in this video we're going to focus on cellular respiration cellular respiration is the process by which we derive energy from food in cellular respiration we're going to take one molecule of glucose which has the chemical formula c6h12o6 and it's going to react with six molecules of oxygen to produce six molecules of carbon dioxide and six molecules of water and this this process is going to release energy so it's exergonic and it releases a lot of energy so that's the reaction for cellular respiration on the left side we have the reactants and on the right side we have the products of the chemical reaction now some of the energy released by cellular respiration or released by the oxidation of glucose is lost as heat energy or thermal energy some of it is captured in the form of atp atp stands for adenosine triphosphate atp is the energy currency of the cell it gives us the energy that we need to move to grow and to do all the things that we do in our everyday lives it provides the energy to drive endergonic reactions and a lot of times it does this by the transfer of a phosphate group so when this energy is released energy is stored by converting adp adenosine diphosphate into adenosine triphosphate so this reaction is endergonic it takes energy to work but to release energy from atp is the reverse due to the unstable phosphate bonds whenever atp loses a phosphate group it releases energy and so that is an exergonic reaction exergonic reactions release energy and organic reactions they require energy they absorb it in order to work now here is a question for you why do cells need atp in the first place why not use the energy released directly from glucose to drive endergonic reactions the answer is efficiency glucose releases a large amount of energy whereas the loss of a phosphate group from atp only releases a small amount of energy as a result there's less energy loss in the form of heat so thus the process of transferring energy from atp to a chemical reaction is more efficient more energy is converted into useful work and that's why cells use atp instead of glucose because it's more efficient to convert that energy into work let's use the internal combustion engine inside a car to illustrate this concept imagine taking all of the gasoline inside a car and react in it with oxygen in a combustion reaction now that process will be very dangerous you'll get one large explosion but you won't be able to convert much of that energy into useful work a lot of it will be wasted in the form of heat but now if you were to use that gasoline in a car in a small car engine instead of having one large explosion you'll have a series of small tiny explosions that drive the piston to cause the vehicle to move as a result because you have you're releasing that energy a little at a time it's more efficient you're better able to convert that energy to useful work and this is why cells tend to store their energy temporarily in the form of atp because that energy can be released in series of small steps in a much safer way but also in a more efficient way so releasing energy all at once is not an efficient process to perform useful work but when you release energy a little at a time the efficiency increases most small car engines tend to be more efficient than bigger larger engines now the next thing that i want to mention is the structure of atp adenosine triphosphate atp has three subunits a five carbon ribose sugar a nitrogenous base the nitrogenous base is called adenine and it has three phosphate groups so that's a simplified structure of atp now let's do an overview of cellular respiration cellular respiration can be broken down into four stages the first stage is something called glycolysis if we break down the word glycolysis glyco refers to a carbohydrate lysis means to split apart so in glycolysis we're taking glucose and we're going to split it into two molecules of pyruvate in stage two we have pyruvate oxidation in this stage pyruvate is oxidized into acetyl coenzyme a in the third step this is known as the krebs cycle in the krebs cycle acetyl coenzyme a is oxidized into carbon dioxide the electrons released from that reaction is used to create nadh and fadh2 in step four we have the electron transport chain which the molecules nadh and fadh2 will give up those electrons and those electrons will pass through the electron transport chain in that process atp will be produced by the way glycolysis you need to know that this occurs in the cytosol of the cell pyruvate oxidation that occurs inside the mitochondria the krebs cycle also occurs inside the mitochondrial matrix and the electron transport chain that occurs in the inner membrane of the mitochondria not the outer membrane but the inner membrane so you need to know where these processes occur in the cell let's begin our discussion with the first stage of cellular respiration that is glycolysis in glycolysis glucose a six carbon molecule is converted into two pyruvate molecules each with three carbon atoms pyruvate contains a methyl group a carbonyl group and a carboxylate group pyruvic acid has a hydrogen instead of an oxygen for negative charge so this is pyruvic acid but if you take away the hydrogen it becomes pyruvate now in this process two molecules of adenosine diphosphate is converted to two molecules of atp adenosine triphosphate this is known as substrate level phosphorylation anytime you add a phosphate group to something it's known as phosphorylation in this video there's two types of phosphorylation events that you need to be familiar with substrate level phosphorylation and oxidative phosphorylation so this is an example of substrate level phosphorylation oxidative phosphorylation occurs at the beginning of the electron transport chain which we'll talk about that later in this video now something else happens two molecules of nad plus is reduced to two molecules of nadh as glucose is converted into two pyruvate molecules now we need to understand the terms oxidation and reduction the conversion of glucose into pyruvate is an oxidation reaction the conversion of nad plus into nadh is a reduction reaction so there's four ways in which you could describe an oxidation reaction number one the oxidation state goes up number two you have a loss of electrons number three you have a gain of oxygen atoms or number four you have a loss of hydrogen atoms you could use any one of these four ways to determine if you have an oxidation or a reduction reaction in a reduction reaction the reverse is true the oxidation number or oxidation state will decrease it's going to be reduced reduction is associated with a gain of electrons it's also associated with a loss of oxygen atoms or a gain of hydrogen atoms so let's use nad plus so let's convert this into nadh so there's two ways in which we could determine that this is indeed a reduction reaction the first has to do with the oxidation state this has a positive charge so the oxidation state is plus one this doesn't have any charge the oxidation state is zero going from one to zero the oxidation state decreased or it was reduced so that's a reduction reaction the second way is to look at the fact that we have a gain of hydrogen nad plus it has hydrogen atoms but when we compare it to nadh we could see that it gained one hydrogen atom and so we can say that it's reduced here's the entire reaction here we have nad plus it reacts with a hydrogen ion and it accepts two electrons in order to convert to nadh so here we have a third way to determine that it's reduction the fact that it's gaining electrons whenever you see electrons on the left side of a chemical reaction it's reduction if the electrons are on the right side of the chemical reaction it's oxidation now glycolysis occurs in 10 steps we're not going to talk about each step in detail but one thing i do want to mention is that there's two important phases you need to know of glycolysis the first half or the first five reactions refers to the investment phase in the investment phase you need to invest atp molecules to get glycolysis started so you're going to lose two atp molecules in this phase during the second half of glycolysis that is the last five reactions this is known as the payoff phase and in this phase you're going to get four atp molecules per one molecule of glucose so glycolysis has a net gain of two atp molecules per glucose molecule so you need to be familiar with this number so glycolysis will yield a net of two atp molecules so here is an overview of glycolysis you could see that it occurs in 10 reactions and notice the amount of atp that's produced and the amount that's consumed so in step one and step three atp is converted into adp so that is the investment phase you're putting in two molecules of atp to get glycolysis started and notice that in the payoff phase you get a total of four atp molecules so you put in two you got back four there's a net gain of two atp molecules in step six we can see that we gain two molecules of nadh keep in mind glucose splits off into two molecules of pyruvate so on the left side you have one molecule of pyruvate and on the right side another molecule of pyruvate now the next thing i want to mention are the enzymes the first type of enzyme is a kinase enzyme a kinase enzyme is typically associated with the transfer of a phosphate group they catalyze the transfer of a phosphate group so here we have hexokinase the phosphate group is leaving from atp in step 3 we have another loss of a phosphate group from atp and the enzyme is phosphofructokinase step 7 we have substrate level phosphorylation and another kinase enzyme and the same is true for 10. so any time there's a transfer of a phosphate group the enzyme that catalyzes such a transfer is a kinase enzyme if you see the word isomerase then that tells you that this enzyme it catalyzes a rearrangement reaction glucose 6-phosphate and fructose-6-phosphate they're isomers of each other they have the same chemical formula they simply have been rearranged so this type of enzyme it transfers a rear i mean it catalyzes a rearranging reaction so i just want to mention those details um just in case you had questions on it and then there's another enzyme that you need to be familiar with that is a dehydrogenase enzyme a dehydrogenase enzyme removes hydrogen from a substrate so prior to this we had glyceraldehyde 3-phosphate g3p and notice the amount of hydrogen atoms in this molecule so we have one two three five now looking at the product one three by phosphoglycerate notice that there's only four hydrogen atoms so one hydrogen atom was transferred to nad plus making nadh and that hydrogen atom was taken from g3p to give it to nadh so going from g3p to bpg we lost the hydrogen and we could see that nad plus it took that hydrogen so dehydrogenase is an enzyme that removes hydrogen kinase is an enzyme that helps with the transfer of a phosphate group and isomerase is an enzyme that catalyzes rearrangement reactions now let's move on to stage two of cellular respiration and that is pyruvate oxidation so as mentioned before pyruvate will be converted into acetyl coenzyme a which looks like this it contains a sulfur and the co a the coenzyme a part so this is pyruvate on the left so what's happening in this reaction let's talk about that notice that we lost a carboxylic acid molecule so therefore this is a decarboxylation reaction a decarboxylation reaction is an oxidation reaction notice that we lost oxygen atoms whenever there's an oxidation reaction there is always a reduction reaction if something lost electrons something else had to gain those electrons and the first electron carrier that we have in cellular respiration is nad plus nad plus is going to pick up those electrons along with a hydrogen ion to produce nadh so that is the corresponding reduction reaction now the reaction that catalyzes i mean the enzyme rather the enzyme that catalyzes the conversion of pyruvate into acetyl coenzyme a this is known as pyruvate dehydrogenase whenever you see this enzyme there's always a transfer of hydrogen somewhere in this case nad plus is the hydrogen acceptor as it accepts the hydrogen it turns into nadh but this leaves a question where did the hydrogen come from because pyruvate has three hydrogen atoms and acetyl coenzyme a also has three hydrogen atoms the answer lies in the product notice the group that we added the reactant looks like this it's coenzyme a with a thio group attached to it so this is the hydrogen that goes into the solution and is later picked up by nad plus so anytime you see a dehydra excuse me a dehydrogenase enzyme there's always a transfer of hydrogen somewhere either from the reactant from the solution there's always a transfer of a hydrogen atom something will lose the hydrogen atom while something else will gain that hydrogen atom now let's move on to step three of cellular respiration and that is the krebs cycle so prior to that we had the oxidation of pyruvate we saw pyruvate being oxidized into acetyl coenzyme a the acetyl part is a two carbon molecule and as we produce acetyl coenzyme a we lost co2 in a decarboxylation reaction which is an oxidation reaction and we also had a reduction reaction as nad plus was converted to nadh so now acetyl coenzyme a enters into the krebs cycle which occurs in the mitochondrial matrix now this two carbon acetyl group is combined with oxaloacetate which has four carbons and it produces citric acid in this case citrine citric acid will have the hydrogen atoms on the carboxylate groups citrate it doesn't have those hydrogen atoms it's just coo minus notice that we regenerate the coenzyme a molecule with the sh style group as you can see here now we're not going to go over all of the individual reactions of the krebs cycle you can review that when you get a chance but the gist of it is this the two carbon molecule the acetyl group will be oxidized into two molecules of carbon dioxide here is the first one here is the second one and then we're going to regenerate oxaloacetate and that's going to pick up another acetyl coenzyme a so this is a cycle it repeats itself and this coenzyme a is going to react again with pyruvate repeating the process now i do want to talk about the enzymes in this reaction the first one is the dehydrogenase enzyme as i mentioned before earlier this is used to catalyze the removal of hydrogen atoms from a molecule or substrate and then transfer it to like nad plus or fadh so here the hydrogen was transferred to nad plus and going from isocitrate to alpha ketoglutarate we could see that we lost some hydrogen atoms this molecule here has five hydrogen atoms and this one here has four so it lost the hydrogen and in step five we have another dehydrogenase enzyme and we can see that nad plus is picking up a hydrogen turning to nadh and the same is true for seven and nine there's a transfer of a hydrogen atom somewhere in step seven fad is converted to fadh2 we can see that sustanate lost two hydrogens as it was converted to fumarate and then going from malate to oxaloacetate there's another loss of two hydrogen atoms this had four this had two and so another dehydrogenase enzyme was used for that so anytime you see a dehydrogenase enzyme you know that it catalyzes the removal of hydrogen atoms and transfer it from one molecule to another now let's not lose sight of the purpose of the krebs cycle which is to oxidize the two carbon acetyl group into two molecules of carbon dioxide keep in mind oxidation involves a loss of electrons those electrons are going to be picked up by nad plus and fad nad plus is the first electron carrier fad is the second one and those electron carriers will then release their electrons in the electron transport chain which we'll talk about later but for now know that one turn of the krebs cycle produces three molecules of nadh one two three one molecule of fadh2 and it produces one molecule of gtp but notice that as gdp gains a phosphate and becomes gtp from step 6 gtp will lose that phosphate regenerating gdp but convert in adp to atp so one turn of the krebs cycle produces three molecules of nadh one molecule of fadh2 and the net of one molecule of atp gtp and gdp they're going to be in a cycle so there's really no net gain there now keep in mind that glucose generates two molecules of pyruvate and thus two molecules of acetyl coenzyme a so one molecule of glucose equates to two turns of the krebs cycle so one molecule of glucose yields six nadh molecules two fadh2 molecules and two atp molecules you may want to write that down one thing i do want to mention is that in this video sometimes i referred to these particles as molecules technically they're ions because they carry a charge but in in biology or biochemistry sometimes you'll see people refer to these as molecules but they're really ions this would be a molecule it doesn't have a net charge co2 is a molecule but citrate isocitrate pyruvate those are ions because they carry a net charge just wanna mention that so if i refer this as a molecule let's say a molecule pyruvate it's really an ion if it has a charge now before we finish our discussion with the krebs cycle there is one more thing i need to talk about and that is fad fad is actually part of the inner membrane of the mitochondria it's not in the mitochondrial matrix it's stuck on the membrane and succinate dehydrogenase it's an enzyme that is in the membrane where fad and fadh2 will be located so even though the krebs cycle occurs in the mitochondrial matrix this enzyme is actually in the inner membrane so fad and fadh2 it doesn't leave the membrane it's there so that's one thing i do want to mention and we're going to talk about that more in the electron transport chain now let's briefly talk about the mitochondria and what you need to know about it with regard to cellular respiration in red this is the outer membrane of the mitochondria the line represented in blue is the inner membrane of the mitochondria the space between is known as the inter membrane space and then on the inside this is the mitochondrial matrix now keep in mind the krebs cycle occurs in the mitochondrial matrix the electron transport chain occurs in the inner membrane of the mitochondria so those are some things that you want to keep in mind as well now let's move on to stage four of cellular respiration and that is the electron transport chain now the nadh molecule that we generated in the krebs cycle and even in glycolysis as well as pyruvate oxidation it's going to give up a hydrogen and some electrons at complex one complex one is called nadh dehydrogenase as all dehydrogenase enzymes go it's going to catalyze the removal of hydrogen from nadh as a result nadh will lose electrons it's going to give up electrons to complex one those electrons will travel to ubiquinone represented by the symbol q ubiquinone is a mobile electron carrier it actually moves to complex one picks up the electrons and then take it to complex stream keep in mind the electrons have a negative charge and on their own they can't move by themselves along the inner membrane because the membrane is made up of phospholipids and the tails of the phospholipids are nonpolar and so they don't interact well with negatively charged electrons so the electrons has to be carried by a mobile electron carrier in this case ubiquinone now ubiquinone is going to pass on the electrons to complex 3. complex 3 is called cytochrome reductase also known as bc1 complex by some textbooks cytochrome c i mean cytochrome 3 rather is going to give the electrons to cytochrome c whenever cytochrome c receives electrons it becomes reduced reduction as we talked about is the gain of electrons and so this name is fitted for complex 3 because it reduces cytochrome c by giving it electrons cytochrome c is another mobile electron carrier it's free to move but it's a surface protein as opposed to an integral protein complex one and three these are trans membrane proteins also integral proteins because they're completely embedded within the membrane now c cytochrome c is going to give up the electrons to complex four also known as cytochrome oxidase this particular transmembrane protein it oxidizes cytochrome c because it takes away electrons from it anytime you have a loss of electrons oxidation occurs now the electrons will flow out of complex four where they're going to meet up with oxygen and some hydrogen ions to form water which is one of the products of cellular respiration now the other electron carrier that we need to talk about is fadh2 now i mentioned this earlier fad and fadh2 they are bound to the inner membrane they're part of complex 2. so i'm going to write f to represent fad and then f h2 to represent fadh2 let me get rid of this for now now in step 7 of the krebs cycle we saw that sustanate converts into fumarate and as a result it gives up electrons and hydrogen as well convert in fad into fadh2 so that's in the krebs cycle succinate dehydrogenase complex 2 is the enzyme that removes hydrogens from susanate converting that into fumarate and then those hydrogen atoms are transferred to fad now in the electron transport chain fadh2 gives up those hydrogens and the electrons turning back into fad so it's a cyclic process so as fadh2 turns to fad the electrons will be picked up by ubiquinone and then it's going to be carried to complex 3 and then to cytochrome and to complex 4. now as the electrons are transferred through these membrane proteins across the electron transport chain protons are pumped from the mitochondrial matrix into the intermembrane space and so each of these transmembrane proteins are pumping out protons into the intermembrane space and so what happens is we have a buildup of positive charge in the intermembrane space so the ph here is going to be relatively low now as these protons are pumped into this region the inter membrane space is going to develop a positive charge and so the mitochondrial matrix will be less positive or more negative with respect to the intermembrane space and so there's going to be an electric force that these protons will fill because they're going to be attracted to the negatively charged mitochondrial matrix the second thing is a concentration gradient you have a large concentration of protons in the intermembrane space so the electric force combined with this concentration gradient will cause these protons to enter this enzyme atp synthase which you can also say it's a membrane protein it's gonna cause the protons to flow through atp synthase and they're gonna cause this portion to basically turn like a rotor a good way to think about this is water flowing down into a turbine causing the turbine to spin so as these protons flow down this membrane they will cause this they will create a mechanical force that will smash adp and phosphate to make atp so this process is known as chemiosmosis because we're using diffusion to create atp so the electron transport chain is basically what we see here the electrons traveling from complex 1 all the way to complex 4. chemiosmosis is the production of atp using the diffusion of protons as it flows through atp synthase when you combine the electron transport chain and chemiosmosis you have oxidative phosphorylation now keep in mind phosphorylation occurs when we transfer a phosphate group to something in this case transferring a phosphate group to adp to make atp that is an example of phosphorylation now an electron transport chain nadh is oxidized to nad plus it's oxidized in a sense that nadh loses electrons to the electron transport chain and you can see its oxidation state increases from zero to plus one so both nadh and fadh2 are oxidized in the electron transport chain and using atp synthase adp is phosphorylated with a phosphate group making atp so combined we have oxidative phosphorylation the first part is oxidation the second part phosphorylation now one more thing that i do want to mention is that there are many electron acceptors in glycolysis we saw that nad plus was an electron acceptor it took electrons as glucose split into pyruvate fad served as an electron acceptor when sustanate was converted to fumarate oxygen is the final electron acceptor in this process oxygen is one of the most electronegative elements besides fluorine and so because of that affinity for electrons oxygen basically pulls electrons through the electron transport chain to itself and so that's really the driving force here it's electronegativity because electrons will travel from atoms that are less electronegative to atoms that are very electronegative so in the beginning the electrons were located in glucose so they were attached to carbon atoms and then in the end those electrons go to oxygen to make water and carbon dioxide so as the electrons flow from carbon to oxygen energy is released carbon is not very electronegative its electronegativity is like 2.5 for oxygen is 3.5 so as we take electrons from an atom that is less electronegative to an atom that is more electronegative we can extract energy from that process a good way to illustrate this is the use of a battery so let's say i'm going to draw a double a battery here is the positive terminal and here is the negative terminal and let's connect this to a lipo let's say this battery is strong enough to light up the light bulb electrons will flow from the negative terminal to the positive terminal and in a process from moving from one side to the other side energy can be extracted from it and in this case lighten up the light bulb so the positive terminal would be the electronegative side of the battery because it pulls the electrons toward it the negative terminal will be the part that's less electronegative because that's where the electrons are coming from in this case carbon would be like the negative terminal of the battery oxygen will be like the positive terminal of the battery because oxygen being electronegative pulls the electrons away from carbon and so anytime electrons flow from one position to another position energy can be extracted as those electrons move from one location to the other as we could see in the case of a battery the same is true for let's say we have a ball rolling down the hill at the top the ball has potential energy but as it moves from one position to another position that potential energy is converted to kinetic energy and in that motion energy can be extracted if you think of water flowing down a hill that water can be used to move the turbine which can then be used to create electricity so whenever you have an object or a particle like an electron moving from one location to another energy can be extracted uh during that process which is what we see here in the electron transport chain so the electrons they travel from carbon to nad plus and then from nad plus they go to complex 1 and then to q and then complex three and then complex four and then finally to oxygen so oxygen has the greatest electronegativity or electron affinity for electrons so here's a question for you which complex has a greater electron affinity for electrons would you say complex one or complex three so according to the sequence because complex three comes after complex 1 we could say that complex 3 has a greater electron affinity or rather a greater affinity for electrons than complex 1. so we can say that complex 3 is more electronegative than complex one now in the case of fad carbon gives its electrons to fad and then fad gives its electrons to complex two which gives its electrons to q so if we were to compare the mobile carrier ubiquinone in complex 2 we would say that complex q is more electronegative than complex 2 because it comes after complex 2. the electrons will always flow from something that is less electronegative to something that is more electronegative spontaneously the only way to make the electrons go back is by putting energy into the system but as electrons flow this way energy is released so now we need to do some math so let's go back to nadh as nadh is oxidized to nad plus we said that it's going to give up electrons which will pass through complex 1 q complex 3 and complex 4. so notice that nadh activates three complexes and these three complexes will be shooting out protons into the intermembrane space it turns out that nadh one molecule of nadh will yield three atp molecules and this is proportional to the number of complexes that nadh activates now as fadh2 turns into fad which is basically inside this complex even though i drew it outside it only activates two of the three complex proteins it activates these two and it turns out that one fadh2 molecule produces two atp molecules which makes sense the proportions have to be the same so keep that in mind because we're going to talk about the net amount of atp that one molecule of glucose can yield in cellular respiration so let's begin with the first stage of cellular respiration which is glycolysis converting glucose into pyruvate in glycolysis we generated a net amount of two atp molecules in addition we generated two nadh molecules now keep in mind one nadh molecule activates three proton pumps in the electron transport chain so we could say that one nadh molecule will generate three atp molecules so if two of them should generate six atp molecules now some textbooks will say that in order for nadh to the nadh that's producing glycolysis to travel to the mitochondria keep in mind glycolysis occurs in the cytoplasm so to move nadh from the cytoplasm into the mitochondrion cell it requires one atp molecule so to transport two nadh molecules into the mitochondria it's going to cost us two atp molecules giving us a net yield of 4 atp molecules now in step 2 pyruvate oxidation two molecules of nadh are produced which yields six atp molecules in step three the krebs cycle we get one atp molecule per turn of the cycle but one glucose molecule yields two pyruvate molecules which corresponds to two acetyl coenzyme a molecules and so that's two turns in the krebs cycle so we get two atp molecules from one glucose molecule now instead of getting three nadh molecules per turn we're going to get six nadh molecules if we multiply that by three that's 18 atp molecules one turn of the krebs cycle gives us one fadh2 molecule so for two turns that's two fadh2 molecules and keep in mind each fadh2 molecule activates two of the three proton pumps so we're going to say that one fadh2 molecule yields two atp molecules so two fadh2 molecules yields four atp molecules so if we add up these numbers 2 plus 18 that's 20 24 30 36 38 so one glucose molecule can yield a maximum of 38 atp molecules now if you subtract the two atp molecules that are needed to transport the two nadh molecules from the cytosol into the mitochondria then we get a net value of 36 atp now this is basically an ideal scenario natural systems are not 100 efficient so the true number might be less than 36 or 38. some of the protons in the intermembrane space can leak through back into the mitochondrial matrix even without going through atp synthase this is what some textbooks suggest so if that happens the yield won't be as high as 36 or 38 it will be less so this is an ideal scenario where we can get a maximum of 38 atp if everything works out perfectly cellular respiration is a type of aerobic respiration the word aerobic means with oxygen so in cellular respiration we saw that glucose was converted to pyruvate during glycolysis and in step two pyruvate oxidation pyruvate was converted to acetyl coenzyme a and during the krebs cycle acetyl coenzyme a was oxidized into two molecules of carbon dioxide and during the electron transport chain the electrons that were carried by nadh and fadh2 they were transferred to oxygen which in the presence of hydrogen ions turned into water so this is what happens in the presence of oxygen glucose is ultimately converted into carbon dioxide and water with the help of oxygen now what happens when oxygen is not present so what happens under anaerobic conditions that is without oxygen in this case we're going to get something called fermentation now it's important to understand that glycolysis does not need oxygen to work in fact glucose can be converted to pyruvate without the help of oxygen so let's say if you're exercising and your oxygen is low let's say if you're undergoing like you're working out or if you're running at your maximum pace when your muscle cells run out of oxygen they can do something called lactic acid fermentation so glucose will be converted to pyruvate and as that happens glycolysis will generate two atp molecules so your muscles will be using these atp molecules for energy in addition nad plus is converted into nadh now here is the problem in order for glycolysis to continue you need to regenerate nad plus because if your cells run out of nad plus glycolysis can continue and your cells won't be able to make atp so this is why fermentation's important pyruvate for some reason i drew acetate so this is pyruvate in lactic acid fermentation pyruvate is going to change into lactate which looks like this the carbonyl group has been reduced to an alcohol group so that's the difference between pyruvate and lactate now nadh is going to be the substance that reduces this carbonyl group to a hydroxyl group so nadh has to be oxidized to nad plus and so this is how we can regenerate nad plus thus allowing glycolysis to continue so that is lactic acid fermentation this is what your muscle cells do when they're running out of oxygen that's how they can make atp to give you the energy that you need but as the lactic acid content in your muscles increases during heavy exercise you're going to feel that that tiredness that soreness that pain sensation but as you take a break as you continue to breathe in oxygen your body will convert lactate back into pyruvate and then pyruvate ultimately into carbon dioxide and water so in the presence of oxygen your cells can generate a lot of atp in the absence of oxygen it turns to lactic acid fermentation generating atp in a very short time frame now let's talk about the other type of anaerobic respiration and that is ethanol fermentation so in ethanol fermentation this is this happens with yeast cells these are single-celled fungi glucose is converted to pyruvate so glycolysis still occurs and as before nad plus is reduced to nadh and we're still going to get our two atp molecules now the next step of ethanol fermentation that is after glycolysis pyruvate undergoes decarboxylation it converts into a molecule called acetaldehyde as you can see it went from a three carbon molecule or rather three carbon ion to a two carbon molecule so we lost co2 so that's a decarboxylation step and then acetaldehyde is reduced to ethanol using a reducing agent nadh as nadh gives up its electrons to and let me say that again as nadh gives up its electrons it is oxidized to nad plus thus reducing acetaldehyde into ethanol so now that we've regenerated nad plus it can go back into the cycle allowing glycolysis to continue producing more atp molecules and so that's what yi cells do when oxygen is not present so if you were to mix the e cells with glucose in the absence of oxygen they're going to make ethanol they convert glucose into ethanol now the carbon dioxide that they emit from this step the decarboxylation step is the reason why bread rises in the presence of yeast the co2 is the gas that expands the bread so that's ethanol fermentation now for those of you who might be studying for a test on cellular respiration here are some practice problems that might be helpful to you so let's start with this one number one which of the following is a product of cellular respiration would you say nadh oxygen gas glucose carbon dioxide or fadh2 well let's begin with the net reaction of cellular respiration so we have glucose c6h12o6 it reacts with six oxygen molecules to produce six carbon dioxide molecules six water molecules and energy glucose is a reactant not a product keep in mind the reactants are on the left side the products are on the right side oxygen is a reactant now in cellular respiration nadh is produced in the krebs cycle in glycolysis but it's consumed in the electron transport chain so therefore this is really an intermediate not a product because we make it and then we consume it carbon dioxide is a product fadh2 is another intermediate like nadh so it's not an overall product in its reaction the answer is d number two which of the following does not occur in cellular respiration feel free to pause the video if you want to try this yourself and then play the video when you have your answer so the first step of cellular respiration as we know is glycolysis that's stage one step two is pyruvate oxidation step three is the krebs cycle and step four is the electron transport chain so we're looking for what does not occur in cellular respiration glycolysis occurs in cellular respiration and the electron transport chain is part of it pyruvate oxidation also occurs in it now the krebs cycle is the same as the citric acid cycle that's just another name for it so we can eliminate answer choice b ethanol fermentation does not occur in traditional cellular respiration ethanol fermentation is outside of that so d is the answer number three which of the following is not a product of glycolysis so glycolysis is a process that converts glucose into pyruvate into two ions of pyruvate and at the same time it converts nad plus into nadh and it converts adp to molecules of adp to two molecules of atp and substrate level phosphorylation so pyruvate is a product we could eliminate answer choice a atp is also a product you could think of as a side product it produces nadh but it does not produce lactic acid not in this step number four how many atp molecules are produced during glycolysis in glycolysis as we saw in the last problem two atp molecules are produced it's not going to be 10 32 36 or 38. it's two so answer choice a is the correct answer number five which of the following statements is false let's look at each one so starting with answer choice a glycolysis occurs in the cytoplasm is that true or false this is a true statement so it's not the answer because we're looking for the statement that is false b lactic acid fermentation occurs in muscle cells under anaerobic conditions is that true or false anaerobic conditions is conditions without oxygen and lactic acid fermentation will occur in muscle cells if you're using muscles and the oxygen content is very very low so this is true c ethanol fermentation occurs when yeast cells consume glucose under aerobic conditions now yeast cells do undergo ethanol fermentation in the presence of glucose but not under aerobic conditions under anaerobic conditions so ethanol fermentation occurs when yeast cells do not have the oxygen they need to complete the traditional cellular respiration so this is false because of the word aerobic it has to be anaerobic so c is the answer for d the tca cycle occurs in the mitochondrial matrix that's true keep in mind the tca cycle the tricarboxylic acid cycle is the same as the citric acid cycle or the krebs cycle and e the mitochondria is responsible for producing most of the atp molecules in a cell keep in mind the krebs cycle and the electron transport chain all of that happens inside of the mitochondria so e is a true statement 36 out of the 38 maximum atp molecules that we can get occurs in the mitochondria the other two is from glycolysis which occurs in the cytoplasm so the majority of the atp molecules produce comes from the mitochondria number six which of the following statements is true let's look at a aerobic cellular respiration yields a maximum of 34 atp molecules is that true or false and that is a false statement traditional or aerobic cellular respiration yields a maximum of 38 atp molecules and if you take into account the two atp molecules that are needed to transport nadh from the cytoplasm into the mitochondrial matrix then that would that would yield a net of 36 atp b substrate level phosphorylation occurs during the electron transport chain is that true or false that is a false statement substrate level phosphorylation first occurs in glycolysis so when glucose splits into two molecules of pyruvate adp two molecules of adp is phosphorylated into two molecules of atp and so that is an example of substrate level phosphorylation c oxidative phosphorylation occurs in glycolysis that is false oxidative phosphorylation begins during the electron transport chain and ends with chemiosmosis when atp is produced d anaerobic cellular respiration yields a maximum of two atp molecules now that is a true statement under anaerobic conditions that is without oxygen fermentation occurs so we have ethanol fermentation and lactic acid fermentation the first step of ethanol fermentation is glycolysis and then after glycolysis once pyruvate is produced pyruvate undergoes decarboxylation to produce acetaldehyde and then acetaldehyde is reduced by nadh into ethanol now glycolysis yields two atp molecules but as pyruvate converts to acetaldehyde and into ethanol it doesn't produce any atp molecules in those steps now for lactic acid fermentation glycolysis is the first step once again and it generates two atp molecules the pyruvate ion produced during glycolysis is reduced into lactate using nadh but no atp molecules are produced in that step so for both ethanol fermentation and lactic acid fermentation only two atp molecules are produced due to glycolysis so that's why d is true anaerobic cellular respiration yields a maximum of two atp molecules because of glycolysis now e is going to be a false statement muscle cells produce ethanol under anaerobic conditions muscle cells produce lactate under anaerobic conditions yeast cells they will produce ethanol under anaerobic conditions so that's it for number six so the correct answer which i kind of scratched off the correct answer is answer choice d number seven which of the following is not a product of pyruvate oxidation so during pyruvate oxidation pyruvate is converted to acetyl coenzyme a now i'm going to draw the structure so this is pyruvate and here is acetyl coenzyme a so notice that we went from three carbons to two carbons this indicates decarboxylation so we lose co2 which means carbon dioxide is a product of pyruvate oxidation so we can eliminate antichoice c acetyl coenzyme a is a product of pyruvate oxidation so that's gone now in order for pyruvate to be oxidized to acetyl coenzyme a something has to be reduced and we know that something is nad plus so nad plus is converted to nadh so nadh is another product of this process so the fact that it says circle each one tells us that more than one answer could be correct under pyruvate oxidation we don't get lactate nor do we get ethanol number eight which the following statements is false starting with a atp synthase is the enzyme responsible for producing atp during oxidative phosphorylation is that true or false this is a true statement oxidative phosphorylation combines the activity of the electron transport chain and the production of atp using the enzyme atp synthase during chemiosmosis so a is a true statement b nadh transfers its electrons to complex one this is true early in the video i had complex one here and then nadh oxidizes into nad plus given off its electrons oxidation always accompanies a loss of electrons so b is a true statement fadh2 transfers its electrons to complex two keep in mind fadh2 is part of complex two and so it transfers its electrons to it which then goes to coenzyme q now d ubiquinone or coenzyme q is a mobile electron carrier transferring electrons from complexes 1 and two to complex three that's true so here would be q this would be the inner membrane of the mitochondria and then this would be complex three and here's complex two so q would transfer electrons from one to three and from two to three so that's the true statement now for e nadh activates complex one pumping protons across the inner membrane into the mitochondrial matrix nadh does indeed activate complex one and it does pump protons across the inner membrane which is right here that's the inner membrane of the mitochondria what it doesn't do is pump it into the mitochondrial matrix complex one takes protons from the mitochondrial matrix and then it pumps it to the [Music] internal membrane space so that's the problem with e it doesn't pump it into the mitochondria matrix it pumps it into the intermembrane space where we have a lot of positively charged hydrogen ions so e is the false statement which is the answer we're looking for number nine which of the following does not occur during pyruvate oxidation so let's write down what we know so here we have pyruvate and during oxidation it converts into acetyl coenzyme a now decarboxylation does occur so a is true now what about b nad plus is reduced to nadh that is also true as we could see the oxidation state goes from positive one to zero so the oxidation state decreases which means that it's reduced and it also means that nad plus received electrons to become nadh so this is the true statement and c nadh is oxidized into nad plus the only way that could be true is if nadh go back to nad plus but that doesn't happen so c is the false statement which is the answer cl2 is produced as a product so d is true and pyruvate loses electrons to nad plus because nad plus is reduced which means it gained electrons so e is true so only c is false nad plus is reduced to nadh in this step it doesn't go from nadh to energy plus so that's why c is false number 10 which of the following is the final electron acceptor in aerobic cellular respiration would you say it's nad plus complex 4 o2 fad or atp atp is not an electron acceptor it simply gives away or transfers a phosphate group the other four are electron acceptors but the last one is oxygen oxygen is the final electron acceptor it's also the strongest of the group at the end of the electron transport chain oxygen with hydrogen ions picks up the electrons to form water so this is the final electron acceptor which creates the final product of cellular respiration or one of the final products which is h2o so the correct answer is answer choice c number 11 which of the following statements is not true let's look at the first one atp is the energy currency of the cell driving endergonic reactions is that true or false this is a true statement atp is definitely the energy currency of the cell all cells use atp to power endergonic reactions now b atp transfers energy to other molecules in coupling reactions by the transfer of a phosphate group that is also a true statement and c atp consists of a nitrogenous base a ribose sugar and three phosphate groups that's true here is the ribose sugar this is the nitrogenous base and then here are the three phosphate groups of atp so c is the true statement what about d the nitrogen is base of atp is called adenosine now that is false now you have to be careful of this because atp is called adenosine triphosphate the base is adenine the adenosine part of atp is the combination of the nitrogenous base plus the ribose sugar so that is called adenosine so make sure you see the difference between the nitrogenous base adenine and adenosine which is the nitrogenous base plus the viable sugar e has to be a true statement atp is produced from adp by substrate level phosphorylation and oxidative phosphorylation so that's true we've seen atp produced in glycolysis so that's an example of substrate level phosphorylation and even in the krebs cycle which is another example of substrate level phosphorylation now oxidative phosphorylation occurs during the electron transport chain and chemiosmosis but the atp part is produced in the chemiosmosis part of oxidative phosphorylation so keep in mind oxidative phosphorylation combines the electron transport chain and chemiosmosis when atp is produced from the enzyme atp synthase number 12. which of the following produces the greatest number of nadh molecules during aerobic cellular respiration is it glycolysis pyruvate oxidation krebs cycle electron transport chain or oxidative phosphorylation what would you say in glycol excuse me in glycolysis two nadh molecules are produced in pyruvate oxidation two nadh molecules are also produced but in the krebs cycle six nadh molecules are produced the electron transport chain doesn't produce nadh molecules in fact it consumes it nadh gives its electrons to the electron transport chain turning into nad nadplus so in that case the electron transport chain doesn't make any nadh molecules oxidative phosphorylation combines the electron transport chain and chemiosmosis during chemiosmosis atp is produced by the enzyme atp synthase and so during oxidative phosphorylation no nadh molecules are produced so the correct answer for this problem is answer choice c during the krebs cycle we get the greatest number of nadh molecules number 13 which of the following electron acceptors has the lowest affinity for electrons now keep in mind electrons will flow from an atom that has a low affinity for it to an atom that has a high affinity for it so oxygen being more electronegative than carbon it has an en value of 3.5 the electronegativity for carbon is 2.5 so electrons will flow from carbon to oxygen because oxygen is more electronegative it has a higher affinity for it now if we follow the electrons throughout the electron transport chain even starting from glucose the electrons they start from a carbon atom in glucose and then nad plus picks up those electrons and then those electrons are transferred to complex 1 and then to the mobile electron carrier ubiquinone or coenzyme q and then it goes to complex 3 and then it gets transferred to cytochrome c and then to complex 4 and then finally to oxygen so that will be the end of the electron transport chain so oxygen has the highest affinity for electrons and carbon has the lowest affinity so we're looking for the one with the lowest affinity it's not going to be oxygen we have complex 3 listed as one of our answer choices we have cytochrome c nad plus and ubiquinone so out of the four that is highlighted the closest one to the left is nad plus so nad plus is the the weakest electron acceptor out of the list that we have here so c is the correct answer number 14 which of the following enzymes is typically used to transfer a phosphate group would you say it's the kinase enzyme dehydrogenase isomerase atp synthase or enolase the kinase enzyme is the answer this is the one that is typically used to transfer a phosphate group so a is the correct answer dehydrogenase is an enzyme that removes hydrogen from a molecule and transfers it somewhere else but typically removes it so that's not the answer we're looking for isomerase is an enzyme that catalyzes a rearrangement reaction the key word isomer it turns one molecule into an isomer of itself which is basically a rearrangement reaction d atp synthase if you think of the word synthase synthesis an ace tells us that we're dealing with an enzyme so this is an enzyme that synthesizes atp as we saw after the electron transport chain the protons flow into atp synthase causing it to rotate smashing adp and phosphates together creating atp in a process known as chemiosmosis chemiosmosis is basically the process where hydrogen ions flow across the semi-permeable membrane or ions in general by means of an electrochemical gradient so that is chemi osmosis now e enolase this enzyme is used in the knife step of glycolysis and it creates a molecule phosphoenol pyruvate if my memory is working but it creates an enol functional group so let me see if i can remember how to draw a phosphoenol pyruvate it looks something like this it's ch2 with a double bond and then there's an oxygen and a phosphate group but this is the enol part of the molecule an enol is basically an alcohol adjacent to an alkene functional group or a double bond so you can see the similarities here so this is called phosphoenol pyruvate so enolase makes that compound it produces that you know functional group in phosphoenol pyruvate but this is the answer here so know that kinase is an enzyme that is capable of transferring a phosphate group number 15 which of the following enzymes is sometimes referred to as complex two nadh dehydrogenase is complex one succinate dehydrogenase that's complex two so that enzyme converts succinate into fumarate at the same time reducing fad into fadh2 now bc1 complex that's complex 3 which is also cytochrome reductase cytochrome oxidase is complex form so the answer for this problem is answer choice b number 16 which of the following component events of cellular respiration produces the greatest number of atp molecules would you say it's glycolysis pyruvate oxidation the krebs cycle electron transport chain or chemiosmosis now glycolysis produces two atp molecules pyruvate oxidation doesn't produce any atp molecules it does produce nadh molecules which eventually becomes atp molecules the krebs cycle produces two atp molecules per one molecule of glucose now d and e this one can be argued because technically speaking the electron transport chain doesn't produce any atp molecules keep in mind the electron transport chain consists of all of the membrane proteins in the inner membrane of the mitochondrial matrix that is involved in transfer transfer electrons from nadh and fadh2 all the way to oxygen so during that process protons are simply pumped into the intermembrane space across the inner membrane of the mitochondria so this doesn't produce any atp molecules now during chemiosmosis when the protons are flowing back through atp synthase this is the part that produces atp in fact this is where we get up to 36 atp molecules as a result of the nadh and the fadh2 releasing the electrons to the electron transport chain so e is a better answer than d now let's say if this was an option sometimes teachers may refer the electron transport chain as everything towards the end the electron transport chain atp synthase they may group that together so on a test if e was an option then i would pick d but technically speaking you don't really produce atp and electron transport chain so e is the better answer i'm gonna go with that because during chemiosmosis that's when you really get the atp molecules number 17 which of the following component reactions of cellular respiration produces water circle each one glycolysis produces pyruvate as a product it produces nadh as a product and it produces atp glycolysis does not produce water so we can eliminate that answer during pyruvate oxidation pyruvate is converted to acetyl coenzyme a so that's a product of that process and it also produces nadh it doesn't produce atp not directly now during the krebs cycle aceto oh wait let's go back to pyruvate oxidation co2 is the product of that step as well now during the krebs cycle acetyl coenzyme a is converted to co2 more nadh is also produced atp is produced as well and in addition to that fa dh2 is produced so those are the products of the krebs cycle now for the electron transport chain the only thing that's really produced is water nadh is converted back into nad plus so that's a product of the electron transport chain and fadh2 is also regenerated during chemiosmosis atp is produced so the answer that we're looking for is the electron transport chain and that's when water is produced so as the electrons come down from complex four it reacts with oxygen gas and hydrogen ions in a solution and it turns into water now this is all happening in the mitochondrial matrix by the way number 18 which of the following component reactions of cellular respiration produces carbon dioxide now based on the last problem we saw that carbon dioxide is produced during pyruvate oxidation and in the krebs cycle during pyruvate oxidation we start with pyruvate and in a decarboxylation reaction this is going to convert into acetyl coenzyme a and carbon dioxide is removed so we lose one carbon dioxide molecule for every pyruvate molecule now in the krebs cycle the acetoenzyme a enters into it now the two carbon acetyl part of acetyl coenzyme a that's converted to carbon dioxide so the krebs cycle gives us two molecules of carbon dioxide for every acetyl coenzyme a that enters into it so that's where the co2 part of the cellular respiration comes from it comes from pyruvate oxidation and during the krebs cycle and then water is produced during the electron transport chain number 19 which of the following is not produced during aerobic cellular respiration is it carbon dioxide water heat energy atp or glucose c6h12o6 well let's begin with the net reaction of cellular respiration keep in mind glucose reacts with six molecules of o2 producing six molecules of carbon dioxide six molecules of water and heat energy so we're looking for what's not produced what's not a product carbon dioxide that's a product water is a product heat energy is a product but what about atp is that a product of cellular respiration keep in mind some of the energy that is produced is not completely wasted as heat energy some of it is used to create atp so during cellular respiration adp with phosphate is converted into atp and we said that the maximum theoretical yield is 38 atp so this is part of the cellular respiration reaction so we can say that glucose and oxygen this is an unbalanced equation plus phosphate plus adp becomes carbon dioxide water atp and heat energy so atp is a product of cellular respiration glucose is a reactant so e is the correct answer for this problem number 20 identify each statement as true or false so part a electrons are donated to the electron transport chain by nadh and fadh2 so that's a true statement these are electron carriers they give up the electrons to the electron transport chain as the electrons flow through the transport chain they pump they cause the membrane proteins to pump hydrogen ions to the intermembrane space from the mitochondrial matrix now for b the investment phase of glycolysis yields four atp molecules per one molecule of glucose this is true keep in mind the payoff phase we need to put in two atp molecules the payoff phase is the first five reactions of glycolysis in the investment phase that is the last five reactions of glycolysis four atp molecules are generated giving us a net of two atp molecules per glucose molecule now for c oxidation refers to a loss of electrons and reduction refers to a gain of electrons so let's review oxidation occurs whenever the oxidation number goes up whenever there is a loss of electrons or if there's a gain of oxygen atoms or a loss of hydrogen atoms so we do have a loss of electrons for c and for reduction just to review redux excuse me reduction occurs whenever the oxidation state decreases whenever there is a gain of electrons or a loss of oxygen or gain of hydrogen so reduction does represent a gain of electrons number three is a true statement d oxidation refers to a loss of oxygen that's not true it refers to a gain of oxygen so d is a false statement now let's move on to e cellular respiration is a redox reaction true or false a redox reaction occurs whenever there is a transfer of electrons oxidation refers to a loss of electrons reduction refers to a gain of electrons both of these they occur simultaneously combined they are referred to as a redox reaction and yes cellular respiration is a redox reaction the carbon atoms in glucose they give away the electrons so they're oxidized and oxygen being the final electron acceptor is reduced when it gains electrons so this is a redux redox reaction f the krebs cycle generates six molecules of atp for every molecule of acetyl coenzyme a is that true or false this is a false statement an acetyl coenzyme a molecule it represents one turn of the krebs cycle and it only produces one atp molecule per turn but it produces two atp molecules per glucose molecule and here this is saying six molecules of atp so that's not correct now the krebs cycle produces three molecules of nadh per turn or six molecules of nadh per glucose molecule so if this was changed to six molecules of nadh for every molecule of glucose then it would be true right now it's false as for g the krebs cycle generates two molecules of fadh2 for every molecule of glucose that's true we get one molecule of fadh2 per single turn but one molecule of glucose represents two turns in the krebs cycle so that gives us two fadh2 molecules now let's move on to h in aerobic cellular respiration glucose is oxidized and oxygen is reduced true or false well we know that oxygen as we mentioned before is the final electron acceptor and it's going to be reduced when it receives electrons at the end of the electron transport chain that's when it converts into water glucose is oxidized into carbon dioxide so this is definitely a true statement glucose loses electrons oxygen gains electrons so oxygen is reduced glucose is oxidized now for the next one i in the first step of the krebs cycle oxaloacetate combines with acetylcholine enzyme to form citrate so this is true and you could look up the krebs cycle diagram to confirm it oxaloacetate is a four carbon molecule and so when it combines with acetoenzyme a it gets two carbons turning into the six carbon molecule citrate and then during the krebs cycle eventually it's going to go back to four these two carbon atoms will be converted to carbon dioxide so going to j four molecules of co2 is produced in the krebs cycle for every molecule of glucose is that true or false so one turn in the krebs cycle equates to one acetyl coenzyme a molecule and that's going to give us two molecules of co2 one glucose molecule gives us two acetyl coenzyme a molecules so that represents two turns in the krebs cycle which gives us four molecules of co2 so this is a true statement now for k two molecules of co2 is produced during pyruvate oxidation for every ion of pyruvate when pyruvate converts into acetyl coenzyme a it loses only one molecule of co2 keep in mind pyruvate is a three carbon atom i mean molecule or ion rather acetyl coenzyme a the acetyl part has two carbons so we lose a carbon so we get one carbon dioxide molecule per pyruvate ion so this is false but we get two co2 molecules from glucose so make sure you understand this for every molecule of glucose we gain two molecules of co2 from pyruvate oxidation and four co2 molecules from the krebs cycle now this makes sense because the total has to add up to six carbon molecules since glucose has six carbon molecules and in the net reaction of cellular respiration the products are six co2 molecules six water molecules so this has to add up to six so that's basically it for this video that is a detailed review of cellular respiration hopefully you found it to be useful and if you like this video don't forget to subscribe and thanks for watching