Hi. In this video, I'm going to be talking about the integration of multiple signaling pathways. So signaling pathways do not at all work independently of each other. They're not linear pathways; instead, they're connected, called signaling networks. They're connected via crosstalk, via interactions, via all these different ways. So they can be connected because there's numerous extracellular signals, which all activate different things at the same time. Protein kinases activated by one pathway are involved in other pathways. And once those kinases are activated, they just go on and activate lots of different things, whether or not it's in the same pathway, so there's this overlap. And then you have crosstalk between second messengers, which what that means is that you have these second messengers that are going on, but they don't just activate something or pass that message to one, they pass that message to really anything that they have the ability to. So they're huge pathways. Now, they can be positive and negative interactions, so things like feedback loops where the end product mediates the activity of an earlier product. So this mediation could either activate or stimulate, but it could also inhibit. So it would be positive, positive, and negative. You have these things called feedforward relays, and this is where the activity of one component stimulates a really downstream component. So if something like, say, product 2 is, like, really active, it can go forward and activate product 7. And that would be like really far down a signaling pathway. And so, the signaling networks in the cell are extremely complex, which is kind of just the summary of this. There are 1500 receptors, 700 kinase phosphatases, and around 2,000 transcription factors. And they all work in interconnected and crosstalk-y ways. So, here is an example of what this looks like. You obviously don't need to know all these abbreviations, but just realize anytime there is text here, this is a different protein making something, doing something. There are all these different receptors, and this is just a sample. Right? Like I said, there were 1500 receptors, and I'm showing 1, 2, 3, 4, 5, 6, 7, 8, 9. Nine of them. So you can imagine how much is going on in the cell at one time with these signaling pathways. It's a freaking huge amount. So with that, let's now turn the page.
Integration of Multiple Signaling Pathways - Video Tutorials & Practice Problems
Integration of Multiple Pathways
Video transcript
Insulin Signaling
Video transcript
Okay. So now I'm going to talk about insulin signaling, and the reason that I'm doing this is because it's an example of how different things work together to have a certain function in the cell. It's a really simple vibe though. So first, we're going to focus on insulin and glucagon, and these are two proteins that work together to maintain stable blood glucose sugar levels in cells. So there are two hormones, the ones that I mentioned. So after you eat, there's a ton of glucose and sugar in the bloodstream from the food that you eat. So when this happens there is a lot of blood or a lot of glucose in the bloodstream. This triggers the production of insulin. Insulin then acts to bind insulin receptors. Now, once these insulin receptors are activated, this triggers a lot of different pathways. One of these pathways is the protein kinase B phosphorylation. This is going to trigger vesicle fusion, import of glucose into the cell, and other pathways as well. But, after you take in all that glucose into the cell, which happens here, your blood glucose levels drop. And so, what happens then is insulin is not being produced, so the receptors are not being activated. And when they're not being activated, the cell then switches on its increase in the secretion of glucagon, this other hormone. Once this hormone is secreted, this causes it to bind to different receptors and stimulate a variety of other signaling pathways that have to do with blood glucose maintenance. So, here is an example of insulin. So, you have insulin, it binds to the receptor, this activates a variety of different pathways. You don't need to know about pathways, but you can see here that just in this very simple drawing, it results in a ton of different cellular responses just in the process of, you know, maintaining this blood glucose level. So complex pathways even in this simple example. So with that, let's now move on.
When insulin binds to insulin receptors what happens to glucose?