In this video, we're going to introduce signal amplification. Once a signaling molecule binds to its receptor, that signal can be amplified inside of the cell in order to maximize the effect of the signal and generate a maximum cell response. If we take a look at our image down below over here on the left-hand side, notice that here we're showing you a cell's plasma membrane and down below we're showing you the cytoplasm or the inside of the cell, and up above with the blue background here we're showing you the outside of the cell with the extracellular fluid. Notice that embedded inside of the cell membrane here we have a receptor, and the signal molecule here in red, we know will bind to the receptor and cause a conformational change. In some scenarios, there may be no amplification at all, and if there's no amplification then that just means that not very many molecules are going to be activated. Here we're only showing you one molecule being activated. If there's only one molecule that's activated, typically that's going to lead to a smaller cellular response. With no amplification, there's a smaller cellular response. But in other scenarios, the signal can be amplified. Notice going in this direction we are showing you signal amplification. With signal amplification, many molecules are going to be activated and we have one signaling molecule that leads to the activation of many molecules and if many molecules become activated then the signal is being amplified and ultimately that's typically going to lead to a larger cellular response. Signal amplification allows for a larger cellular response so that response can be maximized.
It turns out that there are two types of enzymes that are commonly used to amplify the signal inside of the cell. These two types of enzymes are called protein kinases and protein phosphatases. Protein kinases are going to add a phosphate group to a substrate, and protein phosphatases, on the other hand, are going to remove a phosphate group from the substrate. Protein kinases and protein phosphatases are essentially doing the opposite of each other. Protein kinases add a phosphate group whereas protein phosphatases remove the phosphate group. Why is it so important to focus on this phosphorylation, the adding of a phosphate group? It's because phosphorylation, again the adding of a phosphate group to a substrate, is going to alter or change a protein's activity. How that protein's activity will be changed is going to depend on the specific protein, the specific scenario. But phosphorylation will typically lead to the alteration of a protein's activity either by turning the protein on or activating the protein or turning the protein off or deactivating the protein.
Down below, notice over here on the right-hand side of our image, notice that we're showing you a dephosphorylated protein over here on the left-hand side. This dephosphorylated protein does not have a phosphate group attached. However, the kinase enzyme is capable of, again, protein kinase is capable of adding a phosphate group to the substrate. The kinase enzyme is capable of taking the dephosphorylated protein and adding a phosphate group to it. Here we have a phosphorylated protein. The phosphate group typically the source is going to be ATP, getting hydrolyzed into ADP so, the phosphate group originates from the ATP. But ultimately kinases are going to add phosphate groups to get phosphorylated proteins and again phosphorylated proteins are going to have altered activity and so you can see the yellow border around the phosphorylated protein to represent that altered activity. This could represent the activation of this protein. If it's being activated, then it can be part of signal amplification. You could imagine that all of these proteins down below, over here in signal amplification, are proteins that are getting phosphorylated so that they become activated and generate a larger cellular response. When the cell wants to remove that cellular response, essentially dampen the cellular response or turn off the cellular response, then it needs a way to get rid of the altered activity. This is when phosphatases can be important because phosphatases are going to remove the phosphate group. You can see the phosphatase down below here is going to take the phosphorylated protein and remove the phosphate group. This ends up regenerating the dephosphorylated protein that we have here. These enzymes, protein kinases and protein phosphatases can be really important in signal amplification. This here concludes our introduction to signal amplification and we'll be able to get some practice applying these concepts as we move forward in our course. I'll see you all in our next video.
