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Main content
Current time:0:00Total duration:5:56
AP.BIO:
IST‑3 (EU)
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IST‑3.G (LO)
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IST‑3.G.1 (EK)
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IST‑3.G.2 (EK)

Video transcript

what we have depicted here is a signal transduction pathway that gets started with the cholera toxin and we've talked about signal transduction pathways in other videos but it's really this idea that you would have molecules outside of the cell that would interact with receptors on the surface of the cell that would then create a whole chain reaction of events that would cause that cell to do something and so what's happening here is if you were in the unfortunate situation and this is not something that you would wish on anyone if they were to have the cholera bacteria in their gut so let's say that this is the cholera bacteria that cholera bacteria in your intestines will release the what we can call the cholera toxin and here it's depicted in very abstract fashion by a circle on top of a triangle that's not what it actually looks like it's a protein complex with various protein subunits it's just drawn this way so that we can think about this triangle part interacting with this receptor on the epithelial cell and so what happens is this cholera toxin it will interact with this ganglia side receptor you don't have to know the details here really just the idea of what's going on and then once it does that when you see these arrows on these transduction pathways you could view it as that is going to activate the next step or sometimes you might say might promote the next step or make it more likely to happen but what then happens is is once this thing has interacted the a part of the subunit goes in interacts with a g-protein you don't have to know all the details here but G proteins are something that you'll see in a lot of signal transduction pathways there's not just one G protein there's a whole family of proteins called G proteins and you can view them as molecular switches they can get turned on and off based on how they're interacting with other molecules their conformation their shape changes and so that might activate or deactivate them but you can see that you can follow these arrows and you can see what eventually happens and you don't have to know every detail here eventually it leads to a diene elate cyclase then cyclic a and P prote then the protein kinase gets involved but the end result from this pathway is that you have these ions being released from this epithelial cell and with that that causes the water to leave the cell and that's what causes diarrhea so the toxin gets your gut cells gets your intestinal cells to start releasing water so then you're going to have very very very bad diarrhea so that's the big picture but now we can think about what might happen in certain situations so if I were to ask you let's say this epithelial cell somehow had a mutation so its ganglia side receptor does not interact well with the b subunit here with the cholera toxin what would happen then pause this video and try to think about that alright so for whatever reason this epithelial cell had a ganglia side receptor that was a little bit different and it couldn't interact as efficiently with the cholera toxin well in that situation this this activation would not be happening or at least would not be happening as efficiently and so someone with that type of a ganglia side receptor there might be some other negative side effects but they actually would not get as bad diarrhea from the cholera toxin because this whole signal transduction pathway would not be happening or would not be happening as strong now on the other hand it turns out that there's molecules that can disrupt this signal transduction pathway so what we have right over here this is an opioid receptor and if it gets activated then it will activate another g-protein this one is different than the one here but it's part of that same family and when you see this type of thing when you see a line with this flat head instead of an arrow that means it's inhibiting that process so for example this opioid receptor is receptive to a molecule known as and carefully and once again you don't have to know that well you should know is that okay you have this molecule outside of the cell that can interact with the opioid receptor which will then activate a g-protein and what's interesting is that this g-protein is actually an inhibitor of this step right over here and so if you have cholera and the cholera toxins in your gut but you also expose those epithelial cells to in Cathleen well that might make the diarrhea little bit less bad because if this gets disrupted or at least if it gets inhibited then the rest of this pathway will not happen or it will not happen quite as strong so that leaves another question if there was some mutation in the opioid receptor here so it wasn't as good at binding to and calf allene what would be the end result so if your opioid receptor is somehow not as receptive to an Cathleen well then an Cathleen will not be as effective at being able to stop this signal transduction pathway because the in Kathleen will not be able to bind with that opioid receptor and so this inhibition will not occur and so you would just have the regular transduction pathway from the cholera toxin occurring which results in diarrhea so I'll leave you there the big thing to appreciate is when you see these pathways arrows you can view as activation or they're leading to the next step and these lines with these flatheads this is about inhibition and it's pretty typical to see questions and especially if you're scientist you might construct these pathways but you'll also get questions on hey if there's a mutation on something that is activating part of the pathway what will happen and then the pathway won't happen and as much or it may be at all and if there's a mutation in something that inhibits the pathway what would happen well if there's a mutation that makes something that would regularly inhibit a pathway less functional then it won't be able to inhibit the pathway as much and so the pathway will be less inhibited
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