>> 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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