>> Welcome to metabolism and bioenergetics part three.
This video lecture will focus
on the electron transport chain and ATP production.
Let's get started.
So, we're going to have to bring in some biology here
because the electron transport chain is happening
in the mitochondria of the cell.
So let's -- let's work our way
down into the actual organelle, right?
So here is our eukaryotic cell.
And remember that the cytosol is the fluid portion
of the cytoplasm.
And now this is just a reminder, remember so by now -- right --
what -- there's an energetic process that can happen
in the cytosol of the cell.
So ideally there's glycolysis just popping into your brain.
And if not, just keep working on it, right?
So glycolysis, right?
So we do have some cells in our body
that do not have mitochondria.
Our red blood cells and our brain cells,
they don't have mitochondria.
Their entire energy production comes from glycolysis,
which we've already studied.
But right now, we're going to focus on the energy processes
that do occur in the mitochondria.
So that's right here.
And there's quite a few.
And the mitochondria structure --
if we go in and slice out a chunk,
we can see that there is a double membrane, OK?
So here we have the inner membrane --
And then there's an outer membrane.
And then there's this space between them.
The inter-membrane space.
And when we actually start to talk
about the electron transport chain, we will be talking
in particular about this inter-membrane space.
So that's why we're taking the time to make sure
that you understand where these are in the mitochondria.
And in the very center
of the mitochondria -- that is the matrix.
We will also be talking about that a little bit.
And then here, when we see the blow up --
here's the ATP synthase.
After the electron transport chain,
then the ATP synthase actually produces the ATP.
So this is all really complex and it's not very practical
to draw this over and over.
So it gets simplified into this little schematic here.
So here's the citric acid cycle that we've talked about before.
And then what the new part is that we're going to focus
on today then would be here is --
right imbedded in the membrane --
this would be the electron transport chain, all right?
So I'm just going to draw this box right here, right?
That would be -- whoops -- make sure you have enough room.
Right -- this would be the electron transport chain,
all right?
So here, right, so here on the inside, right?
There's the inner membrane, there's the outer membrane
and then here's
that inter-membrane space in the middle.
OK, so the electron transport chain has four complexes.
Complexes one through four and then from there,
that feeds into ATP synthase, which we see in our diagram.
And sometimes, some authors
in some books actually call this complex five.
All right, so coming out of the citric acid cycle,
we have learned -- right, that we get reduced co-enzymes.
Like NADH and FADH2.
And we're also going to need oxygen.
It also comes in as a reactant in the electron transport chain.
It's going to spit out water and then continue on
and then during the ATP synthase,
basically the electron transport chain is going
to generate this proton motive force
that will then fuel the ATP synthase to produce the ATP.
So the electron transport chain is like charging up --
charging up the motor and then the --
and then the motor then is the ATP synthase,
which actually produces the ATP.
All right, so now that we have the big picture
and we understand where this is happening in the cell
and overview of the energy -- let's go in and actually look
at the electron transport chain, all right?
So I put this little diagram here to remind you of --
this is the -- just a small piece of the mitochondria.
And here is the one, two, three, four --
the four complexes of the electron transport chain.
And then here would be the ATP synthase or complex five.
All right, so -- right?
So remember, right, that the citric acid cycle has produced
three NADH's, right?
One turn of the citric acid cycle produces three NADH's
and one FADH2.
Now, it's important to note
that the NADH enters the electron transport chain
at complex one.
And see how complex one crosses through the inner membrane.
And so during complex one, protons are pushed
into the inter-membrane space.
Then these electrons are -- all go through a handoff.
There's CoQ, it's a coenzyme.
It's able to move through the inter-membrane.
It passes off the electrons to complex three
and more electrons are pushed into the inter-membrane space.
And then cytochrome C further pushes the electrons along
to complex four and we get additional protons pumped
into the inter-membrane space.
And then ultimately there --
these protons come back into the matrix and that's
when we get our ATP production.
So, the difference between the NADH and the FADH2 is FADH2 --
it comes in at complex two.
Notice that complex two does not go fully
through the inter-membrane.
So there are no protons pushed in complex two.
So the electrons from the FADH2 go into two, three, to four.
So with FADH2, less hydrogen's are pumped
into the inter-membrane space.
So let's talk a little bit more about this now
that we've carefully looked at the diagram.
Let's talk about the importance, right?
So the accumulation of these hydrogen's, right?
In the inter-membrane space creates stored chemical
and electrical potential energy, right?
Because we've learned about diffusion
when we studied solution chemistry, right?
There's that natural tendency for ions to diffuse from areas
of high concentration to low concentration, right?
So here we have our high H-plus concentration and down here
in the matrix, we have a low H-plus concentration.
So the hydrogen ions want to become homogeneous,
so there's this potential energy that they just want to go,
but they're blocked by the ATP synthase, right?
And so the only way for the protons to reenter, right --
is through the ATP synthase.
So the protons are pumped out of the matrix,
via the electron transport chain, and then they return,
providing energy -- kind of like a water wheel, right?
Spinning at a mill.
And then that's what produces the energy for the ATP synthase
to convert the ADP into the ATP, all right?
So that's the electron transport chain.
And this is a very simplified model of it,
but it's enough for us.
You know, if you really become intrigued and decide
to be a biochemist then you can go in
and learn a lot more about it.
But for us, this serves our needs.
I'd like to look a little deeper at the oxidation
and reduction reactions of the electron transport chain, right?
As we mentioned previously, right, the complexes are fixed
within the inter-membrane and so there are a variety of compounds
that actually move the electrons from one complex to another.
And so this is a great opportunity
to take the oxidation and reduction knowledge
that we've learned and apply it to the electron transport chain.
All right, so there's two tasks here --
label the coenzymes as oxidized or reduced,
and then add the appropriate label
to the reaction arrows, right?
Because during the electron transport chain, if we're going
to have oxidation and reduction reactions, right?
We need oxidizing and reducing agents
to do the compliment reaction so that we can have the handoff.
This would be a good place for you to pause the video
and see how well you do on your own.
And then we can compare answers.
>> OK. Let's see how you did, right?
So here's coenzyme Q -- that often gets simplified as CoQ.
And then here's coenzyme Q and then H2, right?
And this is an organic compound --
we see, right -- the gain of hydrogen.
So even with -- just from the abbreviation we can tell
that this is the reduced form and this is the oxidized form.
But then let's look at the actual structure
to convince you, right here we see, right --
that we have two carbon oxygen bonds
and now we only have one, right?
So this is the oxidized form, more bonds to oxygen,
reduced form, less bonds.
So when the oxidized goes to the reduced, right?
That's going to be reduction.
And then if the reduced goes to the oxidized, right?
So it's important to be clear on the terms, whether we're talking
about the form of the compound or the reaction.
Make sure to answer the question that's being asked, right.
OK, so here iron is a big deal.
It appears in the cytochrome C proteins.
And if we look here -- so here's the iron
in the plus three, right?
And now it's a gaining an electron to the plus two, right?
So this is the oxidized state
and then this would be the reduced state, right?
Because we gained electrons so this is our reduction reaction.
And then it can go back and oxidized over and over again.
Our bodies are so efficient,
that we're the ultimate recyclers.
It's a great thing.
Oh, so we needed to put these on our arrows up here --
we'll put it up here too, just to make sure
that everyone's clear.
OK, and then this last one.
It's pretty straightforward.
And it's very similar.
If you understand cytochrome C,
then here are the iron-sulfur complexes.
So different chemical structure,
but notice that they're still taking advantage of --
here we have the iron three, right?
So the iron three is the oxidized form and then--
oops, oh there it is -- there's the iron three
and then there's the iron two and that's the reduced form.
So it's the exact same answers as before.
So here, there's our reduction reaction gaining electrons
and our oxidation.
So those, as our electrons are handed off,
these coenzymes are needed as part of the electron relay.
All right, so now let's practice this on the next page.
So here is a portion
of the electron transport chain pathway for complex one.
And here are three tasks.
So relate this diagram to the structure of the mitochondria,
where's the inter-membrane space?
And where's the matrix?
And then add the missing elements or ions
and classify each reaction, all right?
OK, let's do A first, right?
So we're going to pump the electrons
in to the inter-membrane space.
So this part of the diagram would be
where the inter-membrane space is.
Oops, lost our plus, OK.
And so that means that the matrix would be
down here, right?
So this would represent the center of the mitochondria,
the inter-membrane space and then the outer membrane.
All right, now at first B can look a little tricky.
Yikes, how do I know what to do?
Well, what do we know about NADH, right?
We know that it has two forms.
So if it's NADH here, it has to be NAD-plus.
So NAD-plus going to NADH, right?
It's gaining a hydrogen so this would be a reduction reaction.
Now as the NAD-plus is being reduced,
the CoQ is being oxidized.
CoQ, right?
So that would be our oxidation.
And then, right -- so now CoQ -- if it goes to CoQH2,
it's gaining hydrogen so that's a reduction.
And right?
Right, reduction and oxidation always have to occur together.
So if the CoQ is being reduced, then the iron would have
to be oxidized to our plus three, OK?
So there's an example of the handout --
of the handoff of electrons in the electron transport chain.
And now we'd like -- I'd like to do one last thing
to put this all together.
We've studied the citric acid cycle
and now we've studied the electron transport chain --
we need to link these together, so --
because they're really part of a bigger system.
So let's focus on what we've learned, right?
So here's the citric acid cycle in a very simplified form.
There are two carbons that enter, right?
And that's from a acetyl-CoA, right?
So the acetyl group, right?
There's that acetyl group -- that two carbon group,
that when I say C2 it's referring
to this acetyl group right here.
OK, and so every time an acetyl-CoA hands off two
electrons to the citric acid cycle, we end up --
right, with reduced coenzymes.
We end up with an NADH here and another NADH here.
And then we get the GTP, which the body is very capable
of isomerizing to ATP.
And some textbooks even show ATP, instead of GTP.
So don't let that stress you out.
Then we get an FADH2 and finally we get one more NADH, right?
So from the citric acid cycle, one acetyl-K goes in
and then ultimately we get -- yes, one ATP, three NADH's
and one FADH2, all right?
Now, these reduced coenzymes are going to go
into the electron transport chain, all right?
So here we have a schematic of the electron transport chain.
And what -- what we need to know before we can finish solving
this is that when one NADH enters the electron transport
chain, ultimately three ATP can be produced.
And when one FADH2 enters the electron transport chain,
only two ATP are produced, right?
And that's because, remember that NADH enters
that complex one and can pump protons though complex one,
complex three and complex four, right?
So NADH pumps more protons
into the inter-membrane space, so we get more ATP.
Where FADH2 enters that complex two,
where no electrons are pumped.
So less protons are pumped, less energy.
I mean you can really -- I think about like one
of those crank flashlights, right?
So the more cranks you do on the flashlight,
the brighter the light will get, the longer it will go.
So NADH is able to crank the flashlight more than FADH2.
All right, so now we need
to bring this information together, all right?
So overall from that one acetyl-CoA
that we started with up here, right?
We get the one ATP and then from the three NADH's, right?
We're going to multiply those.
We get three ATP each, right?
Per NADH
And then we got the one FADH2.
And then from the electron transport chain we get two ATP
per -- FADH2 -- viola -- right?
So now when we add this all-together, right?
We would get 1 plus 9 plus 2, which is 12 ATP.
And that's from -- right?
One acetyl-CoA.
Just fit. OK, all right so that wraps up our overview
of the electron transport chain.
This would be a great time to work a couple
of post video practice problems to reinforce your understanding.