So now that we know from our last lesson video that cell signaling requires a minimum of 2 key components, the ligand or the signaling molecule and the receptor. In this video, we're going to focus on the 3 steps of cell signaling. And so cells receive external signals in a series of 3 steps that we have numbered down below, number 1, number 2, and number 3. And so the very first step of cell signaling is going to be reception or in other words, ligand binding. And so in this first step of reception, the ligand or the signaling molecule is going to bind to a very specific receptor causing the receptor to change its conformation or to change its shape. And so if we take a look at our image down below, what you'll notice is, here, this membrane represents the cell's plasma membrane that's separating the outside of the cell from the inside of the cell. And so over here on the left-hand side, what we have is the outside of the cell or the extracellular fluid. And over here on the right-hand side in the yellow background, what we have is the inside of the cell or the cytoplasm. And so notice that embedded here within the membrane is a receptor, and the signaling molecule or the ligand is here in red. And so in the very first step of cell signaling, which is again reception, what happens is the ligand or the signaling molecule here is going to bind to its receptor, like what we see here. The ligand is now bound to the receptor. And when the ligand binds to the receptor, it's going to cause a conformational change in the receptor, which will lead to step number 2 over here.
And so in step 2, what we have is transduction. So after the ligand binds to the receptor and causes a conformational change in the receptor, this is going to lead to a pathway of interactions in the cell that ultimately is going to transduce as implied by transduction, or, in other words, convert transduce or convert the signal, to change to a change within the cell. And so in the process of transduction, there's really just gonna be a series of interactions, and this series of interactions is ultimately going to convert that external signal or that external ligand, into a change within the cell. So let's take a look at step number 2 down below right here. And so notice step number 2 is transduction. And so with transduction, there's a series of events. Notice that we have, a, b, and c here within step number 2. And so in transduction, what happens is the conformational change within the receptor from step number 1 is gonna lead to, a series of events where, some molecule is going to become activated, which could lead to the activation of another molecule, which could lead to the activation of another molecule, and so on. And ultimately, the transduction step here is going to vary significantly between different pathways. But ultimately with transduction, there's gonna be a series of events, and at the end of transduction, it leads to the last step, which is the cellular response. And so that is our step number 3 of cell signaling. And so the cellular response is going to be the end result of the cell signaling pathway that is going to end up causing a physical or chemical change in response to the extracellular ligand that originated. And so the signaling molecule or the the ligand ultimately is going to be triggering this cellular response. And so the cell response is generated, in response to the extracellular signaling molecule or the ligand. And so, really this here concludes our introduction to the 3 steps of cell signaling. And, again, as we move forward in our course, we'll be able to talk more and more about cell signaling. So I'll see you all in our next video.