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Main content
Current time:0:00Total duration:8:02
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Video transcript

all the examples of cell cell signaling that we've looked at so far have been cells within an organism but what I want to do in this video is point out that you can also have cell cell signaling between different organisms and even between different unicellular organisms and so what we have here these are pictures of yeast cells yeast are unicellular eukaryotic organisms which means they have they have a nucleus and they are officialy fungi and what you see happening in this in this picture right over here it looks like you have a second East cell budding off of the first one this happens fundamentally through mitosis but yeast can actually reproduce in two different ways it can reproduce asexually through mitosis like this but it can also reproduce sexually and that's where we're going to talk a little bit about signaling between the cells and they do this with mating factors and this is just an interesting discussion of yeast generally so if you start with a yeast cell so this is a yeast cell right over here and this is a diploid yeast cell so it has its full it has its full complement of chromosomes so it's going to have 16 16 pairs 16 pairs of chromosomes or 32 total chromosomes that's a diploid so through mitosis it could split apart and it would do so like this the the one that buds off for most for most species of yeast will be smaller although there's some that kind of do more even mitosis but through mitosis you could throw mitosis you could produce two diploid two diploid East tails just like this so all of these characters all of these characters right over here are diploid and actually since just a stress that they are eukaryotes let me draw a little nuclear membrane in here but it can also it can also divide through meiosis so this is mitosis right over here mitosis right over your help produce these two but you can also go through meiosis meiosis and if we go through meiosis we're going to produce four cells and what's interesting about these is that these will have will come in one of two varieties and you could view these as the sex of these East cells so they can either be in the type-a variety so let's make these two type a so that's a type a that's a type A right there or they could be in the type alpha variety so this is a reduce in a different color so this is a type alpha and this is another type alpha and all four of these are going to come through meiosis from this original diploid cell and since we went through meiosis each of these are going to be haploid so these are all going to be haploid so this is going to be 16 chromosomes total 16 chromosomes chromosomes each of them so they're all going to be they're all going to be haploid and in fact each of these can some degree live a life of their own and continue to reproduce through mitosis that's worth pointing out that's interesting you normally wouldn't associate sex cells if we think about humans you wouldn't associate you wouldn't think that sperm cells would be able to replicate on their own or egg cells would be able to replicate on their own but in the case of yeast they actually can so this this type a cell could turn into through mitosis it could turn into to type a cell's so this is just all interesting background mitosis so even the products of meiosis can then my toast themselves with this if that's all interesting this is all the setup to think about how they actually signal because these these haploid cells that are produced as a byproduct of meiosis these are these right over here they all came from the original ancestor which is actually fairly typical when we're talking about reproducing and kind of pseudo sexually reproducing yeast cells they don't have to the may be one of the type alphas came from another ancestor but what happens is they each release what's called mating factors or you can consider them to be mating pheromones so this type a right over here it's going to produce and it's going to produce the type a mating factors and it's going to release them into the space around it so it's releasing the type a mating factors and then the alphas are going to release the type alpha mating factors so I'll do that in this drawer in just brown color so they're going to release the type alpha mating factors and what happens is each type has receptors for the other types factors so so this the type a is going to have receptors for the type alpha for the type alpha it's going to be in all over the outside of the cell and the type alpha is going to have type receptors for the type a receptors I'm going to that an orange it's going to have receptors for the type a let me just draw it like that that's not exactly what they look like or actually nowhere close to what they look like but it gives you a sense of things it gives you a sense of things and as through these receptors it starts bonding a lot of say we're on the Alpha cell right over here it starts bonding to a lot of these these mating pheromones these mating factors then the yeast cell itself it doesn't move but it starts growing in that direction it starts growing in the direction where it says hey I'm sensing a lot of this mating factor so it starts growing in in this direction it starts doing something like that and the corresponding thing is going to happen for the type a cell it's going to have the Alpha factors attached on to it and because of that says okay I'm sensing and once again the the the factor is the ligand it attaches to the receptor that's the sensing part then you have signal transduction and it's actually a it's not too dissimilar from the map K the the the map K transduction pathway that we talked about in other videos and then the response to cell has is once again to start growing in the direction of where it fight where it seems that these mating factors are coming from and these this kind of elongation these outgrowths of these haploid yeast cells they're actually called schmooze so that right there that is a shmoo and you might say where did that come from what came from this character right over here which was a cartoon character in the in in the middle 20th century and I'll you know if you were well it well it will so avoid any snickering and over the course of this video but that's what it looks like and as they grow to each other that actually allows them to join together and form another diploid another diploid yeast cell so this process were to continue if this process were to continue these two schmooze will join together and the the genetic makeup joins together and so we could get another diploid cell and now this diploid cell is going to have a kind of new new combination of DNA so it could benefit from some of the variation of sexual sexual reproduction this is diploid although for yeast cells they're like studying it because it's not clear that these are necessarily coming from a separate gene pools these actually could have the same ancestor molecule so it is a bit of an open question in biology of why do they have you know this type of sexual reproduction especially when they're coming from you know when these are centrally sibling cells as the byproduct of meiosis but anyway the whole point of this is one to appreciate kind of these fascinating things that are happening even at the level of yeast cells and that you do have cell cell signalling not just within an organism but across organisms especially it or even unicellular organisms
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