hi everyone Dr Mark here in this video we're taking a look at everyone's favorite the Krebs cycle also known as the citric acid cycle also known as the tricarboxylic acid cycle so take your pick and let's go the best place to begin is a quick recap of glycolysis and in the process of glycolysis we simply took a six carbon molecule called glucose in actual fact it's C6 h12 06 and the whole purpose of glucose is to pull it apart rearrange it to pull off hydrogen and electrons and in this process of going from glucose down to two three carbon molecules called pyruvate again this process is known as glycolysis feel free to watch the glycolysis video that I've recorded in this process multiple steps we ultimately produced two molecules of nadh and two molecules of ATP now the whole purpose of this cellular respiration so glycolysis Krebs cycle then the electron transport chain is to produce ATP either directly or to produce ATP indirectly via nadh or fadh2 I'll talk about that in a second so this is our net gain from the process of glycolysis keep that in mind now we've created a three carbon molecule called pyruvate in actual fact we've created two of them from one glucose molecule and this pyruvate wants to enter the mitochondria so it can enter the Krebs cycle the mitochondria has an inner and outer membrane it can't get through it needs to be transformed into something that can this is the product here it's called acetyl COA so we've got acetylcholai that pyruvate needs to turn into how does pyruvate do this well as you can see it goes from being a three carbon molecule to a two carbon molecule so it needs to lose a carbon second thing is it needs to add a COA as well why do we snap color so kawas coenzyme a why do we need that well it's a coenzyme so when it's added to carbon chains it helps transport that carbon molecule and facilitate that carbon molecule by being utilized by an enzyme in this process snapping the Calais allows the acetyl to enter the mitochondria and be utilized by the enzyme here to create a molecule called citrate talk about that in a sec so what do we need to do we need to lose a carbon and we lose that carbon in the form of carbon dioxide we need to gain a COA and in addition to this we need to take an NAD plus and we need to turn it into an n a d h plus hydrogen ions now this is probably the most important step or steps in the Krebs cycle and cellular respiration let's talk about this for two seconds what is happening in this process well ultimately NAD plus steals hydrogen from these carbon molecules how does it occur what is hydrogen hydrogen is the first atom on the periodic table it is made up simply of a positive proton in its core and a negative electron flying around the outside that's hydrogen you can see it's neutral because the positive proton is balanced by the negative electron now if I take NAD Plus and I still a hydrogen I'm simply turning NAD plus into nadh plus because it's neutral and it started with a positive it's still going to retain that positive so let's steal one more hydrogen but this time let's just pluck the electron from it and keep that if I do that it then becomes nadh and all I'm left with is a positive proton now another way that you can write a positive proton is h plus so if I still 2 hydrogen from a molecule I get nadh plus h plus that h plus we know is what makes something acidic beautiful so what we're doing effectively is NAD plus is stealing two hydrogen it takes a whole hydrogen with the positive and the negative and it takes one more hydrogen but in actual fact just plucks the electron off it and leaves the positive proton out in the solution that's what this equation is saying You must remember that because that means this molecule here is carrying hydrogens and it's carrying electrons which we'll be using in the electron transport chain here's an important point that no one ever talks about play around with these carbons and to produce carbon dioxide here we need a vitamin B derivative called thiamine pyrophosphate thiamine Pyro phosphate also known as TPP thymine pyrophosphate is a derivative of vitamin B1 so you need Vitamin B1 for pyruvate to go to acetyl-coa kellen's I'm a for that to snap on we need another B vitamin derivative called pantophenic acid pantothenic acid pantothenic acid is actually a vitamin B5 derivative so we need Vitamin B5 here in addition to that nicotinamide adenine dinucleotide which is what NAD is that is a derivative of niacin niacin is vitamin B3 so simply in this one step going from pyruvate to acetyl-coa we need three B vitamins this is the reason why our B vitamin complex is important for cellular respiration now we haven't spoken about the enzyme here the enzyme in this process is actually called pyruvate dehydrogenase and we know it's going to be a dehydrogenase because when you transform NAD plus to nadh or fad into fadh2 it's going to be a dehydrogenase enzyme so now I've got acetyl COA two carbons one COA enters the mitochondria and what happens is the acetyl-colla the two carbon will bind to a four carbon molecule there's four carbon molecule is called oxalo acetate sometimes written as o a a and create a six carbon molecule two plus four equals six this is called citrate and in this process we obviously lose that Calais we don't need it anymore I told you COA is required to help move carbon uh molecules around the place so they can be utilized by their enzymes so we lose that Co a and when we lose a COA we usually use a synthase or a synthetase and in this point here it's going to be citrate synthase that's the enzyme that we use to snap acetyl-coa together with oxaloacetate to form our six carbon molecule citrate citrate needs to rearrange itself so we rearrange some carbon atoms we keep it as a six carbon molecule and because we're rearranging it we call it ISO because it's changed ISO citrate and the way we rearrange it is we lose some water in the process then we gain some water in the process and we use an enzyme called aconitase to do this whole thing foreign times now we have isocitrate isocitrate the six carbon molecule needs to turn into a five carbon molecule called Alpha ketoglutarate Alpha Keto glutamate so we lose a carbon how do you think we lose that carbon we lose that carbon in the form of carbon dioxide now the enzyme that does this is called isocitrate dehydrogenase I'm going to write that down what does that tell you ISO citrate dehydrogenase I told you something about dehydrogenases they're used anytime we're going to be using NAD Plus or fad to steal hydrogen and electrons and that's what's Happening Here NAD plus turns into nadh plus a free proton in the solution so now we've got Alpha ketoglutarate a five carbon molecule it needs to turn into a four carbon molecule going to lose a carbon again and gain a COA so I think I've seen this before if we lose a carbon in the form of carbon dioxide but we gain a COA here that looks very much like what's happening here with the pyruvate dehydrogenase that's exactly what's happening we're using another dehydrogenase here and we also turn NAD plus into nadh so same thing NAD Plus going to nadh plus hydrogen ion so it's a dehydrogenase what do you think it's called Alpha ketoglutarate dehydrogenase Alpha Keto glutarate dehydrogenase now look again remember we're using B vitamins here right we're using a B vitamin here B3 derivative there we're using for coenzyme a we need to use B5 pentothenic acid we need to use B1 thymine pyrophosphate here B3 again so look how important the B vitamins are in their derivatives just in the Krebs cycle so now we've got this molecule here which we haven't spoken about what it's called Alpha ketoglutarate once it loses a carbon gains a COA it's called succinyl COA succinol COA succinyl COA needs to pop that co-a off to Simply turn into something called succinate and in this process of popping that co-a off it actually releases a little bit of energy and in this process of releasing that energy we can actually turn either ADP into ATP or GDP into GTP again just another energy molecule but think about it if that GTP has a phosphate it might be able to just give that phosphate to ADP to now create ATP so we can create ATP in this process a little bit of inorganic phosphate is added in this process two now because we lost a COA here like we lost a COA here I said it's either a synthase or a synthetase here it's a synthetase so it's succinyl COA synthetase succinol COA synthetize now we're left with succinate so here's the thing succinate turns into Fumarate which turns into malate which turns into oxaloacetate succinate Fumarate malate oxaloacetate all right so to go into they're all four carbon molecules here so what's happening in this process so to go from succinate to Fumarate what we need to do is still some more electrons and still some more hydrogen ions how do we do that well this time we're not stealing it using NAD plus we're stealing it using f a d now there's no plus here so we're stealing two hydrogen right so f a d h that's what we're creating two because we're still in two hydrogen so we go from fad to fadh2 and the enzyme that we're using is another dehydrogenase like I said called succinate dehydrogenase something now we've got Fumarate Fumarate turns into malate using an enzyme called fumarase fumarase and in doing so it adds a little bit of water now to go from malate to oxaloacetate we use an enzyme called malate dehydrogenase malate dehydrogenase dehydrogenase tells you it's either going to use NAD Plus or Fad in this case it's n a d plus again forming n a d h plus hydrogen ions and now we're back to the oxaloacetate so what have we done just in the Krebs let's not focus on this part here what have we created remember we have two pyruvate from one glucose so simply one glucose molecule created two pyruvate which created two acetyl-coa which is created two of everything so let's have a look let's first have a look at carbon dioxide we've got two there because remember two of everything two four that's it four so we created four carbon dioxide in the Krebs cycle let's have a look now nadh 2 4 6. we created six nadh what about fadh two of them two f a d h two and what about ATP directly two ATP so what we've created just in the Krebs cycle is four carbon dioxide jump into the bloodstream breathe it out no problem but we've created these hydrogen and electron character these are carrying remember hydrogen ions and electrons this is what we need for the next step which is the electron transport chain and ATP directly which we can use to produce well to do work basically so a final Point well this is the Krebs cycle in its most direct process something that you should probably understand is that you can actually feed things into the Krebs cycle and take things out at different areas so for example you can feed amino acids in to the Krebs cycle or change some of these uh substrates uh into amino acids so for example Alpha ketogliterate can turn into various amino acids and various amino acids can turn into it same down here with the succinate some same with other different areas you can add feeding and remove amino acids that's a really important Point amino acids can feed in and out of the Krebs cycle if we look at fatty acids as a potential energy source we can feed fatty acids into acetyl COA acetyl-coa can actually turn into fatty acids and fatty acids can turn into it so here's where fatty acids can come in now importantly and I'm going to do a whole video on this but this is important process what if we don't have any glucose so somebody is intentionally starved themselves of glucose maybe Atkins diet or maybe they're doing something where they just want to eat fats for whatever reason that may be they ingest all these fats but there's no glucose so what does that mean well it means that's not happening that's not happening right oxaloacetate actually has the ability to jump out turn into malate and turn into glucose oxaloacetate is my point is can ultimately turn back into glucose so if you don't have any glucose in the body the body wants it so much that it pulls oxaloacetate out to turn into glucose now if you don't have any oxaloacetate here right let's just say this is this part here it's gone right the acetyl COA has nothing to bind to now remember I said that fatty acids if you're ingesting fats but you're not ingesting glucose they can turn into acetyl COA so we've still got acetyl COA feeding into the crabs but no locks allow acetate for it to bind to so this process doesn't happen so acetylcholai simply accumulates and when you accumulate acetyl Cutlery it snaps together to form ketones this is what is it ketogenesis so the ketones can then jump out into the bloodstream go to the brain where the brain has plenty of oxaloacetate now this hot this is happening in the liver remember the liver the brain is not making ketones the liver is so the oxaloacetate isn't jumping out to create glucose in the brain the oxaloacetate is fine in the brain so once the acetyl COA in the form of ketones jumps into the brain it can turn back to acetyl-coa and undergo the Krebs cycle that's how the brain uses ketones for energy anyway that's an aside I hope that you enjoyed this video of the Krebs cycle also known as the citric acid cycle also known as the tricarboxylic acid cycle hi everyone Dr Mike here if you enjoyed this video please hit like And subscribe we've got hundreds of others just like this if you want to contact us please do so on social media we are on Instagram Twitter and Tick Tock at Dr Mike tadarovich at d-r-m-i-k-e-t-o-d-o-r-o-v-i-c speak to you soon foreign