In this video, we're going to begin our lesson on chemotaxis. Recall from our previous lesson video that energy from a proton motive force or PMF for short is used to move a cell towards a more favorable environment using its flagella. The term chemotaxis can be defined as the movement of a cell towards a chemoattractant and away from chemorepellants. A chemoattractant is a chemical that attracts a motile cell. Cells are going to be moving towards a chemoattractant.
Scientists refer to this as positive chemotaxis when a cell is moving towards a chemoattractant. A chemorepellant, on the other hand, is going to be a chemical that repels motile cells. Motile cells, cells that are moving, are going to be moving away from a chemorepellant. Scientists refer to this as negative chemotaxis when the cells move away from a chemorepellant. Phototaxis is a specific type of chemotaxis where the cell movement is going to be towards or away from light.
The root 'photo' here is associated with light. When the cell is moving towards light, we call this positive phototaxis, and when the cell is moving away from light, we call this negative chemotaxis. If we take a look at our image down below, we can get a better understanding of this. Notice on the left-hand side over here, we're showing you how cells can swim towards a chemoattractant.
Notice that the chemoattractant over here is representing positive chemotaxis. Notice that the cell is moving towards the chemoattractant in this direction from right to left. On the right over here, we're showing you how cells can also swim away from a chemorepellant. Over here, we're showing you a chemorepellant, which is going to promote negative chemotaxis. Notice that the cell is moving away from the chemorepellant.
This will allow the cell to move towards more favorable environments. It turns out that the actual path that the motile cell takes towards or away from something is not going to be a continuous straight line because these cells move in a series of runs and tumbles. Those runs and tumbles are not going to allow the cell to move in a continuous straight line for a very long period of time. We'll be able to talk more about this idea right here in our next lesson video as we move forward. But for now, this here concludes our brief introduction to chemotaxis, and I'll see you all in our next video.
