Intracellular Receptors and Direct Gene Action - Video Tutorials & Practice Problems
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concept
Actions of Steroid Hormones
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5m
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When we first introduced hormones, we split them into two basic groups based on their chemical structure. We have the amino acid based hormones and we have the steroid hormones. Here. We want to talk about the steroid hormones and how they induce change in the cell. In more detail, we're gonna do that by talking about intracellular receptors and direct gene action. Now, before we really dive in, let's just remind ourselves that steroid hormones and also thyroid hormone, that was sort of our one major exception to our hormone groupings. These hormones can enter the cell membrane and they can enter the cell membrane because they are lipid soluble. That means that they can pass through that lipid bilayer of the cell membrane. Well, if they can pass through the membrane, that means that the receptor proteins for these hormones are located inside the cell. Remember, this is very different from the majority of amino acid based hormones which are stuck on the outside of the cell, which means that the receptor is also gonna be behind the outside of that cell membrane. All right. So let's look at this step by step. But before we do, let's orient ourselves to our image. We have a cell here. We can see the nucleus inside the cell. We see some other things going on there that we'll talk about in a second. But we're gonna start on the outside with this hormone here. And this is a steroid hormone, specifically, this is estrogen. But this is gonna apply generally to all steroid hormones. Now remember in the blood, a steroid hormone is bound to a transport protein because being lipid soluble, it doesn't dissolve in the blood. Now, we don't have that drawn here. But when it gets to the cell, it's gonna separate from that transport protein. And we can see that it is going to pass right through the cell membrane. So the first thing we're gonna say, step one, the steroid hormone passes through the membrane. And now this hormone is on the inside of the cell. And as we follow our arrows here, the next thing we see is this sort of green protein there. And that's supposed to represent the receptor. So this receptor here in the cytoplasm and we can follow it along and we can see that our hormone then binds to the receptor and together they form what's called the receptor hormone complex. So we're gonna say number two, the hormone inside the cell now binds to a receptor protein together, those two things bound together are called the receptor hormone complex. And if we look at our image here, we can see that this receptor hormone complex next goes into the nucleus. So we're gonna say the receptor hormone complex enters the nucleus. Now to be very clear, sometimes that hormone or I'm sorry, that receptor is actually inside the nucleus and the hormone travels into the nucleus before it forms that receptor hormone complex. Sometimes the receptors in the cytoplasm, they bind in the cop cytoplasm and together travel into the nucleus regardless the hormone, the receptor hormone complex ends up in the nucleus and in the nucleus, it is going to bind. We're gonna say that this complex binds to a specific DNA region. And we can see that in our image here, this purple molecule represents the DNA. And we see our receptor hormone complex bound to that DNA and by binding to that DNA that triggers a cure response. Now, if binding to DNA is what triggers a cellular response, that means that we are affecting gene expression. This hormone bound to a protein making that complex is directly bound to the DNA, directly affecting gene expression. That's why we sometimes call this direct gene action. Now again, a reminder, this is very different from those amino acid based proteins, which typically, I'm sorry, amino acid based hormones, which are typically stuck on the outside of the cell. So they rely on these second messenger systems to pass the signal along inside the cell. These steroid hormones, they are in the cell and getting their hands dirty directly in gene expression. Now, when I look at this, it also starts to make sense to me a little bit more clearly. Why when we talk about the endocrine system, we say that it works more slowly than say the nervous system, which is sort of a rapid signaling system. When I think about these steroid hormones, well, the blood travels through the body relatively quickly, maybe takes a minute or so to get everywhere in the body. But how long does gene expression take? Well for a steroid hormone to induce a change? You need to wait for RN A to be transcribed. You need to wait for that RN A to be translated into a protein. You need to wait for that protein to go out and affect physiological change. And sometimes those proteins could last a very long time. So we're talking at the very least many minutes but typically hours or longer and the effects that could last very long times when we're talking about these steroid hormones. All right. With that, the main thing though that you wanna take away, remember, steroids can enter the cell. That means that the receptor is inside the cell, it forms that receptor hormone complex and that receptor hormone complex directly affects gene expression. We'll look at this more in examples and practice problems. I will see you there.
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example
Intracellular Receptors and Direct Gene Action Example 1
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2m
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In this example, we see an illustration of a cell and we have different receptors on the cell. We have purple receptors that are labeled Y and we have green receptors that are labeled X and those purple receptors you can see are on the outside of the cell, on the cell membrane. And those green receptors are in the cell cytoplasm. And then this example tells us that drawn below is a cell that responds to hormone, X and hormone y, the receptors for hormone X are green while those for hormone Y are purple. And we can also see they're labeled with an X and A Y there. So based on this image, we wanna say a, what can you conclude about the chemical structures of hormone X and Y? All right. So remember this is a general rule. There are exceptions, but let's start with X. So X the receptors are inside the cytoplasm here, which types of hormones are the receptors more often in the cell in the cytoplasm. Well, steroid hormones. So I think hormone X is gonna be a steroid that means that hormone y while these receptors are on the cell surface. What types of hormones are the receptors most often on cell surface surface. Well, that is going to be amino acid based hormones. Again, there are exceptions to these, but that's our general rule that we've been following. All right. Next, it asks b which hormone is more likely to be affected by a molecule that inhibits a dilate cyc lase? Well, remember a dilate cyc lase is in this signaling cascade that has to do with G protein coupled receptors. And G protein coupled receptors are some of those receptors that are on the cell surface that respond to these amino acid based hormones. So therefore, I think my answer there is going to be hormone y all right. And then we have, which hormone would you expect to directly interact with the DNA of the cell via a receptor hormone complex? Well, remember, steroid hormones are able to enter the cell, they bind to the receptors forming this receptor hormone complex. And then those go into the nucleus or sometimes receptors in the nucleus, they bind to the DNA and then they're active in gene regulation. So, therefore, hormone X A steroid hormone, I expect to directly interact with the DNA DNA of the cell by a receptor hormone complex. And with that, you've answered our question.
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Problem
Problem
True or False: if false, choose the answer that best corrects the statement.
Steroid hormones are the only hormones that interact with the DNA via a receptor-hormone complex.
A
True.
B
False; all hormones can interact with DNA via a receptor-hormone complex; it depends on what type of receptor is used at the target cell.
C
False; thyroid hormone is an amino-acid based hormone that interacts with DNA via a receptor hormone complex.
D
False; most peptide hormones interact with the DNA via a receptor complex, while most steroid hormones use second messenger systems.
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Problem
Problem
Which pair of terms below correctly matches the molecule with the pathway?