in this video we're going to look at the last major step in cellular respiration known as oxidative phosphorilation and it involves two key steps number one the electron transport chain and number two chemiosmosis so we left off at the end of the citric acid cycle we generated 2 ATP in glycolysis and we had also generated 2 ATP in the citric acid cycle so this was sort of the the total amount of ATP that we have generated for ATP at the end of these numerous chemical reactions what we have generated a lot of clearly not ATP were these high energergy electron carriers so in glycolysis we had two NADHs in the transition phase between glycolysis and the citric acid cycle we generated another two NADHs and again these numbers are normalized to the original glucose the one molecule of glucose we started out with and then in the citric acid cycle we had six NADH's and two FADH2s which were carrying electrons that were of lower energy but still higher than the baseline i'm not including the CO2 here because those were just all waste products the reason why I'm focusing on the total of 10 NADH's and two FADH2s is because they're carrying these high energy electrons that are full of potential energy so what we look at in the first phase of oxidative phosphorilation the electron transport chain we have the potential energy of these electrons and we're going to repurpose or use this energy to do work and the type of work that we're going to do is transport work and we're going to be transporting hydrogen ions up a concentration gradient right so anytime we're moving material up a concentration gradient it's going to require ATP or it's going to require energy right we usually assume it's ATP but the energy in this case is coming from those high energergy electrons and so we're going to take hydrogen ions that are in the matrix and we're going to move them into this fluid space between the inner and the outer mitochondrial membranes we call this the intermembrane space now the procedure is pretty complicated books go into a lot of detail but we're going to keep it relatively simple so the first step is our high energy electron carriers NADH is going to pass these electrons to these very large protein complexes and we're not going to hold you responsible for knowing the names of these protein complexes in essence we're playing a game of hot potato so we're passing these high energy electrons to these ginormous protein complexes and they in turn are passing it to other protein complexes and to other protein complexes and each time the electrons lose a little bit of energy but we all know there is no such thing as loss of energy in fact that energy is repurposed to do work and the work via these protein complexes is to transport hydrogen ions up a concentration gradient so what about that gradient well anytime there's a difference in concentration or gradients that represents potential energy that the cell can harvest to do other kinds of work so in essence we're converting the potential energy that was found in the electrons into the potential energy found in a chemical gradient in this case the hydrogen ion gradient now eventually those electrons that were high energy they go back down to sort of base energy or or a ground state and oxygen gas remember oxygen was very electrogative we talked about this in our chemistry videos it is happy to accept these electrons and as it does it goes through a chemical reaction to form the waste product water now I don't want to spend any deal of time talking about that particular reaction uh because unlike these figures it's not simple it's not as simple as oxygen meets electron meets hydrogen ions boom you have water this is a step as we mentioned in the uh earlier nutrition videos where you generate free radicals because these oxygen molecules are picking up one electrons at a time so they have unpaired electrons so they have to be neutralized by various enzymes but what is missing in the electron transport chain is we're not generating ATP we're just repurposing the energy in those electrons into a gradient and this is commonly misconstrued in several textbooks and sometimes in lectures the electron transport chain actually produces zero ATP it only establishes a proton gradient now why do I have a picture of a hot potato again just to uh create something common with this process when somebody passes a hot potato from one person to the next that potato is going to cool right it's going to lose heat but in essence it hasn't lost heat it has repurposed that to do work because anybody and everybody who has handled that hot potato now has hands that are warmer than what they were before so in the second step kiossmosis you can think of this as sort of the payout phase and the special protein that is involved here is called ATP synthes and this protein sort of reminds me of a water wheel because it has a little rotor and when the protons or the hydrogen ions move through the rotor it causes the rotor to move just like in a bubbling creek the kinetic energy or the energy of motion of the water hits the paddles and causes the paddle wheel to move so in this case what happens is the hydrogen ions having this potential energy they're going to flow down their chemical gradient and as they do they cause this rotor to move so you're converting the potential energy of the gradient now into the kinetic energy of the rotor moving and the rotor will grab a hold of the phosphate as well as the ATP and repurpose this kinetic energy into the kinetic energy found in the chemical bonds of ATP as you form ATP so this is a process that is aerobic it absolutely requires oxygen in ukareotic organisms in some bacteria they can get away with other uh final electron acceptors uh things like carbonate or sulfate uh and they produce really wonky little byproducts uh but in humans it is exclusively going to be oxygen so let's look at a scenario now where oxygen is absent or what happens if oxygen is absent as we alluded to earlier in the video glycolysis is an anorobic process does not require oxygen likewise the citric acid cycle on the surface is anorobic there is no oxygen that is directly involved however the two main functions of the electron transport chain is number one to establish that proton gradient so that you can make ATP and chemiosmosis but the second important function is to recycle those co-enzymes that is to oxidize NADH back to NAD+ and oxidize FADH2 back to FAD so you can reuse that in the citric acid cycle so if there's no oxygen to be the final electron acceptor at the end of the electron transport chain then there is no electron transport chain and if there is no electron transport chain there is no recycling of those co-enzymes so in the absence of oxygen the only course of action is a different one that allows for the recycling of co-enzymes so that is a primary function of fermentation reactions recycle co-enzymes the second main function is to reduce the pyrovate levels so that glycolysis the forward reactions of glycolysis continue to be favored so keep in mind that in fermentation no ATP is produced the ATP is produced in glycolysis shown right over here not in fermentation but some textbooks again will bundle fermentation with glycolysis or they'll call it anorobic respiration so the vocabulary can be a little bit confusing but keep in mind fermentation produces zero ATP but it does give you the capacity to continue to produce ATP in glycolytic pathways so let's look at a quick overview in anorobic metabolism only glycolysis is really going to be working and at the end of the day you're producing a net of 2 ATP you used two but produced four so there's our net ATP no CO2 is produced here because CO2 is produced in pyrovate processing or pyrovate metabolism and the citric acid cycle neither of which is happening since we're not recycling co-enzymes um through the electron transport chain only through fermentation in aerobic metabolism we're going through all three processes and the end of the day we're generating a total of 30 to 32 ATP so two in glycolysis two in the citric acid cycle and 26 to 28 it's not always an exact number because it does take a little bit of energy sometimes to transport materials into the mitochondria now this number actually rises in bacteria um the number in glycolysis and the citric acid cycle stays the same but it's a little bit more efficient uh for oxidative phosphorilation in bacteria they produce 32 to 34 so the grand total there is about 36 to 38 ATP and that's because of their significantly smaller size and you're not losing as much energy to heat and the surroundings but again since this is human uh physio and anatomy we're going to look at the ukareotic number so the grand total is 30 to 32 and this particular figure I purposefully put it in there just to show you that textbooks will put the correct information in the text but then they'll put in a figure like this that is very misleading so this shouldn't say the electron transport system produces the ATP it should correctly say the process of oxidative phosphorilation which is both the electron transport chain as well as kiosmosis so this leaves us with one question this was all started from glucose how do we get energy from proteins or lipids well we're going to see that in future videos so let's examine how some poisons work there are three main types of cellular poisons that are going to impact cellular respiration number one they can block the electron transport chain so some examples of this are cyanide and carbon monoxide and when they block the electron transport chain we fail to generate a proton gradient and so without the proton gradient there is no chemiosmosis and we're not going to be able to produce ATP efficiently the second class of poisons like the antibiotic ligomy inhibits the protein ATP synthes so again there's not enough ATP being produced our third class impacts the permeability of the membrane so the membrane becomes a little bit more leaky which makes it very difficult to establish and maintain a hydrogen ion gradient and so an example of that is the poison d nitrophenol