 This video will cover oxidative phosphorylation. This material comes from chapter 7 of OpenStacks Biology. After watching this video, you should be able to answer the following study objectives. Describe how electrons move through the electron transport chain. Explain how a proton gradient, or hydrogen ion gradient, is established and maintained by the electron transport chain. Define oxidative phosphorylation and explain the chimeosmotic mechanism for the production of ATP. The electron transport chain and chimeosmosis to produce ATP occur in the mitochondria. There are proteins embedded in the inner mitochondrial membrane that are the electron transport chain and ATP synthase that produces the majority of ATP coming from the oxidation of glucose. The electron transport chain is a series of proteins embedded in the inner mitochondrial membrane that shuttle electrons from NADH and FADH2 in order to reduce molecular oxygen producing water. Starting with the first complex known as complex 1 or there's a little bit more complicated name that tells us the function of complex 1. Complex 1 is also known as NADH ubiquinone oxidoreductase. Now the function of complex 1 is to oxidize NADH and reduce ubiquinone. Ubiquinone is shown in the diagram as the letter Q and ubiquinone is a lipid soluble chemical that can diffuse through the plasma membrane. When ubiquinone is reduced it forms ubiquinol which is often shown as QH2. Now as NADH is oxidized to form NAD plus and a hydrogen ion H plus there are hydrogen ions that are pumped across the inner mitochondrial membrane out of the mitochondrial matrix into the intermembrane space and for each NADH that becomes oxidized to NAD we pump four hydrogen ions out of the mitochondrial matrix into the intermembrane space. As electrons move from NADH to ubiquinone forming ubiquinol these electrons are moving from a high energy state to a lower energy state and the energy that's released in that process is used by complex 1 in order to pump hydrogen ions out of the mitochondrial matrix. Now complex 2 of the electron transport chain is also known as succinate dehydrogenase complex which performs one of the reactions of the citric acid cycle where succinate is oxidized to form fumarate at the same time as FAD is reduced forming FADH2. And in the following step what we see here FADH2 becomes oxidized to form FAD and in the process a molecule of ubiquinone becomes reduced to ubiquinol. Then the ubiquinol that is formed by complex 1 and complex 2 diffuses through the membrane to reach complex 3. The full name of complex 3 is ubiquinol cytochrome C oxidoreductase. It performs the oxidation of ubiquinol back to ubiquinone and electrons from ubiquinol are transferred to cytochrome C so cytochrome C becomes reduced. As the electrons are transferred from ubiquinol to a lower energy state in cytochrome C some of that energy released is used in order to pump hydrogen ions across the inner mitochondrial membrane from the mitochondrial matrix into the intermembrane space. Four hydrogen ions are pumped across for each molecule of ubiquinol that is oxidized and each molecule of cytochrome C that becomes reduced. Then cytochrome C will be oxidized in the next step by complex 4 so the full name of complex 4 is cytochrome C oxidase. Cytochrome C oxidase will transfer the electrons from cytochrome C to oxygen combining one half of a molecule of oxygen with two hydrogen ions forming water. So the oxidizing agent in this reaction is oxygen and the cytochrome C becomes oxidized as oxygen becomes reduced to form water and as the electrons from cytochrome C move to form water they're moving from a higher energy state in cytochrome C to a lower energy state in water and some of the energy that is released in that process can be used in order to pump two hydrogen ions from the mitochondrial matrix out into the intermembrane space. The concentration gradient of hydrogen ions that has just been developed by the electron transport chain pumping hydrogen ions from the mitochondrial matrix across the inner mitochondrial membrane into the intermembrane space can then be used to synthesize ATP. This is known as chemiosmosis or the chemiosmotic mechanism for ATP synthesis. The proton motive force is the force driving hydrogen ions into the mitochondrial matrix. There are two factors that contribute to the proton motive force. One factor is diffusion because there's a higher concentration of hydrogen ions also known as the protons that are in the intermembrane space relative to the mitochondrial matrix. The other factor is the membrane potential or separation of charge across the inner mitochondrial membrane because the matrix has a higher concentration of negatively charged chemicals than the intermembrane space. There's a negative charge or an electrical potential across the inner mitochondrial membrane that will favor the movement of positively charged chemicals into the matrix. This actually is the majority of the force that will pull hydrogen into the matrix. This electrical force together with the force of diffusion are the proton motive force that can be then used by the enzyme ATP synthase. As hydrogen ions travel through ATP synthase there's a channel in ATP synthase that allows hydrogen ions to move across the inner mitochondrial membrane and produce motion, a rotation inside of the ATP synthase. That rotation is a mechanical energy that can be then used to perform the work of synthesizing ATP by taking ATP and phosphate, joining them together to form adenosine triphosphate or ATP. You can think of ATP synthase as being similar to a water wheel or a turbine, a turbine that uses the movement of water flowing downhill in order to produce mechanical motion. As hydrogen ions are moving from the intermembrane space to the mitochondrial matrix they'll create motion that's spinning the ATP synthase protein and that mechanical energy of the motion, the kinetic energy of the movement in ATP synthase will then be transferred into the chemical energy of the bond between ADP and phosphate forming ATP. Here we see the big picture diagram putting together the whole process of oxidative phosphorylation that involves the mechanism of chemiosmosis where the hydrogen ion gradient is coupled to the synthesis of ATP and the electron transport chain where the oxidation of NADH and FADH2 are used in order to drive hydrogen ions out of the matrix into the intermembrane space. So the electron transport chain and the mechanism of chemiosmosis that produces ATP together are what we call oxidative phosphorylation. Oxidative because oxygen is used as the oxidating reagent and oxygen is reduced to form water as we oxidize NADH and FADH2 producing the hydrogen ion gradient that can be then coupled to the chemiosmosis mechanism for ATP synthesis and so together the electron transport chain and chemiosmosis form what's known as oxidative phosphorylation You'll remember from our study of glycolysis and the citric acid cycle that we get four molecules of ATP from glycolysis and the citric acid cycle two ATP that are produced from substrate level phosphorylation in glycolysis and two molecules of ATP produced from substrate level phosphorylation in the citric acid cycle one for each turn of the citric acid cycle one molecule glucose will produce two molecules of acetyl CoA that can enter the citric acid cycle and then oxidative phosphorylation will be able to produce 28 molecules of ATP because we get two NADH from glycolysis from the glyceraldehyde 3-phosphate dehydrogenase two molecules of NADH from the pyruvate dehydrogenase complex and six molecules of NADH from the citric acid cycle three from each turn of the citric acid cycle that will give us a total of 100 hydrogen ions pumped across the inner mitochondrial matrix because 10 hydrogen ions get pumped out of the matrix for each NADH and four hydrogen ions will enter the matrix for each ATP that's synthesized because four hydrogen ions are required to make one ATP and we get 10 hydrogen ions per each NADH 10 divided by 4 is 2.5 ATP that we can synthesize for each NADH and 2.5 ATP per NADH times 10 NADH total from oxidation of glucose we can produce 25 ATP just from the NADH alone then the citric acid cycle produced two FADH two molecules one with each turn of the citric acid cycle and each of those FADH two molecules that is oxidized will result in six hydrogen ions being pumped from the matrix into the intermembrane space now as those molecules move back into the matrix it will take four hydrogen ions to move back into the matrix for each ATP that's synthesized and so we can take six divided by four it gives us 1.5 ATP per FADH that's oxidized and so 1.5 ATP per FADH two multiplied by the two FADH two that we get from breaking down one molecule of glucose there will be a total of three ATP that come from FADH two and so that's 28 ATP total from oxidative phosphorylation and 4 ATP from substrate level phosphorylation giving us a total of approximately 32 ATP that can be produced from glucose oxidation