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Cell Biology

Learn the toughest concepts covered in Cell Biology with step-by-step video tutorials and practice problems by world-class tutors

13. Intracellular Protein Transport

Targeting Proteins to the Mitochondria and Chloroplast



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Hi in this video we're gonna be talking about targeting proteins to the mitochondria and chloroplasts. So mitochondria and chloroplasts. They have a ton of proteins they do a ton of things but they have to get into those organelles. Um And that's actually done through a really specific process which I'm going to walk you through. So the first thing is that proteins that need to enter into the mitochondria and chloroplasts have special signal sequences that direct them to the organ l now this isn't that unusual. Right? The er has signal sequences the gold. Yes signal sequences. Everything has signal sequences. So the mitochondria and chloroplasts do as well. So this signal sequence is going to be recognized for a some type of chaperone protein and that is going to help carry that protein to the proper organ. Al in this case the mitochondria or chloroplasts. Once it's there it no longer needs to be bound to that chaperone. Right That chaperone was just needed to get it there. So it has to actually unbind from that. And of course you're going to need energy to break that. So that energy that is um that energy comes from a teepee hydraulic sis so that breaks apart the protein from the chaperone and then it's like okay we're ready I'm ready to enter them right here next to the mitochondria. Let's enter. So the first thing that it does is it interacts with this protein complex called the T. O. M. Which is also called the T. O. C. For chloroplasts. Um Obviously the M. Is for the mido and the C. Is for the chloroplast and that's how you remember it. And so um these are protein complexes they're found on the outer membrane and they recognize the signal sequence of sound on the protein that needs to get in. So once that signal sequences bound that protein actually is unfolded and led into the inter membrane space, remember both of these have two membranes. So you have this inter membrane space here inter membrane space and you have your outer membrane and your inner membrane. Then once the protein has arrived in this space so it's here it needs to get into the internal membrane So then it binds to another complex called the TIM or the T. O. C. Depending on mitochondria chloroplast again. So this is gonna be outer outer mitochondria mitochondria outer chloroplast. Um In our four plus this is supposed to be an I. T. I. C. Um And that approaching complex is going to recognize a separate signal sequence. So this is gonna need to signal sequences. So once it recognizes that the energy that it needs to pump that across is actually provided by a hydrogen gradient seen hydrogen gradients a lot. That is used a lot of times to produce a T. P. But in this case that energy is used to um pass the protein through the T. I. M. Or the T. I. C. Complex. And so once it's it's it's the idol. Once it's into its proper place chaperone proteins chaperone proteins become super important again to help them re fold. So let's look at this um in this drawing. So first we have this protein here's the protein and it was brought to um this talk Andrea core class by a chaperone. It's then unfolded um and it passes through the tom and the tim and it does this through this hydrogen gradient at least for the tim. The hydrogen gradient is super important for this protein passing through. And then once it's on the inside a chaperone protein comes in and helps it refold. So this is the process of proteins getting in to either the mitochondria or the chloroplasts. So but not all proteins need to get inside. Some of them need to actually get into the membrane of the mitochondria for class. And so there are or into one of the many different compartments. There are all these different structures inside the mitochondria and chloroplasts, proteins actually can be directed to many compartments within the organelles. So like I said there are many sub compartments, things like the chris day or the silo coid or any of these sub compartments um proteins need to get in and so there are special signal sequences for each one of these compartments. So if a protein needs to get there it's going to have a certain signal sequence. And um that's how it gets there. And then sometimes like I said the proteins actually need to insert into any of these compartment membranes. And this inserts exactly the same way as we've talked about proteins inserting into the plasma membrane. So you've seen this image before in other videos where we talked about insertion of the proteins in the membrane. But essentially it works the same way you have these sequences start transfer and stop transfer, which insert into particular proteins which allow them to transport. Um and eventually the start sequence is going to be cleaned. And so you're left now with a single pass trans membrane protein that's inserted into the silo coid membrane. But it could be the mitochondrial membrane, it could be um you know, a Christine membrane. It could be anything any type of sub compartment within the mitochondria or chloroplasts. So with that let's now move on.

True or False:Proteins must remain intact in order to cross the membrane and enter the mitochondria or chloroplast?


The energy to insert proteins through the TIM/TIC complex comes from what reaction?