The Three Domains of Life
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The Three Domains of Life


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pardtx560tx1120tx1680tx2240tx2800tx3360tx3920tx4480tx5040tx5600tx6160tx6720pardirnatural f0fs28 cf0 Hi. It’s Mr. Andersen and in
this podcast I’m going to talk about life. I’m actually going to talk about a lot about
life. Because this is the first in a series of podcasts I’ll call life on earth where
I’m going to talk about the diversity of life on our planet. In this one we’re going to
talk about the general characteristics of life and the three domains of life. But in
each of the subsequent podcasts we’ll talk about viruses and fungi and plants and animals
and vertebrates and invertebrates. And so let’s get started. And so let’s start with
the history of life on our planet. So if the earth formed about 4.6 billion years ago,
life pretty much shows up when the crust starts to cool. So life actually could exist then
it does. First life on our planet is single cell. These are some of the most ancient fossils
on our planet. These are actually stromatolites. And these would be some modern day stromatolites.
Remember life on our planet, first life, had to be underneath the ocean because there was
so much UV radiation. Until we had an atmosphere life had to be underneath the water. But basically
it’s single cell, prokaryotic life. We have photosynthesis show up. And so oxygen starts
to accumulate. Then eukaryotic life, multicellular life, like 1 billion years ago. And then all
the things we think of as life. Like animals, plants, dinosaurs, flowers, those things show
up fairly recently in the evolutionary history of life on our planet. And so there are some
characteristics that all life shares. In other words if you don’t have all seven of these,
then you’re not alive. And so first one is homeostasis. Basically you can maintain a
stable internal environment. And we do that through the use of mostly negative feedback
loops. You have to be organized. We go all the way from atoms and molecules all the way
up to the level of biosphere when we’re talking about biology. But there’s organization. Most
life, in fact all life, is built on cells. Next you have to have metabolism. That’s the
sum of all chemical reactions you have inside that allows you to harness the energy or the
free energy available to live. You have to get bigger, grow, develop. You have to be
able to evolve or adapt over time. You have to be able to respond to your environment.
And then you have to be able to reproduce. Either sexually or asexually. And so if we
were to play the quick alive or not alive game, is bamboo alive? Yes. Is a panda bear
alive? Yes. Is lightning alive? No. Is a stomach alive? No. It’s not. It’s part of a living
thing, so it’s not able to adapt or reproduce on its own. It’s just part of a living thing.
And so when we’re talking about life, we’re not generally talking about viruses. We call
these things non-cellular replicators. And so they’re not classified as life. Now can
they evolve and change over time? For sure. But they do that, here’s some bacteriophages
injecting their DNA into a bacteria. They do that by using other cells to do the hard
work. Or to do the growth from them. And so when we look at life we classify life into
one of three domains. And so this right here would be the last universal common ancestor.
So that would be LUCA right here. In other words this right here would be the ancestor
that is shared by all life on our planet. And so basically it’s broken down into three
domains. We’ve got bacteria. So something like e. coli. We’re going to have archaea
bacteria. That’s going to be ancient bacteria. Things that would live like in the hot pots
of Yellowstone Park. And then we have eukaryotic life. An example of that would be animals,
fungi and plants. And so why do we classify life into these three domains? Because we
really started doing that, you know, just in the last 30 years did we come up with this.
And so basically let’s look at a venn diagram. This is a venn diagram right here. This would
be the eukaryotic cells right here. This would be the bacteria cells in here. And this would
be the archaea bacteria in here. And so first let’s talk about what’s in the middle. What’s
some characteristics that are shared by all life on our planet? Well, like we said they’re
made up of cells. They’ve got some kind of genetic material. So they have DNA and they
use RNA to do their work. What else do they have? They’re going to have a membrane around
the outside. A cell membrane or a plasma membrane. What else do they have? They’re going to have
ribosomes because they have to actually make a living. So they’re going to have to actually
use this DNA to make proteins. And then they’re going to have some kind of a cytosol or cytoplasm.
So all life on our planet shares all of this. But they don’t share all the characteristics.
So if we were to look at this, what is something eukaryotic life have, up here, that bacteria
and archaea bacteria don’t? Well they’re going to have a nucleus. That’s where the name comes
from. What else are they going to have? They’re going to have organelles. Now are all of these
multicellular? Not necessarily up here. But they’re definitely going to have a nucleus
and organelles. If we look down here at bacteria, what’s something that bacteria have that neither
of the other two have? Well just one thing to quickly get started, they have what’s called
peptidoglycan. So they have a chemical in a bacteria, so if this is a bacteria, they’ll
have their DNA right here in a circle. They’re basically going to have a chemical that makes
up the cell wall around the outside. And that’s made up of a chemical called peptidoglycan.
Luckily they have peptidoglycan because we can use antibiotics to actually kill them.
If we look over here at archaea bacteria, we classify them with the bacteria in a group
called monerans for a long period of time. But basically we realized that they don’t
have peptidoglycan. And they’ve got differences that make them their own domain. And so one
thing that you probably are familiar with is that archaea bacteria live in incredibly
harsh environments. But you probably didn’t know is that they have the characteristic
that makes them much different. So if we were to look at their membranes. This is going
to be a phospholipid. So if this is a phospholipid in a typical eukaryotic cell. So like this.
Remember our membrane is made up of a phospholipid bilayer. So it’s going to be a number of these
repeated over and over and over again. If you were to look at it in a eukaryotic or
bacterial cell it’s going to look just like that. But if we were to look at it in, let’s
find a different color, in an archaea bacteria, their’s looks way different. So they’re going
to have not only these hydrocarbon tails, but they’re going to have branched hydrocarbon
tails. So they’re going to branch off like that. And they also sometimes will form, so
if this is the other side, they’ll actually attach on either side like that and they’ll
form just a monolayer. So it’s going to be attached all the way across. And so this is
going to be a characteristic that just archaea have. Why do they have a membrane that looks
like that? Well if they live in a harsh environment, that allows their membrane to kind of stay
attached together when the temperature gets really high or the pH changes radically. And
so basically what scientists did is they looked at all the characteristics of archaea, bacteria
and eukaryea and they found that there’s a whole heck of a lot more in this area, things
that are shared by eukaryotes and archaea and not shared by bacteria and archaea. And
so we ended up classifying us more related to archaea bacteria then them. And so that’s
basically our three domains. But now we’re going to kind of work into more detail in
each of these different groups. And we’re going to spend a lot of time in the eukaryotes
because that’s what we are. And so that’s the first start. That’s life. And I hope that’s
helpful.}

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