hi it's mr. Andersen and welcome to biology essentials video number 38 this is on signal transduction pathways signal transduction pathways are very important in the actions of cells but they're sometimes misunderstood so I want to start with a analogy and so when Jimi Hendrix plays the guitar um he would vibrate the strings on the guitar those would then be transduced in other words the pick up in a good guitar the electric pick up in the guitar as magnets and wires inside it and what it does is it transduces that message of the wires into an electrical signal it then goes into an amplifier where you can make it really really loud and so we can hear and that's what he was famous for and so signal transduction pathways in cells do the same thing it starts with a message and that message is in the form of a chemical message and then that's transduced into actions within the cell and it also can be amplified and so signal transduction pathways all work in the same way and there are a couple of ways that their actions work sometimes they'll actually modify a protein or change the shape or the conformation of a protein but mostly what they'll do is though there will be what's called the phosphorylation cascade in other words a phosphate group which remember carries energy will be passed off from one chemical to another to another to another until it eventually has an action and and protein kinase azar important in that and so the example that I'm going to give you today a message comes in a message is picked up by a receptor and so this line we could say is the cell membrane on the outside of the cell that message will dock with the receptor and when it does that in this case it'll change the shape of that receptor the example I'll give you is what's called the G protein receptor on then we'll have transduction transduction remembers when we're switching that message and we're changing that from a signal message on the outside of the cell to a message within the cell we use what are called secondary messengers the one that I'll give you an example of is called cyclic a MP it's a very common messenger in cells and then that will eventually target the cells in this case it's going to target cells in the liver and it's going to make them release glucose from glycogen and so that's kind of signal transduction pathway it starts with a message and then it eventually has some kind of a target within the cell and so let's get started this is an animation of this typical liver cell and how epinephrine can affect it and so we're going to go through and I'll pause at a couple of different spots and explain it so epinephrine is the messenger epinephrine is going to be given off from the adrenal gland it's going to move throughout your body but it's going to especially affect cells in the liver so epinephrine is going to dock with this receptor and in this case it's called a g-protein receptor and so the epinephrine is what's called a ligand and so a ligand is going to be a chemical it's a chemical that can't make its way through this cell membrane we can't make it through this hydrophobic region so it's going to dock with the g protein on the outside g protein is a protein that's embedded within it's actually it's a snaky looking kind of a protein it's embedded within that cell membrane so it's got a portion on the top and it's got a portion on the bottom it's got these units on the bottom they're called sub units and so what happens is when that likened attaches in this case epinephrine with the g-protein it causes a conformational change in that protein so it's changing the shape of the protein and what happens when it changes that shape is it actually releases one of those alpha subunits and so one of the subunits called the alpha subunit will be released and it's going to move to a protein just right down the way in the in the cell membrane this protein is called adenylyl cyclase and it'll make sense why it's called cyclase in just a second but essentially what it is is before the actual alpha subunit comes it's an inactivated enzyme in other words it's an enzyme that's not working yet it hasn't changed its shape so it's actually a functioning enzyme but once the alpha subunit is in place it's ready to do its job as an enzyme and in this case what it does is it converts ATP adenosine triphosphate into cyclic AM P or we sometimes called this camp now what is ATP remember know we know oh that that has three phosphates attached on the outside it carries energy mostly in cells we're very simple very familiar with how ATP can be converted to ADP when it drops off one of those phosphates but it can also drop off two phosphates and that's what happens in this case and now it becomes a MP or mono phosphate but there's also a cyclic portion to it and so it adds right where we come off of the the sugar it's actually going to make a cyclic portion I'll put a picture in here of of that molecule a ATP and now we've created these messengers messengers are going to spread throughout the cell this is called cyclic GMP and those secondary messengers in this case are going to target something called the protein kinase protein kinase it's made up of a number of different subunits of protein but kinase means it does something or does action in this case this protein kinase is going to have two catalytic subunits catalytic means things that are going to speed or speed up chemical reactions and then it has these two regulatory subunits and so once that as long as the regulatory portions are attached to the catalytic portions protein kinase is in activate it's not going to do anything but let's watch what happens to the cyclic GMP it'll actually bind to those regulatory portions of the protein kinase and it releases the catalytic portions and so now we have this cascade in other words we have this cascade of energy those catalytic portions are going to become phosphorylated in other words they're going to pick up energy from ATP and they're going to become activated and they change now from agreeing to kind of a yellow activating color they then can act on enzymes within the cell sometimes they'll act through a number of different cells a number of different excuse me molecules within the cell in this case it's going to drop off that phosphate to phosphorylate and it's going to activate phosphorylase so it can release glucose from glycogen within the cell now once we don't have that ligand attached anymore we don't make that cyclic a MP then the whole thing is going to shut down again and so the signal transduction pathway is simply a way that we can take this message and we can move it throughout the cell and then have desired consequences within the cell okay so let's do a little review and if you've ever watched the show Dora the Explorer there will be times where she just kind of pauses and looks awkward Lee if the person who's watching the show and so that's where you have to jump in and help a little bit so let's do a little bit of review so we start with this at the top we've got epinephrine and KITT at the top and so what do we call this that's right it's called the ligand a ligand is a chemical that can't make entry into the cell but it's going to attach to them to the receptor so this is called the receptor do you remember what that's called that's right it's called the g-protein and so what will happen is that Ligon will attach to the g-protein it's got a number of different subunits this one right here on the end is called the alpha subunit that's right hey if you're not getting any of these you may want to go back and watch the earlier portions of the video we've got this over here and this is the probably the one that you're going to struggle with the most what's the name of that that's right adenylyl cyclase and so what happens is the alpha subunit is going to attach to a dental Leal cyclase we then have an enzyme that's functioning it's going to take in these little starbursts those aren't starbursts they're called that's right ATP ATP will then be converted to cyclic a.m. P or camp and cyclic AMP e are now going to go work on this protein kinase that's right protein kinase it has two portions that are catalytic and to that our regulatory that's right okay so the cyclic AMP II is going to move over to that but let's watch what happens for a second because there's not just a few cyclic AMP es in the cell they're going to be lots of cyclic AMP es and lots of protein kinase 'iz in the cell and so remember when we talked about our analogy of Jimi Hendrix this is where we can amplify the message so we just have this one ligand of and we can have all this action I didn't want to anima animate all of that so I went back to just one protein kinase so we will free up the catalytic portions we now add energy to them what's that called phosphorylation that's right we're going to add a phosphate group to them they're going to turn yellow and now they're able to pass on that phosphate group to phosphorylase so it's activated and it can break down glycogen into glucose within the cell and so that's the signal transduction pathway it's fairly simple it's got a lot of steps in it but it's just like playing the electric guitar and so I hope that's helpful