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  • 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.

Hi. It's Mr. Andersen and in this podcast I'm going to talk about archaebacteria

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B1 中級

古菌 (Archaea)

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    Cheng-Hong Liu 發佈於 2021 年 01 月 14 日
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