Intracellular Receptors – Modes of Cell Communication

by Georgina Cornwall, PhD

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    00:00 Now let's move on and look at intracellular receptors. With intracellular receptors, recall that the ligand or the signal molecule must be able to pass through the membrane. It has to pass through that hydrophobic region. And so things like steroid hormones are perfect examples of intracellular receptors.

    00:23 When we look at how these work we will bind directly to a receptor inside the cell and then that receptor directly binds to DNA in order to have DNA transcribed and translated into whatever cellular effect we're looking for. So we'll make proteins that themselves illicit the cellular response. Some of the ligands will bind to intracellular receptors that are in the cytoplasm while others will actually bind to the receptors inside the nucleus. So, much closer to the DNA. And the effects that they have are fairly broad.

    01:04 We can see that each one though in order to bind to DNA must have three functional domains.

    01:12 The first of which is a domain that the ligand binds to. The next is a domain that binds to the DNA.

    01:22 So those are two key domains. But in order for transcription or translation of this proteins to actually happen, we also have to have a place for the coactivators that start the process of transcription and translation to bind. We'll explore what those coactivators are. Those factors that help the receptor actually begin its cellular effects. We are going to be exploring those in our module on genetics.

    01:53 Finally, some of our intracellular receptors can actually act as enzymes. The nitric oxide system is a great example of this. Nitric oxide can be released by a neighbouring cell and then have an effect on its neighbour. What happens here is nitric oxide will come through and activate the enzyme, diffuse into the neighbouring cell, activating the enzyme guanylyl cyclase. Guanylyl cyclase will take GTP and make it into cyclic GMP. Cyclic GMP we'll see often in our following lecture. And it acts to activate other proteins. So it's going to activate protein kinase G in this case. Protein kinase G then has its effect on blood vessels by causing them to dilate.

    02:46 You're maybe familiar with nitric oxide in pills that people take for chest pain when they're having or at risk at having a heart attack, it causes dilation of a blood vessels.

    02:57 Now, there is another drug that's particularly interesting. When we think about viagra, viagra uses this nitric oxide system on a version of cyclic GMP phosphodiasterase, no, protein kinase G phosphodiasterase. And that phosphodiasterase actually shuts down the pathway for blood vessel dilation. Well the drug viagra acts on that phosphodiasterase enzyme to shut it down so that levels of cyclic GMP remain high and thus activate the protein kinase that keeps blood vessels dilated. And that phosphodiasterase is specifically found in cells of the penis and so it works really well only in that location. So, pretty neat trick with nitric oxide and those pathways. So in this lecture, you have learned about different modes of cell signalling. By now, you should be able to describe some of the mechanisms that cells use to signal each other. Think about the example of being in a room of crowded people. Do we need talk very locally or do we need to have an endocrine long distance signalling mechanism. And you also should be familiar with the idea of phosphorylation. That phosphorylation could activate or deactivate a protein kinase pathway or a cellular response. And then finally you should be able to differentiate between intracellular receptors and cell surface receptors. We looked at several different cell surface receptors and then we looked at a couple of different forms of intracellular receptors. In the next lecture, we'll be examining with more specifics these second messenger systems. Thank you so much for listening and I look forward to seing you there.

    About the Lecture

    The lecture Intracellular Receptors – Modes of Cell Communication by Georgina Cornwall, PhD is from the course Cellular Structure.

    Included Quiz Questions

    1. ...are hydrophobic molecules.
    2. ...can bind directly to the receptor and DNA to elicit an effect.
    3. ...need a channel protein to access the cell.
    1. The dilation of penis blood vessels due to high levels of cGMP is the main reason behind erectile dysfunction.
    2. The activity of gene expression regulating intracellular receptors is determined by 3 functional domains: ligand binding, DNA binding, and coactivator bind sites.
    3. Viagra, sildenafil citrate, selectively inhibits cGMP specific phosphodiesterase type-5 enzyme which is responsible for erectile dysfunction.
    4. In cardiac arrest medication, the drugs activate the guanylyl kinase of nitric oxide system and help in maintaining the higher levels of cGMP for blood vessel dilation.
    5. The steroid hormones, being hydrophobic, pass through the cell membrane and particularly bind with intracellular receptors to control gene expressions.

    Author of lecture Intracellular Receptors – Modes of Cell Communication

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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