Our example gives us the steps of a signaling cascade, and it wants us to put them in order by writing the correct letter on the blanks here. So, before we do this, remember, we had a memory tool for remembering the cyclic AMP signaling cascade. I'm going to write that out first. My memory tool was "Holding really great activities at camp kinase". The first letter of each one of those words matches up with one of the major players, one of the molecules in each one of these steps. So, as we go through, we see the order here is going to start with a hormone binds an extracellular receptor. Well, that's our first two letters here with the hormone binds a receptor binds to a receptor. I'm going to cross those out because we already have those down. And then we're going to say, well, from the receptor, we go to something with the 'g'. The receptor activates a G protein. So, I think that's going to be my next step. And there it is. C, the G protein, is activated. So, I'm going to put C on the line here, and I just cross this out to keep things organized.

Alright. So then we go from our G protein to something that starts with an 'a'. Remember, the G protein activates adenylate cyclase. Alright, and adenylate cyclase is activated. That's right there. That's option D. So, I'm going to put D on the next line, and I'm going to cross this out again just to keep things organized. Alright, so now our adenylate cyclase enzyme is activated and adenylate cyclase is going to go to cAMP. Well, cAMP stands for cyclic AMP, so adenylate cyclase is going to produce cyclic AMP and that's option B here. ATP is converted to cyclic AMP. So I'm going to write B on my next line, cross this out down here just to stay organized, and then finally, cyclic AMP is now in the cytoplasm, and it's going to go bind to a kinase. Alright. Well, look at that. Our option here a protein kinase is activated. It's activated when cyclic AMP binds to it. So, that's going to be A is next and the kinase is going to go out. Kinase phosphorylates protein, so it's going to phosphorylate all sorts of proteins and that's going to lead to our cellular response. And we did it. We got from a hormone that can't cross the cell membrane. It's stuck on the outside of the cell. We went through this signaling cascade using secondary messengers to initiate a cellular response. That's how we do it.