>> Hi everyone and welcome
to the Penguin Prof Channel.
Today I want to talk about
the joys of fermentation.
If you don't love
fermentation in one way, shape,
or form you really should.
The dairy industry uses
bacteria and lactic fermentation
to make cheese and yogurt.
This is one of my favorite
cheeses, its called raspadura.
For those of you who don't
know, I am Italian by marriage
and we travel to Italy
once a year to partake
of the amazing fermentation
products that they have.
Check out this Parmigiano
cheese,
now that is a lot of cheese.
We also do lactic acid
fermentation by the way.
Here's another reason to love
it; if you do body building
and you're trying
to get chiseled muscles what
you're actually doing is pushing
your muscles into
anaerobic respiration.
And when the muscles run
out of oxygen they have
to do lactic acid
fermentation in order
to keep supplying
the cells with ATP.
But let's get back to some
other things that we eat
that are products
of fermentation.
Fermentation takes
soybeans into soy sauce
and cabbage into sauerkraut.
If your digestive juices
aren't flowing just
yet we've also got baking and
wine making that rely on yeast.
Yeast's so yummy.
Yeasts are single
celled fungi, by the way,
in case you didn't know that.
And humans have using yeast and
their fermentation capacities
for thousands and
thousands of years.
They just found a
9000year-old human here,
a tomb with human remains
in China, northern China.
And they found pottery
containing a fermented drink.
9,000 years, that is
really a long time ago.
I mean, to put that into
perspective I just got
to say do you realize
how long ago that was?
Because we've visited
Djoser step pyramid
in Saqqara this was
considered sort of the beginning
of the old kingdom of Egypt,
that was 4.600 years ago.
So, you know, 9,000 years we've
been fermenting fruits in order
to make alcoholic beverages.
That is a long time.
So the history of wine making
obviously goes way back.
If you go to places like Italy
you have to visit vineyards
and see how the wine
is actually made.
Tuscany's certainly one of
the most beautiful places
on the planet and the
wine is just outstanding.
If you go to the
winery you'll visit --
you know, see how
they make the wine
and the wine is of course aged.
And you'll notice that -- this
is a slightly larger scale here
but there's a lot of gas piping.
And you might be wondering
what all the piping is for.
And actually this video
is going to explain that.
So fermentation is the
harvesting of chemical energy
from organic molecules using an
endogenous electron acceptor.
Okay. Don't panic.
Okay? Don't panic,
think of pizza.
Think of pizza, relax.
Endogenous just means that
the electron acceptor comes
from within the system.
So you don't need
anything from the outside.
Okay. What do I mean by that?
In typical aerobic respiration
where not only glycolysis
[phonetic]
but also the citric acid cycle
and the electron transport chain
the electron acceptor we call
it exogenous.
Means it comes from the outside.
Oxygen is the final
electron acceptor.
So the electrons stop there.
Now, you have to keep
continually supplying the system
with oxygen in order to
drive aerobic respiration.
And that's kind of the point.
So the role of oxygen is
to the accept the electrons
and you make water as a result,
it's called metabolic
water production.
The problem is if
oxygen runs out.
If oxygen runs out then you
can't keep the system going.
And all you can run in
the absence is glycolysis.
So we're going to explore
fermentation and we're going
to answer a couple of
questions, try to get rid
of some misconceptions
that people have about it.
The number one misconception
has to be
that fermentation produces
ATP, which is does not.
We're going to see
why, we're going see
if anaerobic environments
are actually required.
We're going to see if
anaerobic environments are
actually required.
And we're going to explore
what fermentation is actually
for biochemically.
Okay. So for the sake
of comparison the first thing
we're going to do is we're going
to look at what happens when
there is oxygen present,
when you do have oxygen as
a final electron accepter.
Okay. In the first phase we
have the splitting of glucose.
Right? In the process
of glycolysis.
Hopefully this is
somewhat familiar.
I know it's probably your
all-time favorite thing
in the whole world.
We get some ADP two actually
-- well actually four.
ATPs get produced but
it's only a net of two
because it costs you two
ATP to run glycolysis.
So as glucose is being
oxidized two by pyruvate.
Of course you love redox.
Right? So if something is being
oxidized somebody else has
to be reduced.
And that somebody else is
the electron carrier NAD.
Okay. This is something
to pay attention to.
As NAD picks up those
electrons from the splitting
of glucose NAD gets
converted to NADH.
In aerobic situations what
happens to those electrons
that NADH is now carrying
is they get transported
into the mitochondria
and they get sent
into electron transport chain.
Right? So most of the
ATP that is produced
in aerobic metabolism
comes from chemosis
in the electron transport chain.
It's extremely efficient,
we make, you know,
overall about 34 molecules
of ATP in this process.
And that's where the
electrons end up.
This requires oxygen as the
final electron acceptor.
That's key.
What happens if there's
no oxygen present?
How can we continue to make
ATP in the absence of oxygen?
That's what we're
going to look at next.
Okay. So here we have
lactic acid fermentation.
And something should
look familiar.
And that's this first step.
This is still glycolysis.
Glycolysis does not change.
You still have the
production of ATP.
And you still have to have
an electron carrier to pick
up those electrons
that are liberated
when you're doing those
oxidation reactions.
Now, here's the key.
NAD gets reduced to NADH in
the process of glycolysis.
In aerobic conditions the
NADH donates those electrons
to the electron transport chain.
But in the absence of
oxygen who is NADH going
to donate those electrons to?
So here we have a reaction that
confuses students all the time
because they focus
on the product.
And the product of lactic
acid fermentation is
of course lactic
acid or lactate.
Right? That's just the
ionized form of lactate.
So lactic acid, lactate.
Right? Same thing depends
on the pH of the system.
The thing about lactic acid
or lactate is the cells don't
want it, it's a waste product.
So why do we do it?
Why do we make it?
The misconception is that
somehow the conversion
of pyruvate to lactate
produces ATP.
It does not.
The only reason we
run this reaction is
because it gives NADH something
to donate its electrons to.
We regenerate NAD.
The key to this whole story
is we got to make more of this
in order to keep running.
Glycolysis.
So lactic acid fermentation
does not make ATP.
The reason why we run
it is to regenerate NAD.
Let's look at another example.
Here we have alcoholic
fermentation.
The first part of the
story exactly the same.
Glycolysis does not change.
This is the only source
of ATP production.
Same thing.
And once again when glucose is
getting oxidized somebody else
must be reduced.
Just like in lactic acid
fermentation this product
ethanol is a waste product.
And the cells don't like it.
In fact you can naturally
only produce a wine
of about 14% ethanol before
the cells actually die.
So ethanol is a waste product.
They don't run this reaction
in order to make it per say.
They run reaction because you've
got to have a place for NADH
to donate those electrons.
It's the same story.
The goal of this
is keep NAD coming
so can keep running glycolysis.
Glycolysis is the
only source of ATP.
But you cannot continually
oxidize a carbohydrate
without regenerating the
androgynous electron carrier.
Now, I know that sounds
all very confusing
but the reality is you can't
keep splitting bonds unless
you've got an electron carrier
that is constantly ready
to accept those electrons.
If you don't have
oxygen you have
to keep recycling the electron
carriers within the cell.
So now hopefully you understand
what these pipes are for.
Right. You say that in
alcoholic fermentation one
of the other product in addition
to ethanol is carbon dioxide.
So if you don't have
an outlet for that gas.
Right? You could
have an explosion.
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As always I hope this
was helpful, good luck.
