In this video, we're going to begin our introduction to the classes of signaling receptors. And so recall from our previous lesson videos that receptors are biomolecules, typically proteins, that are going to change conformation when bound to a very specific ligand or signaling molecule. It turns out that receptors can be categorized into 2 major classes. The first class are cell surface receptors, and the second class are intracellular receptors. Moving forward in our course, we're going to talk about the cell surface receptors and the intracellular receptors in their own separate videos. But we'll start off with the cell surface receptors. So I'll see you all in our next videos to talk more about these cell surface receptors.
Classes of Signaling Receptors - Online Tutor, Practice Problems & Exam Prep
Signaling receptors are categorized into two main classes: cell surface receptors and intracellular receptors. Cell surface receptors, embedded in the cell membrane, include G protein-coupled receptors (GPCRs), receptor tyrosine kinases (RTKs), and ligand-gated ion channels. Intracellular receptors, found within the cell, interact with small hydrophobic signaling molecules that diffuse across the membrane, triggering cellular responses. Understanding these receptors is crucial for grasping signal transduction pathways and their roles in cellular communication.
Classes of Signaling Receptors
Video transcript
Cell-Surface Receptors
Video transcript
In this video, we're going to introduce cell surface receptors. Cell surface receptors, as their name implies, are receptor proteins found embedded in the cell membrane, or in other words, on the surface of the target cell. There are three major types of cell surface receptors that are involved in most signal transduction pathways. Each of these three major types of cell surface receptors operates in its own unique way.
The first major type of cell surface receptor that you all should be aware of is the G protein coupled receptors, or GPCRs for short. You can see GPCR stands for G Protein Coupled Receptors. Taking a look at the image down below, you can see that the GPCR here is in this tannish color, and the G protein portion is highlighted in green. The ligand here can bind to the GPCR, and ultimately, the GPCRs have their own unique way of operating.
The second major type of cell surface receptor that you all should be aware of is the receptor tyrosine kinases, or RTKs for short. The RTKs usually have two domains. You can see the two domains of the RTK. The RTKs, or receptor tyrosine kinases, also have their own unique way of operating and functioning.
The third and final major type of cell surface receptor that you all should be aware of are the ligand-gated ion channels. Down below, we are showing some ligand-gated ion channels, which you can see on the left-hand side are in a closed position. It is not until the ligand binds that the receptor changes conformation into its open position, allowing ions to flow through the membrane. It is the ligand that binds to cause the channel to open up and allow for ions to diffuse across the membrane.
To learn more about the details of each of these different types of receptors and exactly how they operate and function, that's something that you are not typically going to be held accountable for in an introduction to biology course. We do have videos here at Clutch Prep that cover the details of GPCRs, RTKs, and ligand-gated channels. But you'll be able to find those details in our more advanced biochemistry courses. For now, this concludes our brief introduction to the cell surface receptors, and we will be able to talk about the intracellular receptors in our next video. So, I'll see you all there.
Intracellular Receptors
Video transcript
So now that we've introduced cell surface receptors in our previous lesson video, in this video, we're going to introduce intracellular receptors. Intracellular receptors, as their name implies, are receptor proteins found on the inside of a target cell, which is what intracellular means—on the inside of a cell. Recall from our previous lesson videos that really small hydrophobic molecules or signaling molecules are going to be able to freely diffuse across the membrane and into the cell. If we take a look at our example image down below at this basic intracellular signaling pathway right here, notice that we have a membrane representing the cell membrane. Up above in the blue background, we have the outside, the extracellular fluid, and down below here with the yellow background, we have the inside of the cell or the cytoplasm of the cell. Notice here, in red, we have a really small hydrophobic signaling molecule or ligand. Because it's small and hydrophobic, it can freely diffuse across the cell surface or the plasma membrane, and so its receptor is not going to be found on the cell surface or the plasma membrane. Instead, the small hydrophobic molecule will diffuse through the membrane and into the cell where it can interact with an intracellular receptor, which is this blue molecule you see right here. When the small hydrophobic molecule binds to the intracellular receptor, it will lead to a cascade of events that ultimately generates a cellular response. Intracellular signaling and intracellular receptors will be found specifically on the inside of the cell, not in the cell surface or the plasma membrane. This concludes our introduction to intracellular receptors. As we move forward in our course, we'll be able to get some practice applying the concepts that we've talked about. I'll see you all in our next video.
The molecules that convert extracellular signals into intracellular signals are:
a) Neurotransmitters.
b) Hormones.
c) Cell surface receptors.
d) Intracellular receptors.
Which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?
a) Receptor tyrosine kinase.
b) G protein-coupled receptor.
c) Ligand-gated ion channel.
d) Steroid receptor.
e) Intracellular receptor.
Why does testosterone, a lipid-soluble / hydrophobic signaling molecule, not affect all cells in the body but only specific cells?
a) Only target cells have the cell surface receptor able to bind with testosterone.
b) Only target cells contain the genes regulated by testosterone.
c) Only target cells possess the phosphorylation cascade uniquely activated by testosterone.
d) Only target cells possess the intracellular receptor able to bind with testosterone.