Carbohydrates are essential energy
sources for almost every cell on the
face of the earth. So it's
essential to understand then
of these important compounds.
This lecture will focus on probably the most
important carbohydrate and that's glucose.
Glucose is broken down
in a pathway called glycolysis which will
be subject of the first part of the talk
and then I will finish with
the end product of glycolysis
which is pyruvate and how it's metabolized
further and how that impacts fermentation.
Now in glycolysis we have the breakdown of glucose
then glycolysis literally
means the breakdown of glucose.
Glyco referring to the glucose part
and lysis referring to the breakdown.
Glycolysis is a primary
energy source for cells
but it's not within the pathway itself
overly energetic, and as we will see
what glycolysis is important for is providing its
end products for further oxidation.
Glycolysis is what we call
a central metabolic pathway.
Now central metabolic pathway means that it
feeds into so many other pathways and
if we pull this pathway out of a cell, it would mean the cell
would really have to rearrange everything that it does.
The reactions of glycolysis occur in
the cytoplasm of eukaryotic cells.
Glycolysis occurs in
what we call two phases.
Our first phase in which ATP energy
must actually be put into molecules
to start the process. The
ATP would be recovered later
in the second part of glycolysis
where additional ATPs are made,
reduced electron carriers are made
and two pyruvates are also made.
Pyruvates is our connecting point
for other pathways and
the oxidation of pyruvates generates
a tremendous amount of energy.
Now glucose's structure is
seen on the right here.
In the body, it's stored, at
least in animals, it's stored
in the form of glycogen.
So the breakdown of glycogen
releases essentially glucose for cells to use.
In plants, amylose and amylopectin
are used as the storage form.
But the end product in each case of breakdown is the
same, we get glucose that can be used for energy.
The advantage of having glucose as a primary
energy source for cells
particularly for a multicellular organism
is that it is very readily released
from storage and it's also very
easily to travel in the blood.
Traveling in the blood is important because
fat actually stores more energy
per carbon than glucose does.
But in a liquid or in a
aqueous organisms such as we are,
that fat has to be packaged up in
order to travel and that takes time.
Now another advantage of glucose is that it
can be made from very simple precursors
as we will see in another one of these lectures
in a pathway known as gluconeogenesis.