 In this video, I'm going to talk a little bit about different types of cells. There are two main classes of cells. One of them is combined, bacteria and archaea. These are traditionally called prokaryotes. I'll tell you why I don't like that term in a minute. And then there's eukaryotic cells that tend to have a lot more complexity and structure. So the name eukaryote means has a karyote, means nut, and is probably because eukaryotic cells have a nucleus. Prokaryote means before nut, but not all bacteria and archaea evolved prior to eukaryotes. They're evolving today, just like eukaryotes are. And so we'll talk later about how bacteria, archaea and eukaryota are evolutionarily related to each other. But today I'm going to talk about the composition of the cells. So in both cases there is the boundary with cell wall plus a membrane. And these features keep the cell intact, keep all the things that the cells need on the inside contained within the cell and not letting say the DNA leak out. So the bacteria have their DNA in a single circular chromosome, and this is true of archaea as well. So they have a single circular chromosome. So this in bacteria and archaea, this chromosome is just inside the main part of the cell, which is the material that's supporting it in here is called the cytoplasm. The cytoplasm is full of organic molecules and enzymes and fibers that give the cell structure. There are plasmids, which are little membrane bound molecules that can have DNA inside them. There are other vacuoles, various things that can hold things the cell needs or things the cell wants to get rid of and compartmentalized. Bacteria and archaea can have various things on the outside. So for example, flagellum and pilus. The pilus are just little molecules that stick outside the cell that help it move by say attaching to other things and contracting whereas the flagellum spins around and helps propel the cell. So in general, the parts of the cell, I should also say that these little red dots, which are the ribosomes here, they are what take the genetic material and actually make those enzymes. And they are scattered throughout the cell, usually close to the DNA. So archaea and bacteria just have all of these components more or less dispersed in the cell. There'll be variations in the concentration and they're organized somewhat by these protein filaments, but it's basically not really subdivided. In contrast, eukaryotes have a lot of different subdivisions. And this light tan color here represents membranes that surround different organelles. And organelles are basically sites with specific functions. So much like the cells have a cell wall and a plasma membrane that holds it in, organelle has its own membrane that helps concentrate the activities of that organelle into a single location. So this particular one with the genetic material in it is the nucleus, of course. And surrounding it is the endoplasmic reticulum, the rough one and the smooth one. And that endoplasmic reticulum holds the ribosomes. The chromosomes are, of course, inside the nucleus and they are strands of DNA that are packaged into intercoils. But they aren't in the circular form that we have in the bacteria and archaea. The endoplasmic reticulum holds the ribosomes close to the nucleus because the ribosomes are what take the genetic material when genes are expressed, the messenger RNA, and convert it into enzymes. Having those really close to the genetic material makes it more efficient for those messenger RNA molecules to actually get to the ribosomes. There are some ribosomes scattered throughout the cells as well. Almost all eukaryotic cells also have mitochondria. These mitochondria are the places where the cells react the organic matter and the oxygen to produce energy. So in bacteria and archaeal cells, a lot of that reaction, those reactions actually occur in the plasma membrane. But in eukaryotic cells, they're concentrated within these mitochondria which have a membrane around them and then membranes inside where the enzymes that extract the energy are actually embedded. And then eukaryotes often also have like gold diaparatus which helps shape proteins. And they have a lot of these protein fibers that structure the cells. These strands and filaments hold the nucleus in place, the mitochondria in place, and help shape the cell structure. In eukaryotes, they also have little molecular motors that can track along some of these filaments. And these motors help deliver different enzymes, different compounds to different places in the cell where they're actually needed. So there are lots of other things that can be in eukaryotic cells. But one of the main differences between the eukaryotes and the archaea is really this localization of function into specific areas of the cell. So here in this case, the function are compartmentalized. So one of the interesting things about this compartmentalization is it can be seen in the mitochondria. So there's a little bit of DNA that's in the mitochondria that is outside the nucleus. Most of that the DNA in eukaryotic cells is in the nucleus. But the mitochondria have a little bit of their own. And when we look at this DNA and the sequences, it actually is the DNA that's very closely related to bacteria and a very specific type of bacteria. And that DNA plus the actual structure of the mitochondria has given rise to this idea that the mitochondria actually evolved from bacteria. Originally the mitochondria were free living bacterial cells that started living within a host eukaryotic cell some billions of years ago, and then eventually became completely merged with the eukaryotic host cells except for this little bit of DNA. And that process is called endosymbiosis. Endo means inside and symbiosis is one of those reactions that we talked about that's mutually beneficial. So it's a mutually beneficial relationship where the bacteria produces energy for the host cell and the host cell provides a consistent environment for the bacteria through that process of homeostasis. And so this is the case where eukaryotic cells, all of them that have mitochondria actually represent the merger of two different ancestral life forms. One from bacteria and one from the beginning of the eukaryotic cell line. Thanks for watching.