We are almost done with cellular respiration!
We will be doing the same procedure as for
the last two.
We'll go over the process of fermentation
then I will be asking you questions that you
should know for the exam.
If a cell doesn't have access to oxygen, it
can't undergo aerobic cellular respiration.
Some cells, such as brewer's yeast and your
muscle cells, can switch over of another process
when there is no oxygen.
We call this process fermentation.
Fermentation is a way to regenerate NAD+ so
that glycolysis can continue.
If you don't continue glycolysis, you don't
get the two ATPs that are generated by glycolysis.
You may be thinking that the cell would be
wasting the NADH is generated during glycolysis,
but NADH doesn't last very long, so it's not
like the cell can store it while it waits
for oxygen to show up so it can get respiration
online again.
So, here in this diagram, the products of
glycolysis, two pyruvate molecules, have an
acid group clipped off.
This leaves as CO2.
We now have two acetaldehydes.
They could go to the citric acid cycle, but
that would generate more NADH and the cell
can't use what it has.
The hydrogen from a NADH is placed on the
an acetaldehyde, which regenerates NAD+.
The NAD+ can go back to the glycolysis cycle.
Once a hydrogen is added to acetaldehyde,
we have ethanol, the most famous fermentation
product.
This is why non-distilled alcoholic beverages
are bubbly, from the CO2.
If we are making bread, we want this CO2 to
cause the bread dough to rise.
Otherwise, you have a tortilla or a cracker.
During baking, the ethanol in the bread evaporates
off.
Your muscles and the bacteria that ferments
dairy products have a slightly different process.
Rather than clipping off the acid group from
the pyruvate, the hydrogen is placed direction
on the pyruvate from the NADH.
This regenerates NAD+ and lactic acid.
That way, you don't get drunk when you exercise.
Also, that's why yogurt and sour cream aren't
fizzy.
Once again, for both types of fermentation,
I want you to know the why, the where, the
starting substrate or substrates, the energy
used, the energy produced, and the ending
product or products.
