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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

14. Cell Signaling

Overview of Cell Surface Receptors


Cell Surface Receptors

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Hi in this video, I'm going to be doing an overview of cell surface receptors. So there are three types of cell surface receptors which makes it easy to remember. So the first is going to be an ion channel coupled receptor and so this is going to be a receptor that responds to different types of electrical gradients stemming from ions which makes complete sense. Um And ion channels also have a unique ability to be able to convert chemical signals from like ion gradients into electron signals or vice versa. So this is most commonly found in the nerve signaling that we've talked about before. And so ion channels are super important for that now. We're going to spend more time talking about the other two because we've talked about ion channels in the past. Um And so the next one that we're going to talk about is G protein coupled receptors and these work pretty much by once they're activated they go on to activate g proteins that are found in the side of saul and then these G proteins go on to act on whatever they want to within the cell so they can act on, they connect on ion channels and they can act on different proteins whatever they want to act on. But generally this results in some kind of signaling cascade. So activation of G protein leads to activation of an enzyme which leads to activation of another protein which goes on and on and on and on and on creating this huge cascade of events. So we're going to talk a lot about G protein coupled receptors in future videos. And then also we're going to talk a lot about this final one which is an enzyme coupled receptor. You may see this as a protein kinase receptor however you see it as how you should memorize it. There's exactly the same thing and these receptors act as enzymes usually in some type of complex. So there's actually a portion on this protein usually in the c terminal domain. So that's going to be in the side us all that acts as an enzyme. And so when these are activated they turn into these enzyme complexes that can then go on to activate other things. So here are the three types of cell surface receptor you have your ion channel receptor which will pass ions through and respond to different electrical or chemical gradients. You have your G protein coupled receptor which looks a little funny, we're gonna go over about how it passes through the membrane um and this structure will become important but right now just know that this is a different type and then activate G proteins which go on to do other things in the cell. And then you have your enzyme coupled receptor which usually have some type of domain usually in the side of sol that acts as an enzyme once they're activated and usually they work in a receptor complex. So here I've shown as timers which is going to be the most common form. But like I said, we will go over all the specifics of these future videos but just now know that there are three classes and they kind of look like this. So even though there are three different classes, there are commonalities that exist between the three main receptor types and their signaling pathways. So usually these receptors are activated by binding to some type of ligand and this is normally going to be an extra cellular Ligon, something outside the cell that's going to bind to the receptor. And then once it's there it can activate a variety of different things depending on the receptor that it is, whether it's an ion channel or G protein or enzyme or protein dinos. Now sometimes this ligand will remain for a really long time which you can imagine will just continually like fire the signaling pathway which the cell may want but generally doesn't. And so if the ligand just stays for a really long time, what happens is the cell is like whoa, that's way too much ligand. I don't need to activate these pathways for you know, so intensely so they usually end up down regulating the receptor so that what that means is the cell says, whoa, I don't need this much again but it's out there so I need to respond less to it. And the only way I can do that is by removing that receptor off the plasma membrane so that then it can't interact with it. Um there's another thing um Protein kindnesses are usually found downstream of every single one of these receptors. And so remember protein kindnesses add phosphates and phosphate asses remove phosphates. And so usually the addition or removal of phosphate results in activation or inhibition of protein and pretty much at most steps in signaling pathways involved in these receptors, phosphates are added or removed which affects the activity of that protein. And then there's finally a last vocab word that we need to know and that's the second messenger. So what that is is that second messengers are molecules that act to they don't sign the act to signal. Um Use downstream I remember you know keep going downstream down the pathway of the receptor ligand binding. So the receptor and ligand they bind that activates the receptor. Then the receptor goes on to activate something else and that something else is usually some type of second messenger which then goes on to signal downstream. And so the second messengers make up what are known as signal transaction pathways. And these are going to be the collection of stepwise events. So the receptor activates a protein protein a protein A activates protein B, protein B activates protein C, protein C activates protein D. And you can go all the way to Z and back around again and these signaling pathways because they're so long and so complicated but they're called signal transaction pathways and then usually it gets to the end. So we'll say protein Z. Has now been activated. So what is proteins e what is the very last protein? What does that protein do once it's activated? Usually what this protein does is it acts as acts as a transcription factor to activate or inhibit different types of different genes. So generally the signaling pathways leads to some difference in gene expression by the end. So here's an example of a signaling transaction pathway. We do not at all need to understand what all these abbreviations mean. Just sort of understand it's complicated. So if we have, you know, a ligand that binds to a receptor, this receptor activates this. It then activates these three things. These one of them goes on to activate this series of proteins which is gonna be a signal trans deduction pathway. But eventually what happens is that one of them activates some type of transcription factor which travels to the nucleus to support gene expression and support whatever it wants to support whether that survival or apoptosis or proliferation or differentiation. Whatever the signal is supposed to do, it will do by activating a transcription factor in the end. So that's the overview of cell surface receptors and signal transaction pathways. So with that let's now move on

Which of the following is not a type of cell surface receptors?


Which of the following receptors responds to an electrical gradient across a membrane?