this video will cover all the higher level parts of C 1.2 on cell respiration in this topic you're going to hear a lot about a molecule called n a and NAD stands for nicotinamide adenine dinucleotide it's one of the few molecules that you don't actually have to know the long term for it you are allowed to use the abbreviation even in your writing and it's an example of what we call an electron carrier I love this term it's exactly what it sounds like it is a molecule that carries electrons so another way of thinking about that is it is easily oxidized and reduced so reduced meaning it can easily gain an electron and oxidized meaning it can easily then lose that electron or pass it along um but in the meantime it is a temporary electron carrier now in reality electrons don't come from nowhere and they don't go to nowhere they're passed between molecules so when a molecule loses an electron that is called oxidation but that electron doesn't just go into space it is immediately gained by another molecule that gain of electron is called reduction okay so the loss of electrons is oxidation and the gain of electrons is called reduction and those two processes happen simultaneously so anytime you have the movement of electrons from one to the other something is getting oxidized and simultaneously something is getting gained you may have heard that or someone is gaining electrons you may have heard that referred to as redo those oxidation and reduction reactions um occurring simultaneously now there are a lot of things that go along with Redux and if you're also taking things like chemistry you'll learn a lot more about this from a biological perspective it's important to keep your eye on two things where is the electron and then where is the energy so in general these electrons are going to be carrying energy so if you're gaining electrons I want you to think of that as that molecule is gaining energy if something is losing electrons we can think of that as it is losing energy okay so just something to keep an eye on on as we move forward in this topic we're going to take cell respiration and break it down into four major steps so those will be glycolysis the link reaction the kreb cycle and the electron transport chain which goes along with ch osmosis let's first talk about this glycolysis step so this is the very first step in this respiration process and I love it because it's exactly what it sounds like glyco means Sugar ltis means to break so I'm literally breaking apart a sugar and this is going to occur in the cytoplasm we're not in the mitochondria yet and it is anerobic so that means that it does not require oxygen and it's going to happen with a series of enzyme catalyzed steps the net products and we'll draw this in just a moment at the end of glycolysis I'm going to come um I'm going to end with two ATP two molecules of pyruvate and two molecules of reduced NAD so we're going to go ahead and diagram this out I'm going to use these gray circles here each one of these represents a carbon so I have a 1 2 3 4 five six a six carbon compound glucose that we will start with here and eventually I need to be able to break this in half but the problem is that glucose is very stable so before I can break it in half I need to destabilize it and I'm going to do that by adding a phosphate group so I want to add a phosphate group to both ends here and this is a step called phosphorilation I'm literally adding a phosphate group here H who do I know that has phosphate groups that I can borrow from ATP okay so ATP is going to donate um a phosphate group and it's going to become a DP now I need two phosphate groups which means I need two atps so I have to spend two atps just to get this process started once I've done that now this is unstable enough to where I can break it in half and that process is called licis okay so I've got two processes that I've done so far all part of glycolysis okay I'm just working with glycosis phosphorilation then Lis and now we are going to go into the next phase which is an energy harvesting phase so there are two things that I'm going to get out of these intermediates and by the way you don't need to know the names of these intermediates but you do need to know the steps and what we end up with so I'm going to go through two phases and the first is oxidation so this molecule is going to get oxidized it's going to lose electrons and that means something else is going to get reduced and so what will get reduced is that molecule called NAD NAD is going to pick up those electrons and you can write this out um either way you can either say it becomes reduced NAD or you can call it nadh that's up to you and this produces two molecules of this okay so I can reduce one molecule of AD of NAD um using this intermediate and second molecule of NAD using this product so that's the oxidation bit now what we left out earlier on is that when this molecule actually breaks in half um it is phosphorated a second time now it doesn't use phosphorus from ATP just because of um bonding reasons okay um there it's able to attach an inorganic phosphate group to that molecule but anyways at the end of the story and you don't again you don't need to know all the intermediates each one of these actually has two phosphate groups and that's going to be very important for our last phase which is called ATP formation so if I take a phosphate group off of this molecule I can actually use that to turn a DP into a TP okay so I can make a TP this way and I have 1 2 3 four phosphate groups available so that means I can actually take four ATP or sorry four ADP and turn them into four ATP and so here's what I'm going to end up with in this process I started out by having to use 2 ATP so I'm 2 ATP in debt and I make 4 at ATP in the end okay so this gives me a net gain of 2 ATP in the process of glycolysis what else am I making well I am making two molecules of reduced NAD so again I can write that either way I can either say reduced NAD or I can call it nadh that's up to you and then I have two molecules at the end each of these three carbon molecules is called pyruvate so this is where we are getting these two pyruvate molecules you may also see them R referred to as pyruvic acid right but at the end of the day I've taken a six carbon molecule and I've broken it down into two three carbon molecules and I've made a couple of other important byproducts as well now in order for glycolysis to happen I must have ADP and NAD shouldn't be a problem if I don't have any ADP that means I have a lot of ATP and if I have a lot of ATP I shouldn't be doing glycolysis anyways there's no need there okay now if um oxygen is available that reduced NAD that we make in glycolysis is converted back into regular NAD during the electron transport change so I should have a continual um resupply of this NAD the problem becomes that there is no oxygen available so if there's no Oxygen available what has to happen is this pyruvate needs to get converted into lactate and you may remember that's the product of anerobic respiration anyways and the reason to um that our cells do that is because we need to regenerate NAD so that reduced NAD or nadh depending on where you're reading it is converted back into na a by donating this hydrogen and then electron to the lactate and the whole reason why we produce lactate as a byproduct of Anor robic respiration is to regenerate the NAD that we need so that glycolysis can continue okay so in Anor obic respiration we make two ATP and two reduced NAD molecules if there's still no oxygen available that lactate production uses the two reduced NAD okay and produces to NAD um and then we are left with just the total of 2 ATP so if I have to do Anor robic respiration the only energy um products that I'm producing are these 28 TP and then that pathway then ceases so let's do a quick summary of these different Pathways right so in glycosis glucose is converted to pyruvate that's Universal doesn't matter whether you have oxygen or not okay if oxygen is available then the aerobic pathway will result in carbon dioxide and water be produ being produced as a byproduct in the anerobic pathway so no oxygen it really depends on what organism that we're talking about out humans and some bacteria they're going to produce lactate as a byproduct we just talked about that to um regenerate NAD yeast on the other hand aren't going to do that they are going to do what's called alcoholic fermentation it's a two-step process again the whole goal is to regenerate that NAD so that glycolysis can start again the end result of that is that yeast will produce two byproducts carbon dioxide and ethanol all so one of the things that's tricky here is that yeast produce carbon dioxide whether they are doing things anerobic or aerobically so that's a little bit tough um to remember but if we want ethanol to be produced then we really have to make sure that we deprive the yeast of oxygen yeast is a facultative anoro okay so that means it can do both anerobic and aerobic fermentation it will always do aerob obic um respiration when oxygen is available just because you get so much more ATP out of that pathway so if we want to produce ethanol on purpose you must deprive the yeast of oxygen and that's important for two commercial processes one of which is bread baking so if you've ever done this before you mix water and yeast um and you let it forment and so that means that you're going to let it go through the process of aerobic respiration first but once you cover it you're going to eventually find that that yeast runs out of oxygen and it will switch over into anerobic respiration either way that yeast is producing carbon dioxide and you're going to notice your bread dough getting bigger and bigger and that um rise in the bread is caused by all the carbon dioxide that is getting trapped within the bread dough now where does all the alcohol go it burns off during baking okay but one of the cool things um again about yeast and the reason why we're using it for bread is to produce carbon dioxide and it's producing that both in the early aerobic stages and in the anerobic stages later on and the other commercially important use of this alcoholic fermentation is of course Brewing alcohol things like beer wine and other Spirits so in this case you would want to take some kind of sugar like grapes if you're making wine grains if if you're making beer and you're going to add yeast and let that yeast go through the anob pathway that alcoholic fermentation to produce ethanol and carbon dioxide so this carbon dioxide will be seen as these bubbles here um if you're going to produce alcohol you need to make sure it's Anor robic otherwise it will go through the aerobic pathway and you need to let off the carbon dioxide okay so have some kind of a valve for this to escape you can make quite a bit of alcohol content here so the more sugar that you add the more alcohol you're going to get up to about 15% um and the limit there becomes because this alcohol ends up killing you the yeast these make some really cool IAS by the way if you're interested in doing that um and this of course is something that we can use to create alcoholic drinks or even biofuel so some really cool implications there so we're going to switch back over to talking about the aerobic pathway but before we do that let's create a mental map of where all of these reactions are going to occur so I of course here have a mitochondria mitochondria has an outer membrane and it has an inner membrane with these folds called christe so the inner membrane is folded into christe on the inside of the inner membrane we had this area known as The Matrix and this small area between the membranes is called the intermembrane space so we've already talked about glycolysis okay and that is going to happen in the cytoplasm we've got a few different reactions that we'll talk about next one of which is the link reaction so that is happening in The Matrix and then we have the Krebs cycle and that is also happening in The Matrix of the mitochondria and then you have the electron transport chain and chemiosmosis and I'm drawing it like this because it really happens on the folds of the inner membrane on these chiste and it Bridges both the Matrix and the intermembrane space so this is where I want to kind of remember that is happening so let's get on with this link reaction here you may recall at the end of glycolysis we had three carbon molecules called pyruvate okay that was the product of glycolysis this link reaction takes place in The Matrix of the mitochondria so pyruvate is going to move into the mitochondria and undergo a couple of changes so I find it easier to think about and I'm just running out of room it doesn't actually go down but I find it easier to think about what's Happening Here by talking about or by envisioning what's going on at the end so at the end of this link reaction I should have a two carbon molecule with a Cod enzyme attached and this two carbon molecule is called acetal COA okay so that's the end product here well what has to happen in order for me to go from this pyruvate to this acetal COA well one of the obvious things is that one of these carbons has to come off okay so one of these carbons is going to come off of pyruvate and that is called decarbox it's the removal of a carboxy group Co and it's going to come off in the byproduct form of carbon dioxide the other thing that's going to happen there are two other things that need to happen one of which is I need to add on this COA that stands for co-enzyme a it's almost like a chaperone molecule So Co a is going to be added in and the last thing that I'm going to do is go through a series of oxidation and reduction so pyruvate is going to get oxidized it is going to lose electrons okay so think about if I'm breaking this Bond I'm going to be losing energy losing electrons or liberating that energy liberating those electrons and that means that something else is going to get reduced pyruvate is oxidized something else gets reduced who do we know that loves to be reduced well that would be NAD so NAD is going to get reduced and it's going to form you guessed it reduced NAD now remember all of this happens twice because at the end of glycolysis I had two pyruvates okay so at the end of glycolysis if I had two pyruvates I should be having two acetal coas two molecules of carbon dioxide two molecules of reduced NAD and that acetal koay is going to enter into the kreb cycle you may have heard this referred to as the TCA cycle or citric acid cycle um the IB is pretty consistent with using the KB cycle this is going to occur in the mitochondrial Matrix and it is a cycle we're going to start and end with the same molecule and there will be a series of enzymes at each step helping us to take apart that acetal COA I'm going to be decarboxylating things I'm going to be oxidizing things and at the end of this I'm going to produce carbon dioxide reduced NAD reduced fad and ATP so let's draw that out here's my acetal COA and this acetal COA is going to be attached to a four carbon molecule so these green circles each one of these is carbon I've colored them a little bit differently just to so that we can trace what's happening here but they're all carbons okay so a four carbon molecule called oxaloacetate is going to attach itself to acetal COA then this co-enzyme a is going to pop off okay it's just kind of like a chaperon to help get this Krebs cycle started and so I'll be left with this once that co-enzyme a comes off I now have a six carbon molecule so I have my two carbons from acetyl COA and my four carbons from oxaloacetate what we're going to do is we're going to go through a series of decarbox and oxidation reactions so when we say decarbox we mean removal of a carbon okay and so that carbon will come off as a carbon dioxide molecule and I will be left with a five carbon compound after this this step now I also said oxidation so that part is the decarbox this molecule this intermedia is going to get oxidized which means something else will get reduced what is the something else well that's NAD so NAD will be reduced to form reduced NAD so I'm going to be able to form reduced NAD in between this six carbon and five carbon compound now we're going to repeat that process one more time so we go through decarbox we go through oxidation and now I'm left with a four carbon molecule wouldn't you know it it looks a lot like the four carbon molecule of oxaloacetate that I started with and that's why we call this a cycle now there are enough residual electrons still attached to this four carbon molecule that I can continue to reduce a few things so I can reduce one more molecule of n a i can also reduce another electron carrier called f a to make reduced fad and I can even manufacture one molecule of ATP so I can also reconvert or regenerate ATP from a DP so what have I managed to make in this kreb cycle two molecules of carbon dioxide 1 2 three molecules of NAD one molecule of reduced fad and one molecule of ATP but don't forget that this entire cycle is going to turn twice per molecule of glucose because we had two pyruvates two acetal coas okay so at the end of this basically what we need to understand is that all of our original carbons that were in glucose are gone they've all been picked apart either in the link reaction or the decarbox silation reactions here in the KB cycle so all of the carbons are gone where is all of the energy it's in a small amount of ATP okay so we made two in glycolysis we'll have made two here in the KB cycle one for each turn of the KB cycle so I've got four ATP it's not a ton most of the energy after the KB cycle is being carrier carried by those electron carriers so I've got a bunch of reduced NAD now I've got a some reduced fad and those electrons are going to carry that energy to the final step in the cell respiration process so let's figure out where we are in this diagram if I take a look at this mitochondria um what I've done here is I've zoomed in on a space that's maybe like right here okay so I'm looking at the inner membrane that's right here and right above it is the intermembrane space that space between the inner and outer membranes and right below it is the Matrix embedded in this inner membrane are a series of electron carriers um they are easily oxidized and reduced so what's going to happen is something like reduced NAD or it could be reduced fad it doesn't really matter is going to donate an electron to these electron carriers when it does that it is no longer reduced NAD now it is just regular NAD again okay so in reduced NAD has been oxidized and this electron carrier has been reduced it can also pass that electron to the other electron barriers okay in which case every time it loses an electron it becomes oxidized gaining an electron reduced so on and so forth now every time that electron gets passed from carrier to carrier that's going to liberate some of the energy from that electron and the energy from that electron is going to be used for active transport so embedded within that membrane we have proton pumps that are going to pump protons from The Matrix into the intermembrane space so every time that electron is passed protons are going to be pumped into the intermembrane space okay again that is then going to be passed to the next electron carrier and the next electron carrier so on and so forth every time that happens protons are going to be pumped into the intermembrane space using active transport that's what that energy is used for now the intermembrane space is very small so that is going to create a high concentration gradient of protons and that will be very important in just a moment for now let's go ahead and highlight the difference between reduced NAD and reduced fad the electron that is carried by reduced N A has a little bit more energy it has enough energy to pump 10 protons into that intermembrane space whereas reduced fad only has enough energy to pump six protons into that intermembrane space But at the end of the day what's important to understand is that the energy from those electrons is being used to pump protons into the intermembrane space I have that going upwards here okay it doesn't matter remember I could have drawn a portion of the mitochondria down here in which case the intermembrane space would be down below so how do we differentiate we using our eyeballs where is the Matrix where is the intermembrane space look for the direction that protons are being actively pumped they will be actively pumped into the intermembrane space using the energy from the passing of that electron so what we just talked about was the electron transport chain right the passing of that electron that is coupled with a process called chemiosmosis so chemiosmosis is the movement of protons from a high concentration to a low concentration through ATP synthes so we actively pumped them to get them into the intermembrane space now they are going to move via facilitated diffusion through this very special intermembrane or transmembrane protein called ATP synthes Okay so this ATP synthes is a protein that does two different things okay and it's what is right here it acts as a channel protein for the facilitated diffusion of those protons it also acts as an enzyme to catalyze the conversion of my up is missing here of ADP to ATP so when these protons I'll show you again when these protons are are moving through ATP synthase it actually turns a part of that enzyme and that kinetic energy can be used to convert a DP into ATP okay so this is where we're getting most of the ATP in Aerobic cell respiration is from chemiosmosis the movement of these protons back into the Matrix passively through ATP synthes so here's a closer look this ATP synthes molecule has a part down here that actually rotates so as these protons move through the channel protein this part rotates creating kinetic energy and that kinetic energy allows a DP to be converted into a TP so we can phosphorate this ADP add on that other phosphate group now the greater the concentration gradient of those protons the more kinetic energy we have the more ATP we can produce so remember reduced NAD can put 10 protons into that intermembrane space whereas reduced fad can only produce um or can only provide enough energy to pump those six protons into that space so that's going to mean less energy and less ATP produced and I can see that I have this written the other way so let's go ahead and correct that fadh is how I would just write it if I'm writing it as reduced fad I don't need this H okay they are synonymous but let's just maybe fix that for now so again just to go back and make sure that we're clear nadh is the same thing as reduced NAD fadh2 is the same thing as reduced fad I would try to maybe be consistent and call them this but aside from the naming part um what we need to know here is how these are produced and it has to do with um kinetic energy and re phosphor lating that ATP and that I can get a little bit more ATP out of the reduced NAD compared to the reduced fad now I want to go back to that electron transport chain for just a moment remember we've been passing this electron from carrier to carrier to carrier and that happens when one molecule has a higher affinity for electrons than the one that it's stealing it from well at the end of the electron transport chain we've already used all the energy from this electron to power those proton pumps so we have this electron left over and we need to do something with it well that is the role of oxygen so oxygen is the final electron acceptor in the electron trans transport chain and it makes such a good electron receptor because it has a very high affinity for oxygen now don't forget that down here in The Matrix we've got lots of those protons remember those hydrogen ions well what do I get when I combine oxygen with electrons and those hydrogen ions or protons that we've been pumping well you probably already guessed this this is going to all combine to make water so if we think about where things have come from here the carbon dioxide byproduct of cell respiration has come from the deep carboxy reactions in the link and kreb cycle the carbon dioxide byproduct or sorry the water byproduct is coming from the electron transport chain oxygen is the final electron receptor here it's going to capture that electron and it's going to combine with those hydrogen ions and that's how we are getting water and that in fact is the only reason why we need oxygen for aerobic cell respiration that's it Oxygen's only role is to be the final electron receptor without oxygen there's nothing to accept that electron so all of the electron carriers stop accepting electrons because they already have them which means reduced NAD and reduced fad can't donate their electrons which means I have no way of regenerating the NAD that I must have for glycolysis so if I don't have NAD then after glycolysis making that pyruvate I've got to regenerate NAD which means I'm making lactate which means I'm going through the Anor robic pathway unfortunately that also means I'm making less ATP because I don't have the electron transport chain going so the whole point of this is to to Showcase this idea of interaction action and interdependence the electron transport chain glycolysis crab cycle link reaction they all seem different and separate but they are interdependent on one another the electron transport chain requires those reduced fad and NAD molecules and glycolysis to start another round of cell respiration also relies on that as well and so we need to understand the role of molecules within each reaction but also how they allow all the these steps to interact um and work together and we'll end this video with talking about what we can use as a respiratory substrate okay so when I'm thinking about what we can use for energy we can use things like carbohydrates or lipids now they have different energy contents so carbohydrates have about four calories per gram whereas lipids have 9 calories per gram and the reason for that being being is that in lipids there are a lot of um carbon and hydrogen bonds and in carbohydrates there's a lot um more oxygen okay so if you look at the components um carbohydrates are about 1 to two to one ratio we're not going to see the same ratio here so these bonds are going to be oxidized much differently with a much a much different energy content okay all right so let's maybe change this lots of oxygen okay all right glycolysis um carbohydrates must go through the process of glycolysis first so we have to go through that process of making pyruvate then it can be turned into a cedal COA lipids on the other hand do not go through glycolysis they go right into that um manufacturing of acetal COA so they don't go through that glycolysis process however lipids can also not be used for anerobic respiration only carbohydrates can be used for anerobic respiration so there are some really cool opportunities here for investigating um some rates of cell respiration and may be checking out these different uh substrates