you one of my very favorite topics when we talk about eukaryotic cell structure is to spend a few minutes talking about the origins of mitochondria and chloroplasts we know that the firt the last Universal common ancestor was a very simple prokaryote and yet when you look at life today there's all this diversity including many really complicated and and specialized eukaryotic cells and so one of the questions that evolutionary biologists have asked is you know how do we go from a prokaryotic cell to a eukaryotic cell and the first person to propose a plausible theory that's that's really been accepted now and it's in the textbooks it was a woman named Lynn Margulis she died I believe in 2011 or 2012 the People magazine story here is that she was married to Carl Sagan who was the person who did the original cosmos if you you're old enough to remember the original cosmos in the 1980s and he left her for a younger woman if you're interested in the the gossipy details that said lynn margulis and they have a son together so Carl Sagan's only child was with Lynn Margulis I digress her theory which is incredible and she got a lot of flack for it and persisted and now it's been like I said it's in every textbook her theory was that larger bacteria and we're thinking now one and a half billion years ago and and we just have prokaryotes but some larger ones began to develop some sub structures and engulf smaller bacterial cells and that these smaller bacterial cells provide functional structures became functional structures inside to larger cells and that this is where mitochondria and chloroplasts came from this is a wonderful video and what I'm going to do is put a link to it on the slide I encourage you to spend a few minutes watching it it'll it'll it's not completely necessary so it's not required but it's something that I often show in class if I have time and it'll sound better if you watch it from the link rather than if I play it from my computer alright so here's an Oh symbiotic theories this is what we think happened we have our proto eukaryote so this is that and festival cell and it's a prokaryote you see it's got no nuclear membrane and the first thing that happened was that plasma membrane began to fold inward and it gave rise to the original nucleus and endoplasmic reticulum and serviced first parts of the endomembrane system and that after this happened what you ended up with was some small aerobic bacteria bacterium that could survive the presence of oxygen which we know had increased in the atmosphere a great deal at this point and that these these proto eukaryotes ended up absorbing these aerobic bacteria and then instead of digesting them and using them for food they took advantage of these aerobic bacteria their capability of actually using oxygen and generating a tremendous amount of ATP and eventually these bacteria lost the ability to live freely they became dependent on this heterotrophic eukaryote for for food but they were able to provide a way for them to sell to make a lot of energy by the same token these cells some of them also took up photosynthetic bacteria and some of those bacteria became our modern photosynthetic eukaryotes and the mechanism is mechanism is similar the idea here is that these provided an advantage to the cell because they were able to use energy from the Sun and generate sugars which the salt leaves self-feeding the cell could use for food so in this particular case and of course these are two separate paths at this point because we know we have both heterotrophic eukaryotes and photosynthetic eukaryotes present on earth today but these would be the precursors to modern plants and these this would be the precursor to modern animal cells that we would see all over the planet if you just look around one of the things that I like students to be able to do is describe the evidence for lynn margulis theory and so let's go over some of the arguments that she made in favor of endosymbiotic theory so one of the arguments was that prokaryotes have a single circular chromosome we've talked about that earlier and when you look at mitochondria and chloroplasts in eukaryotic cells and photosynthetic eukaryotes they also have a single circular chromosome so these salesmen you know they they their genetics look a lot more like a prokaryote than a eukaryote eukaryotes again have multiple linear chromosomes you have 23 pairs and they're there in the nucleus when a prokaryotic cell divided that uses a process called binary fission it's basically it makes a copy of its DNA and splits into two and that's exactly how eukaryotic mitochondria and chloroplasts divide they just make a copy of their DNA and divide into two but we know that our eukaryotic cells are actually very complex they go through a process of mitosis so maybe you remember prophase anaphase telophase I forgot metaphase in the middle there right you've got those those all those steps prophase anaphase metaphase sila face I think I've got them in order so so it's a much more complicated process and and the replication in mitochondria and chloroplasts is much more similar to bacteria remember those pesky 70s ribosomes in prokaryotes guess who also has them mitochondria and chloroplasts so really this is a very strong argument that these structures originated from these cells and not from some evolutionary process after eukaryotes were formed the electron transport chain in the prokaryotic cells is found in the plasma membrane and this is also true of mitochondria and chloroplasts however in eukaryotic cells the electron transport chain is found only in the mitochondria in chloroplasts so it would make sense that this originated from these ancestral prokaryotes the size of a prokaryotic cell is between 1 and 10 microns exactly the same size of mitochondria and chloroplasts but eukaryotic cells are typically much larger think of that University of Utah cell size and scale interactive that we talked about at the beginning of this lecture lastly anaerobic bacteria showed up about 3.8 billion years ago photosynthetic about 3.2 and aerobic bacteria about 2.5 so these are you know this sort of falls in line with what we understand about the oxygenic events were developed although so to guess and these are developing at different times but evidence for eukaryotic cells mitochondria and chloroplasts indicates that they all showed up at exactly the same time it doesn't indicate that you that these formed later and this came first so it really does make sense that these all formed at the same time by an ancestral prokaryote taking up other solar prokaryotes that became today as mitochondria and chloroplasts so that's the evidence and you should be familiar with this in case it shows up on a test alright and again this is just summarizing the evidence that we have sighs about a country and chloroplasts the idea that the inner membranes have bacterial proteins and that's actually not on the chart but when you look at some of the inner membranes of mitochondria and chloroplasts they have proteins very similar to their bacterial ancestors the idea that they divide by binary fission they have a single circular chromosome and they have a much more similar ribosome to prokaryotes so they have those 70s ribosomes instead of the 80s ribosomes that we associate with eukaryotes we also can look at relationships with modern bacteria so if you look at chloroplasts they actually very similar to a cyanobacteria I have a picture to show you in a moment and then mitochondria resemble members of the purple bacteria the rise of bacteria that a grow bacteria and the Rickettsia so it we there's other evidence to just comparing these structures with modern bacteria that may have been there the ancestors of these bacteria may have been the ones that became mitochondria and chloroplasts all right and this is a nice comparison of a cyanobacterium with a chloroplast and you can see how many structures now some of them are individual but in this zone here you know all of these structures are found in both a chloroplast and a mitochondria so you can see that there's an awful lot of similarities between these two all right that's our last slide for this lecture set next time we are going to talk about viruses and viral structure in the viral life cycle