January 18, 2011

018 Agonists and Antagonists

In this video, watch as Leslie explains how agonists and antagonists affect the receptor sites of the cell.


Transcript of Today’s Episode

Hello and welcome to another episode of Interactive Biology TV, where we’re making biology fun! My name is Leslie Samuel. In this episode, Episode 18, I’m going to be talking about agonists and antagonists. It almost sounds like a plot for a movie, but it’s not a movie, unless it’s a movie happening inside your body. Anyhow, for today, let’s get into what we’re going to be talking about.

The first thing we’re going to talk about is “What is an agonist?” An agonist is a molecule that mimics the effect of a neurotransmitter, so it does what that neurotransmitter would normally do. An example of that would be succinylcholine mimics the neurotransmitter acetylcholine. So what I’m going to do is I’m going to draw the receptor here, and here we have the cell membrane of the neuron. I’m going to draw it a little different than I’ve been drawing it before. I’m going to have these as the receptor sites. This is where the acetylcholine normally binds to the nicotinic receptor.

I’m going to draw acetylcholine here, but I’m not going to draw it coming here. What I’m going to do is I’m going to draw something that’s slightly different, let’s just say it’s a different color. It’s a similar shape to acetylcholine, and we’re going to call this succinylcholine. When that comes here and it binds to the receptor, same thing here, it comes and it binds to the receptor, the channel opens, which is what it would normally do if acetylcholine binds. And then, sodium ions on the outside end up coming inside the cell. So this would be an example of an agonist. It’s not acetylcholine, it’s something else, and let’s say, in this case, it’s succinylcholine, and that comes, binds to the receptor and causes a similar response. That is an agonist.

Now, let’s look at what an antagonist is. You can probably guess just by reading the word, but an antagonist is a molecule that opposes the effect of a neurotransmitter. So it does the exact opposite. An example of that would be curare, which is an antagonist to acetylcholine that can actually block the binding sites for acetylcholine. So here, we have our nicotinic receptor again, and it’s in the membrane of the cell, and here we have the binding sites.

Out here, we have acetylcholine that wants to bind. However, we have something else that’s around that’s not exactly like acetylcholine and let’s say that its shape looks something like this. That binds to the receptor, and what that does is it blocks the receptor site. So acetylcholine wants to bind and it wants to cause that channel to open, but it’s being blocked so that it cannot bind, and it cannot open the channel for sodium to come in. This would be an example of what curare does. It’s an antagonist, and in fact, curare can cause muscles to become paralyzed because they cannot be activated and sodium cannot rush into the cell, exciting the cell, and exciting the muscle to contract. So that can be a serious thing if you have curare binding to these receptor sites.

That’s really all for this video. I hope you understand the difference between an agonist and an antagonist. If you have any questions or comments about that, go ahead and leave them below. I’ll be happy to answer your question, and maybe even make a follow-up video answering your specific question. That’s it for this video, and I’ll see you on the next one.

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