- [Instructor] In this video,
we're going to talk about
what is arguably my favorite enzyme,
and that is ATP synthase.
And you might be able to predict
from its name what it does.
It synthesizes ATP.
Now you've probably seen it before.
We saw it when we looked at respiration,
or you will see it when
you look at respiration,
which is going on in most
of the cells of your body.
And you also see it when
you study photosynthesis.
The general thing that it does is,
is it sits across a phospholipid membrane.
And through other processes,
you will have hydrogen
ion concentration increase
on one side of the membrane,
have a higher hydrogen ion concentration
on one side than on the other side.
You still might have a few over here.
And a hydrogen ion is
essentially a proton.
So on this side of the membrane,
it'll be more positive,
so there will be a electromotive force
to go to the other side.
And also, you just have
a higher concentration,
so there's a chemical gradient,
a concentration gradient,
where if there was some
way for these protons
to get to this side, they
would want to get there.
So there's an electrochemical gradient
that they would want to go down.
And ATP synthase provides a
channel for those protons.
But as those protons travel
through the ATP synthase,
they turn this part of it,
which drives this axle,
and then this axle nudges
these parts of the protein
so that they jam together an ADP
with a phosphate group to produce ATP.
So down here, you, going into
this part of the complex,
you'll have an ADP and a phosphate group.
And then that rotation force
that's provided by that
electrochemical gradient,
that then produces
our ATP.
And that's going to be the
case both in respiration,
which occurs in the mitochondria,
and in photosynthesis,
which occur in chloroplasts.
Now there's a few differences.
In mitochondria, the
hydrogen ions, these protons,
the concentration builds up
in the intermembrane space right over here
because of the electron transport chain.
And we studied that in other videos.
And then the protons travel
through the ATP synthase.
You could see a little mini
version right over here.
You could imagine that
what we see really big,
that is a blown-up version of
this part of the mitochondria,
and this is, of course, is not to scale.
So in the case of a mitochondria,
this would be the inner membrane.
Right over here would be
the intermembrane space
between the inner and the outer membrane,
intermembrane space.
And right over here would be
the matrix of the mitochondria.
And so as the protons go through,
they're able to produce ATP in the matrix.
Now in chloroplasts,
the hydrogen protons build
up inside the thylakoids,
which are these parts of the chloroplast.
That space inside the thylakoid
is often called the thylakoid space,
sometimes called the lumen.
That proton buildup inside
the thylakoids happens
because of the light reactions,
the first phase of photosynthesis.
But then those protons will travel
through the thylakoid
membrane, through to this area,
which is known as the
stroma in chloroplasts,
and they produce the ATP in the stroma.
But then the ATP is
used in the second phase
of photosynthesis to synthesize
carbohydrates, which is,
you could view as one of the
end products of photosynthesis.
So the big takeaway of this video is, one,
ATP synthase is incredibly cool.
If you look up on the internet,
you can find some simulations
that show ATP synthase
and how it acts like a motor
to jam the phosphate group
to the ADP to produce ATP.
And ATP synthase in
mitochondria and chloroplasts
are remarkably similar,
although they sit in different
parts of these organelles.
And the ATP in mitochondria,
you can view as the end
product of respiration,
while the ATP produced in chloroplasts
is an intermediary store of energy,
which is then used to
synthesize carbohydrates.
