In this final video on energy processing,
we'll talk about what happens to the breakdown
of food molecules for energy in the absence
of oxygen.
Well, we call this type of respiration fermentation
or anaerobic respiration.
Aerobic means “with oxygen”.
Anaerobic means “without oxygen gas”.
Different types of organisms will approach
fermentation or anaerobic respiration in different
ways.
In yeast and bacteria, the most common form
is through what's called alcoholic fermentation.
In this process, glucose is broken down during
glycolysis into pyruvate as we would normally
see, but then that pyruvate, instead of being
broken down into carbon dioxide, is converted
into ethyl alcohol.
Animals do not typically perform alcoholic
fermentation.
However we do have a form of fermentation
that can happen within our muscles and within
our cells and it is known as lactic acid fermentation.
We’ll talk about these two processes and
why they happen.
If you recall, with oxidative phosphorylation,
high-energy electron carriers are dropping
off their electrons at the electron transport
chain and oxygen is there to pick up those
electrons at the end of the chain.
Well, if oxygen gas is not present, those
electrons cannot keep passing down that electron
transport chain and those shuttle buses will
get filled up and not be able to empty.
And so, for this reason, when oxygen is absent,
instead of those high-energy electrons being
taken all the way to the electron transport
chain, they're dropped back off with pyruvate
and this is when the conversion occurs either
into ethyl alcohol or into lactic acid.
Now, the thing about both ethanol and lactic
acid is that these are still energy-rich molecules.
There's a lot of energy still in them.
This can be evidenced with alcohol, because
it's flammable if you have a high enough proof
or concentration.
Within the bodies of humans and other organisms,
instead of the production of carbon dioxide
and alcohol, these pyruvate molecules are
converted into lactic acid and this can start
to generate that burning sensation in muscles
when you're doing things like sprinting or
playing in an athletic event or some sort
of workout regime.
For alcoholic fermentation, not only is alcohol
produced, but also carbon dioxide gas.
This happens in bread dough.
As the bread dough rises, what's happening
is that bubbles of carbon dioxide gas are
being formed.
When the bread is baked, all of the alcohol
leaves the bread.
However, the air bubbles remain behind.
That's what makes the bread light and fluffy.
Conversely, if the goal is to brew beer or
to brew wine, often the carbon dioxide is
released and what's kept is the ethyl alcohol
and occasionally something like a sparkling
wine or a champagne will include both carbon
dioxide and ethanol produced by the brewing
yeast.
Whether we're talking about alcoholic fermentation
or lactic acid fermentation, the only energy
gains that are received are those that come
through glycolysis.
And so, only two ATP are produced when oxygen
is absent compared to the over 30 ATP that
are released when oxygen is present.
As a large animal with high energy demands,
we cannot survive simply through anaerobic
respiration.
We need to have oxygen in order to live.
Hopefully this journey through the metabolism
of eukaryotic cells helps us to understand
a bit about how we get our energy and also
why oxygen gas is so important.
Thanks for your attention and I'll see you
in the next video!
