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Current time:0:00Total duration:11:22

Video transcript

when we first learned about glycolysis we saw that if you start with a molecule of glucose and you carry forward with glycolysis that glucose which is a six carbon sugar it's got oxygens and hydrogen's well but it's a six carbon sugar it gets split into two pyruvate molecules and each pyruvate has three carbons and the process of doing so were able to produce a net of two ATP's we use two ATP's in the investment phase then we produce four ATP's in the payoff phase for a net of two ATP's but that's not all that happens you also have two nad molecules nicotinamide adenine dinucleotide getting reduced to NADH and why is it getting reduced well we see it's a positive it's a positive molecule here becomes a neutral molecule it gains electrons so this over here becomes becomes reduced now the next question you might have is well what happens next well if you're me or you you might continue on and if you have enough oxygen you'll continue on with cellular respiration things move on to the mitochondria because the pyruvate and the NADH is can be can also be used to produce more ATP the pyruvate gets more broken down and the Krebs cycle also known as the citric acid cycle and also and that produces ATP's and NADH is and the NADH is can participate in the electron transport chain which eventually leads to even more ATP's being produced but what if you're in a situation that maybe we don't have oxygen or maybe you're just like the you're just the type of of organism that doesn't like to use oxygen or or doesn't know how to use oxygen what happens next well what we're going to talk about in this video is one potential pathway and that's lactic acid fermentation which is one of the two major forms of fermentation lactic acid fermentation fer men lactic acid fermentation and lactic acid fermentation isn't so much about producing more ATP's it's more about recycling the pyruvate and the NADH even though the pyruvate and NADH can it has free energy to give that could be converted to ATP if we're going to be doing lactic acid fermentation we kind of give it give up on that and then we actually use the pyruvate to oxidize the NADH to become nad plus so that we have more nad plus for glycolysis to occur again so organisms that do that do fur Montaine their main energy source is the glycolysis and then the fermentation is all about recycling what it views as waste materials probably ovate and NADH so that you can have more nad to have glycolysis occurring again now we mean you might say oh is this just some strange thing that we don't encounter much in life but probably every day or maybe at least every week you probably consume some organisms that perform lactic acid fermentation this right over here this is a picture of yogurt yogurt is what we get when you have the when you have species of lactobacillus digesting the sugars in the milk and then they're performing glycolysis and then they perform lactic acid fermentation converting the pyruvate into lactate or if it has if you if you view the conjugate acid version of it lactic acid you could say pyruvic acid lactic acid pyruvate is the conjugate base for pyruvic acid lactate is the conjugate base for lactic acid but that's what's giving it that's what's giving it it's uniquely yogurt taste it's it's this it's this bacteria here the lactobacillus is this is just one variation of it and there's slightly different variations of lactobacillus that do each of these foods but this is yogurt this right over here if you're into Korean food this is kimchi this uses a variation of lactobacillus to once again perform lactic acid fermentation on the sugars and the vegetables this is sauerkraut once again a variation of lactobacillus a species of lactobacillus performing lactate lactic acid fermentation on the sugars in the cabbage sauerkraut literally means sour cabbage and that's that's what it is and so let's think a little bit more about what's going on so as I mentioned it's all about taking your taking your pyruvate or your pyruvic acid the way I've drawn it right over here this is pyruvic acid pie ruvik pyruvic acid right over here because we have our hydrogen proton if we lose our hydrogen proton this is the same thing drawn again but now we don't have the hydrogen proton here this oxygen kept that electron and all of the other hydrogen's all the hydrogen's here there they are implicit so the three hydrogen's here they're implicit on this carbon I just drawn it with a different notation and so this one where we've lost the proton we would call this pyruvate hi pie roommate and what we have happening is of the pyruvic acid or the pyruvate is used to oxidize the NADH take away a hydride take away an electron from well actually more than just electron but net-net you have the NADH losing electrons and so if it's losing electrons it's getting oxidized so it's oxidized so that the nad plus can be reused in glycolysis and when pyruvic acid does this to the NADH it gets it gets a reduced it gets reduced it gets reduced it gains electrons and if we're thinking about the acid forms it would turn into this right over here is lactic acid lactic lactic lactic acid and that's why we call it lactic acid fermentation because you're taking that pyruvate if you had action around if you knew how to do it use the oxygen you might continue on with cellular respiration and use that for energy but lactic acid fermentation we use it to oxidize the NA NADH so we get more nad plus and let's just now get a better appreciation for all of this happens so the first thing that I want to show you because a lot of times in biology classes you just learn nad NADH and it just seems like this somewhat abstract molecule but this is a picture of it this is Nick nicotinamide adenine dinucleotide and it's kind of a mouthful but when you break it down you see these patterns that you see repeatedly in biology this is this right over here this is an this one is what gives us the nicotinamide this right over here is our good friend ad mean we see that in a teepee we see that also is one of the nitrogenous bases in DNA and RNA you have ribose right over here so it's derived from ribose you have a phosphate group you have a phosphate group so nicotinamide adenine you have a nucleotide right over there you have another nucleotide right over there so it's nicotine adenine dinucleotide so the name makes a lot of sense but I wanted to show this to you to get an appreciation that it's a it's a fairly it's not a you know it's it's a it's a fairly involved molecule over here you know sometimes when you just see the letters nad you don't get a full appreciation for it and it's a it's a coenzyme and we learned about coenzymes in other videos where the the enzyme that catalyzes this is lactic acid dehydrogenase and remember enzymes enzymes are for the most part just these big you know protein structures so I'll fold it up in all different different ways and then you have the nad the nad or in the case in the case of lactic acid fermentation right over here you have the NADH so this is the NADH right over here and I'm just kind of drawing what it could look like this isn't actually what it looks like it's going to react it's going to react with the pyruvate and let me do that in a it's going to react with the pyruvate and by doing so even though the pyruvate you might formally consider to be the substrate of the enzyme the whole purpose is to get your NADH to be oxidized to lose a hydrogen and an extra electron so hydrogen proton a hydrogen electron and another electron so really lose a hydride so how does that happen what happens because you have this nitrogen here it has an extra lone pair of electrons so it can form that lone pair can form a double bond right over there well if that carbon if this has a double bond this carbon has to let go of this double bond so that goes over there that goes over over there and then if there's now a double bond over years which we see in the end product this carbon is going to have to let go of a bond and it lets go of the entire covalent bond with this hydrogen so both of the electrons so it's going to let go of both of these electrons right over here and then both of those electrons can attach can attach to this carbon right over there now that carbon gets forms a new covalent bond it has to let go of one of its covalent bonds and so it could let go it could let go of one of these double bonds with this oxygen and those could either go back to that oxygen or more likely they can be used to grab a hydrogen proton maybe from a passing water molecule or hydronium molecule and so I could draw it like this could grab a hydrogen a hydrogen proton and so what do we end up with well this the lone pair of electrons is now there this we now have a double bond right over there now we've lost one of these hydrogen's I obviously haven't drawn all of the hydrogen's in these molecules so now we have now we are back to nad and since this this this nitrogen has essentially it was neutral before but now it is it is instead of keeping these two electrons it's sharing these two electrons so now it's going to have a positive charge so this is why we call it nad nad plus it lost a hydrogen and an electron a hydrogen the hydrogen's electron and another electron so now it has a positive it now has a positive charge and the pyruvate the pyruvate is now the conjugate well the way I've drawn it here since we show it deprotonated I would say that this is now lactate this is now lactate if we had our proton over here we would call it we would call it lactic acid so anyway hopefully you you get a kick out of this I know I do it's it's kind of interesting that all of this can happen I mean lactobacillus isn't the only is it the only organism that does this but this is a fairly useful organism for all sorts of all sorts of delicious food that we have and just get appreciation you know I'm all minds always blown that these fairly complex processes are constantly occurring in nature all around us sometimes even in our own bodies and in these organisms that we would consider quite quite all for example this lactobacillus right over here this is on the order of this is on the order of 5 to 10 micrometers 5 micrometers so five millionths five millionths of a meter
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