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I am a professor in the Biology
Department at MIT.

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And I will be co-teaching this
course with Penny Chisholm who is a

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professor in the Department of Civil
and Environmental Engineering,

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as well as a professor in the
Biology Department.

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As well, Penny was recently
featured in the journal Nature.

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She is a very well-known
oceanographer who has become

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deservedly famous for discovering a
very small bacterium that's capable

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of carrying out photosynthesis.
For many years oceanographers used

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filters whose holes were big enough
that this bacterium went through.

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And so when they were doing their
studies of the ocean and how the

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biomass that was there and all the
fluxes and so on,

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they didn't know this organism
existed which can form up to 50% of

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the biomass in parts of the ocean.
So Penny is really a wonderful

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lecturer, a wonderful person,
and she'll be teaching the component

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of 7.014 which deals with ecology
and the environment.

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And this is a section of 7.
14 that makes it different from the

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other two versions,
7.012 and 7.013. So for me

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personally this is an absolutely
wonderful and exciting opportunity

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to be able to teach this
Introductory Biology course.

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For some of you I know that biology
is going to either be a major part

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of your career or quite possibly,
even if you're in engineering or

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something else,
you will find yourselves working

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with a biological system.
You can see that happening all over

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campus these days that more and more
engineering departments are finding

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that they're working on problems
that come from biology or have a

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biological component.
I'm sure there are at least a few

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of you here who are only here
because it's a required course and

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you might well wish you
were somewhere else.

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However, I will do my best to try to
communicate to you why you need to

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know some biology,
too. I think most of you know you

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can hardly pick up a newspaper these
days without running into something

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that demands a knowledge of biology,
something about stem cells,

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something about cloning humans,
something about a new drug, lots of

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things having to do with biological
affects on the environment

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and so on.
You're also going to be confronted

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with decisions about your health,
about the health of your loved ones

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concerning cancer,
concerning whether a child might

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have birth defects,
all sort of issues that will affect

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your personal lives that demand an
understanding of biology.

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So I feel with some passion that
whether you think you're going to

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need biology in your professional
career or not,

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everyone in this institution needs
some understanding of biology to

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just live their ordinary lives.
I also think as MIT students you're

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going to be looked at,
as you go through your lives,

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as people who are knowledgeable
about science and engineering.

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And you'll be asked questions that
go far beyond your immediate

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area of expertise.
And again I think that's another

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reason for needing to know some of
biology. Anyway,

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it's an absolutely wonderful time to
teach biology because things have

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just been exploding over the last
two or three decades and things are

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moving faster than ever.
And another wonderful thing about

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teaching biology is that MIT is an
absolutely marvelous place

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to teach it.
Just to sort of drive this home,

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in the Biology Department alone
there are four Nobel laureates who

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got honored for critical discoveries
in biology. Gobin Khorana who is

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just down the hall from me
synthesized the first gene.

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It was an extraordinary feat of
synthesis of organic chemistry

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synthesizing DNA.
When I was an undergrad I was a

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chemistry major but I had to take an
introductory biology course.

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And at that point the DNA wasn't
mentioned in the high school course.

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So the first time that I heard
about DNA was in my introductory

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biology course.
And that determined by career

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direction. I thought that was such
an interesting molecule that I

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wanted to work on it and I talked
myself into one of the labs in

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Ottawa, Canada where I grew up that
was trying to synthesize DNA,

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synthesize pieces of the gene.
And, as it turned out later,

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competing unsuccessfully with my now
colleague Gobin Khorana.

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Susumu Tonegawa got a Nobel prize
for discovering the amazing

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molecular operations that underlie
the diversity of the immune system.

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Your immune system has the capacity
to recognize viruses and bacteria,

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all sorts of different pathogens,
including molecules.

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It can recognize molecules that
haven't even ever been synthesized

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in the history of life.
And we'll talk towards the end of

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the course about the way that
happens. And you'll see why Susumu

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got his Nobel prize.
Phil Sharp got his for discovering

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RNA splicing completely
unanticipated component of the very

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heart of molecular biology.
And then Bob Horvitz who was of

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pure mind when he started at MIT at
the same time and our labs were side

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by side for many years,
got his Nobel prize in 2002 for

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discovering a phenomenon,
the general term is ìprogrammedî

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cell death.
And it plays all sorts of important

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roles in biology from sculpting the
shapes of organs and tissues.

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We initially have webs when we're
developing between our fingers,

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and those go away because of the
programmed cell death that the cells

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that were making the web disappear.
And another role of that is prevent

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cancer. That if cells sense that
something is very messed up they

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have a sort of suicide program that
would make them destroy themselves.

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And if that doesn't happen those
cells could go on and become more

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and more abnormal and eventually
turn into an invasive cancer.

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Anyway, there's a picture of Bob
when the institute was celebrating

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his Nobel prize.
He was getting a congratulatory

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kiss from Martha Constantine-Paton,
also a professor in the Biology

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Department who happens
to be Bob's wife.

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Most of you know that the human
genome has now been sequenced.

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That was one of the huge
undertakings and most important

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undertakings in modern biology over
the last while.

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It was an incredible feat.
Each cell has, as most of you know,

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46 chromosomes. And that's a total
of about two meters of DNA

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in every human cell.
And that two meters of DNA is

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composed of about 3 million DNA base
pairs, these letters A,

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T, G and C that we'll be talking
about as we go through the course.

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So to sequence the genome you had
to work out the sequence of the

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exact run of these A,
G, T and Cs along the backbone for 3

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billion base pairs.
And somewhere that genome encodes

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somewhere between 20,000
and 30,000 genes.

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And we'll be talking about the
proteins that are encoded by most of

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those genes and their important
roles as we go on in the course.

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What some of you may not know is
the key role that MIT played in this.

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About a third of the genome was
sequenced at the Whitehead MIT

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Genome Center.
And here are some of the robots

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that were used to sequence
that DNA.

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And that sequencing effort was led
by Eric Lander whose name some of

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you may recognize because he teaches
the fall version of 7.

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12 along with Bob Weinberg.
So here are just a few examples of

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why I think it's important for you
to understand biology regardless of

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whether you're going to go on and
use it professionally.

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Most of you know one of the biggest
challenges we face on this planet is

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this AIDS epidemic.
It's caused by a certain kind of

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virus called HIV-1 that gets into
particular cells of your immune

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system that normally defends us
against infection and destroys those.

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And then people die from infections
by other organisms that normally you

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can fight off.
It's a huge problem with vast

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societal and economic implications.
And it's one that we're still,

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as a mankind still trying to deal
with and grapple with.

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Here's another example.
Just a couple of years ago there

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was the scar of anthrax.
It's a bacterium that's very

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pathogenic and kills its host fairly
easily. It does it by making

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particular toxins.
The details shown here don't matter,

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but just reminding you that this is
something that was in the front

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pages of the paper just
a little while ago.

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A couple of years ago,
when I was teaching this,

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we had the scare of the SARS virus
that went all the way during the

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course when I was teaching it from
the initial discovery of the virus

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to the actual sequencing of the
genome which had happened by later

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on in this course.
Smallpox was a disease we thought

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that we eliminated,
but now it's come back as a

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bioterrorism treat and there is
increased study of smallpox.

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It's something we have to worry
about again. Here's another example.

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This is a picture showing the start
of a transgenic animal.

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We'll talk about how this process
goes later in the course.

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And it's related also to this whole
issue of cloning,

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using the sense of the word such as
in trying to clone a human or clone

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an animal to make a genetically
identical copy.

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So you'll see there are a couple of
different uses of the word cloning

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as we go through the course.
There's a lot of fuss in the news

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and the newspapers about genetically
modified food,

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and people have different positions
on it. Here's a case where I think

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the benefit of a genetically
modified food could hardly be argued

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with. About two-thirds of the
world's population uses rice as

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their primary source of food.
One of the problems with rice is

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that it doesn't make beta-carotene.
And beta carotene is what our bodies

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take and use to make vitamin A.
And if you have a vitamin A

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deficiency people are prone to
infection. They have immune

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deficiencies in their immune system
and blindness.

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And this deficiency of vitamin A
caused by eating rice afflicts about

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400 million people worldwide.
Well, rice is only two chemical

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steps away from being able to make
beta carotene.

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This is a genetically modified
version of rice that has those two

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extra steps inserted in it.
And you can see it's golden because

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it's making beta carotene.
If people were to eat that form of

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rice then they wouldn't have this
problem with vitamin A deficiency.

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Penny Chisholm in her part of the
course will be considering things

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that are more global level.
Here's a picture of our planet,

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and there are issues that you know
about there. This is the carbon

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dioxide levels in the
atmosphere rising.

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And that's a real phenomenon.
This shows from 1960 to 1995.
damage our cells if we
were exposed to it.

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This is associated with a global
warming that again is undeniable

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that it's happening.
You'll see stuff in the papers.

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And these gases, particularly
carbon dioxide and methane,

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they're known as greenhouse gases
are playing a role in that.

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And probably mankind is playing a
role in the production of those

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gases and, hence,
in global warming.

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And Penny will talk to you a little
more about that.
it would have been a real disaster.
And that seems to be, the efforts

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Right here at MIT Mario Molina in
EAPS discovered the ozone hole and

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got a Nobel prize for that.
Ozone is important because it

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absorbs UV, a critical component of
ultraviolet radiation that would

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And because of the emission of
fluorocarbons in the environment

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this large hole developed over
Antarctic. If that had spread,

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to cut down the release of
fluorocarbons seem to be helping

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with that. But,
again, Penny will have more to say.

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Those of you who've lived around
here for a little bit probably know

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that the fishing industry just
locally has had a very hard time.

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There is a fishing boat just up in
Gloucester, just up the coast less

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than an hour from here.
And part of the problems,

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again, are caused by mismanagement
of the resources where the fish have

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been, stocks have been over-fished
so some of the fisheries have come

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to the point of collapse or near.
Places such as the Grand Banks off

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of Newfoundland there has been a
collapse, and it's not at all clear

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that it can be reversed and whether
they'll be cod in large quantities

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every again there. OK.
So there a variety of ways that we

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can study biology.
And I think I'm going to begin by

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outlining how we do that.
Biology is an experimental science

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and it's one of the really important
themes that we'll run through

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in this course.
You cannot study biology by just

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sitting down with a pen and paper in
a room and thinking.

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You have to get out and find out
what's there. You need to make

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observations. You need to try
experiments. You need to formulate

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hypotheses and test them and either
modify your hypothesis or reject it

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and so on. But it's a continual
cycle of experimentation and making

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hypotheses and testing.
It's the Scientific Method at work.

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But you can carry that out at
different levels.

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The very highest level would be the
biosphere. Here's one example.

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That's earth. It's here. There
are many, many species of life that

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are on there. There are many more
than a million.

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And the estimates of how many there
are range from,

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in total, 10 to the 20 million
estimated. And one of the big

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worries right at the moment is that
as rain forests are being depleted,

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parts of the world that are a rich
source of biological diversity,

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as those are disappearing we're
losing diversity at quite a rate.

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Just a couple of years ago I had a
chance to fly over

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a part of Brazil.
And it was just scary to see from

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the plane how the rain forest was
just being cut down.

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And you could just see how fast
some of the rain forest was

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disappearing, and with it many
different types of species that only

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can live there.
One can look instead,

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going down a level, at an ecosystem
which is a particular

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environment --

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-- and the species of life found in
it. And just to give you a couple

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of examples of that,
it could be a salt marsh as shown

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here. Or here's an interesting
environment that Penny Chisholm will

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tell you more about.
This is a black smoker.

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There's a vent several miles deep
in the Pacific Ocean.

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The water temperature that's
gushing out of here is around 360

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degree centigrade.
And there's a particular community

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of life that's able to grow around
these deep vents.

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And Penny will tell you more about
that. Then going down yet another

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level you can come to a population.

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And this is interacting --

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-- or interbreeding organisms.
An example might be the fiddler

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crabs in a salt marsh.
Or here we see an interesting

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population. These are tube worms
that are up to a meter or more in

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length that you find down at these
black smokers.

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If we move down yet another level --

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-- we come to organisms.
Organisms have three important

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sorts of characteristics that we'll
talk quite a bit about in this

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course. They carry out metabolism
which is the sum of all the

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different chemical reactions
necessary for life.

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They undergo regulated growth --

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-- and they reproduce.
And the sort of fundamental unit of

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life that we will talk about over
and over again in this course is

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known as a cell.
And life comes in two kinds of

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species.
There is unicellular life where the

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organism is just a single cell and
multicellular forms of life that are

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made of many different types of
cells. What's a cell?

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One of the secrets to life.
It's a little tiny bit of the

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universe that's surrounded
by a boundary.

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And it's given the special name of a
membrane. It's selective,

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not very permeable to most things.
And cells are able to put little

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importers and exporters and things
that control the passage of things

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across the membrane by isolating the
inside of a cell from all the rest

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of the universe.
That is one of the principles that

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makes life possible.
We have a couple of examples of

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organisms here.
Here are some clams that grow down

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at those black smokers,
and they can get pretty large.

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And, as I say, Penny will talk a
bit more about this.

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And we have this really amazing
diversity of life forms that we find

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on this planet.
However, if we think about this

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division into unicellular and
multicellular organisms.

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Unicellular organisms include things
that you're familiar with.

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They're bacteria. There is a
picture of just E.

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coli cells. And we'll be talking
about E. coli quite a bit as a model

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organism as we go through the course.
By studying E.

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coli, scientists have learned many
important things that apply

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to all of life.
Another kind of important

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single-celled organism,
unicellular organism is yeast.

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Those are pictures of yeast
saccharomyces that are used in

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00:21:46,000 --> 00:21:52,000
baking bread or in brewing beer or
making wine. And another one you're

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00:21:52,000 --> 00:21:58,000
all familiar with are algae which
are single-celled organisms that are

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able to carry out photosynthesis.
And we'll be talking about that.

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If we think of an example of a
multicellular organism then we see

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there are different levels at which
we can think about this.

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We could take, for example,
a picture of me, just an

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anatomically correct diagram here,
that I'm made up, as you are, of

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about ten to the fourteenth
human cells.

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We all started out as a fertilized
egg, which is a single cell.

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And by the time we're grown up,
where we have about ten to the

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00:22:48,000 --> 00:22:53,000
fourteenth human cells.
Just a tremendous amount of cell

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growth that had to happen
and specialization.

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The other thing you may not
appreciate is that we have an

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ecosystem inside us in our
gastrointestinal tract.

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This part, the intestine having the
highest concentration of

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microorganisms.
But there are about ten to the

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fourteenth bacteria also inside of
our gut. So we're actually almost

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00:23:20,000 --> 00:23:25,000
the same number of human cells and
bacterial cells.

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And if we don't have those bacteria
then our digestive systems

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00:23:29,000 --> 00:23:35,000
don't work well.
So if we go down from a whole

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00:23:35,000 --> 00:23:41,000
organism, a whole multicellular
organism, a level,

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then we come to an organ.
An example of that might be an eye.

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And I think we have a diagram of an
eye which is made up of different

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00:23:53,000 --> 00:24:00,000
parts. If we go down another level
we come to a tissue.

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00:24:00,000 --> 00:24:07,000
Which is now you can begin to see
that tissue are made up of groups of

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00:24:07,000 --> 00:24:14,000
specialized cells.
An example might be the retina of

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00:24:14,000 --> 00:24:21,000
an eye. And if we continue to go
downwards we'll get to single cells.

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And at this point we're at the same
level of the tail as when we're

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talking about a unicellular
organism.

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If we continue down then --

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-- we can get to organelles.
These are involved in energy

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production, energy management.

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And mitochondrion and chloroplasts
are the two principle examples of

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00:25:10,000 --> 00:25:16,000
organelles that we'll talk about.
And if we go down yet another level

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00:25:16,000 --> 00:25:22,000
of organization we get to molecules.
And part of the reason that biology

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00:25:22,000 --> 00:25:28,000
has flourished so well over the last
few decades at MIT is there has been

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a real emphasis on looking at things
at a cellular and molecular level.

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So you're going to be hearing a lot
about cells and a lot about

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00:25:38,000 --> 00:25:42,000
molecules as we go through this
course. Here's an example of

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00:25:42,000 --> 00:25:46,000
rhodopsin. That's a protein.
We'll be talking about what

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00:25:46,000 --> 00:25:50,000
proteins are, but it's a very
important class of molecule in

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00:25:50,000 --> 00:25:54,000
nature. In this case,
proteins involved in sensing light

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00:25:54,000 --> 00:25:59,000
and play an important
part in your vision.

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00:25:59,000 --> 00:26:02,000
Here is another protein.
You cannot really tell what it's

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00:26:02,000 --> 00:26:06,000
doing by just looking at it,
but in this case this is one of the

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00:26:06,000 --> 00:26:10,000
lethal factors that is made by
anthrax. It's one of the proteins

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00:26:10,000 --> 00:26:14,000
that anthrax makes that's capable of
killing you if you get infected with

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00:26:14,000 --> 00:26:18,000
it. Here's another molecule we'll
talk about in great detail.

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00:26:18,000 --> 00:26:22,000
This is DNA. You probably all know
it's a double helix,

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00:26:22,000 --> 00:26:26,000
two strands of DNA that are held
together by forces we'll

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00:26:26,000 --> 00:26:30,000
be discussing.
It's an absolutely beautiful

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00:26:30,000 --> 00:26:36,000
molecule. It's fascinated me
through all of my life.

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00:26:36,000 --> 00:26:41,000
And we'll be talking quite a bit
about that as the course goes on.

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00:26:41,000 --> 00:26:47,000
OK. So if we're thinking about
cells there are two important kinds

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00:26:47,000 --> 00:26:53,000
of cells that one finds
on this planet.

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00:26:53,000 --> 00:27:01,000
Prokaryotic cells.

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00:27:01,000 --> 00:27:07,000
Prokaryotic organisms and
eukaryotic organisms.

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00:27:07,000 --> 00:27:14,000
They each are made of cells that
are distinguishable from each other.

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00:27:14,000 --> 00:27:20,000
I've indicated that a cell is a
little bit of the universe that's

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00:27:20,000 --> 00:27:27,000
surrounded by a boundary or a
membrane. But inside there,

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00:27:27,000 --> 00:27:34,000
inside of this is the DNA which
functions as the genetic material.

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00:27:34,000 --> 00:27:40,000
It's the blueprint for everything
that that cell is going to make and

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00:27:40,000 --> 00:27:47,000
be able to do.
Ultimately everything is encoded

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00:27:47,000 --> 00:27:53,000
there. And in a prokaryotic cell
the DNA is free within this membrane.

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00:27:53,000 --> 00:28:00,000
The eukaryotic cell also
has a membrane.

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00:28:00,000 --> 00:28:08,000
But the DNA inside is inside another
membrane compartment known as the

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00:28:08,000 --> 00:28:16,000
nucleus. And this is the DNA.
These prokaryotic cells tend to be

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00:28:16,000 --> 00:28:24,000
of the order of a kilometer in
length. And eukaryotic cells are

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00:28:24,000 --> 00:28:32,000
usually larger,
can be ten to a hundred kilometers.

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00:28:32,000 --> 00:28:36,000
There's quite a bit of variation,
but that gives you at least some

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00:28:36,000 --> 00:28:40,000
sense of the range.
Now, I've for years,

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00:28:40,000 --> 00:28:45,000
when I did a diagram like this,
I wanted to somehow be able to show

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00:28:45,000 --> 00:28:49,000
you that these cells were impressive
than just what's on the board.

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00:28:49,000 --> 00:28:54,000
So here are a couple of pictures to
try and do that.

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00:28:54,000 --> 00:28:58,000
This shows a picture of E.
coli swimming along. And the way

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00:28:58,000 --> 00:29:03,000
this image is being taken lets you
see what are called flagella but

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00:29:03,000 --> 00:29:07,000
which are basically the propellers
that E. coli have that let it swim

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00:29:07,000 --> 00:29:12,000
through the water.
These are long structures made of

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00:29:12,000 --> 00:29:17,000
proteins that are several times the
body length of the bacterium.

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00:29:17,000 --> 00:29:22,000
And there's a molecular motor
imbedded in the bacterium that

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00:29:22,000 --> 00:29:27,000
whirls it around at about somewhere
between 10,000 and 100,

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00:29:27,000 --> 00:29:32,000
00 RPM. And that's what drives the
bacteria forward.

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00:29:32,000 --> 00:29:36,000
So that was a prokaryotic cell.
Here's a paramecium. This is a

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00:29:36,000 --> 00:29:41,000
single-celled eukaryotic organism.
And, as you can see here, it's

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00:29:41,000 --> 00:29:46,000
capable of movement as well.
In this case it has cilia along the

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00:29:46,000 --> 00:29:51,000
outside that allow it to move.
Here's an interesting one. I don't

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00:29:51,000 --> 00:29:56,000
know if any of you can guess what
these were. These were cells from

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00:29:56,000 --> 00:30:01,000
the skin of a mouse.
They're on an Auger surface.

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00:30:01,000 --> 00:30:05,000
And, as you can see,
they too can move. There are a

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00:30:05,000 --> 00:30:10,000
couple of things that are important
about this. I got this slide from

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00:30:10,000 --> 00:30:14,000
Linda Griffith who is in the
Biological Engineering Department.

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00:30:14,000 --> 00:30:19,000
At the time I got it from her I
think it was in Chemical Engineering

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00:30:19,000 --> 00:30:23,000
several years ago.
And what was important about this,

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00:30:23,000 --> 00:30:28,000
apart from it being a very nice
little movie showing you a mammalian

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00:30:28,000 --> 00:30:32,000
cell moving around,
was that I saw Linda show this

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00:30:32,000 --> 00:30:37,000
during one of her research
seminars.

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00:30:37,000 --> 00:30:41,000
So here is an engineer at MIT who
was showing this picture as part of

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00:30:41,000 --> 00:30:45,000
her research talk.
And I think those of you who are

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00:30:45,000 --> 00:30:49,000
going onto engineering,
you may be surprised at the extent

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00:30:49,000 --> 00:30:53,000
to which you need to know about
biology as you go through your

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00:30:53,000 --> 00:31:01,000
professional careers.

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00:31:01,000 --> 00:31:08,000
OK. So one of the great discoveries
that has happened over the last few

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00:31:08,000 --> 00:31:15,000
years that came out of our ability
to look at DNA and RNA was the

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00:31:15,000 --> 00:31:22,000
discovery that the forms of life
that are prokaryotic actually split

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00:31:22,000 --> 00:31:30,000
into two distinct Kingdoms that are
very, very different.

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00:31:30,000 --> 00:31:34,000
The archaea and the bacteria.
And just to give you a sense of the

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00:31:34,000 --> 00:31:39,000
diversity of life,
I'll just mention a couple of these.

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00:31:39,000 --> 00:31:44,000
These archaea look like bacteria
but they are diverged from the

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00:31:44,000 --> 00:31:49,000
bacteria as they are from the
eukaryotes. So there were sort of

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00:31:49,000 --> 00:31:54,000
three really major Kingdoms of Life.
And the archaea, many of them can

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00:31:54,000 --> 00:32:00,000
live in specialized environments.
For example, sulfolobus can live at

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00:32:00,000 --> 00:32:07,000
about 90 degrees centigrade and a pH
of somewhere between 1 and 2.

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00:32:07,000 --> 00:32:14,000
So if you see something like a hot
springs, there are organisms such as

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00:32:14,000 --> 00:32:21,000
this that are able to grow in that
environment. Or there are halophyes,

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00:32:21,000 --> 00:32:28,000
salt-loving archaea that can grow,
for example, in formula sodium

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00:32:28,000 --> 00:32:34,000
chloride.
And if you've,

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00:32:34,000 --> 00:32:38,000
for example, ever flown into San
Francisco airport coming up from the

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00:32:38,000 --> 00:32:42,000
south over San Jose,
you've seen things that look sort of

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00:32:42,000 --> 00:32:46,000
like these pictures where seawater
is being evaporated down to collect

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00:32:46,000 --> 00:32:51,000
the salt. And you'll see they're
colored, and the reason they're

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00:32:51,000 --> 00:32:55,000
colored is that these halobacteria
are photobacteria that are able to

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00:32:55,000 --> 00:32:59,000
use light as an energy source.
And they make pigments that absorb

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00:32:59,000 --> 00:33:04,000
the light, and that's why these salt
areas get colored.

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00:33:04,000 --> 00:33:11,000
A third example would be methanogens.
These are organisms that produce

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00:33:11,000 --> 00:33:18,000
methane. If you've walked into a
lake and stepped on the bottom and

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00:33:18,000 --> 00:33:25,000
seen little bubbles come up,
those are little bubbles of methane.

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00:33:25,000 --> 00:33:32,000
Or another place where you find
methanogens are inside of cows.

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00:33:32,000 --> 00:33:37,000
Now, some of you may not know that
the cow is more or less a walking

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00:33:37,000 --> 00:33:42,000
anaerobic fermentor here.
If we have an anatomically correct

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00:33:42,000 --> 00:33:47,000
picture of a cow.
The inside of the cow,

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00:33:47,000 --> 00:33:52,000
there's a large chamber known as the
rumen where there's no oxygen,

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00:33:52,000 --> 00:33:57,000
and there's a culture of
microorganisms there that

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00:33:57,000 --> 00:34:02,000
include methanogens.
And it's this combination of

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00:34:02,000 --> 00:34:07,000
microorganisms that enables cows to
each grass that we cannot manage to

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00:34:07,000 --> 00:34:12,000
get energy from.
And as a byproduct of this

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00:34:12,000 --> 00:34:17,000
specialized type of metabolism
produces methane.

403
00:34:17,000 --> 00:34:23,000
And a cow burps something of the
order of 400 liters a day of methane.

404
00:34:23,000 --> 00:34:28,000
OK. So one last thing then just to
kind of pull this all together is

405
00:34:28,000 --> 00:34:33,000
that these organelles that I
mentioned, which are also membrane

406
00:34:33,000 --> 00:34:38,000
compartments that are found in
eukaryotic cells, are

407
00:34:38,000 --> 00:35:50,000
the mitochondria --

408
00:35:50,000 --> 00:35:31,000
-- or chloroplast.
There's pretty strong evidence at

409
00:35:31,000 --> 00:35:13,000
this point that these arose from
bacteria that were things that

410
00:35:13,000 --> 00:35:07,000
you're more familiar with.
Things like E.

411
00:35:07,000 --> 00:35:15,000
coli or streptococcus that causes
strep throat or the lactic acid

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00:35:15,000 --> 00:35:23,000
bacteria that causes the milk to
turn into yogurt which some of you

413
00:35:23,000 --> 00:35:29,000
probably had for lunch today.
That these organelles,

414
00:35:29,000 --> 00:35:33,000
the mitochondria and the chloroplast
were derived from particular type of

415
00:35:33,000 --> 00:35:37,000
bacteria that probably first got
transiently associated with

416
00:35:37,000 --> 00:35:41,000
developing eukaryotic cells sometime
back in evolution,

417
00:35:41,000 --> 00:35:45,000
and eventually became captured and
became a permanent part of the

418
00:35:45,000 --> 00:35:49,000
eukaryotic cell.
The mitochondrion is thought to

419
00:35:49,000 --> 00:35:53,000
have derived from something that
looks like today's present day

420
00:35:53,000 --> 00:35:57,000
rizobia, which we'll talk about,
that form an intracellular infection

421
00:35:57,000 --> 00:36:02,000
of plants, or rickettsia which is
chronic intracellular pathogen.

422
00:36:02,000 --> 00:36:05,000
The mitochondrion look as though
they came from something related to

423
00:36:05,000 --> 00:36:09,000
that. The chloroplasts look as
though they came from a bacterium

424
00:36:09,000 --> 00:36:13,000
that was able to carry on
photosynthesis which we'll also be

425
00:36:13,000 --> 00:36:17,000
talking about.
I want to close by giving you just

426
00:36:17,000 --> 00:36:21,000
a quick little snapshot of evolution
because I'm hoping this will maybe

427
00:36:21,000 --> 00:36:25,000
make some of the things that we talk
about in this course clearer.

428
00:36:25,000 --> 00:36:34,000
So what we're going to do is we're
going to look back from 4.

429
00:36:34,000 --> 00:36:44,000
billion years ago when the earth
was just forming --

430
00:36:44,000 --> 00:36:57,000
-- to now. I'm just going to try

431
00:36:57,000 --> 00:37:03,000
and give you a few key sort of
landmarks as we go along.

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00:37:03,000 --> 00:37:09,000
So about 4.5 billion years ago there
was methane, carbon dioxide,

433
00:37:09,000 --> 00:37:16,000
ammonium, hydrogen gas, nitrogen gas,
water, but importantly no oxygen at

434
00:37:16,000 --> 00:37:22,000
that point. There was a lot of
debate as to how life initially came.

435
00:37:22,000 --> 00:37:29,000
One of the prevalent theories at
this point is there's something

436
00:37:29,000 --> 00:37:35,000
called an RNA world.
This is just a hypothesis in which

437
00:37:35,000 --> 00:37:40,000
it's thought that perhaps the
molecule RNA, which we'll talk about,

438
00:37:40,000 --> 00:37:45,000
played role as both something that
was able to catalyze chemical

439
00:37:45,000 --> 00:37:51,000
reactions and therefore did things
actively and also stored information.

440
00:37:51,000 --> 00:37:56,000
But, in any case,
the best guess is that the first

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00:37:56,000 --> 00:38:01,000
life that was about 3.
billion years ago, somewhere in

442
00:38:01,000 --> 00:38:06,000
that vicinity.
It was something that probably

443
00:38:06,000 --> 00:38:10,000
resembled most closely a present-day
bacterium, a single-celled organism,

444
00:38:10,000 --> 00:38:14,000
something like that. Now, initially
when life got started it's thought

445
00:38:14,000 --> 00:38:18,000
that there were a lot of organic
chemicals that had been made as a

446
00:38:18,000 --> 00:38:22,000
consequence of lightening strikes
and all sorts of chemistry that had

447
00:38:22,000 --> 00:38:26,000
happened so there was sort of a soup
of some kind, some molecules

448
00:38:26,000 --> 00:38:31,000
that could be used.
So probably these first organisms

449
00:38:31,000 --> 00:38:35,000
where able to basically use some
preformed nutrients.

450
00:38:35,000 --> 00:38:40,000
And then as the soup began to get
depleted by using it they had to

451
00:38:40,000 --> 00:38:44,000
learn to synthesize,
at least develop systems that would

452
00:38:44,000 --> 00:38:49,000
synthesize these building blocks.
And they also had to begin to worry

453
00:38:49,000 --> 00:38:54,000
about what to use as energy.
And so somewhere in here, something

454
00:38:54,000 --> 00:38:58,000
that I'll call,
in a silly way, photosynthesis

455
00:38:58,000 --> 00:39:03,000
released number one.
But this was a system that enabled

456
00:39:03,000 --> 00:39:08,000
the organism to capture energy from
sunlight so that it wasn't now

457
00:39:08,000 --> 00:39:14,000
dependent on getting energy by
eating some preformed ingredient.

458
00:39:14,000 --> 00:39:19,000
It was then able to take carbon
dioxide and make it into forms that

459
00:39:19,000 --> 00:39:24,000
were useful, of carbon that were
useful for life,

460
00:39:24,000 --> 00:39:30,000
and it produced molecules such as
sulfur as a waste product.

461
00:39:30,000 --> 00:39:36,000
There was a bit later in evolution,
somewhere in here, something we

462
00:39:36,000 --> 00:39:43,000
might think of as photosynthesis
release two. This was an improved

463
00:39:43,000 --> 00:39:49,000
version of photosynthesis.
It captured more energy, worked

464
00:39:49,000 --> 00:39:56,000
better, but it developed,
it had a waste product which was

465
00:39:56,000 --> 00:40:02,000
oxygen.
Well, oxygen hadn't been in our

466
00:40:02,000 --> 00:40:06,000
atmosphere. And the first thing
that sort of happened was that the

467
00:40:06,000 --> 00:40:10,000
world started to rust.
All the iron, a lot of the iron

468
00:40:10,000 --> 00:40:14,000
started to interact with the oxygen.
And Penny will tell you that at the

469
00:40:14,000 --> 00:40:19,000
base of the sea there are huge beds
of iron oxide that came from this

470
00:40:19,000 --> 00:40:23,000
slow rusting of the earth.
And so it took many, many years

471
00:40:23,000 --> 00:40:27,000
before oxygen levels started to rise.
As you know it's about 20% of our

472
00:40:27,000 --> 00:40:32,000
atmosphere now.
Even at this stage it was only a few

473
00:40:32,000 --> 00:40:37,000
percent of our,
made up a few percent of our

474
00:40:37,000 --> 00:40:43,000
atmosphere, even by here in
evolution. The first eukaryotic

475
00:40:43,000 --> 00:40:48,000
cell is thought to have appeared
somewhere here.

476
00:40:48,000 --> 00:40:53,000
Again, it was likely a
single-celled organism like some of

477
00:40:53,000 --> 00:40:59,000
those pictures I showed you.
And evolution continued to go.

478
00:40:59,000 --> 00:41:04,000
Somewhere around a billion years
ago sex was evolved which enabled

479
00:41:04,000 --> 00:41:09,000
eukaryotic organisms to exchange
genetic material,

480
00:41:09,000 --> 00:41:15,000
and therefore evolve at a fast rate
than they could previously.

481
00:41:15,000 --> 00:41:19,000
The Cambrian Period was about a 0.
billion to 0.6 billion years ago.

482
00:41:19,000 --> 00:41:24,000
And there was a veritable explosion
of life forms.

483
00:41:24,000 --> 00:41:28,000
And you can still see in the fossil
records how much diversity was

484
00:41:28,000 --> 00:41:33,000
generated at that point,
some of which went on to become life

485
00:41:33,000 --> 00:41:38,000
forms and other which probably were
more evolutionary dead ends.

486
00:41:38,000 --> 00:41:46,000
Finally we get to the dinosaurs that
were about 245 to 65 million years

487
00:41:46,000 --> 00:41:55,000
ago which would place them somewhere
here on this timeline.

488
00:41:55,000 --> 00:42:04,000
So in honor of this course,
I've commissioned a full scale model

489
00:42:04,000 --> 00:42:13,000
of anatomically correct
[NOISE OBSCURES].

490
00:42:13,000 --> 00:42:18,000
So we'll put our dinosaur here,
if I can get him to stay put for a

491
00:42:18,000 --> 00:42:23,000
minute. All right.
And at this point in evolution

492
00:42:23,000 --> 00:42:28,000
things started to get interesting.
So somewhere about here, 4 million

493
00:42:28,000 --> 00:42:34,000
years ago we've got the first
evidence of hominoids.

494
00:42:34,000 --> 00:42:39,000
Maybe 20,000 years ago we found the
cave paintings in France.

495
00:42:39,000 --> 00:42:45,000
And then there was the Roman Empire
and Columbus discovered America.

496
00:42:45,000 --> 00:42:51,000
And you were born and the Red Sox
won the World Series and the

497
00:42:51,000 --> 00:42:57,000
Patriots have just won the Super
Bowl. And we are now here at the

498
00:42:57,000 --> 00:43:03,000
peak of evolution which is,
as you all know, the MIT student.

499
00:43:03,000 --> 00:43:06,000
So we'll put our MIT student here,
who I can probably not get to stay

500
00:43:06,000 --> 00:43:10,000
put because you can never get MIT
students to stay anywhere.

501
00:43:10,000 --> 00:43:14,000
But, in any case, this is sort of a
silly demonstration.

502
00:43:14,000 --> 00:43:18,000
But there is a very profound reason
why I'm doing it.

503
00:43:18,000 --> 00:43:22,000
And I must say I don't think I'd
ever fully appreciated it until I

504
00:43:22,000 --> 00:43:26,000
actually thought of doing this demo
for the class.

505
00:43:26,000 --> 00:43:30,000
But what I think you can see is
that evolution,

506
00:43:30,000 --> 00:43:34,000
for the most part,
happened at the single cell level.

507
00:43:34,000 --> 00:43:38,000
Many people tended to think
evolution, that was about dinosaurs

508
00:43:38,000 --> 00:43:42,000
and all that stuff.
We can say that dinosaurs are,

509
00:43:42,000 --> 00:43:47,000
practically now, most of evolution
occurred at the level of single

510
00:43:47,000 --> 00:43:51,000
cells, and that all this amazing
diversity we see around us was very

511
00:43:51,000 --> 00:43:56,000
recent embellishments in evolution.
So that means when you study

512
00:43:56,000 --> 00:44:00,000
biology at the cellular and
molecular level you find tremendous

513
00:44:00,000 --> 00:44:04,000
commonalities.
If you look inside a sulfolobus

514
00:44:04,000 --> 00:44:08,000
growing in hot spring,
if you look inside an E.

515
00:44:08,000 --> 00:44:12,000
coli, if you look inside a yeast and
you look inside one of our cells you

516
00:44:12,000 --> 00:44:16,000
find that, to a huge extent,
many, many of the cellular

517
00:44:16,000 --> 00:44:20,000
components are common.
They arose similarly in evolution

518
00:44:20,000 --> 00:44:24,000
that they're shared by all forms of
life. Of course,

519
00:44:24,000 --> 00:44:28,000
there are some things that developed
later and are different.

520
00:44:28,000 --> 00:44:32,000
But that's one of the reasons that
you can learn so much by studying

521
00:44:32,000 --> 00:44:36,000
biology at the cellular molecular
level and why we'll emphasize it a

522
00:44:36,000 --> 00:44:41,000
fair bit in this course.
The other thing that I'd like to

523
00:44:41,000 --> 00:44:45,000
make out of this,
a theme that you'll hear along is

524
00:44:45,000 --> 00:44:50,000
that organisms modify their
environment. You can see that in

525
00:44:50,000 --> 00:44:54,000
the case of oxygen back when the
earth formed. There was no oxygen

526
00:44:54,000 --> 00:44:59,000
in our atmosphere. Now
we have a lot of it.

527
00:44:59,000 --> 00:45:03,000
The reason it's there is because it
was generated by organisms carrying

528
00:45:03,000 --> 00:45:08,000
out photosynthesis and generating
oxygen as a waste product.

529
00:45:08,000 --> 00:45:13,000
And that was an absolutely critical
thing to enable creatures such as

530
00:45:13,000 --> 00:45:18,000
ourselves, which are dependent on
oxygen for us just to be alive,

531
00:45:18,000 --> 00:45:23,000
if we hadn't had this change in
environment things like us could

532
00:45:23,000 --> 00:45:28,000
have, organisms like us
couldn't have evolved.

533
00:45:28,000 --> 00:45:32,000
So, anyway, I hope that will give
you a little sort of snapshot of

534
00:45:32,000 --> 00:45:37,000
evolution and will help guide your
understanding of this course.

535
00:45:37,000 --> 00:45:40,000
We'll see you at the next lecture.