if you're studying AP Bio unit 3 cellular energetics then you might be feeling nervous or anxious because AP Bio unit 3 is a tough unit it includes topics like cellular respiration and photosynthesis but don't worry the goal of this video is to teach you everything that you need to know to crush that next unit exam or the AP biot test here's what we're going to cover we're going to start with enzymes then we'll move on to Cellular energy and ATP that'll lead us into photosynthesis where we'll look at the big picture the light reactions and the Calvin cycle will end with cellular respiration again the big picture glycolysis the link reaction in the KB cycle and we'll end with the electron transport chain my name is Glenn woken Feld also known as Mr W I'm a retired AP biology teacher I love b i o l o g y to help you study I've put together a checklist that you can download at AP bios. c/ checklist I'm also the author of The learn biology.com AP Bio curriculum and the biom Mania AP Bio app I'll tell you more about those later topics 3.1 to 3.3 enzymes describe the Key properties of enzymes enzymes are usually proteins there are some rnas that act like enzymes that catalyze reactions in cells they lower the activation energy of the reactions that they catalyze increasing the rate of those reaction reactions so in this diagram you see a reaction that's catalyzed by an enzyme number two and a reaction that's not catalyzed at number one and the difference is that the activation energy for the enzyme catalyzed reaction is much less than the non-enzyme catalyzed reaction enzymes are highly specific because their active sight complements the shape and charge of their substrate which is the substance that an enzyme acts upon here's an active sight here's the sub subate this is the enzyme as a whole it would be a large protein here's the enzyme interacting with the substrate and here we have the products enzymes are both highly specific and have a narrow set of conditions where they can function at or near their Optimum explain enzymes are proteins with secondary tertiary and quaternary level structures that involve hydrogen bonds ionic bonds and hydrophobic clustering changing pH temperature or ion concentration interferes with these bonds changing the shape of the active site keeping the enzyme from binding with its substrate enzymes therefore have a pH ionic or temperature Optimum at which the shape of their active site best fits their substrate environmental change can cause denaturation a change in the shape of the enzyme that lowers or completely negates enzyme function describe how enzyme activity is affected by changes in the pH of its environment most enzymes have a pH optimum where they operate at Peak efficiency here's the optimum right here as pH moves above or below the optimum enzyme performance drops this is the rate of enzyme activity and you can see that is the pH drops it goes down as the pH increases it goes down why it's for all the reasons we talked about in the previous slide it's that enzymes are proteins if you change the pH you disrupt the bonds that hold that protein in it specific shape the result is denaturation and less good fit between the enzyme and its substrate describe how enzyme activity is affected by changes in the temperature of the enzyme's environment up to a certain point enzyme activity increases with temperature and that's because there's more kinetic energy that increases molecular motion and it increases the chance that the enzyme will bind with its substrate and therefore be able to catalyze the reaction but at a certain temperature Beyond two in the graph the enzyme will denature it'll change its shape reducing the enzyme's catalytic ability is because it'll no longer be able to bind with its substrate what's the difference between reversible and irreversible enzyme denaturation reversible denaturation is where the restoration of optimal conditions restores the enzyme's function as it regains its optimal shape if you can imagine that an enzyme has an optimal shape at seven you you move it up a little bit the enzyme starts to denature but then if you restore the pH the enzyme shape might go back to its previous form thereby going back to its optimal rate of efficiency but irreversible denaturation is where the enzyme shape is permanently changed and its catalytic ability is destroyed and this isn't exactly with enzymes but if you think about what happens when you cook an egg the egg white goes from clear to a solid and it will never go back even once you cool it back down that's irreversible denaturation of a protein imagine the same for an enzyme explain how enzyme activity is affected by substrate concentration with low substrate concentrations the probability of the enzyme meeting its substrate is low and the product is produced at a very low rate as substrate concentration increases the collision and the reaction rate will also increase but at a a certain point you get to a saturation point and at that point all the enzymes have their active sites interacting with substrate so there's a peak in the rate and you don't go any higher compare and contrast competitive and non-competitive inhibition in competitive inhibition a foreign molecule one that's not part of the cell or the organism that's not the enzyme substrate so this is number four over here blocks the enzyme's active sight and that keeps the substrate from binding here's the substrate and that inhibits the rate of the reaction it's inhibiting by competing for the active site in non-competitive inhibition which is shown over here a foreign molecule not one that's part of the organism binds away from the active site at a region that's called the allosteric site over here so here's the allosteric site here's the allosteric site that's occupied by this foreign molecule binding at the alisic site causes a ripple effect throughout the protein that causes a change in the shape of the active site therefore the substrate can no longer bind the active site and that diminishes or blocks enzyme activity topic 3.4 Cell Energy I'm Mr W from learn biology.com where we believe that successful learning requires interaction and feedback and we're so sure of that that a subscription to our website comes a money back guarantee what is a metabolic pathway a metabolic pathway is a linked series of enzyme catalyzed chemical reactions occurring within a cell so here you can see that these are all separate reactions but they're linked together above one two and three are all enzymes a is the initial reactant B and C are what we call intermediates and D is the final product examples of metabolic reactions that you'll come to know well include glycolysis the kreb cycle the Calvin cycle all of which we'll deal with in this unit and these reactions can be linear so glycolysis is a linear reaction you have a beginning point and an end point or they can be cyclical like the kreb cycle and the Calvin cycle so for example in the kreb cycle this compound over here aalo acetate it's the beginning compound gets modified and it also comes back and it's the ending compound a similar thing happens in the Calvin cycle what are autot tropes compare and contrast photo autot tropes with chemo autot tropes autot tropes are organisms that can produce their own food we are not autot tropes but plants and certain bacteria and ARA are so photo autot trops include plants and cyanobacteria they use the energy and light to create organic compounds that they need to survive through photosynthesis whereas chemo aotrs include some bacteria some archa Aras that third domain the energy for their life processes comes from a process called chemosynthesis and that involves oxidizing inorganic substances including iron sulfur or hydrogen sulfide what are heterotopy and matter they need to live grow and reproduce heterotrofos capture the energy present in organic compounds produced by other organisms they can be ecological consumers decomposers or parasites and they get their energy in matter by metabolizing the organic compounds and organisms that they eat or absorb or in the dead remains of other organisms here's a heterotroph and here's another heterotroph what's the difference between an exonic reaction and an endergonic reaction exonic reactions release energy and increase entropy so here's an extonic reaction over here and the energy of the reactants is less than the energy of the products and you can't see this but like for example if you burn a piece of paper or a piece of wood you start with cellulose over here and you wind up with many unorganized atoms of carbon dioxide and water so that's an increase in entropy because you've decreased organization cellular respiration most hydrolysis reactions are extonic reactions andronic reactions require energy and decrease entropy and examples include photosynthesis or almost any dehydration synthesis reaction describe the structure and function of ATP explain how ATP can be used to store and release energy the structure of ATP involves a five carbon sugar that's called a ribos a nitrogenous base that's called adenine and three phosphate groups the function of ATP is to power work within cells every cell makes its own ATP there's no sharing of ATP between cells and to store energy what happens is that cells take energy from food during cellular respiration or light during photosynthesis and use that to combine ADP and a phosphate group into ATP and to release energy for work cells remove a phosphate group from ATP they break off this terminal phosphate group and that creates ATP and phosphate and that makes energy available to do cellular work what is energy coupling energy coupling is the linking of an extonic reaction to an endergonic reaction and that linking drives the endic reaction forward here's an example cellular respiration which is exergonic drives the formation of ATP from ATP and phosphate so this exonic reaction is driving this endergonic one and example number two ATP to ADP and phosphate makes this endergonic reaction possible or muscle contraction also an endon reaction it's made possible by the breakdown of ATP to ADP and phosphate at learn biology.com we understand why students struggle with AP Bio it's a hard course the material is complex the vocabulary is ridiculous and the pace is withering it's natural to feel overwhelmed and inadequate to get an A or a four or a five you need an easier way to study and that's why we created learn biology.com it has quizzes it has flashcards it has interactive tutorials about every topic in the AP Bio curriculum it has a comprehensive AP Bio exam review system use learn Das biology.com and you'll gain the skills and confidence that you'll need to Ace your biology course and to crush it on the AP Bio exam so here's your plan go to learn biology.com we've got free trials from June through March for both teachers and students you won't believe how much you'll learn photosynthesis the big picture what happens during photosynthesis what's its chemical equation is it endergonic or exonic in photosynthesis using light energy here's the sun photo autot tropes like plants combine carbon dioxide and water to create carbohydrates that's what the plant is made of oxygen is released as a waste product it's the source of biomass and the base of almost every food chain the formula is 6 CO2 six carbon dioxides plus 6 H2O 6 Waters with light energy to power the reaction are combined into glucose glucose C6 h206 and six oxygens this is an endergonic reaction for two reasons it takes two low energy inputs carbon dioxide and water and converts them into a high energy product glucose it reduces entropy that means it increases organization and you can sort of count that out so there are 12 molecules on this side of the equation and there are seven on this side so we've taken something that was disorganized made it into something more organized highly unorganized carbon dioxide it's diffuse it's a gas and it's made into solid matter and that's a huge decrease in entropy when did photosynthesis first evolve what are some of the consequences of photosynthesis in terms of when based on fossil and chemical evidence about 3.5 billion years ago that's relatively soon after the emergence of Life at 3.8 billion years ago its consequences were vast first of all when the Earth First form there was no oxygen in the atmosphere it's photosynthesis which splits apart water to release oxygen that created the oxygen rich atmosphere and that made our aerobic metabolism possible and it also created an ozone layer that's a protective layer in the atmosphere that Shields us from ultraviolet radiation and that made life on land possible so we owe everything to photosynthesis what are the two phases of photosynthesis and what does each accomplish we start with the light reactions that's on this side of this diagram and it converts light energy into chemical energy and that chemical energy is in the form of ATP and nadph you already know about ATP nadph is like nadh it's an electron carrier the Calvin cycle is the second phase of photosynthesis and it converts the chemical energy that's in nadph and ATP into carbohydrate and it does that by using carbon dioxide as an input and it fixes that low energy gas into high energy sugars describe the role of chlorophyll in photosynthesis explain the absorption spectrum of chlorophyll and other pigments chlorophyll is the pigment that absorbs light energy in photosynthesis and here you can see its structural formula it's got a hydrocarbon tail that enables it to fit into the phospholipid by layer of the phids and it's really this structure over here this nitrogen ring with the magnesium in the center that enables chlorophyll to help plants convert light energy into electrical energy as we'll see in a little bit an absorption Spectrum shows the amount of light absorbed at different light wavelengths by a pigment by a substance that absorbs light energy and chlorophyll has two forms they're different based on this functional group here's Chlorophyll B here's chlorophyll a and you can see that they both absorb most most energy in the blue part of the spectrum and in the red part of the spectrum but very little in the green part of the spectrum and that's why leaves are green because leaves are reflecting green light whereas they're absorbing other light wavelengths there are other pigments that are also involved in photosynthesis one's called a carotenoid and they absorb other wavelengths what is the action spectrum of photosynthesis the action Spectrum which looks a little bit different from the absorption spectrum that we just looked at shows how various light wavelengths drive photosynthesis and blue and red Drive the most photosynthesis and green drives very little this was determined by the Engelman experiment Thomas Engelman in the 1800s did a cool experiment where he grew a filament of algae under light from a prism that divided the light up into its various wavelengths and aerobic bacteria GRE grew around the filament best in the blue and the red part of the spectrum and they were able to do that because that's where the most oxygen was being produced you can in the lab and I actually hope that you did recreate this experiment with the famous photosynthesis spinach leaf disc experiment where these discs of spinach leaves will rise based on the amount of oxygen that they produced and you can set different variables like the intensity of the light or the uh wavelength length of the light connect the structure of chloroplast to the reactions of photosynthesis so chloroplast where do you find them so here they are this is a cross-section of a leaf these are cells within the top part of the leaf and these are chloroplast there are many per cell there's only a couple shown here and in terms of the structure of the chloroplast itself it has an outer membrane and an inner membrane the outer membrane is a vestage of The evolutionary origins of chloroplast there's DNA which is a vestage of the fact that the sus Swan's an independent living cell there's also ribosomes they're there for the same reason and then there are thids shown at number five over here those are membrane bound sacks and they contain the membranebound photos systems and chlorophyll for the light reactions of photosynthesis they're organized into these Stacks called Grana and surrounding them is the stroma which is essentially the cytoplas as of the chloroplast it contains DNA it contains ribosomes and it's where the Calvin cycle occurs so that's where carbohydrates are actually created the light reactions of photosynthesis topic 3.5 of AP biology what do the light reactions produce where do these reactions occur what are the inputs and the outputs the light reactions convert the energy in light into the chemical energy of nadph and ATP nadph is an electron carrier it's like nadh in cellular respiration ATP is the molecule that cells use to build things it's the Workhorse of the cell where does it occur it occurs in the phids oxygen is the waste product the inputs are light and water the outputs of the Calvin cycle are the inputs of the light reaction so nadp plus and ADP and P are the inputs those get fed into the light reactions ATP and nadph go out what are the key structures involved in the light reactions so we have a chloroplast over here and then at n we have a Grana and a single phid membrane so this whole thing here is a Philo covid membrane within the phid membrane there are photos systems those are complex Assemblies of proteins and they have embedded chlorophyll molecules those green dots are chlorophylls and those photos systems those are the things that actually convert light energy shown here at a and shown here at D into a flow of electrons this whole array is kind of like a solar panel that's converting light energy into electricity they're also splitting water molecules and that happens in photosystem too let's just get this out of the way right now in the organization of the photosystems and the the thyo covid membrane photos system 2 comes before photos system one for years biology students have been memorizing that and you have to memorize it too so this is the electron pathway through which electrons flow and at one point those electrons flow through proton pumps they're labeled as cytochromes but there's other stuff going on too and what these do is they pump protons from the stroma into the phylloid space and over here is an enzyme called ATP synthes and as the protons that are trapped here diffused through this they generate ATP this is where nadph is created this is an overview we're going to go through the details right now describe how the light reactions of photosynthesis create ATP photo excitation of chlorophyll in photosystem 2 leads to a flow of electrons along an electron transport chain in the thilo covid membrane that electron transport chain that's an electrical current and it Powers a device in this case the device is a proton pump that's embedded in the thilo covid membrane and that pumps protons from the stroma into the thilo space so here's the stroma here's the thilo covid space we're pumping from the stroma in into the Philo covid space and that creates a chemiosmotic gradient chemiosmotic what does that mean well there are all these protons that are over here and there are very few over here it took energy to do that and that gradient is a diffusion gradient and it's also an electrical gradient and that causes these protons to want to diffuse from the thilo covid space back to the stroma they can't do it through any part of the phylloid membrane except through this channel that's called ATP synthes the ATP synthes channel is also an enzyme and as protons diffuse through the kinetic energy of those protons is used to power an endergonic reaction of taking ADP and phosphate and making it into ATP now note that there's also this water splitting complex that's part of photosystem 2 and what it does is it takes water molecules splits them apart to create oxygen that's a waste product but also to create protons and those protons accumulate in the thid space that enhances the gradient and it Powers additional ATP production describe how the light reactions create reducing power nadph that can be used in the Calvin cycle so we're going to start over here we're looking at photosystem one photo excitation of chlorophylls in photosystem one one is how the process starts that creates a flow of electrons that's flowing through the electron transport chain of photosystem one and over here those electrons flow to this enzyme it's called nadp plus reductase and that reduces nadp+ into nadph reduction that's a thing from chemistry reduction is gain of electrons so that any DP plus is going to gain electrons and uh hydrogen making it into nadph and why because During the Calvin cycle that nadph provides the electrons and hydrogens that reduce carbon dioxide into carbohydrates use the Z scheme to summarize the light reactions so the Z scheme is a graphical representation of everything that happens in the light reactions this axis over here the Y AIS shows electron energy so what happens light drives electron boosting from photosystem 2 remember photosystem 2 comes first and so that electron goes to a much higher energy level and at the same time water is split apart into protons and oxygen gas then there's electron flow through the electron transport chain of photosystem 2 and that goes through proton pumps that power the synthesis of ATP from ADP and phosphate those electrons arrive at photosystem one they're relatively low energy at this point you can see that by their position on the graph but light comes in and it stimulates chlorophylls and another electron gets boosted to a high energy level into What's called the primary electronic scepter that's in the phylloid membrane and that passes it off to the electron transport chain of photo system one it flows to the enzyme nadp+ reductase and nadp+ reductase creates nadph from nadp plus and a proton so we have the two products of the light reactions ATP and nadph beautifully explained by the Z scheme photosynthesis part three we've covered the big picture and the light reactions and now we're going to talk about the Calvin cycle what are the three phases of the Calvin cycle so let's remember the Calvin Cycle takes the products of the light reactions and carbon dioxide and uses it to create sugars so that occurs in three phases and the first phase is called the carbon fixation phase carbon dioxide gas is brought essentially into the biosphere that is followed by the energy investment and harvest phase where matter is actually pulled out and that matter becomes part of the plant and ultimately part of you and then finally there's the Regeneration of the starting C compound this is a cyclical reaction this compound rubp ribulosebisphosphate is at the end and it's at the start now we'll go into each phase describe what happens during the carbon fixation phase of the Calvin cycle the fixation phase begins as carbon dioxide is combined with rubp that is a reaction that's catalyzed by the enzyme rubisco fun fact that might be the most abundant protein on Earth it creates a six carbon product which isn't shown so think about this rebp has five carbons each should these black dots represents a carbon atom CO2 has one carbon you'd think that would create a six carbon product but immediately that six carbon product dissociates into two three carbon molecules so that's how we end the carbon fixation phase describe what happens during the energy investment and harvest phase of the Calvin cycle we ended the carbon fixation phase with this three carbon molecule and that three carbon product is reduced and phosphorilated so here's a phosphorilation in other words ATP contributes a phosphate to this molecule this had one phosphate group this one has two over here so that's a phosphorilation and reduced so NAD pH donates an electron to this molecule so at the end we have this molecule g3p glycer aldhy 3 phosphate it's also called pgal biomass because that's ultimately where it came from describe what happens during the last phase of the Calvin cycle before we do that I want to talk about a way to think about the entire Calvin cycle that's really going to make you think about it in a more sophisticated way and that way pays attention to the number of carbon atoms that are present at each stage of the cycle so we talked about how during carbon fixation rubp is combined with CO2 but a more proper way and correct way to think about it is that it's three RPS rubp is a five carbon compound so that's a total of 15 carbon atoms get combined with three Carbon dioxides 15 + 3 is 18 and we've talked about how the three six carbon compounds immediately dissociate into two three carbon compounds so what we have over here the end of carbon fixation is six three carbon molecules and that's a total of 18 carbons makes sense 5 * 3 is 15 + 3 is 18 and we've got 18 carbon atoms over here now in the energy investment and harvest phase during energy investment we're just going to phosphorate and we're going to reduce we're adding energy but we're not adding carbon so what we wind up with over here is six molecules of g3p glycer alide 3 phosphate 6 * 3 is 18 we had 18 over here we have 18 over here but what we're going to do in the Harvest phase is we're going to pull one of those g3ps out so 18 minus 3 we're left with 15 carbon atoms 5 * 3 now during the next phase these 5 g3ps are rearranged by a variety of enzymes that's why I have multiple arrows over here and they're rearranged into three five carbon R ubps and along the way a phosphorilation occurs and that's again energy from the light reactions that's invested over here and rebp is one of the substrates of carbon fixation along with carbon dioxide but now we've accounted for all of our carbons we start with these 15 over here 15 carbons and after the whole process is done we again have 15 carbons and if you can explain that you're set up for an A and A five on the AP Bio exam and that is now an appropriate time for me to say congratulations because you've hung through one of the most difficult parts of this review we're going to do cellular respiration next you're a hero keep with it you're going to get a five on the AP Bio exam I want to acknowledge how difficult and complex some of these Concepts can be and I want to encourage you to go to learn dm.com and with a free trial you can do the tutorials and you can use our unit reviews and it's going to really help you to get on top of this material setting you up for Success on your unit test or the AP Bio exam cellular respiration the big picture what's the chemical equation for cellular respiration is it endon or extonic where in UK carotic cells does it occur the equation C6 h206 or glucose plus six oxygens yields six carbon dioxides six water molecules plus energy in the form of ATP it's an exonic reaction it releases energy and it creates disorder it takes an organized molecule like glucose and creates much less organization over here and it occurs in various phases the first phase is glycolysis that occurs in the cytoplasm then the link reaction brings the product of glycolysis into the mitochondrian and in The Matrix we have the kreb cycle and then finally the phase which reduces the most ATP is oxidative phosphorilation and that occurs based on enzymes and proteins along the mitochondrial membrane using the intermembrane space to create a chemiosmotic gradient briefly describe what happens in each phase of cellular respiration here we've got the whole process let's break it down the process begins with glycolysis so energy in glucose generates ATP and nadh nadh like nadph that we met in photosynthesis it's an electron carrier and the end product is a three carbon molecule called pyruvic acid or pyruvate one glucose a six carbon molecule becomes two pyruvates which are each three carbon molecules in the link reaction what happens is that that pyruvate enters into the mitochondrial Matrix and enzymes along the way convert it to a molecule called aetl COA with two carbons the carbon that's removed is released that's onethird of the carbon that you exhale and that conversion is uh Powers the reduction of an NAD plus to nadh and that's later going to be used in the electron transport chain in the kreb cycle over here what enzymes do is they oxidize these two carbons in a cetl COA and that powers the production of three nadhs one fadh2 that's another mobile electron carrier like nadh and it creates one ATP that releases two carbon dioxides and that's the other 2/3 of the carbon dioxide that you exhale and note that for every glucose that enters cellular respiration the kreb cycle runs twice as does the link reaction and then finally you have the electron transport chain the Etc and what that does is it takes these reduced products these reduced mobile electron carriers and it oxidizes them and that creates electron flow that powers through chemiosmosis the production of ATP from ADP and phosphate that's where most of the ATP during cellular respiration is produced cellular respiration Parts two and three glycolysis the link reaction and the Krebs cycle what happens during glycolysis include phases inputs and outputs in your answer I've got a great song about glycolysis that goes like glycolysis come on sugar come on sugar for the breakdown it occurs in the cytoplasm it doesn't require oxygen it's anerobic and it has three parts to it investment cleavage and energy harvest in terms of investment what happens is that enzymes phosphorate glucose so glucose is a starting compound enzymes which aren't shown here but are implied by the arrows take a phosphate from ATP and plant it onto intermediate compounds by the end of that process you have fructose 16 bisphosphate and that goes into the next phase where enzymes take fructose 16 bisphosphate loaded with energy and cleave it apart into two molecules of g3p g3p is the same molecule that gets harvested from the cvin cycle of photosynthesis in the Harvest phase enzymes again indicated by these arrows do two things they take g3p and they oxidize it that means it's going to lose energy lose electrons and those electrons go to NAD plus it's a mobile electron carrier which gets reduced to nadh and that's later going to be used in the electron transport chain in addition there are other enzymes that take ADP and phosphate and phosphorated to ATP they're using the chemical energy in g3p to bring that about we're getting a gross energy yield of four atps and that leads us to the next idea what's the net yield of glycolysis we get two atps Y 2 even though there are four over here it's because two were invested at the start of the process so we net two and we also get two nadhs one produced over here from this g3p one produced over here and we wind up with two MO ules of pyruvate or pyruvic acid that's still loaded with energy and that's going to power the next phases of cellular respiration what happens between glycolysis and the kreb cycle the answer is the link reaction what we have ended glycolysis with is pyruvic acid and that's transported across the inner and outer mitochondrial membranes that's something that's represented by B in this diagram into the mitochondrial Matrix as that happens enzyme remove a CO2 from this pyic acid you see this carboxy group over here it's basically a CO2 and that is onethird of the CO2 that you and any other animal that does cellular respiration plants too for that matter wind up releasing other enzymes oxidize the resulting two carbon molecules so we had three carbons now we're at something with two carbons it's actually called an acetal group and the oxidation of that acetal group oxidation loss of electrons where do those electrons go they go to NAD plus a mobile electron carrier we just met it in glycolysis and that NAD plus gets reduced to nadh and that has electron energy that can get used in the electron transport chain finally enzymes take that acetal group and they attach it to a carrier molecule called co-enzyme a and the result is a seetal COA that's the starting point for the kreb cycle the describe the kreb cycle the kreb cycle which I have a great song about occurs in the mitochondrial Matrix and it's a cyclical series of reactions that generate nadh fadh2 and ATP it starts with enzymes all of these are enzymes over here enzymes taking this two carbon acetyl group from acetyl COA and transferring it from oxal a acate also known as AIC acid to citric acid which is also known as citrate the alternative names of the kreb cycle are the citric acid cycle or the tricarboxylic acid cycle TCA cycle and that's for this carboxy group over here this carboxy group over here this carboxilic acid over here so three carboxilic acids TCA cycle what happens next is that enzyme after enzyme oxidizes citric acid and oxidation is loss of electrons those electrons get transferred to the mobile electron carriers nad+ which becomes reduced to nadh that happens over here over here and over here and there's also a reduction of fad another mobile electron carrier to fadh2 along the way other enzymes over here power a substrate level phosphor correlation of ADP and phosphate into ATP there's actually a complication involving GTP but you don't need to worry about that for an AP bio class for each acetal COA that enters the cycle one ATP three nadh and one fadh2 are generated and that's probably worth memorizing and CO2 is released as a byproduct there's one over here over here that's the other 2/3 of the CO2 that you exhale and oxaloacetate is the starting and ending compound that's the CB cycle cellular respiration part four the electron transport chain and oxidative phosphorilation this is such a beautiful and important process let's go through it in the previous phases of cellular respiration glycolysis the link reaction KBS we've been creating nadh and fadh2 those are mobile electron carriers they've been accumulating in the mitochondrial Matrix and they diffuse over to the inner membrane where they're oxidized oxidation is loss of electrons those electrons now flow through an electron transport chain that's this yellow arrow over here and that's a series of membrane embedded proteins that are in the mitochondrial inner membrane so it's as if there's an electrical current that's flowing along the mitochondrial membrane through these various proteins notice that nadh comes in first it has a little bit more energy in its electrons than fadh2 which drops its electrons off a little bit further on down the chain some of these electron transport proteins are proton pumps and they pump protons from The Matrix to the intermembrane space pumping is active transport that requires energy where's the energy from it's from this flow of electrons notice that there's less protons over here and more over here again active transport requires energy and that creates an electrochemical gradient there's more protons over here fewer over here there's more positive charges over here there's fewer positive charges over here it's also a pH gradient because the pH is much lower in the intermembrane space than it is in The Matrix all those protons are are trapped oxygen acts as the final electron acceptor and what it's doing is it's so Electro negative that it's pulling electrons down this electron transport chain and as it does it absorbs electrons and protons that are available in The Matrix and that increases the gradient this is why you need oxygen to do aerobic respiration because it's the final electron acceptor in the electron transport chain now all all of these protons have been accumulated here they can't diffuse through any part of the inner membrane except through one channel that's called ATP synthes it's the same that we discussed when we discussed photosynthesis it's a channel and it's an enzyme as protons diffuse through so that's diffusion it's facilitated diffusion their kinetic energy is used to create ATP from ADP and phos pH fate that's how the electron transport chain generates ATP cellular respiration can be used to generate heat instead of ATP explain in newborn humans and other mammals and hibernating mammals there are cells that are called Brown fat cells they're extremely dense with mitochondria that's where the heat is generated when body heat is needed hormones induce a protein Channel called thermogenin or UCP it's also called the uncoupling channel to form in the inner mitochondrial membrane so here it is over here now notice in normal cellular respiration protons that are trapped have to diffuse through ATP synthes which creates ATP but now there's an additional channel so protons diffuse back to the Matrix from the intermembrane space without passing through ATP synthes but all all of this activity in the electron transport chain here called the respiratory chain still has to happen and think about the fact that when electrons move through a wire that generates heat through resistance well basically you can think of the electron transport chain as a wire the electrons that are moving through it generate heat but in this case they generate heat without generating ATP and that's how cellular respiration can be used to generate heat instead of ATP how is ATP generated in mitochondria and chloroplast similar in unit 3 we've talked about these two great metabolic reactions photosynthesis and the electron transport chain of cellular respiration and there are deep similarities to the way that they work and this kind of cross topic thinking is essential to your success in the AP Bio exam both of these processes use an electron transport chain to pump protons to an enclosed space creating a proton gradient and in photosynthesis here's the electron transport chain we're pumping protons from the stroma to the thid space in cellular respiration we're pumping protons from The Matrix to the intermembrane space and both use a subsequent process of chemiosmosis diff Fusion of protons through an ATP synthes channel to generate ATP and that's not a coincidence as we'll see in unit 7 where we'll talk about Evolution the similarities that are present between mitochondria and chloroplast indicate that at some point in very ancient history they had a common ancestor ATP synthes evolved once and then it became shared by the ancestors of chloroplast and mitochondria it's an incredible ride seeing biology and seeing evolution in process Science music videos has so much music related to AP Bio unit 3 I'll put the links Below have a big party sing these songs it's a great way to learn this material cellular respiration part five Anor robic respiration and fermentation compare arobic and anerobic respiration aerobic respiration oxygen is required it involves essentially the whole shebang of respiration that we've talked about glycolysis plus the link reaction plus the CB Cycle Plus the electron transport chain generate a lot of ATP 32 atps approximately for every molecule of glucose that enters most of the ATP is generated over here in the mitochondria there's a small amount that's generated through glycolysis Anor robic respiration occurs when oxygen is lacking or insufficient or I should add when the organism doesn't have the enzymes to do aerobic respiration glycolysis is really the key part of Anor robic respiration so it involves glycolysis followed by fermentation and it generates a total of Two atps And it occurs entirely in the cytoplasm the mitochondria are not involved what is fermentation and why does it occur fermentation is glycolysis that's followed by reactions that regenerate nad+ so here we have one form of fermentation it's called alcohol fermentation here we have lactic acid fermentation but the key thing is that they produce nad+ that's kind of the opposite of what glycolysis does why does fermentation happen it's because if you're an aerobic organism but you need to uh keep on moving and there's not enough oxygen available because you're working so hard then you can continue to get two atps per every glucose and that sure isn't as good as 32 or more that you get from aerobic respiration but at that moment you just can't do it glycolysis however can only create those two atps if NAD plus is available it's a substrate for one of the reactions of glycolysis so 2 ATP are better than none and that's why animals like us that do lactic acid fermentation perform it when oxygen is unavailable compare and contrast alcohol and lactic acid fermentation alcohol fermentation really what we're talking about is ethanol fermentation because there are other alcohol fermentations occurs in yeast when you're baking bread and you use yeast you're doing an alcohol fermentation enzymes remove a carbon dioxide from pyruvic acid remember that's the molecule that ends glycolysis that produces acid aldhy and acid aldhy is then by other enzymes reduced to ethanol well reduction is gain of electrons something has to lose electrons and nadh is oxidized to nad+ that allows glycolysis to continue interesting and fun fact this CO2 that makes with the bubbles in beer which come about through an alcohol fermentation that also makes up the bubbles that uh cause bread to be spongy and have its spongy form now lactic acid fermentation occurs in muscle tissue under anerobic conditions it's a little bit simpler than alcohol fermentation what happens is that pyruvate is reduced catic acid and again um as that reduction occurs something has to be oxidized and nadh is oxidized to nad+ that allows glycolysis to continue There are all kinds of Anor robic sports like weightlifting or doing push-ups or things like that and you're doing them at a level where muscle tissue can't really get enough oxygen so during that time they're doing lactic acid fermentation you feel that lactic acid build up and then eventually you have to stop exercising until you can recover aerobically if you really want to crush your AP Bio course and the AP Bio exam then sign up for that free trial at learn biology.com our unit 4 video is coming up it's going to help you review that difficult material related to cell communication cell division cancer ptosis feedback homeostasis I'll see you there