all right welcome to the third and final video for chapter 7 again we're going to be looking at what happens after glycolysis when we don't have oxygen we're also going to look at how proteins and lipids can be metabolized and enter different parts of the cellular respiration Pathways finally we'll look at how cellular respiration can be regulated so what happens when we don't have oxygen remember that glycolysis did not need oxygen right it happens whether you have oxygen available or if you don't have oxygen available it doesn't matter but one of the reactants for glycolysis was nad+ because you're going to reduce that and form nadh when you have oxygen and you go through remember that last step oxidative phosphorilation when oxygen is present when we went through that we regenerated nad+ when we were looking at that electron transport chain because n DH gave its electrons to the complexes within the electron transport chain regenerating n+ so that glycolisis can continue but what if you don't have oxygen you still need to somehow regenerate nad+ in order for glycolosis to happen and so you can make some ATP through that process of substrate level phosphorilation it turns out when you don't have oxygen you go through a step known as fermentation so glycolysis is first and if you don't have oxygen it's lacking then the next step is fermentation instead of the oxidation of pyate so through fermentation you can regenerate Ned Plus in an anob environment anerobic means you have no oxygen there are two types of fermentation one is called lactic acid fermentation the other one is alcohol fermentation one of these happens in hum humans as well what do you guys think so this happens a lot when we are working out and you're running low on oxygen you start feeling tired you want to stop running for example well when I work out I know it's not alcohol fermentation because this would mean as I work out the harder and harder I work out I'm going to get like drunk from working out so that's not going to happen in humans when we rely on anerobic processes to happen because we don't have enough oxygen or running low then we start going through lactic acid fermentation so that happens in many cells and we're going to see other organisms like yeast can go through alcohol fermentation so when and where does lactic acid fermentation take place so I mentioned earlier it happens in muscle cells when are running out of oxygen it happens in our red blood cells mature red blood cells actually don't have uh organel like mitochondria so we're going to have lactic acid fermentation happen instead of the processes like citric acid cycle Etc it also happens in some bacteria like the ones that we find in our yogurt the enzyme that catalyzes this reaction is known as lactate dehydrogenase and it catalyzes both the forward and reverse of this reaction and this is going to happen in the cytoplasm of the cell so fermentation happens in the cytoplasm that makes sense because glycolysis also happens in the cytoplasm of the cell so let me look over here at this picture on the left remember glycolysis was when we take glucose and chop it in half to make two pyate Mo uh two pyrovate molecules remember pyate is also known as pyic acid and if I don't have oxygen I need to regenerate my nad+ because I used it it's a reactant for glycolysis so I go through lactic acid fermentation which is the lower half of this diagram so during lactic acid fermentation I'm going to take pyrovate and convert it into lactic acid also known as lactate and that is a Redux reaction so it looks like I'm going to oxidize nadh forming nad+ so that is oxidized and this is reduced all right what about the other kind of fermentation the other one is alcohol fermentation it does not happen in humans but it happens the most common example are yeast species that are anob remember fermentation is anerobic and it involves two reactions the first one is catalyzed by an enzyme called pyrovate decarboxylase and I can see that is the first step over here I'm going to take pyic acid also known as pyat and I'm going to lose a carbon so this is a three carbon MO molecule and acetal dhide is formed acetal dhide has two carbons and then acetal deide along with nadh we're going to convert that into ethanol and NAD plus through an enzyme or using an enzyme called alcohol dehydrogenase so my nad+ can be reused again for glycolysis and here our book gives us a picture of fermentation tank this is when they're uh making wine it looks like this process is for wine when you ferment grape juice into wine you produce carbon dioxide as a product and these fermentation tanks have valves so that we can release um CO2 the pressure from the carbon dioxide gas that's produced if you're drinking champagne they keep some of that CO2 in there to create those bubbles and this is a nice summary of how fermentation Works hand inand with glycolysis this is for lactic acid fermentation but it could also be for um we could draw something similar for alcohol fermentation so glycolysis I'm generating pyate and I remember I need nad+ as a reactant if I don't have oxygen I go through fermentation and you can either generate lactate like we have here and those nad+ that we can reuse for a glycolysis or this could be also substituted with the reaction we just saw with alcohol fermentation we would still generate nad+ so that we can continue to go through glycolysis glycolysis remember generates ATP and in anerobic organisms they only generate ATP through glycolysis this is through substrate level phosphorilation so many years ago when digital books started becoming big um my husband and I bought a bunch of digital books because they were like 10 for a dollar and one of the books that we got was written by a doctor a physician who wrote a book about zombies and vampires and he kind of like Incorporated Concepts from biology and Medicine into the book which I found kind of cool so he kind of used this chapter the material from this chapter in his book and let me show you how it's related so think about zombies zombies are slow right in the movies zombies are slow and and they're dead right so they're probably not breathing zombies are slow and probably produce ATP using what do you guys think aerobic respiration or fermentation let's see I just said that they're not breathing and they're really slow so I don't think it's aerobic cuz otherwise they would make like 30ish ATP per glucose and be faster so I'm going to choose fermentation because they they don't breathe and they're only making 2 ATP per glucose which would explain why they're so slow they can't really power anything vampires on the other hand are really fast and they drink blood what's in blood lots of oxygen in the blood right so they're probably going through aerobic respiration because I know when you have oxygen you can make around 30 to 36 ATP Pro glucose so that could explain why they're so fast so this is the idea that the doctor uses when he writes his book about zombies and vampires and that was his explanation about why they're fast or slow and that was kind of fun and although we focus on glucose as the main reactant for glycolysis what goes into the reaction for cellular respiration we don't just eat glucose right we eat other types of carbohydrates like sucrose remember sucrose is a disaccharide made up of glucose plus fructose we eat lactose which is glucose and galactose um we have we eat starches carbohydrates glycogen is stored in our muscles all of these different types of sugars these carbohydrates can be broken down or modified to enter glycolysis and even proteins and lipids can be modified to enter glycolysis or different parts of the cellular respiration Pathways because think about people for example who are on low carb diets or who don't even eat carbs at all if you're only eating proteins and fats how are you going to go through this process and make ATP it turns out that pretty much anything can be modified and shuttled into this pathway at some point amino acids can be modified and enter glycolysis glycerol which is remember glycerol and Three fatty acids create our triglycerides or lipids can also enter glycolysis amino acids can enter the citric acid cycle or Pate oxidation and fatty acids can also be metabolized and ENT citric acid cycle and it's not shown here but even if we're desperate for energy even our nucleic acids remember our DNA and RNA can be modified to enter different components of the citric acid cycle as well okay so you do not have to memorize this scary picture but the purpose or the point of this picture is to tell us that Amino acids can enter the citric acid cycle remember amino acids are the subunits of proteins so if you're on a low carb diet and you're relying mainly on proteins for energy then their proteins can be chopped up into their individual amino acids and these are all the names of different types of amino acids remember amino acids kind of look like this let me sketch it out really quick carboxy group our Pro our hydrogen atom and then our side chain or R Group we have to get rid of the amino group and that usually turns into ammonia and is eventually released from the body in the form of Ura Ura is excreted through the kidneys as urine it also is released as sweat the remaining portion can enter different parts or different stages of the citric acid cycle or even earlier if we look at how cellular respiration can be regulated it can be regulated by whether or not we allow gluc ose to enter the cell and that's usually through hormones I'll show you in the next slide it can be regulated by enzyme reversibility and if you have a reaction catalyzed by just one enzyme usually the reaction is reversible and you can eventually reach equilibrium um we can also look at enzyme or reaction that's irreversible reactions that are irreversible are usually reactions that are controlled by two different enzymes one enzyme going in the forward direction of the pathway and then a different enzyme that catalyzes the reverse reaction this allows a pathway to exceed equilibrium enzymes power these metabolic pathways so if I change the pH um for example due to too much lactic acid being formed I know that changes in PH can denat or change the shape of proteins and most enzymes are proteins so I can slow down or change the rate of enzyme activity by changing pH and there are also additional feedback controls we'll learn later on in the course as well as your second course in the series in 4B so here's that example of the hormonal control of the levels of glucose I need glucose for glucose catabolism to happen and one way I can control this is through the hormone insulin it turns out that after a meal so you just ate a bunch of food you have high blood sugar levels high blood glucose levels what happens is insulin is released by the pancreas insulin binds to a receptor on the cell and that triggers a bunch of changes inside of the cell to allow glute four receptors to be embedded into the membrane of the cell and now that you have glute four receptors glucose which is a polar molecule that cannot cross the cell membrane can be shuttled into the cell so if increase in cellular glucose or the amount of glucose in the cytoplasm means you can go through glycolysis at a faster rate there are many other ways that we can control cellular respiration in terms of feedback but you do not have to memorize this chart let me point out a few important Trends so one I mentioned earlier is glucose 6 phosphate so glucose is phosphorilated right away in the first step of glycolysis through an enzyme called hexokinase so remember kinases phosphorate things they add phosphate groups and the purpose of phosphor the glucose in the first step of glycolysis was to trap it inside of the cell if you don't it might just leak out of that gluc four receptor and then you run out of glucose and you can't go through glycolysis another way to regulate cellular respiration is by looking at how much of the reactants you have and how much of the product you have if you have an increase in the number of reactants such as ADP every time you have an increase in the reactant you're going to have a greater rate of the pathway those reactions will happen at a faster rate but anytime you have a greater amount of the products like ATP then that's going to result in a decrease in the rate in that pathway all right and that takes us to the end of our third and final video for chapter 7 in our next chapter chapter 8 we'll talk talk about photosynthesis