字幕表 動画を再生する 英語字幕をプリント Hi. It's Mr. Andersen and in this podcast I'm going to talk about archaebacteria or archaea. Basically when we first discovered archaebacteria and separated that as its own domain, we thought they lived just in the harsh environments on our planet. So we discovered them in the hot pots of Yellowstone Park. We discovered them in the Great Salt Lake. We discovered them in swamps. And so we thought these archaebacteria kind of lived on the edges of life. But what we really hadn't looked everywhere. And once we started looking out here in the ocean we used a method called PCR. And that's polymerase chain reaction. It's basically a way to take a little bit of genetic material. So a little stretch of DNA. And then make millions and millions and millions of copies of it. And so we could actually study it. And what we found is that when we started looking in the ocean, you know almost 10 percent of all the life we were finding are archaebacteria. And so archaebacteria are everywhere. They're found in the gut of a cow, the gut of you. They're found everywhere. We just didn't really know what we were looking for. And so if we look on the phylogenetic tree of life, basically this is that first, right here we would say that last universal common ancestor that all life on our planet has. Basically we had a branch in this direction that went to form the bacteria. The domain bacteria. And then we had another branch that broke off and formed both the eukaryotes like you and then the archaebacteria. What does this mean? Basically you're more related to an archaebacteria than you are to a bacteria. But always remember this. That there's horizontal gene transfer. In other words there's like mitochondria that formed over here. And so there's probably quite a bit of this horizontal transfer back and forth. And so it's not as simple as that. But know that archaebacteria share more in common with eukaryotes then they do with bacteria. What are some characteristics then of archaebacteria? Basically they're prokaryotic. And that's a term that's lost meaning. But basically it means that they don't have a nucleus. And they don't have organelles. So they're not going to have their DNA separated in a nucleus. And they're not going to have things like mitochondria or golgi apparatus. So they're basically going to just be a cell. And that cell is going to have its genetic material on the inside in like a nucleoid region. So they're going to be that. They're still going to have cytoplasm. They're still going to have ribosomes. They're still going to have a lipid bilayer around the outside. Now one thing that they also have that's similar to bacteria is that they're going to have a cell wall. So there's going to be a cell wall that goes around the outside of the archaebacteria. And in bacteria this is going to be made up of peptidoglycan. But in archaebacteria it's not made of peptidoglycan. It's made of a simpler kind of a connecting subunit. So we call that a S layer. But the big difference between the two, the big difference between eukarya and archaebacteria is going to be found in the membrane. And so remember the membrane is made up of these things. They're called phospholipids. And so the phospholipids in your membrane are going to look just like this. They're going have a fatty acid hydrocarbon tail. And then they're going to have a glycerol head with a phosphate on the top. And so if you look at this one, this would be a phospholipid found in you or in bacteria. If we look at the ones found in archaebacteria, well there's a few things that are going to jump out. First thing that is going to jump out is that they're the mirror image, in other words, it's right hand meets left hand. And so the glycerol head is going to be pointed in the other direction. We're also going to have right here where it connects to the fatty acid tail, in us we're going to have what's called an ester linkage. So that's going to be right here. But in archaebacteria they're going to have a ether linkage. And then the other thing that they're going to have is these branched hydrocarbons. So those hydrocarbons are actually going to have little branches that come off of the side. And sometimes they'll actually form, instead of a bilayer like we have right here. They'll actually form a monolayer. And sometimes there will actually be chains or rings that form there. And so you might be thinking well why is that? Why is their membrane so different? Well a lot of archaebacteria remember can live in these harsh environments. And if you have a monolayer or if you have a more complex hydrocarbon tail you can deal with bigger temperatures, higher temperatures. And so also bigger fluctuations in pH. And so those are some of the characteristics of archaebacteria. How do they make a living? In other words what do they use for metabolism? Well basically just like bacteria, they're going to have a lot of ways to make a living. Some are phototrophs. That means they use energy of the sun. And example would be a halobacterium. Halobacterium are a type of archaebacteria that live in really high concentrations of salt. In fact their proteins don't even work unless the concentrations of salt are really really high. But what they're using is energy of the sun. They're using energy of light to do something similar to photosynthesis. They'll use a different, instead of chlorophyll, they're going to use a different pigment to pick up that energy. But it's similar. There are also things that are allied lithographs. Those are actually breaking down not organic but breaking down just simple chemicals to get energy. An example would be a methanogen. If you breakdown that word they're generators of methane gas. If you're looking for a great place to find methanogens, it would be in the gut. Like the gut of a cow. What they're doing is they're breaking carbon dioxide that's produce through cellular respiration. And then they're producing methane gas from it. And they're making a living out of that. So they're actually using chemicals, not feeding on life. And then we're going to have organotrophs. Those are going to be similar to us. They're breaking down organic material. An example would be sulfolobus. Those would be found like in hot pots for example of Yellowstone Park. Some of them can actually breakdown sulfur and add oxygen to it to make energy. But sometimes they're breaking down organic materials. And so we would point to these ones up here, phototrophs being those similar to plants that we have. And these being similar to animals. But again, there's quite a bit of different variety. How do they reproduce? Well there's going to be no mitosis. No meiosis. They reproduce just like bacteria. So basically they'll take their chromosome. And I should have pointed this out. This is another difference between us and archaea. Instead of having chromosomes that are linear. They're going to be in a loop. But basically when they want to reproduce they're simply going to copy their genetic material. And then they're going to split in half. And so we call that binary fission. Each of these are going to be identical to that original cell. But remember, just like in bacteria, they have what are called plasmids. Little bits of extra DNA. And they can exchange those with other archaebacteria. And they can get mutations. And so they can get quite a bit of genetic variability. But they live everywhere on our planet. So for example a termite is able to eat wood because they're going to have some archaea bacteria inside their gut that can help them breakdown that cellulose. They're also going to be really important inside the rumen of a cow. To help them digest food. But we also use it in like breakdown of sewer or sewage cleanup. Or we build biogas using archaebacteria. And so basically archaebacteria, they're prokaryotes. Single cell critters. They look a lot like bacteria, but they're actually more related to us. They live in harsh environments, but they also live everywhere else. And I hope that's helpful.