine and norepinephrine to be produced which causes an extreme hypertensive crisis so a very very dangerous condition but just seeing any type of mutation this enzyme can lead to this condition of fiochromosytoma all right cool so again remember that this is enzyme complex 2 it's a part of the electron transport chain and it's converting FAD to FADH2 but it's also reversible so this reaction can be reversible all right cool so that's that step now we're going to take the fumemerate and we're going to convert that into the mali okay this enzyme is really really simple nothing crazy about this enzyme this enzyme is called fummerase and look we got Humpty Dumpty he's sitting on this reaction humpty Dumpty is actually going to do what he's going to throw some water into this reaction he's like "Ah let me help out in this reaction to the best of my abilities." And he throws water into this reaction but again remember that this reaction is reversible so what does he do in this reaction humpty Dumpty takes and throws water into this reaction to convert fume into mal now you might be like "Okay simple must not be that important of an enzyme." He is very important you know in the in a condition which there's a deficiency in this enzyme it can lead to the formation of what's called leomas or leomyomas too and leomas are usually going to be tumors that develop within smooth muscle tissue usually they're benign perfect example this one is is they also call them fibroids but it's some type of uterine very very common in the uterine smooth muscle and even in the kidneys okay so this can happen in the uterine smooth muscle and it can happen in the kidneys but usually there's some type of leoma and again just a deficiency in this enzyme can cause that significant change unbelievable okay so now we got malate malate has this Hades looking enzyme look at this look at this freaking guy this guy right here is a cool enzyme i like him he's called malate dehydrogenase you guys should automatically think again NAD positive2 NADH so what's happening here i'm taking NAD positive and I'm converting it into NADH why because there is a dehydrogenase enzyme present when there's a dehydrogenous enzyme present it's converting NAD positive to NADH in this step this enzyme is also reversible so this reverse reaction can occur OA to mali and we'll see that in throughout more videos where we cover a little bit on gluconneioenesis and even electron transport chain okay now that we've done that we've covered all of these different enzymes that are involved in this in these steps here now one other thing I want to do I want to tell you guys is is that when I'm taking this acettocoa what am I doing right i'm taking this acceto I'm combining with the oxalo acetate and having it react with citrate centase to form citrate citrate is reacting with a conantase to make isoccitrate isocitrate is going to be acted on by isoccitrate dehydrogenase to make alpha ketoglutarate alpha ketoglutarate gets converted into sueninoa when acted on by alpha ketoglutate dehydrogenase the suino sueninocoa synthetase is going to be taking sueninoa and converting it into suxenate which generate a little bit of ATP in that step and then suxenate is converting it into fumemerate and then fummerate is being converted into malate and malate back to OA how many acetto should I really be having going through this this cycle this is crucial i have two pyuvates well two pyuvates get converted into two acettocoas that means I make two turns well if I make two turns don't I really develop two FADH2s don't I really develop two NADH's and don't I develop another two NADH's right here and another two NADH's right here and technically two ATP and two COAs right and two COAs being added okay so how many CO2s did we generate out of this we generated two in this step and we generated two in this step so 2 plus 2 is four so we got four CO2s out of this okay what about NADH's i generated six NADH's how did I generate six NADH's let's look we generated two NADHs in this step going from Mali to oxalo acetate right so that's two i generated two NADHs in this step going from isoccitrate to alpha ketoglutarate that's four and I generated two more NADHs going from alpha ketoglutarate to sueninoa that's six then what was the last thing that we generated two FADH2s okay cool so I got two FADH2s last thing how many ATP did I generate two ATP and by what type of phosphorilation substrate phosphorilation so again I'm generating by substrate phosphorilation and where is that happening that's happening when I'm going from sueninal COA to suinate remember I'm taking the GDP to GTP and having the ADP pick off that phosphate to form ATP two of them by substrate level phosphorilation so out of this this is going to be the main products that you'll get out of this and these NADHs and FADH2s will go and take these hydride ions to the electron transport chain will they be used to make ATP by oxidative phosphorilation all right ninj so we went over a lot of information in this video i hope it all made sense i hope you guys did enjoy it if you did please hit the like button subscribe put a comment down in the comment section i nerds until next