in this video, we're going to begin our lesson on chemo taxes. And so recall from our previous lesson video that energy from a proton motive force or P. M. F. For short is used to move a cell towards a more favorable environment using its flow gela. And so the term chemo taxes can be defined as the movement of a cell towards a chemo attractant and away from chemo repellents. And so a chemo attractant is a chemical that attracts a motile cell and so cells are going to be moving towards a chemo attractant. And scientists refer to this as positive chemo taxes when a cell is moving towards a chemo attracted, now a chemo repellent, on the other hand, is going to be a chemical that repels motile cells. And so motile cells, cells that are moving are going to be moving away from a chemo repellent. And so scientists refer to this as negative chemo taxes. When the cells move away from a chemo repellent. Now photo taxes is a specific type of chemo taxes where the cell is going to be, the cell movement is going to be towards or away from light. And so you can see the photo route here is associated with light. Now, when the cell is moving towards light, we call this positive photo taxes. And when the cell is moving away from light, we call this negative chemo taxes. And so if we take a look at our image down below, we can get a better understanding of this. So notice on the left hand side over here, we're showing you how cells can swim towards a chemo attracted. And so notice that the chemo attractant over here is representing positive chemo taxes. And so notice that the cell is moving towards the chemo attracted in this direction from right to left and on the right over here, what we're showing you is how cells can also swim away from a chemo repellent. And so over here we're showing you a chemo repellent, which is going to promote negative chemo taxes. And so notice that the cell is moving away from the chemo repellent. And so this will allow the cell to move towards more favorable environments. Now, it turns out that the actual path that the motel cell takes towards or away from something is not going to be a continuous straight line. And so 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. And so 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 year concludes our brief introduction to chemo taxes and I'll see you all in our next video

in this video, we're going to talk more about cell motility during chemo taxes and so recall from our previous lesson videos that motile cells will use their flow gela and a run and tumble mechanism changing their directions during each tumble event. And the run events is what allows the cell to move smoothly in a single direction. Now, when an attractant such as a chemo attractant is present, a cell is going to begin to move in the direction of the higher concentration, the highest concentration of that chemo attracted. And so the cell has this amazing ability to be able to sense concentration changes and the ability to sense concentration changes comes through very complex cellular mechanisms and processes. But ultimately the cell can sense the concentration changes and is able to respond to the concentration changes by controlling the length of each run. And so what we'll see is that if the concentration gets really really low or too low, then the runs become longer until the concentration starts to get higher. And so when the concentration gets higher, then the runs become shorter and the cell knows that it's in an area where it is near the chemo attracted since the concentration is highest there. And so if we take a look at this image down below, what we're showing you is the swimming motility of a pair trickiest sell uh in the absence and presence of a chemical attractive. And recall that patrick. This is just the flu gellar distribution and how the flow gela are distributed along the entire surface of the bacteria and so on the left over here, what we're showing you is the swimming motility of a para trick to sell when there is no attractant whatsoever in the absence of an attractive and so notice that the cells movement is occurring in a series of runs and tumbles, runs and tumbles, runs and tumbles. And so every straight line represents a run and every corner represents a tumble, a change in direction. And so when there's no attracted notice that the the end result and the starting position is they're very close to each other. And so really the cell has made no progress, no net progress in terms of its overall direction, its overall movement, it's moved in a direction here, but it's now ending in a position that's very similar to its starting position. And so really there is no net movement when there's no attractive, however, noticed that in the presence of a chemo attracting, when there is a chemo attractive notice that the starting position is going to be very different from the ending position. And so notice that ultimately the cell is able to move towards the higher concentration. Uh and so notice that there is a higher concentration of the chemo attractant over here and the dark, shaded green and a lower concentration of the attractive uh brackets is uh something that means the concentration of, so we have, the concentration of the attractant is low on the left hand side of the box, and the concentration of the attractant is high on the right hand side of the box. And so notice that the runs are going to be really, really long or much longer when the concentrations are low and when the concentration start to get higher than the runs get shorter. And so the red lines represent the shorter runs when it when it recognizes that the concentrations are getting hired. And so ultimately what you can see is that the net movement is towards the attractant. The net movement is towards the attractive. So you can see the starting position and the ending position over here. And so the cell is moving towards the attractive. Now, if we were using a chemo repellent instead of a chemo attractive, then basically the opposite effect would occur. So the opposite effect would occur when a cell encounters a repellent or a chemo repellent. And so really what you can see here is that the movement of these bacteria is not in a straight, smooth fashion. Instead, it occurs in a series of runs and tumbles until the cell is making its way towards the area that has the highest levels of chemo attracting. And so this year concludes our brief lesson on cell motility during chemo taxes and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.