[Music] hi it's Mr Anderson and in this podcast I'm going to talk about one of my favorite topics in all of biology and that's Endo symbiosis if you didn't know this there are two major groups of cells we have procaryotic cells and then we have eukaryotic cells an example of a procaryotic cell is like a bacteria they simply have a cell membrane cell wall all of their DNA is organized in a nucleoid region um and and they're fairly simple and fairly small in a eukaryotic cell we're going to have a nucleus we're going to have organel like endoplasmic reticulum gogia apparatus um mitochondria but what we find is when we look in the fossil record life started about 3.6 billion years ago and we just see procaryotic cells for the longest of times in other words we don't see eukaryotic cells show up until around two billion years ago and it puzzled scientists how this shift was made because there are clearly two different evolutionary Pathways the pathway of the small procaryotic cells and then the larger eukaryotic cells and they eventually settled on an idea called endosymbiosis and what does that mean well let's break it down Endo means within symbiosis means together and bio just means living and so basically we have organisms that are living together within one another so that's weird what does that mean well basically when I read about this the first time it puzzled me um what we think is way back in the day we had these aerobic bacter ones that were doing cellular respiration so they were breaking down food in the presence of oxygen we also had these cyanobacterium that were doing photosynthesis and they were essentially engulfed by another host cell and they became the mitochondria and the chloroplast that we have today and so that's pretty cool in other words these cells became part of a cell and eventually became that cell that means that the mitochondria that are found in all of your cells are kind of like hijackers that have been inside our cell for billions of years now you can see why scientists would have a hard time kind of believing that this is true in the first scientist to really be a proponent of endosymbiotic evolution in eukaryotic cells was Dr Lyn margulis and in the 1960s I think in 1967 she wrote an article a journal article talking about this this idea that maybe this is how mitochondria and chloroplast came to be she shopped it around and no scientific journals would pick it up after going to about 4 14 different journals one journal on theoretical ideas eventually published it and it was kind of you know not laughed down but it was kind of uh put aside for a long period of time and that's because there wasn't a lot of evidence that showed that this was true but Dr M margul kept working and working and working and pretty much today we accept this as scientific fact or as close to fact as it could be and so I wanted to start before I get to the evidence of why this is probably true to talk about how symbiosis works on our planet planet and so you're maybe familiar with symbiotic relationships maybe like the enemity and the clown fish but it becomes way more intimate than that and so this is a type of coral and this Coral can do photosynthesis but Coral is an animal so how does it do photosynthesis well basically they have an algae called symbiodinium it's a type of dinoflagellate and this is eaten by the Coral in other words the coral is taking in this algae just like it would be taking in food but it doesn't break it down it doesn't destroy it the algae lives within the coral and you can see in this electron microscopy you can see these little individual algae cells that are found within the tissues of the coral and so what is it doing it's producing food through photosynthesis and that food is then taken in by the coral and return the coral is giving it a place to live and so we think something like this happened you know billions of years ago and that created these first eukaryotic cells well what evidence do we have that this is true well let's just take a look at two so basically we have a type of bacteria that looks a lot like a mitochondria they have a lot of similar properties and so what evidence do we have that mitochondria came from bacteria well that membranes are going to be very similar in both of these and the mitochondr we have this double membrane we're going to see the same thing in these bacteria the way they reproduce is very similar now eukaryotic cells how do they reproduce basically they copy their chromosomes the chromosomes line up in the middle and then it divides in half and we call that mitosis now that's not what happens in bacteria bacteria are going to copy all their DNA and then they just pinch in half and we call that binary fision what we find is that even in your cells the mitochondria are making copies of themselves through a process of asexual reproduction that looks a lot like um asexual reproduction in bacteria and so this is another piece of evidence but why this really this idea was set aside for a long period of time is that the the technology to answer this question wasn't quite there and once we got DNA and the ability to look at the actual nucleotide sequences within the DNA were we able to compare the DNA in these procaryotic cells and in the mitochondria and we find that it's very similar what does that mean mitochondria have their own DNA so they're like a cell within our cell and so this is coding for proteins that are used by the mitochondria and this DNA looks a lot like a specific type of bacteria and so again all of this evidence is piled up and so we now believe that this is one of the ways that cells became eukaryotic we think they also may have infolded in other words the membrane may have folded in on the side to create some of the complexity but we're pretty sure that chloroplast and mitochondria came through this idea of endosymbiosis and so I remember reading about that and then thinking of this question and I think it's a pretty good one and a lot of my smart students will come up with this and the idea is okay if mitochondria are within our cells but they weren't technically part of our cells then how are they copied from generation to generation in other words where do I get my mitochondria from well you can thank your mom for that and so basically what happens is in an egg cell in your mom we've got a nucleus and but we also have all these other parts of a cell and so in that egg cell you're going to have a bunch of mitochondria mitochondria that have been passed from mother to daughter to mother to daughter All Through Time and so basically what happens is when that egg is fertilized by a sperm the sperm doesn't bring mitochondria with it it just gives genetic information because the mitochondria are already there and so when that cell splits in half we've got mitochondria in each of those individual cells and so mitochondria used to be cells of their own they're now obligate symbient inside us that means that they can't live on their own but we have this wonderful relationship where we let them make energy for us and in Plants they have chloroplast and mitochondria that came from the same Origins and so that's endosymbiosis and I hope that's helpful