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Lecture 15

BIOC13H3 Lecture 15: BIOC13 Lecture 15

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Biological Sciences
Jason Brown

BIOC13 Lecture 15  Uncoupling means no longer nadh oxidation with atp synthesis  Uncoupling agents can be used for weight loss, but if not used controllably they can lead to too much weight loss and death  Still don’t know how exactly they work  We have known how they work from like the first world war  Mitochondria are like avid ebayers  They want a proton gradient to have as a source of energy to make ATP  Even when mitochondria are resting (not producing atp) they have their proton gradient at its highest  When we give the mitochondria ADP and Pi, that’s when the magnitude of the proton gradient starts to drop, that’s because the protons are going through the channels  In reality the mitochondria always wants its proton gradient to be high so as it starts making atp, and the gradient goes down, then you need to start oxidizing more nadh to try to build that gradient back up  As we start doing atp synthesis, the cell will simultaneously start oxidizing nadh (oxygen consumption) and use that energy to pump protons to build the gradient back up, and that gradient goes down by the atp synthase  If we add uncoupling agent, it causes the proton gradient to drop even further  Because of this, it stimulates a huge rise in nadh oxidation (oxygen consumption)  How does dnp dissipate the proton gradient?  Does so by providing an alternate way of moving the proton across the mm, and so there’s no atp synthesis, because protons are not flowing through the atp synthase  Dnp has a hydroxyl group on it, which is able to bind and unbind protons  When it is in the intermembrane space, where there is high proton concentration, it will bind a proton on the hydroxyl group and goes through the mm and into the matrix  Once in the matrix where there is a much lower concentration of protons, the proton will be unbound from DNP  Once dnp unbinds a proton, it leaves dnp with a negative charge, this is important because charged species have a difficult time crossing the membrane  How does it get across the membrane?  Another thing uncoupling agents need to do is be able to delocalize the negative charge by spreading it over a larger area  DNP can do resonance, so it can shift electrons to spread the negative charge all over the place  Now the DNP is able to get across the mitochondrial membrane, once across it can bind a new proton and do the cycle again  The importance of this idea is that not only does it explain how uncoupling agents work, but also faces another problem  There are lots of different uncoupling agents, and they have different structures so how can these molecules all have the same kind of function inside the mitochondria  FCCP structure compared to DNP is that they only share a benzene group, other than that its all different  There are only 2 properties, a place to bind, unbind protons and have a way to delocalize negative charge  FCCP has those 2 properties, it has an ionisable proton and has double and triple bonds for delocalizing (resonance)  The other people said that the uncoupling agent somehow work to destroy the chemical intermediate  First 3 experiments support or can be interpreted as supporting, but they also don’t explicitly refute the other hypothesis  The next 2 studies serve to transform the Chemiosmotic hypothesis to a theory  A theory is an idea that has support, in the general population theory is used differently than in science  4 experiment is the reconstituted oxidative phosphorylation  Best way to support the Chemiosmotic hypothesis is to make a system that has only the 3 things required; proton pump, proton impermeable membrane, ATP synthase  Racker created a an artificial structure with just those 3 things  Added bacteriorhodopsin is a light driven proton pump  He took his mitochondrial atp synthase from an animal, took the rhodopsin form bacteria, so they shouldn’t be able t
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