Professor Kevin Ahern: Okay
folks, let's get started!
Captioning provided by
Disability Access Services
at Oregon State University.
I have a request to talk about
the photosynthetic fish today.
And it's actually relevant
to what we're talking about.
So I'm going to give you a blueprint
for how to make a photosynthetic fish,
and all I want is a postcard
out of it or something.
But if you make your million
dollars out of this idea,
then I want some kind
of credit or something.
I don't know.
So last time I got started
talking about the mitochondrion,
I talked mostly about structure,
and I gave you some
terms to be aware of.
I'll briefly tell you that mitochondria
are interesting organelles
in several perspectives.
One perspective is that
they are the only non-nuclear
organelle in animals
that has its own DNA.
So mitochondria have their own genome,
and it is called the
mitochondrial genome.
And it appears that
mitochondria have their origins
originally as a primitive bacterium
that got engulfed by another cell.
And over evolutionary
time what has happened
with the mitochondrion is it
has given up many of its genes,
and those genes have migrated
to the nuclear genome of cells.
So the mitochondrion doesn't
have everything that it needs
to make a mitochondrion.
A lot of those genes are actually
now in the genome of the cell.
But the mitochondria does
make many of its own proteins.
And the number of proteins it makes
varies from one organism to another.
The reason that we suspect
that it was engulfed
from a primordial cell is
that when we look at the way
that the sequences are
used in mitochondria,
they're more similar to the
way that bacteria use them
than the way that
eukaryotic cells use them.
So pretty good evidence
that mitochondria
were originally free-living
organisms of their own.
The other organelle
that has its own genome
are the chloroplasts.
And the chloroplasts are in fact
related to the mitochondrion.
And it appears that they, too,
probably were originally engulfed cells.
Now when we talk about
reduction-oxidation,
which I have briefly mentioned
and I'll briefly mention again,
we remember that reduction-oxidation
always occur together.
Every reduction leads to an oxidation.
And that's because reduction
means gain of electrons
and oxidation means loss of electrons.
So in order for something
to gain electrons,
something else has to lose them.
We can measure the tendency
with which that occurs
by doing some fancy experiments
that I'm not going to talk about
and create what is
called a redox potential.
And they're expressed in voltages.
You can see these voltages up here.
And the voltages are such that
the more positive the voltage,
the redox potential
voltage, actually is,
the stronger the pull is for electrons.
So we see that at the
very bottom of this scale
that oxygen really has very
good affinity for electrons.
And it's no surprise
that oxygen is in fact
the terminal electron acceptor
of the electron transport system.
The result of oxygen
accepting those electrons
plus two protons is that
we create molecular water.
Now what I want to do is dive into
the electron transport
system and say a few words
about how it works, and
you probably had this
in other classes before.
So I'm probably not going to
at least at the surface level
tell you anything that's
basically very new.
Electron transport system
is a system where electrons
are moved from one, what I
will call, complex to another.
And these complexes are
located in the membrane,
the inner mitochondrial membrane.
This is the membrane I've
told you that was so important
because it was impermeable to protons.
And this inner mitochondrial membrane
has many, many, many
proteins embedded in it.
The inner mitochondrial membrane,
I've mentioned in class before,
it has as much as 90% of its
mass comprised of proteins.
So it's very, very rich in proteins.
And as we will see, these
proteins largely are these guys
that you see on the screen.
So what happens in electron transport?
Well, if you recall in glycolysis
and in the citric acid cycle,
we made reduced electron carriers.
This included NADH in glycolysis,
it included NADH and FADH2
in the citric acid cycle.
Now you see the citric acid
cycle depicted on the screen.
And the reason you see the citric
acid cycle depicted on the screen
and not glycolysis is that
glycolysis occurs in the cytoplasm.
And cells cannot directly get
NADH into the mitochondrion.
They have to use a shuttle.
They have to use some tricks
whereas the reduced electron carriers
NADH and FADH2 that are
produced in the citric acid cycle
are just sitting here waiting
to donate their electrons.
Well, in the electron transport system,
we see that NADH and FADH2
have two different routes
that they can take.
NADH donates its electrons to Complex 1.
And if you get looking through
books, you will see some very long,
mouthful names for Complex 1, Complex 2,
Complex 3, and Complex 4.
We're not going to use
those long, mouthful names.
We're going to call them
Complex 1, Complex 2,
Complex 3, Complex 4.
Very simple things.
Now NADH donates electrons to Complex 1.
When that happens, NADH becomes NAD.
So that's how we're regenerating
NAD in the mitochondrion.
We're regenerating NAD by
donating electrons to Complex I.
Complex I takes those electrons,
and this is a transport
system so the electrons
are moving from one position to
another, to another, to another.
This figure is a little
misleading in that
it looks like Complex 1 electrons
are going through Complex 2.
That's not correct.
Complex I donates its electrons directly
to this little thing called coenzyme Q.
Coenzyme Q is the only portion
of the cycle that's not a protein.
It's a small molecule.
And coenzyme Q has an
interesting and important ability.
Coenzyme Q has the ability
to accept electrons in pairs.
When NADH donates its electrons,
it is donating a pair of
electrons to Complex 1.
And Complex 1 is donating that
pair of electrons to coenzyme Q.
However, coenzyme Q has the
ability to accept two electrons,
but it passes them off one at a time.
And that turns out to be important,
because Complex 3 can't
take a pair at a time.
They can only take one at a time.
So coenzyme Q is what I refer
to in the mitochondrial membrane
as the traffic cop.
It's deciding when electrons
are passing through,
it's accepting them in pairs,
passing them off one at a time.
FADH2 you recall was also
produced in the citric acid cycle.
That's also a reduced electron carrier.
And that also needs to
be converted back to FAD.
FADH2 dumps its
electrons into Complex 2.
And Complex 2 also donates
electrons to coenzyme Q.
So now we see the traffic
cop nature of this.
We see electrons coming in from
a couple of different directions,
we see them coming in in
pairs, and we see coenzyme Q
passing them off one at a time
because these guys downstream can
only handle them one at a time.
Well, coenzyme Q passes its
electrons off to Complex 3.
We'll see that cycle
up close and personal
in a couple of minutes in
something called the Q Cycle.
Complex 3 passes its electrons
off to another protein.
It's not shown on here,
which is another reason
I don't like this figure,
called cytochrome c.
It's a small protein.
It's located in the inner
mitochondrial membrane as well.
Cytochrome c accepts those electrons
and passes them off to Complex 4.
And it is in Complex
IV that those electrons
reach their final destination,
that final destination
being oxygen to make water.
Now in the process of this happening,
there's a couple of
considerations that we have.
The first one I'm going to
give you is something I'll come
and talk about later,
and that is that electrons
are starting in pairs, they're
hitting the traffic cop,
and they're going off in ones,
and they're reducing
molecular oxygen to water.
Obviously, you're
going to make two waters
if you do this because
you have two oxygen atoms.
In order to make two water
molecules, it takes four electrons.
Four electrons.
Those electrons are coming
through one at a time.
If something interrupts
the flow of electrons,
we make oxygen species that
have unpaired electrons.
Those are what we refer to
as reactive oxygen species
because they are very reactive.
And because they're reactive,
what we see is that
they can cause damage.
They will react with things that
we don't want them to react to.
And one of the things that we
see in mitochondria as they age,
we look at the
mitochondria of an old cell
and we compare it to the
mitochondria of a new cell,
say that of my cell versus your cells,
my mitochondria are going
to look more beat up.
And that's because my
mitochondria have had more chances
to make more reactive oxygen species
and react with things that
I don't necessarily want them
to react with and cause
damage to the mitochondria.
Important consideration.
Now that's one consideration.
So reactive oxygen species, I'll
say a little more about later.
But before I do that, I need to tell you
the most important component
of the electron transport system
besides the oxidation of NADH and FADH2.
The most important
consideration for the cell
is the fact that the
movement of electrons
through three of the complexes
causes the complexes
to pump protons out.
So we see Complex 1, as
electrons move through it,
protons get pumped out.
Complex 3, as electrons move through it,
protons are pumped out.
Complex 4, as electrons
are moving through it,
protons are being pumped out.
You may recall that
a gradient of protons,
that is more protons
outside than inside,
creates an electrochemical potential.
You saw how that could be used
to do things in the
membrane transport lecture.
That electrochemical
potential in the mitochondrion
is used to make ATP in
oxidative phosphorylation.
So like in that schematic diagram
that I showed you on Monday,
this process is charging the battery.
It is putting those protons
out there, creating a gradient.
Those protons want to come back in.
And we will see that in the
oxidative phosphorylation process,
they come in through a
protein that makes ATP.
Very important thing.
Another thing that we note
is we look at the fate of
electrons that come in through NADH
and we compare them to
the fate of electrons
coming in through FADH2,
and we see that electrons
coming through NADH
have one more opportunity
to pump protons
than FADH2 because FADH2 is
bypassing that very first step.
Now people do calculations.
And I want to emphasize these
calculations are approximations.
We always want to say
there's one of this,
one of this, one of this because
you get taught in chemistry
that one NaCl makes one
Na and one Cl-, right?
Stoichiometrically,
that's what that means.
When we start measuring amounts
of products that are made here,
they are not stoichiometric.
We can approximate how much ATP is made
by how many electrons flow through.
So let me just tell
you about that, alright?
For every pair of electrons
that start with NADH,
there's enough
electrochemical gradient made
to synthesize approximately three ATPs.
People argue about the exact amount.
It really doesn't matter.
It's approximately three ATPs
for each pair of
electrons coming from NADH.
Now FADH2 doesn't get the opportunity
to generate so many
protons pumped as does NADH,
and so we would expect
that FADH2 would result
in the production of less
ATP, and that's correct.
Approximately, again approximately,
two ATPs per pair of electrons coming in
through FADH2 are produced.
Now I want to emphasize these ATPs
are not produced in electron transport.
They are produced in
oxidative phosphorylation.
We're charging the battery here.
We're discharging it in
oxidative phosphorylation.
It's the discharge of the battery
that yields the production of ATP.
Yes, back there.
Female student: Is the
electrochemical gradient
different than the proton motor force?
Professor Kevin Ahern: Is
the electrochemical gradient
different from the proton motor force?
And the answer is they
are one and the same.
Ulterior motives.
Right here and then back there
to you Jarrod in just a second.
Male student: The
reactive oxygen species,
are those different in anyway
from calling them free radicals?
Is there a distinction?
Professor Kevin Ahern: Are
the reactive oxygen species
different from free radicals?
They are a type of free radical.
They are specifically
an oxygen free radical.
Yes, sir.
Jarrod: Are these complexes…[inaudible]
Professor Kevin Ahern:
That's a good question.
Jarrod asked if they're
organized like we see them here
or are they more chaotic than that.
The answer is they are
more chaotic than that.
We're actually looking
at a slice right here,
and so we put that
slice very simply there.
In fact, a membrane has two dimensions
or almost three dimensions that's there.
And so these guys are bouncing around
with each other quite a bit.
So it's a lot more chaotic
than what you actually see here.
Yes, sir.
Male student: Does that
high proportion of protein
in the mitochondrial inner
membrane make it more inflexible
and enable it to maintain the cristae?
Professor Kevin Ahern: His
question is does the high
concentration of protein in
the membrane make the membrane
less flexible and less
able to support cristae,
I think that was sort of…
Male student: More able.
Professor Kevin Ahern: More able, okay.
I don't know the
answer to that question.
You would expect that
if a membrane had a lot…
I would expect that if a membrane
had a lot of protein in it,
it would in fact be less flexible.
But I don't know the
answer to your question.
Male student: They don't
have like a cytoskeleton?
Professor Kevin Ahern:
Not a cytoskeleton per say
like we think of in the cytoplasm, no.
Yes?
Male student: So is cytochrome
c an integral membrane protein?
Professor Kevin Ahern:
Is the cytochrome c
an integral membrane protein?
The cytochrome c is actually
what we would classify as
a peripheral membrane protein.
So it's only embedded in
one layer of the bilayer.
Good question.
I'm going to say a little bit
more about some of these things.
I've just given you an
overview there of the cycle.
I wanna say a little bit
about inhibition of this cycle.
Now don't let these names confuse you.
There's Complex 1.
There's Coenzyme Q.
There's Complex 3.
There's cytochrome c.
There's Complex 4.
And we see that if we were to bring in,
Complex II would come in right here.
Now, the reason I show you
this figure is not to give you
a bunch of names to confuse
you because as I said,
I'm not asking you to know what
the names of those complexes are,
but rather to show you that
the cycle can be blocked
by various chemicals.
And these turn out to be
interesting and useful things.
The first one is the block of
the electrons out of Complex 1.
The movement of
electrons out of Complex 1
can be blocked by two
compounds, rotenone and amytal.
Rotenone is an interesting compound.
It is actually used as an insecticide.
It is a natural compound.
It is actually produced by some plants.
And so it's actually used in
organic gardening and farming.
And it has a very
nasty effect on insects.
So insects are much more
susceptible to rotenone than we are.
I don't recommend eating
rotenone, for example.
But insects are much more
readily killed by rotenone.
And the way it's acting is it's acting
on the movement of electrons
through their Complex 1.
Well, you sit here, and you
think, 'Well, if I block Complex 1,
could I still have electron
transport going on?'
And the answer is yes
I could to some extent,
because I could shuttle
things in through Complex 2.
I'm not recommending for career purposes
that you shut off your Complex 1,
but that does give you an
alternative if you have Complex 2.
If we look at the movement of electrons
out of Complex 3 into cytochrome c,
that movement can be blocked
by the compound antimycin A.
And if you're thinking that antimycin A
might be a nastier compound
to us than rotenone is,
you would be correct.
You might think that it
would just completely kill us.
And to be honest with you,
I don't know its exact poisonous nature.
But I will tell you
that there are some ways
of getting electrons in past Complex 3.
They're kind of unusual,
but there may be a very minor
way of bypassing a block here.
The compounds that are
the most poisonous on here
are the ones that you see at the bottom
because they stop things
from moving through Complex 4.
Let's imagine we stop things here.
If we can keep everything
else going down here,
we're not so bad off.
If we stop things here and we
can keep everything going here,
we're not so bad off.
But if we stop everything
here, there's no bypassing that.
There's no bypassing a block here.
So if we block things at Complex
4, we're pretty much hosed.
Well, look at the things that are there.
Cyanide.
That's the CN.
Cyanide is nasty stuff.
Carbon monoxide.
I told you last term carbon
monoxide kills you two ways.
One, it nails your hemoglobin.
Two, it nails your
electron transport system.
Boy, talk about a way
to really get rid of you.
It's getting you in two ways.
So if we block in any of these places,
we're going to have some consequences.
And the biggest consequences
are going to be if we block right here.
Let's see.
Keeping things as simple as we can,
I'm going to move past the
quinones and the structures there,
which I don't think tell us much,
and instead show you a mechanism,
one mechanism that we'll talk about,
and it's not as nearly
as bad as it looks.
It's a mechanism for how electrons
are moving from Coenzyme Q
into Complex 3 and through it.
So let me orient you for
where we're at right here.
As we look at the screen, here
is something called the Q pool.
Why do we call it the Q pool,
and why don't we call it Coenzyme Q?
Well, we can think of the Q pool
as being composed of two things,
Coenzyme Q that has gotten electrons
and Coenzyme Q that
hasn't gotten electrons.
So we've got a mixture of those
in the mitochondrial membrane.
Some of them have electrons.
Some of them don't have electrons.
We call that mixture of the
two the Coenzyme Q pool, okay?
Coenzyme Q I told you is capable
of accepting two electrons
and passing them off one at a time.
In this system, the two
electrons are shown right here.
When you see QH2, you have
something that has two electrons.
When you see something
that has one electron,
it's written as a Q dot minus,
and when you see something
with no electrons,
you simply see it as a Q.
That blue and the black
are the same thing there.
Two electrons.
One electron.
No extra electrons.
Well, what's happening in the Q cycle?
Remember this big complex is Complex 3.
The green guy on top
of it is cytochrome c.
I'm sorry, Complex 3
is passing electrons
off to cytochrome c.
The Q pool starts the process
by putting into Complex
3 two different Qs.
One Q has two electrons.
You see it right there.
One Q has no electrons.
You see it right there.
So these two guys start the process.
So don't pay attention
to anything else there.
We've just started the process.
One of these has two electrons.
One has no electrons.
Well, what happens?
We see in this process
that the electrons
go two different directions.
This guy that has two
electrons dumps one of them off
upwards to cytochrome c.
It takes the other one
and dumps it downwards
onto the Q that had no electrons.
That results in a Q having one electron.
And since it's given
up its two electrons,
it's lost both of its electrons,
it also gives up its protons.
It becomes Q.
And that's all there is to this.
We're going to finish
it up in the next cycle,
but that's all that happens.
QH2 brings in two electrons
and passes them off
two different directions, one
to cytochrome c and one to Q.
Are we clear on that?
The key is that we started
with one that had two electrons
and one that started with no electrons.
Well, this guy's done its thing.
It's given up its electrons.
It's given up its protons.
You'll notice that protons
are getting pumped out.
This guy isn't worth anything anymore.
So what happens?
It gets kicked back into the Q pool.
It's kicked out.
What happens to cytochrome c?
Well, cytochrome c is only capable
of taking one electron at a time.
So it says, "I'm outta here."
That's not shown on here.
That's a dumb thing in this figure.
Cytochrome c with that
electron takes it off.
It's going to go find
Complex IV to give it to.
So at that point, we
have nothing in here.
It would be nice if
they had a middle thing.
We have nothing in here.
And we have nothing up here.
And down here we're still
sitting here holding this one guy
that's got this one electron.
We're getting ready to
finish the whole process.
What's going to happen next?
Well, the cytochrome c that has
no electrons is going to come in.
A new QH2 is going to come in.
And what we saw happen here
is going to happen again.
Electron goes to cytochrome c.
Bang.
Electron goes to this
Q that has one electron.
And how many electrons does it have now?
Well, you can do the math.
It's got two.
We've completed the cycle.
These guys go away.
This guy goes away.
We start with an empty complex.
And we are right back where we started,
ready for a new Q and a new QH2.
I'll stop there and take questions.
This is usually where I have questions.
Yes, sir.
Male student: So were you saying
that there was an intermediate stage
where you have a Q with nothing
and a Q with one electron on it?
Professor Kevin Ahern:
So the intermediate stage
you can think of as Complex 3.
And let's say it's right here.
It simply has this guy right there.
This site is empty,
and this site is empty.
Then both of those sites
fill to get us over there.
Yes, Connie.
Connie: What is the Q pool equal to?
Professor Kevin Ahern: The
Q pool is equal to QH2 + Q.
Qs that have two electrons
and Qs that have no electrons.
Jodi?
Jodi: That's entirely in
the membrane itself, correct?
Professor Kevin Ahern: It's
entirely in the membrane itself.
Jodi: So if you're looking at this,
there should actually be a
band of membrane with Q pool,
and then matrix on the bottom,
and intermembrane on the top?
Professor Kevin Ahern: That's right.
Female student: Is it only…[inaudible]
Professor Kevin Ahern:
The one, that's why
it gets held in here.
The cell doesn't let that loose.
That guy's reactive, and
Complex III just holds onto it.
That's why even in this
intermediate state, it's still there.
Good question.
Yes?
Student: [Inaudible]
Professor: Say it again.
Student: For the second part
of the Q cycle [inaudible]
Professor: So keep in
mind, people want to say
this proton goes there
and this proton goes there.
We've got enormous numbers
of protons in this solution.
We're seeing two protons come in.
They can come from anywhere.
So we're not directly tracking
one proton going to that proton.
Keep in mind this process.
I'm just showing you one of these.
There are thousands of these
going on in every mitochondrion
in every cell of your body all the time.
So these are being pulled
out just generically
from the pool of protons that are there.
Student: How does Complex
3 facilitate all this?
Does it kind of just hold everything?
Professor: How does Complex
3 facilitate all this?
It facilitates it by
having these docking sites.
If you think about it,
and it's a good question
because Complex 3 is
doing a lot of stuff here.
Complex 3 is just a meeting place
for all these things to come together.
We can think of it as
like in the old days
when they had what was
called a telephone exchange.
And I'm not even old enough I know this,
but I can read history books, okay.
In the old days when
you had a telephone,
every town had their exchange.
And the exchange had an
operator who sat there,
and a person calls up and
says, "I wanna call so and so."
Well, the operator has to say, "Okay.
“Here's your line.
“I'm going to plug it
into this line over here."
So the telephone exchange provided a way
to make connections
between a variety of things
and because of that, make
communications possible.
This is what's happening here.
Here's a connection.
Here's a connection.
These connections are
wired such that electrons
and protons can move accordingly.
It's a good thing to think about.
There's a lot of complexity here.
Student: So when you
say that the complex
is pumping protons out,
is that the protons coming
onto that Q…[inaudible]
Professor: So again, you're
trying to track the protons.
But in this case I can
answer your question, yes.
The protons that are being pumped out
are in fact the protons
that are on right there.
What I'm saying you can't
track is you can't track these,
because these are just
being pulled out of solution.
Student: But it's not like one proton
going all the way through.
Professor: Protons
are going from QH2 out.
That's where they're going from.
Where do these guys come from?
Well, look where they came from.
They came into here to make this.
So ultimately the protons
did come from the matrix,
alright, but in the immediate
moment they're coming from QH2.
Look over this.
It's fairly straightforward.
Like I said, the main thing is
QH2 splits electrons each way.
You got it.
Don't confuse electrons and protons.
Protons get pumped.
Electrons get moved.
The force that makes
the protons get pumped
is the movement of electrons.
That's the force.
That's the energy that
makes the protons get pumped.
Let's take a minute and
think about Complex 4.
Complex 4 is interesting.
Now, when we look at Complex 3,
what we see is that we
have involvement of hemes
that facilitate this
movement of electrons.
Heme we saw of course in hemoglobin.
And that heme, you
remember, is that structure,
that flat structure that
we had in hemoglobin.
It had an iron in the middle of it.
Hemes have iron.
However, when we look at Complex 4
So for example, Complex 3 has hemes;
those hemes have iron;
our mitochondria need iron
so that electron transport can occur.
However, Complex 4 is interesting
in that addition to having
iron, we have copper.
So we see a variation
on this theme here.
We have copper.
There's heme to remind
you what heme looks like.
We have copper ions that
are able to facilitate
the movement of electrons.
So now I'm moving to Complex 4,
and I'm going to show you how
oxygen is converted to water.
Here's Complex 4.
Here is an incoming cytochrome c.
And again, this isn't the
best figure in the world,
so I've got to talk you
through it a little bit.
Remember that electrons
come in one at a time.
You're seeing them coming
in as two cytochrome c's,
but in fact it takes one.
The first one has to let go
of its electron and go away.
Then a second one has to come in,
and let go of its electron, and go away.
That process is happening
as we are right here.
What we're doing is we're
taking an oxidized iron
and we're taking an oxidized copper.
What does it mean to
have an oxidized iron?
An oxidized iron has a charge of +3.
An oxidized copper has a charge of +2.
If we add one electron to each of those,
we create an iron with a charge of +2
and a copper with a charge of +1.
That's what we see here in red.
So the very first step,
one electron gets pushed
all the way over here to copper.
One electron gets pushed to iron.
And we're here.
So we've got two electrons
that have come in.
The next step in the
process, molecular oxygen sees
this as a great thing
to bind to, and it does.
And molecular oxygen, you may
recall on that redox scale,
really likes electrons.
What's it going to do?
Well, it's going to pull
electrons towards itself.
And you see these nice,
red, reduced guys became blue
because oxygen is
gobbling up the electrons.
And again, we see them coming in singly
even though they're showing two here.
One comes in.
Then another one comes in.
And the result of the addition
of these two more electrons
causes these guys to become
hydroxyl groups on an iron
and on a copper.
The next step in the process,
two protons look at these guys
and say, "Oh, we can make water."
That's what they do.
Water comes off, and we're left back
with the oxidized iron and copper.
Now it's at this point we think about,
'Well, what if only one
electron came in, what happens?'
Well, I'm going to make something
in here that's very reactive.
What if I get stuck here?
I've got something that's very reactive.
If I make only one of these,
I've got something that's very reactive.
Anytime I don't complete this cycle,
I'm making something in
here that's very reactive
and the way that very reactive thing
is going to react is going to
be difficult for me to predict.
It's going to cause some problems.
Questions about this?
You guys all look worried now.
Yes, sir?
Male student: So in this particular step
where the two protons come in
and you form the hydroxyl groups,
do the electrons actually come in first
and then nucleophilically attack protons
from the matrix over them?
Or does it solvate instead?
Or does it really matter?
Professor Kevin Ahern: So the protons
are in fact attacking this.
Those electrons have to come in first.
You have to make that hydroxyl
before the proton will attack that.
Yes, Connie?
Connie: How often does the
electron stream get cut off?
Professor Kevin Ahern: How
often does it get cut off?
Well, we like to think about things
in the macroscopic world as,
"I can turn the lights off.
And then the lights are off.
And that's that."
But when we think about
the chaos that's happening
inside of cells, that we
have thousands of these
going on constantly, it's
a little different scenario.
And if you want an answer
in terms of a percentage,
I can't give that to you.
And the reason I can't give that to you
is that it will vary upon the
circumstances of your nutrition.
It will vary upon the
circumstances of your exercise.
A whole bunch of things.
Does this mean that
if you exercise more,
you make more reactive oxygen species?
The answer turns out surprisingly no.
So this is not a reason not to exercise.
Dang!
"I'm looking out for my health
“sitting here on the
couch watching the tube."
Alright, so that's
basically what I want to say
about electron transport.
I want to jump to
oxidative phosphorylation.
I'm going to come back
and talk about superoxide
dismutase next time.
Because it is very relevant right now
that we think about
oxidative phosphorylation.
Oxidative phosphorylation,
when it was first proposed
by Peter Mitchell back
in the early 1960s,
it was Mitchell's Folly.
People said, "There's no way
that this is the way we make ATP."
Now he proposed this mechanism
that turned out to be right,
and he later won the Nobel Prize for it,
because nobody could find
a really good way that ATP
was being made by mitochondria.
The reason was that everybody
was looking for
substrate-level phosphorylation.
You've seen substrate-level
phosphorylation.
If you recall, that's
where a high energy molecule
transfers a phosphate
to an ADP to make an ATP.
And that does happen to some extent.
We see it happen in glycolysis.
We see it happen in
the citric acid cycle.
That's how GTP gets made.
But neither one of those
reactions could account
for the vast majority
of ATP that's being made.
So people said for the longest time,
"Well, there's got to be a
really high energy phosphate
“that's being made in the mitochondrion,
“and then it's transferring
that phosphate to an ADP."
Well, people looked, and looked,
and looked, and looked,
and nobody could find it.
The reason they couldn't find
it was because it didn't exist.
Well, Mitchell says,
"We've got to rethink
“how ATP is being made.
“We have to think about the
mitochondrion being like a circuit."
And what happens is what
I've already described to you.
Electrons move through complexes.
They pump protons out.
That gradient is the energy source.
And when the protons come
back in through Complex 5,
which I'll show you in
a second, ATP is made.
And the idea of cells
having the equivalent
of a circuit in them was so
foreign in the early '60s,
as I said, it was
literally Mitchell's Folly.
Well, he turned out to be exactly right.
It's better to be right
than to go along with
the crowd in my opinion.
My mother always used
to tell me that, right?
Did your mothers ever
used to tell you that?
"I suppose if they went
and jumped off a cliff,
“you would, too, right."
He was right.
He stood by his guns, and he was right.
His hypothesis was called
the Chemiosmotic Hypothesis.
The Chemiosmotic Hypothesis.
It's what you've already seen.
You already accept it as fact.
He had to derive it from what
he knew about mitochondria
and how they worked.
Let's think about what it
requires for it to work.
What do we have to have?
Well, first of all we have to
have pumping of protons, right?
We have to have movement
of electrons, right?
We have to create an
electrochemical gradient,
which means that we
can't break the gradient.
If we use dinitrophenol, what
going to happen to the gradient?
It's going to disappear, and
we're not going to make ATP.
That was the miracle
diet drug, remember?
So we have to have an intact
mitochondrial inner membrane.
And last, we have to have ADP.
Because if we don't have ADP,
we're going to be in trouble.
Now you'll see why that's
the case in a second.
So those are the things
we have to have in order
for this guy to go forward.
Here's what's happening.
These guys have been pump,
pump, pump, pump, pumping.
High concentration of protons.
Protons want back in.
This is an intermembrane space.
This is like the folding
of a cristae right here.
What you see in red on the screen
is something people call Complex 5.
And you can call it Complex 5.
But just because it has the
word "complex" in its name,
does not mean it's part
of electron transport.
It's not.
It is dependent upon electron transport,
but you see no electrons
involved with Complex 5.
What Complex 5 does is
it provides a channel,
and there's another channel for us,
it provides a channel for
protons to pass through it.
And here's the remarkable thing.
I used to have a video
I could show you of this.
And the link broke, and
they don't use it anymore.
So I can't show you, unfortunately.
But it's beautiful.
Movement of protons
through this guy right here
causes this mushroom structure
like you see to spin like a propeller.
It spins like a propeller.
It literally spins.
Hundreds of rpm.
The spinning of this guy
is what makes the ATP.
I will show you how ATP is
synthesized there in just a second.
It's a remarkable thing.
When we think about nanomachines,
we think about little complexes
that we can make that do things.
You always see these
headlines about people
who've designed a new
nanomolecule that can walk.
Well, nature figured these things out
long before we started
playing with these guys.
Nature figured out how
to make a propeller.
Or if you want to think
about it like a turbine.
I like to think about it
like a turbine in a waterfall.
The spin that's making electricity.
This guy's capturing
energy with its spinning
and using that energy to make ATP.
How does it work?
Well, another name for
Complex 5 is ATP synthase.
Either one of those,
I'll take either name.
ATP synthase.
This is where it looks
like at the level.
Now unfortunately, it's
flipped from what it was before.
So the mushroom structure
we saw before was on top.
Now it's on the bottom.
It doesn't really matter
relative to our purposes.
This mushroom structure of Complex 5
has a stem that's embedded in
the inner mitochondrial membrane,
and it has a head, the head
of the mushroom is down here.
It is in the head where the ATP is made.
So orienting you here, we
are in the matrix down here.
We are in the intermembrane space above.
The entry of protons comes
from the top downwards.
And they come in this
little slot right here.
It is like loading a gun or something.
It comes in that
little slot right there.
The proton then migrates to
one of these little blue tubes.
The migration of that proton
is what causes that spinning to occur.
Once a proton gets in there, it spins.
Another proton, it spins.
Another proton, it spins.
It keeps spinning.
Eventually, it spins
all the way back around
and comes out this side over here.
So the proton goes on a
little joyride in there.
It comes in here.
It goes out here.
And in the meantime it
causes this guy to spin.
Well, what does that spinning do?
It doesn't spin the top.
The spinning is inside of the top.
So I lied to you a little bit before.
The spinning is inside of that top.
That's where the propeller is.
It's the spinning inside of this
top that causes ATP to be made.
So we'll see that the
movement inside of this top
causes conformational changes
that cause ATP to be synthesized.
Does everybody got this visualized?
Protons in.
Spinning here.
Attachment here.
And this thing right here is spinning
in the middle of this complex.
How was ATP made?
ATP is made.
Now we're looking at that stalk.
Not the stalk, I'm sorry,
the head of the mushroom.
Here is the head of
the mushroom right here.
What we see is that there
are two identical units
called alpha and beta. . . I'm sorry.
Two units, three of which are identical.
Alpha, alpha, alpha.
Beta, beta, beta.
You see that they have slightly
different configurations
on the screen.
And the reason they have
different configurations
depends upon which direction
this middle spinning
thing is pointing to.
In this case, it's pointing downwards.
And when it's pointing
downwards like we see here,
that beta unit is in
the T configuration.
There's three
configurations it can be in.
This beta unit over here is
facing a different portion
of that middle propeller,
and it's in what is
called the O configuration.
This guy over here doesn't
have anybody to play with,
and it's in the L configuration.
What do L, T, and O correspond to?
L, T, and O correspond
to loose, tight, and open.
They each have a function.
Open is basically releasing.
It's a little misleading here.
But it's basically releasing ATP.
Once it releases ATP,
ADP and Pi come back in.
Loose is more tight than open.
We've closed the doors, and
we've got everybody inside now.
Tight is where ATP is made.
What's happening in tight
is this conformational change
known as T is literally
scrunching ADP and Pi together
so that chemically
they react and make ATP.
This slight change in
structure that's happening
upon the configuration of T
is scrunching these two
guys together to make an ATP.
When this guy now flips
into the open configuration,
what's going to happen?
ATP is going to get released.
Well, what's happening?
These three aren't changing position.
The middle thing is changing position.
So now when this guy rotates
one-third of a revolution,
what's going to happen?
This portion is going
to be pointing there.
What's going to happen to it?
It's going to go to the loose, right?
We're going to go to loose.
This guy over here is
going to go to become tight.
And this guy down here
is going to become open.
Loose, tight, open.
Loose, tight, open.
That's how things move through.
Yes, ma'am.
Female student: So can ATP only
be produced in the beta subunit?
Professor Kevin Ahern: ATP is
produced in the beta subunit.
That's correct.
Female student: And there's
always ATP. . . [inaudible]
Professor Kevin Ahern: There's
always, well, not always
because as I said this isn't
showing the release of ATP.
So this guy is releasing
ATP and then allowing new ADP
and Pi to come in.
Yes, Jarrod?
Jarrod: [Inaudible]
Professor Kevin Ahern: Say it again.
Jarrod: This reaction is reversible?
Professor Kevin Ahern:
The reaction is reversible.
Jarrod: And then you could
also move hydrogen backwards by…
Professor Kevin Ahern: You
could move hydrogen backwards.
Again, that would be an
unusual thing to happen,
but that is possible to have happen.
Okay, I was going to talk about fish,
but I don't have time.
Let's sing one song.
And it's relevant to this,
and then we'll call it a day.
Anybody like Monty Python?
Lumberjack song.
I'll sing a line.
You sing back at me.
[I'm a Little Mitochondrion
by Kevin Ahern]
[professor sings] Oh I'm
a little mitochondrion
Who gives you energy
I use my proton gradient
To make the ATPs
[class sings] He's a
little mitochondrion
Who gives us energy
He uses proton gradients
To make some ATPs
[professor sings] Electrons
flow through Complex 2
To traffic cop Co-Q
Whenever they arrive there in
An FADH-two
[class sings] Electrons
flow through Complex 2
To traffic cop Co-Q
Whenever they arrive there in
An FADH-two
[professor sings] Yes
tightly coupled is my state
Unless I get a hole
Created in my membrane by
Some
di-ni-tro-phenol
[class sings] Yes tightly
coupled is his state
Unless he gets a hole
Created in his membrane by
Some
di-ni-tro-phenol
[professor sings] Both
rotenone and cyanide
Stop my electron flow
And halt the Calculation of
My "P" to "O" ratio
[class sings] Both rotenone and cyanide
Stop his electron flow
And halt the calculation of
His "P" to "O" ratio
Professor Ahern: Alright, guys.
Thank you.
See you on Friday.
[END]
