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PROFESSOR:So lecture
one, introduction.

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00:00:39,980 --> 00:00:42,520
When people teach biology at
different universities, they

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00:00:42,520 --> 00:00:46,230
teach many different things.

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00:00:46,230 --> 00:00:48,780
You could focus on
the ecosystem.

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00:00:48,780 --> 00:00:52,300
You could focus on memorizing
different phyla.

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You could focus on
many things.

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00:00:54,170 --> 00:00:56,370
Biology is huge and diverse.

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We have a certain point of
view in the way we teach

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7.012, and really a point of
view in the way that MIT

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00:01:02,450 --> 00:01:04,680
organizes its biology.

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00:01:04,680 --> 00:01:10,180
And so I want to point out the
levels of organization of life

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00:01:10,180 --> 00:01:12,440
and indicate where we will be.

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You could decide to study
the entire biosphere.

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00:01:23,560 --> 00:01:26,570
By the biosphere, I
mean everything.

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All the world's ecosystems
working together to create a

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happy, healthy living planet.

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00:01:37,400 --> 00:01:43,570
There are, oh I don't know,
something like 10 to the sixth

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00:01:43,570 --> 00:01:48,640
eukaryotic species on this
planet, more than a million

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species of things you can see
with your eye, and there are

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10 to the God knows how many
species of microbes.

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00:01:55,690 --> 00:01:59,180
And in fact, it's even hard to
define species for microbes.

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So it's a fantastic diversity.

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00:02:02,180 --> 00:02:06,320
And if we think about examples,
the number of

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00:02:06,320 --> 00:02:12,940
examples of biospheres that
we are aware of is one.

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00:02:12,940 --> 00:02:15,020
Currently, it's the earth.

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There might be other biospheres,
but we're not

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00:02:17,160 --> 00:02:18,780
aware of them.

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00:02:18,780 --> 00:02:22,110
Alright, that's one level
of organization.

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00:02:22,110 --> 00:02:24,420
We will have virtually nothing
to say about that level of

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00:02:24,420 --> 00:02:29,200
organization other than
that we're fond of it.

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00:02:29,200 --> 00:02:31,143
Next, you can study
an ecosystem.

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00:02:35,110 --> 00:02:36,850
Now what do we mean
by ecosystem?

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00:02:36,850 --> 00:02:54,170
That's some interacting
community of organisms, like a

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00:02:54,170 --> 00:02:57,700
forest, let's say.

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You've got trees, and you've
got, oh I don't

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00:03:01,970 --> 00:03:05,530
know, mice and deer.

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00:03:05,530 --> 00:03:08,780
And you've got fungi growing
down there on the bottom, and

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00:03:08,780 --> 00:03:12,920
maybe you have, I don't know,
some MIT student walking

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00:03:12,920 --> 00:03:14,880
through the forest or
something like that.

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That's all part of
the ecosystem.

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00:03:17,620 --> 00:03:22,000
Alright, now the next level down
you could think about is

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whole organisms.

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So here we're talking about one
individual, an individual

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00:03:30,990 --> 00:03:32,240
in a species.

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00:03:36,140 --> 00:03:38,380
And one can study how does
that individual work, the

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levels of physiology within
an organism, the overall

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integration of signals, the
distribution of oxygen across

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the body, things like that.

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This is a popular
topic to study.

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We'll have a little bit to say
about physiology, but that

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won't be our major focus, that
whole organismal level of

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physiology.

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Example of an organism, say a
human, in particular, let's

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say an MIT student.

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OK.

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Next up, we could study
an individual organ.

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So by an organ, I'm thinking
about some part of the

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organism that's a group of
tissues that are organized

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together to carry
out a function.

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So it's a group of tissues that
are organized to carry

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out a function.

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And we have the eye, the
eye on that human.

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So we've got these
muscles here.

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We've got some photoreceptors
there on the back, and they

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send back nerve terminals
going there.

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All these tissues working
together to provide vision.

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OK.

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Going down one level below
that we have tissues.

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These are more homogeneous
groups of cells.

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So we could have,
say, the retina.

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Then those tissues are
made up of cells.

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So cells of course are bounded
by a membrane.

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They have nuclei, at least
in eukaryotes.

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So let's say within the retina,
we could pick a

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photoreceptor cell.

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So the MIT student is walking
through the forest and with

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her eye is getting light
on the retina, which is

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triggering photoreceptor
cells.

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They each have a distinctive
shape, and that shape--

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there's our nucleus.

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The light comes and impinges
there, sends a signal

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out the other end.

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00:06:23,465 --> 00:06:23,870
OK.

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That's a cell.

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Then we get down
to organelles.

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These are distinct components
within a cell.

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For example, this photoreceptor
is using up a

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lot of energy.

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It has mitochondria.

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These mitochondria in here
are involved in producing

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00:07:05,660 --> 00:07:08,990
efficiently ATP.

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00:07:08,990 --> 00:07:12,165
And then finally, we
have molecules.

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A wide variety of different
molecules in the cell: sugars

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and DNA's and-- but I'll say ATP
will be our example here.

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00:07:29,680 --> 00:07:30,630
Molecules.

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So if you think about it, we
have sets of levels of

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organization, all the way up
there from biospheres to

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ecosystems to organisms to
organs to tissues to cells to

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organelles to molecules.

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And biology thinks about all of
those different levels, and

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in principle, they
all interact.

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00:07:46,020 --> 00:07:49,230
Of course, it's somewhat hard
to keep in mind, say, the

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connection between the entire
biosphere and a ATP at any

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given point.

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It's a bunch of levels
going up and down.

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00:07:55,910 --> 00:07:59,625
At MIT, we tend to focus more
on the bottom of the picture

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00:07:59,625 --> 00:08:01,730
than the top of the picture,
and that's what this class

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00:08:01,730 --> 00:08:03,450
will focus on.

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You run the risk that you'll
forget there is a top of the

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00:08:05,600 --> 00:08:08,210
picture, that there are
ecosystems, there are

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organisms, physiology
and all that.

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Oh well.

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What can I say?

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Why do we focus the bottom
of the picture?

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Why do we focus so much on, say,
the molecules of life?

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You're going to get a lot of
molecules of life in the

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00:08:21,460 --> 00:08:23,460
beginning of this course.

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00:08:23,460 --> 00:08:24,920
We're going to focus on--

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00:08:24,920 --> 00:08:26,750
we'll think about organelles
and cells.

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You'll hear less about tissues,
less about organs,

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00:08:29,500 --> 00:08:32,280
less about organisms
as a whole.

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And the reason is life is most
universal down at its bottom.

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That is what's shared
across all life.

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Rather than, say, focus on
the glorious, wonderful

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differences between all the
different phyla and learning

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00:08:50,020 --> 00:08:52,570
all sorts of genuses and of
all sorts of interesting--

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we want to focus on that which
is most universal.

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Now, there are some
differences.

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We will look differently at
microbe, prokaryotes versus

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eukaryotes and all.

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But for the most part, what
we're trying to do is ask what

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00:09:03,880 --> 00:09:09,710
are universal principles that
apply across all organisms?

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What are the ways organisms
are built up?

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Commonalities, like the genetic
code, that applies

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pretty broadly across all
organisms, commonalities of

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signalling systems, regulatory
systems.

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Things like that are what we're
most interested in,

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because once you learn that,
it's much easier to layer on

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00:09:25,910 --> 00:09:28,750
top of it the differences, the
unique differences, that makes

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00:09:28,750 --> 00:09:32,830
a fruit fly a fruit fly
or a tree a tree.

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00:09:32,830 --> 00:09:36,680
So anyway, that's our
perspective on it, and I hope

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you like it.

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But it's the only prospective
we've got, so there you go.

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Next, a few dates
to keep in mind.

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Important dates in the
history of life.

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Again to provide perspective,
we're not going to focus on

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lots of them, but a few
that you should know.

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About 4.0 billion years ago--

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BYA means billion years ago--

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00:10:06,000 --> 00:10:07,250
the earth cooled.

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00:10:10,050 --> 00:10:12,370
Before that, it was a
hot, molten mass.

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There until it cooled, there was
no real prospect of life.

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One of the things I find
absolutely wonderful is that

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by 3.7 billion years ago, there
was clear evidence of

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00:10:24,290 --> 00:10:26,940
the first life.

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Whatever it was, it didn't
take that all

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long to get life going.

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Somehow, it can't be that hard,
although I got to say we

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don't quite understand
all of it.

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Increasingly, people are looking
back to how early life

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can form out of prebiotic
materials.

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And these things were
prokaryotic organisms, like

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bacteria, and they played a
very important role, for

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example, in changing the entire
atmosphere of the earth

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to contain oxygen, which made
possible other things.

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So--

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00:11:00,330 --> 00:11:03,530
sorry, in shaping the content
of oxygen in the atmosphere.

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So 1.5 billion years ago, one
has a totally amazing

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invention, which is the
first nucleated cells.

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These bacteria lack nuclei.

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00:11:17,060 --> 00:11:19,110
Here we have nucleated
cells, eukaryotes.

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Major event, and it occurred
because of a fusion of two of

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00:11:30,010 --> 00:11:32,650
these prokaryotic-type cells.

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00:11:32,650 --> 00:11:36,460
One takes up residence in the
other, and there is a

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symbiosis between two
cells and that gave

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rise to your nucleus.

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The one that lives inside the
other eventually discarded

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most of its functions there.

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Sorry--

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00:11:47,560 --> 00:11:51,150
yes, that gave rise to
a nucleated cell.

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It's a fusion between two
different prokaryotic

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00:11:55,580 --> 00:11:58,730
organisms that had different
properties, one of which is

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the nucleated cell, the other
of which you see in the

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00:12:01,040 --> 00:12:02,890
mitochondria, for example.

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00:12:02,890 --> 00:12:06,060
There's still a genome in the
mitochondria, for example.

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00:12:06,060 --> 00:12:09,420
And so we can recognize that
there was this prokaryotic

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00:12:09,420 --> 00:12:11,620
fusion event.

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00:12:11,620 --> 00:12:14,960
Notice it took 2 billion years,
more than two billion

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00:12:14,960 --> 00:12:19,760
years, to make eukaryotes and
only 300 million years to make

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00:12:19,760 --> 00:12:21,370
the first life.

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00:12:21,370 --> 00:12:23,300
I find that quite remarkable.

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00:12:23,300 --> 00:12:25,330
What does that tell us?

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00:12:25,330 --> 00:12:28,860
That it was that much harder
to make a eukaryotic cell.

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00:12:28,860 --> 00:12:30,170
Maybe.

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00:12:30,170 --> 00:12:33,140
Or maybe it tells us about
the power of competition.

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00:12:33,140 --> 00:12:35,400
Once you have some life--

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00:12:35,400 --> 00:12:38,280
that the first prokaryotic
cells-- it's so much harder to

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00:12:38,280 --> 00:12:40,850
get anything else that can come
in and compete with it,

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00:12:40,850 --> 00:12:42,160
because it has to be better.

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00:12:42,160 --> 00:12:43,953
Maybe the first life didn't have
to compete with anything,

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00:12:43,953 --> 00:12:45,170
and it was easy.

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00:12:45,170 --> 00:12:48,100
And then in an innovation like
the eukaryotic cell, well,

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00:12:48,100 --> 00:12:50,380
maybe that was a lot harder to
accomplish, because it had to

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00:12:50,380 --> 00:12:54,240
be better than the prokaryotic
cells it was competing with.

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00:12:54,240 --> 00:12:57,160
I'm not sure, but I find that
difference in time to be kind

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00:12:57,160 --> 00:12:58,890
of a remarkably interesting
thing.

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00:12:58,890 --> 00:13:02,250
That that was short, and
that took a lot longer.

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00:13:02,250 --> 00:13:07,760
0.5 billion years ago, roughly
speaking, what you have are

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00:13:07,760 --> 00:13:10,470
multicellular organisms
with body plans.

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00:13:13,930 --> 00:13:17,620
Up to this point, you have
single-celled organisms.

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00:13:17,620 --> 00:13:20,190
Now you get multicellular
organisms with body plans.

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00:13:20,190 --> 00:13:24,150
And another remarkable thing,
once body plans, multicellular

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00:13:24,150 --> 00:13:27,700
body plans, are invented, they
explode very quickly.

220
00:13:27,700 --> 00:13:32,380
Somehow it was hard to invent
multicellularity, to get cells

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00:13:32,380 --> 00:13:35,230
to work together and be an
organism, but once it was

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00:13:35,230 --> 00:13:39,510
invented, it was not hard to
diversify it into zillions of

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00:13:39,510 --> 00:13:41,390
different body plans
and forms.

224
00:13:41,390 --> 00:13:43,350
That tells us something.

225
00:13:43,350 --> 00:13:46,860
That as soon as we see
multicellularity, we start

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00:13:46,860 --> 00:13:48,640
seeing huge numbers
of different body

227
00:13:48,640 --> 00:13:50,010
plans pretty quickly.

228
00:13:50,010 --> 00:13:51,270
Very interesting.

229
00:13:51,270 --> 00:13:52,650
A few other important dates.

230
00:13:52,650 --> 00:13:53,800
Two other dates.

231
00:13:53,800 --> 00:14:01,680
0.005 billion years
ago are humans.

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00:14:01,680 --> 00:14:04,500
Just to put yourself in your
place on this scale.

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00:14:04,500 --> 00:14:16,695
And 0.00000015 billion years
ago, MIT was founded.

234
00:14:19,260 --> 00:14:22,400
Just to put this
in prospective.

235
00:14:22,400 --> 00:14:24,710
Alright.

236
00:14:24,710 --> 00:14:28,680
Couple of other things
you should know.

237
00:14:28,680 --> 00:14:31,900
The types of cells I've
been referring to.

238
00:14:36,360 --> 00:14:38,830
There's really two fundamental
types of cells.

239
00:14:38,830 --> 00:14:40,570
And I've been using
the word already.

240
00:14:40,570 --> 00:14:42,900
Let me just get it out there.

241
00:14:42,900 --> 00:14:44,150
Prokaryotes.

242
00:14:45,820 --> 00:14:47,070
Eukaryotes.

243
00:14:51,740 --> 00:14:54,506
Karyo refers to nucleus.

244
00:14:58,030 --> 00:14:59,810
Eu- means true.

245
00:14:59,810 --> 00:15:02,880
Pro- means primitive, before.

246
00:15:02,880 --> 00:15:05,555
So eukaryotic cells--

247
00:15:09,010 --> 00:15:11,730
you're, by the way,
a eukaryote.

248
00:15:11,730 --> 00:15:12,880
Right?

249
00:15:12,880 --> 00:15:14,950
Just in case you haven't read
the owner's manual, you're

250
00:15:14,950 --> 00:15:17,680
eukaryotes.

251
00:15:17,680 --> 00:15:19,520
--have true nuclei.

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00:15:19,520 --> 00:15:25,230
Inside the nucleus, there's your
DNA, which is organized

253
00:15:25,230 --> 00:15:27,470
better than I just drew it
there, because, in fact, it's

254
00:15:27,470 --> 00:15:29,760
very, very long and has
to be packed up well.

255
00:15:29,760 --> 00:15:33,250
It'll have organelles
like mitochondria.

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00:15:33,250 --> 00:15:34,780
It could have chloroplasts.

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00:15:34,780 --> 00:15:36,390
It could have other
organelles.

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00:15:36,390 --> 00:15:38,410
It'll have other things
we'll talk about--

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Golgi apparatuses
and endoplasmic

260
00:15:40,590 --> 00:15:43,370
reticula and all that.

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00:15:43,370 --> 00:15:47,140
Bacteria don't have
a true nucleus.

262
00:15:47,140 --> 00:15:50,310
It's not that they're DNA isn't
somehow organized, but

263
00:15:50,310 --> 00:15:52,600
it doesn't have a true nucleus
with the wall around it.

264
00:15:52,600 --> 00:15:55,140
There's no wall around that
nucleus like that.

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00:15:55,140 --> 00:15:57,790
They often have interesting
cell walls.

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00:15:57,790 --> 00:16:00,520
A striking thing, although I've
drawn them as the same

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00:16:00,520 --> 00:16:03,250
size, these are much smaller.

268
00:16:03,250 --> 00:16:07,730
These are 1 to 2 microns.

269
00:16:07,730 --> 00:16:13,570
These, 10 to 40 microns
in diameter.

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00:16:13,570 --> 00:16:18,400
And so that means that if we
talk about volume, we cube it.

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00:16:18,400 --> 00:16:22,050
So the volumes of these guys
are something like 1,000 to

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00:16:22,050 --> 00:16:24,930
60,000 times bigger.

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00:16:24,930 --> 00:16:30,090
Eukaryotic cells are large
compared to prokaryotic cells.

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00:16:30,090 --> 00:16:34,130
Now, remember these are the
guys who were early.

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00:16:34,130 --> 00:16:35,770
These guys come along later.

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00:16:35,770 --> 00:16:37,650
And there are important
differences that we'll talk

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about in eukaryotic and
prokaryotic cells.

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00:16:42,380 --> 00:16:45,780
You're a eukaryote, all animals,
all plants are

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00:16:45,780 --> 00:16:46,680
eukaryotes.

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00:16:46,680 --> 00:16:49,500
Fungi, such as yeast,
et cetera.