Lecture 8 - Lecture 8 If a cell divides, how does it make...

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If a cell divides, how does it make sure that each daughter cell gets the right number and type of organelles? Clicker Question: A mutation occurred in cytochrome C. The possible consequence of this mutation is: C) Electron transport stops. Uncoupling proteins uncouple electron transport from ATP production. How can you do this? Remember that all those protons that are being excluded to one side? All you have to do is open up a channel and let them flow back in. That, of course, wrecks everything (including proton motive force and no ATP systhesis), but electrons are still moving. Proton gradient drives ATP synthesis. However, if you put in an uncoupling protein, any proton that is pushed out will flow back in, which means that you won’t do any ATP synthesis. But, since the electrons are still moving, the mitochondrion heats up. If this is happening inside the cells and you uncouple every single mitochondrion, the whole cell heats up. One of the substrates that get oxidized in cells are fatty acids. Fatty acids can accept protons from the space between the outer and inner membrane of the mitochondrion. If you move enough of these fatty acids from the matrix of the mitochondrion into the inter- membrance space, that is actually moved by an uncoupling protein. Essentially, they are synced for protons and again no ATP is made, but since electrons are moving, the cell heats up. Uncoupling protein is the product of gene expression. So is there an advantage to uncoupling? When the mitochondrial membrane potential is very high, you are really pouring out a bunch of protons and creating ROS. These are the free radicals that can form when you are pushing out massive protons. Free radicals (ROS) can be very damaging and eventually they can kill the whole mitochondrion. In a case like this, the mitochondrion can activate superoxide dismutase and that turns on an uncoupling protein, which uncouples electron transport and stops ATP production. This stops the production of ROS. When you get rid of ROS, the system gets turn on again. Therefore, you cannot have uncoupling protein expressed all the time and must be under very tight control. You have these pancreatic beta cells, which metabolize glucose and take ATP to secret insulin. You don’t want to uncouple pancreatic beta cells (when using ATP to secret insulin). In hyperglycemia, there is too much glucose and that really increases electron transport activity in the mitochondria, creating ROS. So you express an uncoupling protein, the membrane potential stops, and you make less ATP and insulin, but in a hyperglycemic person, that’s what you want to do. So, turning these uncoupling proteins on/off in the pancreatic cells regulates glucose metabolism. Thermogenesis- generation of heat from uncoupled mitochondria
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Lecture 8 - Lecture 8 If a cell divides, how does it make...

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