If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:13:30

Video transcript

we've already learned that cellular respiration can be broken down into roughly three phases cellular respiration work down to three phases the first is glycolysis glycolysis which literally means the breaking down of glucose breaking down of glucose and then this this can occur with or without oxygen if we don't have oxygen then we go over to fermentation we'll talk about about that in the future go over to fermentation and in humans it produces lactic acid and in other types of organisms it might produce alcohol or ethanol but if we have oxygen and for the most part we're going to assume that we can proceed forward with oxygen if there is oxygen that we could proceed forward to the Krebs cycle Krebs cycle sometimes called the citric acid cycle because it deals with citric acid the same thing that's in orange juice or lemons and then from there we proceed to the electron transport chain electron transport chain and we learned in the first overview video cellular respiration that this is where the bulk of the ATP is actually produced although it uses raw materials that came out of these phases up here now what I want to do in this video is just focus on glycolysis just focus on glycolysis and this is kind of a you know it's it's sometimes a challenging task cuz you can really get stuck in the weeds and I'll show you the weeds in a little bit in the actual mechanism it can be very daunting but what I want to do is simplify it for you so you can kind of have the big takeaways and then we can appreciate and then maybe when we look at the the weeds of glycolysis we can we can make a little bit more sense of it so glycolysis or really cellular respiration it starts off with glucose it starts off with glucose and glucose we know its formula it's c6 h-12 o-6 and you know I could draw its whole structure would take a little time but I'm just going to focus on the carbon backbone so we could you know it could it is a ring or it can be a ring but I'm just going to draw it as six carbons six carbons in a row there's two kind of important phases of glycolysis that are good to know one I call the investment phase and the investment stage phase actually uses two atps so use two it actually uses two ATP so you know the whole purpose of cellular respiration works to generate ATP s but right from the get-go I actually have to use two ATP's but I use two ATP's and I'm then I'm going to essentially break up the glucose into two 3-carbon into two 3-carbon compounds right here that actually also have a phosphate group on them the phosphate groups are coming from those ATP's they also have a phosphate group on them this is often called well there's a lot of names for it out you know sometimes called P gal you really don't have to know this or phospho phospho glyceraldehyde really challenging my spelling skills right here that's not that important no all you have to know is in this first phase you use two ATP's that's why I call it the investment phase if we use a business analogy investment investment phase and then each of these 2p gal molecules can then go into the payoff phase so in the payoff phase and the payoff phase each of these P gals turn into pyruvate which is another three carbon and but it's reconfigured but the process of it going to pyruvate and let me write pyruvate in blue because this is something that's at least it's good to know the word and I'll show you its structure in a second pyruvate sometimes it's called pyruvic acid same thing pyruvic acid and that's essentially the end product of glycolysis so you start off with glucose and the investment phase you end up in this phosphoglyceraldehyde which essentially you broke up your glucose and you put a phosphate on either end of it and then those each independently go through the payoff phase so you end up with two molecules of pyruvate for every molecule of glucose you started off with now you're saying hey so I was a payoff is what did what was our payoff well our payoff we got for each infer from this let me write this down as a payoff phase this is our payoff payoff phase and I apologize for the white background I did it because the mechanism of showing you I copy and pasted it from Wikipedia and they had a white background so I just ran with the white background for this video but I personally at least like the back black background a lot better but this is the payoff phase right here and so when we go from the phospho blitzer aldehyde to the pyruvate or the pyruvic acid we produce two things or i guess we could say we could produce three things we produce each of these each of these pee gals two pyruvates produce two ATP's two ATP's so I'm going to produce two ATP's there I'm going to produce two ATP's there and then they each produce an NADH and a d H may I do in a darker color and a d H and a D H and of course they're not producing you know they're not producing the whole molecule in a vacuum essentially what they're doing is they they're starting with the raw material of an NAD+ so they start off with an nad plus and they essentially they essentially reduce it by adding a hydrogen remember we learned a couple of videos ago that you can view reduction as a gain and hydrogen so the NAD gets reduced to NADH and then later on these NADH s are used in the electron transport chain to actually produce ATP s so the big takeaway here if I were to kind of write the reaction that we get for for glycolysis is that you start off with the glucose you start off with glucose and you need some nad plus and a D plus and actually for every mole of glucose you're going to need two na D pluses you're going to need two ATP's you're going to need two ATP so I'm just writing all the ingredients that we need to start off with and then you're going to need well let me say what these guys are going to be a DPS before we turn them to ADP so I'll write plus for a DPS and then after performing glycolysis glycolysis and let me write it here let me write also a sorry that was an ad a/d Peas let me just rewrite that part right there for a DPS and then you maybe need two phosphate groups because we're or we're going to need four phosphate groups plus four I'll just call them sometimes they're right written like that but maybe I'll write it like this for phosphate groups I'll do it for phosphate groups like that and then once you perform glycolysis once you perform glycolysis you have two pyruvates two pyruvates you have two NADH is na D H's the nad has been reduced it gained a hydrogen r IG oil-rig reduction is gain an electron but in the biological sense we think of a gaining the hydrogen because hydrogen is very non electronegative so you're hogging its electrons you gained its electrons so two NADH is and then plus these two ADP ATP s get used in the investment phase that's why I kind of wrote them a little separately so these two get used so then you're left with 2a d P's and then these guys essentially get turned into ATP so plus for a tea peas I guess we didn't need four we only needed a net of two phosphate groups because to jump off of here and then we need a total of two more to get for jumping on there but the big picture is you start with glucose you end up with two pyruvates you use up two ATP's you get four ATP's so you have a net of two ATP's formed let me write that very big net what you get out of glycolysis is two ATP's you get two NADH --is that can each later be used the electron transport chain to produce three eight GPS but you get to nadh s and you get to pyruvates which are going to be re-engineered into acetyl co ways that are going to be the raw materials for the krebs cycle but these are the outputs these right here are the outputs of glycolysis so now that we have that big picture let's actually look at the mechanism because this is a little bit more daunting when you see it here but we'll see the same themes that I just talked about we're starting with the glucose right there it is a six chain it's in a circle it's in a ring one two three four five six carbons I could write it like that just to make it a huge oversimplification goes through a few steps I use an ATP here so that's let me do that in a color we do it in orange whenever I use an ATP I use one ATP there I use one ATP there and just like I told you they have a slightly different name for it but this is the phospho glyceraldehyde right here they call it bliss or aldehyde three phosphate it's the exact same molecule but as you can see just you know when I drew it very roughly before you've got one two three carbons there one two three carbons there and it also has a phosphate group on it the phosphate groups actually attached to the oxygen but for just for simplification I draw the phosphate group just like that and we draw we showed that right here this was the phosphoglyceraldehyde right here this is the actual structure up here but I think you know sometimes when you look at the structure you it's it's easy to miss the big picture and there are two of these they kind of say that you know you can go back and forth with this with this other kind of isomer of this but the important thing is you have two of these compounds that are now three carbon compounds glucose has been split and now we're ready to enter the payoff phase remember you have two of these compounds two of these compounds right here that's why when they drew this mecca's and they wrote x two right there because the glucose has been split into two of these molecules so each of the molecules are now going to do this right here and for each of the glyceraldehyde 3 phosphates or pee gals or phospho glyceraldehyde we can look at the mechanism we can look at the mechanism say okay look here there's going to be an adp turning into an ATP there so this is plus one a teepee and then we see it again happening here on our way to pyruvate on our way to pyruvate right there then we have another plus one ATP so for each of the P gals of the phosphoglyceraldehyde z-- that were produced the phosphoglyceraldehyde x' that we produce we're producing two ATP's in the payoff phase now there were two of these so total for one glucose we're going to produce four ATP's in the payoff phase so the payoff phase four ATP's in the investment phase we used one two ATP's so total net ATP's directly generated from glycolysis is two ATP's right four gross produced but we have to invest two in the investment phase and then the nad and the nadh s we see right here for each phosphoglyceraldehyde or glyceraldehyde 3 phosphates or P gals or whatever you want to call them at this stage right here you see that we are reducing nad plus to NADH so this this happens once for each of these compounds and obviously that there are two of these glucose got split into two of these guys so two NADH is two NADH s are going to be produced and later these are going to be using the electron transport chain to to actually each produce three ATP's and then finally when everything is said and done we're left with the pyruvate and it's nice do they at least that they made it nice and big we can take a look at what a pyruvate looks like and just as promised you know we can look at all the oxygen bonds and all of that but it is a three carbon structure as a three carbon backbone so the the end result is that that carbon that the glucose got split in half it got oxidized some of the hydrogen's got stripped off of it as you can see there's only three hydrogen's here we started off with 12 hydrogen's and glucose and now it has but it's it's it's carbons is bonding more strongly with oxygen so it's essentially having its electrons stolen by the oxygens or hogged by the oxygens so carbon has gotten oxidized in this process there's going to be more oxidation left to do and in the process we were able to generate two net ATP's two net ATP's and - na da jizz that can later be used to produce a TPS anyway hopefully you found that helpful