hello everybody my name is Iman welcome back to my YouTube channel today we're gonna continue our chapter on carbohydrate metabolism part two last video we talked and focused on how pyruvate gets converted to acetyl-coa and also the steps of the citric acid cycle today we're going to move on to the third part of cellular respiration which is the electron transport chain and oxidative phosphorylation our main objective here of course in this chapter talking about cellular respiration is to learn how cells harvest the energy of glucose and other nutrients in food to make ATP but the metabolic components of respiration that we've actually discussed so far which is just glycolysis and the citric acid cycle only produce like four ATP molecules per glucose molecule all through substrate level phosphorylation right two net from two net ATP from glycolysis and tuna ATP from the citric acid cycle at this point really molecules of nadh and fadh2 account for most of the energy extracted from each glucose molecule what we want to talk about now is the third and final step of cellular respiration which is oxidative phosphorylation which is where most of the ATP molecules are generated and it's done so by the energy that's released by the electron transport chain to power ATP synthesis now the electron transport chain is a collection of molecules that are embedded in the inner membrane of the mitochondria and eukaryotic cells now once again we're going to see here that structure fits function those infolded membranes that infolded membrane of a mitochondria and with its you know houses these electron carrier molecules and with its placement of electron carrier molecules in a row one after another it's really well suited for the series of sequential redox reactions that will take place along said electron transport chain now most of the components of the electron transport chain shown here are proteins and they usually exist in multi-protein complexes they're numbered one one two three and four and we're going to really take a closer look at what each step does here um so we're going to take a closer look at each of these complexes in the electron transport chain all right so complex one all right now just keep in mind actually one more thing just keep in mind that right the electron transport chain involves a series of these of protein complexes that we're going to discuss now that transfer electron and that will ultimately generate ATP all right complex one all right also known as nadh dehydrogenase is the first protein complex in this electron transport chain all right it uses iron sulfur cluster all right and its main role is to accept electrons from nadh which is a molecule that we generated during the breakdown of glucose in earlier stages of cellular respiration and it's going to take those electrons and it's going to transfer these electrons to a coenzyme Q shortened as Coq all right and it does this while pumping protons h plus across the inner mitochondrial membrane from the mitochondrial Matrix to the inter membrane space all right then we have complex 2 which is known as succinate dehydrogenase all right and unlike complex one complex two does not directly accept electrons from nadh it is also an iron sulfur cluster and what it does is it's involved in the oxidation of another molecule called succinate which is produced during the citric acid cycle complex 2 passes the electrons from succinate to coenzyme q and it does this without pumping protons across the membrane so it's not like enzyme it's not like complex one which pumps hydrogens h plus across the membrane complex two does not do this all right now also complex two transfers electrons from succinate by the way to first fad and then to coenzyme Q I want to make that clear all right no proton pumping here cool then we have complex three which is known as cytochrome bc1 complex all right complex three receives electrons from coenzyme Q which carries them from both complex one and two and what it does is it then transfers these electrons to cytochrome C A Small mobile protein located in the inter membrane space and by the way complex three also pumps protons across the inner mitochondrial membrane like complex one did all right which contributes ultimately to the electrochemical gradient all right last but not least complex four is called cytochrome oops misspelled that cytochrome C oxidase all right it's the final protein complex in the electron transport chain it receives electrons from cytochrome C and it transfers them to molecular oxygen which serves as the final electron acceptor complex 4 uses these electrons to reduce molecular oxygen and form water as a byproduct similar to complex one and three complex 4 also pumps protons across the inner mitochondrial membrane all right so overall the electron transport chain is a sequential process where electrons pretty much flow from nadh and succinate to molecular oxygen in the process it generates a proton gradient across the inner mitochondrial membrane and it is this protein proton gradient that's used by ATP synthase to produce ATP and we're actually going to talk about that a little bit more so now that we've covered this all right let's take a step back and look at the proton gradient right that's formed as electrons are harnessed down the electron transport chain all right what happens here all right well as hydrogen increases in the inter membrane space two things happen your pH drops in the intermembrane space and the voltage difference between the inter membrane space and the Matrix increases due to proton pumping and so together these two changes contribute to what is referred to as an electrochemical gradient it's a gradient that has both chemical and electrostatic properties and because it's based on protons we often refer to it to the electrochemical gradient across the inner mitochondrial membrane as the proton motive Force now any electrochemical gradient stores energy and it's going to be the responsibility of ATP synthase to harness this energy to form ATP from ADP and phosphate all right so the electron chain transport chain it makes no ATP directly instead it eases the fall of electrons all right breaking a large free energy drop into a series of smaller steps that are going to release energy in manageable amounts step by step all right and then the ATP synthase is going to take advantage of this proton motive gradient to produce ATP all right how do how does the mitochondria couple this electron transport uh chain and energy release release to ATP synthase well the energy the the answer is a mechanism called chemo osmosis the production of ATP using the process of chemo osmosis in mitochondria is what's called oxidative phosphorylation and we're about to get into the details of ATP synthase but I want to make mention of one important thing really quickly all right so this is a side note so I'm just going to scroll down to this free page really quickly all right and make this important note here all right we notice how this first step right nadh kind of transfers its electrons to complex one all right one note about nadh here that's really important is that it does not cross the inner mitochondrial membrane all right so therefore one of two available shuttle mechanisms are can can go in play to transfer electron in the mitochondrial Matrix one of those is called the glycerol 3-phosphate shuttle or the g3p shuttle all right what happens here are electrons um are transferred from nadh to dihydroxyacetone phosphate so electrons are moved from nadh to dhap all right and that's going to then form g3p all right these electrons can then be transferred to fad mitochondrial fad to form fadh all right another kind of shuttle is called the malate aspartate shuttle I'm going to shorten it to ma shuttle all right in the ma shuttle electrons are transferred from nadh to oxaloacetate all right forming malate all right and then Malik can cross the inner mitochondrial membrane and transfer the electrons to mitochondrial M NAD plus to form n a d h all right so there's shuttles for nadh to cross the inner mitochondrial membrane that's that's through a shuttle and not directly because nadh cannot cross the inner mitochondrial membrane directly it needs a shuttle and these are two kinds of shuttles that can do that all right so this is just a quick side note that is important to keep in mind anyways back to um chemo osmosis and ATP synthesis all right we've actually now finally arrived at the payout site of aerobic respiration all right ATP synthase through the use synthesis through the use of ATP synthase all right so populating the inner membrane of the mitochondria right are many copies of a protein complex called ATP synthase right this is the enzyme that makes ATP from ADP and inorganic phosphate and ATP synthase it works like an ion pump running in reverse all right so what happens here is um rather than hydrolyzing ATP to pump protons against their concentration gradient under the conditions of cellular respiration ATP synthase is going to use the energy of an existing ion gradient to power ATP synthase this ion gradient that was formed as a consequence of the electron transport chain now the power source for ATP synthase is a difference in the concentration of H Plus on opposite sides of the inner mitochondrial membrane this process right in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work this is called chemo osmosis I want to repeat that and the production of ATP using the process of chemo osmosis in the mitochondria is called oxidative phosphorylation all right so this step is the electron transport chain this step is the oxidative phosphorylation step in general all right let's look in general this is how ATP synthase work Works let's go through the steps all right h plus ions are going to flow down their gradient and enter a channel and the ATP synthase called the stator all right h plus enters the stator and then it proceeds into the rotor all right and once it enters the rotor it's going to change the shape of each subunit then all right then h plus makes one complete turn before leaving the rotor all right and and and and passing through a second Channel all right this spinning rotor is going to cause an internal Rod to the internal Rod to spin as well and that's going to turn on um and activate catalytic sites that are going to pair ADP and phosphate together to form ATP all right so in short let's go through this again h plus interstatter and then moves into the rotor um unit of the ATP synthase it's going to make one um when it enters the rotor it's going to cause a change in the shape of the subunits it then is going to make one complete turn before leaving the rotor and passing through the internal Rod as it passes through the internal Rod it's going to also the spinning rotor is also going to cause the internal Rod to spin as well and that's going to turn um and activate the catalytic sites in ATP synthase to generate ATP from ADP and inorganic phosphate all right now that's a lot of things that we've covered so far for cellular respiration and it can be hard to keep track of everything that is produced in each of the steps of cellular respiration so we're going to go ahead and we're going to review every step and what's produced as a net product in each step to kind of summarize this chapter all right we have glycolysis all right that's the first step it happens in the cytoplasm all right it happens in the cytoplasm all right now what is the input for glycolysis it's one glucose molecule all right 2 ATP and two nadh all right so we're going to write input what does glycolysis require as an input it's going to be glucose which is by the way remember a six carbon molecule it's going to require two ATP and two NAD plus that's what you need to get glycolysis started now what's the output of glycolysis what do we get at the end of glycolysis we get two pyruvate molecules we get four ATP molecules N2 nadh molecules all right so what is the net of glycolysis the net of glycolysis is 2 ATP N2 nadh all right then the second step is this citric acid cycle citric man I cannot spell let me let me try that one more time citric oh I think I got an acid cycle where does this happen in the mitochondrial Matrix awesome all right what is the input for this the input is two acetyl-coa molecules right acetyl coase pyruvate gets converted to acetyl-coa all right and those two acetyl-coa molecules are the input for the citric acid cycle what's the output of the citric acid cycle all right per cycle all right per cycle one cycle all right two cycles per glucose molecule remember that all right so the total would be four one glucose molecule which is two cycles is going to be four CO2 molecules six nadh molecules two fad H2 molecules and two ATP all right the net so far at the end of glycolysis and the citric acid cycle then is a total of four ATP molecules two fadh molecules fadh2 molecules and about eight nadh I say about a a nadh because you form you can form a few more during the formation the the step where you convert pyruvate to acetyl-coa but we're going to leave it like that all right so the net so far is 4 ATP 2fadh2 molecules and eight nadh all right so far with the glycolysis plus the citric acid cycle all right let me make that clear cool I don't want that to be misunderstood awesome all right then in the electron chance per chain that's our third all right electron transport chain plus oxidative phosphorylation which happens in the inner Mida chondrial Matrix membrane sorry membrane all right what's our input here well in our input 4 the electron transport chain is going to be an nadh molecule and an fa dh2 molecule all right what do we produce here we produce water and about 32 ATP all right this is contested sometimes you you can get a Range 32 to 34 ATP molecules produced here so knowing that range is good enough all right anywhere between 32 to 34 ATP approximately generated through oxidative phosphorylation all right so then what is our net product now after all three steps Absolute Total here all right the absolute total here water um is going to be about 36 ATP molecules all right about 36 2 I guess the range would be 36 to 38 ATP molecules all right that is that was the point of us covering cellular respiration right to understand how we can take things like glucose and convert it into energy and what we notice here is that the final total of ATP at the end is anywhere between 36 to 38 Total ATP molecules all right it's appropriate it's important to note these numbers are approximate approximate and they can vary depending on specific conditions in cellular context but for the general view of this course this is good all right in terms of information to know all right and that sums up our chapter on carbohydrate metabolism part two let me know if you have any questions or comments down below other than that good luck happy studying and have a beautiful beautiful day