Hormone Signaling

by Jason Amores Sumpter
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As I said previously, steroid hormones can readily cross the membrane because their lipid soluble in fact, cholesterol, is a major, important component of the cell membrane. And because steroid hormones will readily move through the membrane, they actually tend to have interest cellular receptors or just receptors that air found inside the cell. And they tend to act in ways that modify gene expression. And they'll do this either by binding to a receptor and having that receptor hormone complex act as some type of transcription factor. Or they will trigger some signal in the cell that will activate other transcription factors. Now the elements that ah hormone receptor complex will bind you. Thio help initiate transcription is known as a hormone response element, and you can see that whole process kind of playing out in this image behind me, where we have a steroid hormone that would have had to been transported through the blood assisted by proteins because it's not water soluble, but it's gonna easily diffuse through the cell membrane bind to this interest cellular receptor, and that's gonna actually move into the nucleus where this is going to find its hormone response element, and it's going Thio, Modify transcription. And here you can see in this case it's going to lead to the translation of some new protein. Now it's worth noting that although thyroid hormones are actually a mean hormones, they behave like steroid hormones because they're non polar. And this is due to the iodine atoms, uh, that air found in thyroid hormones. Uh, we'll talk more about thyroid hormones and just a bit. I do just want to point out this exception because thyroid hormones are again going to behave similar to what we see happening in this image as opposed thio how water soluble hormones will behave Now Water soluble hormones are gonna bind to cell surface receptors because they can't cross the membrane. And what they'll end up doing is activating some type of signal transaction pathway that's going to communicate that hormone signal within the cell. Often, they're gonna be using G couple G protein coupled receptors as well as second messengers to transmit these signals, and you can see a little model of that happening here with this hormone is gonna go ahead and bind to this G protein coupled receptor. Here, you can see the GTP being exchanged for the GDP, and this is going to go ahead and let me jump out of the way. Activate this protein here, which is a dental liel cyclists and dental cyclist is going to take at P and turn it into cyclic ATP and sick. I'm sorry. Cyclic a m p not ATP Cyclic A M P is a very common second messenger used and will frequently be part of these signal transaction pathways. Now, a second messenger to be clear is just any non protein intracellular signaling molecule. And often these signature instruction cascades will involve ah, Siris of activations or in activations, where both of various molecules, you know frequently you will have, you know, protein kindnesses and phosphor laces and defrost for laces. Uh, you know, phosphor awaiting and defrost for relating each other in a Siris of steps that, um, you know, will transmit the signal. What's cool about that, though, is along the way, the signal can get amplified. And you know, this is due to the fact that you know to just sort of model it really quickly, Let's say, like one signaling molecule can actually activate two other downstream signaling molecules and If those guys come both activate to, then you can see how over time or rather, over the course of transmission of the signal, it gets amplified mawr and more molecules air communicating that signal. So these were just common features of these water soluble hormones. With that, let's flip the page.