Let's begin our discussion of biochemistry. Four topics with bio signaling. Now, signal transaction actually has five features to it and those are specificity. And this is specificity, just like we've seen with basically every other protein that we've been talking about. And usually the signals are chemical in nature. However, for example, they can also be electrical. We're not really gonna deal with anything outside of chemical signals, though. So again, specificity Just like the specificity we've seen with all the other proteins we've talked about amplification, which is basically the concept of how one molecule can actually lead Thio. You know, 1000 downstream molecules, so one molecule binding to a receptor can activate a number of enzymes, and those enzymes will produce a number of molecules. And so the signal gets amplified along the way as it progresses through the path modularity, which is basically how some proteins air able to interact with multiple components of a signaling pathway. So, um, a protein can interact with bind something like that, interact with, you know, a signal and then also interact with, uh, some sort of response element way also have adaption, which is basically how feedback modulates receptor presence or activity. And this is sort of like any type of feedback regulation we've seen with enzymes, of course, gonna work a little differently with signal transaction, because theme, the feedback isn't necessarily going to go directly to the receptor to modulate its activity. Feedback can happen through gene expression and variety of other things, too. But the point is that, um, thes signal transaction pathways can be attenuated. So, you know, some sort of downstream signal will be able thio affect how the upstream part of this signal pathway like the receptor, how it behaves, it'll modulate its activity. I probably shouldn't use the word modulate because we have modularity there, So I should say it attenuate sits, activity right, adapt its activity. You also have integration, which is basically the idea that all signals are integrated into other signals to give the appropriate response. And we're going to see a figure a little later. That should hopefully illustrate just how crazy and complicated all of the signals a cell has to integrate our I mean, you're going to see this figure you're gonna be like, Oh my God. There's so much going on in a cell and this figure on Lee is showing a little bit. Honestly, it's not even like the full picture. Um, the, You know, the main idea is signals don't exist alone. We're gonna talk about, like, six single signal pathways. But you have to remember that you know, there's a million other Well, not a million, but, you know, a bunch of other signal pathways going on at the same time. And all of these pathways are integrating together so that the cell is producing the appropriate responses. Now, the first type of receptor we're gonna talk about this G protein coupled receptor and basically with G protein coupled receptor thebe fining feature is that it uses this protein that we see right here. This is G and it uses this protein. G two, you know, carry out its signal. Basically. Now the receptor has a sort of defining feature about it in that it has these seven trans membrane domains G protein coupled receptors have these seven trans membrane domains Um, just a little interesting feature about them. But again, most important part is that they use this protein g. So in our figure, here we have our receptor. This is G right here it is both the yellow and the blue part. This whole thing is G G actually has three sub units. You can see it better in this image of G here. The red, yellow and blue parts. Um, and this over here in green, This is a dental liel, cyclists, cyclists, and we're gonna talk about what that does in just a second. So basically, when you have ligand binding to your g protein coupled receptor and the case of our example, we're gonna be taking a look at hormone binding. And this is very common. So we have our LaGon during this case hormone binding into our receptor here in red. And then what's gonna happen is G as you see right here, G actually already has in it. So back here, GRD has inside of it draw like a blob GDP. And when When the hormone Bynes, what's gonna happen is where we see here We're GTP is actually going to come in and be exchanged for that GDP and the GDP is gonna be released. And this reaction is actually catalyzed by stuff that we don't see here in this picture there called guanine exchange factors. Um, so they're gonna help carry out that reaction, that swap of GDP and GDP. And just to be precise, this is this is happening in the Alfa sub unit. Um, so off the sub unit there and once GTP is bound, that's sort of when G becomes activated. So I'm actually gonna hop out of the image here just so you can see it better. And basically, um, when she is activated, it is going to cruise on over to a dental real cyclists like you see here shouldn't be drawing my arrow coming from the Alfa sub unit there anyways, so as you can see here we have G and it is now interacting with an activating a dental Liel cyclists again, this is Dan Lil. Too many wise, Too many l's site place. And what a dental Liel cyclists does is it actually converts ATP into this molecule called cyclic amp, So, uh, you guys know a MP Dennis ing Monta phosphate? Well, this is cyclic a Dennis ing Monta phosphate. Basically, it's just a cycle ized version. And, uh, this cyclic a m p. Which I'm just gonna call camp from now on. just because it's easier to say so. Camp is a second messenger secondary messenger, almost that protein. It's not a protein secondary messenger, and it's it's a nucleoside, right, not a protein. So it's a secondary messenger, and it's going to do a variety of things that we're going to talk about momentarily. But for now, I just want to finish up by talking about G a little bit more. Because you see G is actually a GTP ace and so on its own, it'll slowly break down the GTP inside of it and leave the Alfa sub unit inactive. All right, so let me just say that again. GT R G is a GTP ace. And so the GTP that it has bound inside of it will be broken down by G very slowly. Andi, this will result in GTP being turned into GDP, right? And that's gonna leave Alfa inactive. That's basically going to take us back to where we were over here. Um, what's interesting is there these GTP activator proteins or gaps, and they actually can increase the rate of G of the breakdown of G, T, P and G D. P. And this is going to be important in terms off modulating signals and attenuating signals. All right, let's flip the page