Practice: Oxidative Phosphorylation 3 - Video Tutorials & Practice Problems
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The reactive oxygen species made in quinones during electron transport are released into the mitochondrial matrix as superoxide radicals. So these are O2- which are called superoxide radicals and you might recall that these are actually converted into hydrogen peroxide by super oxide dismutase and we talked about this, first when we looked at the pentose phosphate pathway because, this hydrogen peroxide is then converted to water by glutathione peroxidase and that enzyme, actually uses glutathione and oxidizes it and it, has the glutathione then has to be reduced by NADPH which is one of the uses of NADPH and part of the reason it's generated in pathway. Now, given the standard reduction potentials here, what is the overall standard redox potential of electron transport? So, hopefully, you realize that, NADH is going to, actually be the beginning of electron transport, right? So we have to reverse this equation. So we are going from NADH to NAD plus +H+2electrons, right? Meaning that our reduction potential is actually going to be positive.32 And the reason this is significant is our overall equation is the potential for oxidation plus the potential for reduction. So, we had 2 reduction potentials given to us but we needed this to be, flipped so that it would be the oxidation potential So that makes, our overall equation 0.32 +0.82 which equals 1.1 oops. 1.14 volts, right? Because we are dealing with volts here. Now, what is the energy released as one mole of electrons moves between cytochrome a3 and a1 in complex IV. So here, we actually are looking for the energy and we're given reduction potential. So we are going to need to use this equation, Delta g equals negative n f e. And here, delta g is obviously the change Gibbs free energy, n is the number of moles, and f is Faraday's constant which is equal to 96 1,500 joules per volt times mole or sometimes it's put as 96.5 kilojoules per volt times mole, right? Be careful about that determine our reduction potential, right? Well, where are the electrons going from? Where did they come from and where do they go? Cotton eyed Joe. Tell me that. So they come from they come from a1 and they go to a3, so a1 is going to be oxidized, meaning this has to be flipped. We get that delta G equals negative one. Right? N is 1. Just 1 mole. Times 96,500. This is joules per volt times mole times and E here is going to be equal to 0.35 minus 0.29. These are both volts. So our answer, our overall answer is negative 5,790 joules per mole or negative 5.79 kilojoules kilojoules per mole if you prefer. Same difference. Alright. Let's flip the page and finish up with some photophosphorylation questions.