Now another very important consideration
particularly in places where
there is high fructose corn syrup is a reaction
I am gonna show you on the screen here.
Now high fructose corn syrup is produced in
some places primarily in the US from corn.
And high fructose corn syrup has, as its name
suggests, high quantities of fructose within it.
It has greater than 50 % fructose. So if you eat sucrose for example,
you get fructose and glucose in about equal quantities.
If you eat high fructose corn syrup, the
balance is shifted in favor of fructose.
Now what I am going to tell you here relates
more to sugar metabolism in general
than just fructose but I use fructose as an
example to show you why this could be problematic.
Now besides the enzymes in glycolysis
that I have talked about,
there are other enzymes that handle
other sugars. So for example
the enzyme fructokinase, that you
see on the screen, converts fructose
into an intermediate called fructose-1-phosphate.
Now that's a fairly simple reaction, there is
simply the addition of a phosphate
onto fructose using the energy of ATP.
That's very much like we saw the hexokinase
reaction although it uses fructose and it's putting
phosphate in a different place.
Nonetheless a simple reaction.
Fructose-1-phosphate is the target of
another enzyme called fructoaldolase.
And what fructoaldolase does is it converts
fructose-1-phosphate into two
molecules of 3 carbons each.
One molecule is called dihydroxyacetone
phosphate, you remember that from glycolysis.
The other molecule is called glyceraldehyde
and you learned part of that in glycolysis
in the form of glyceraldehyde-3-phosphate.
Well, the only difference between glyceraldehyde
and glyceraldehyde-3-phosphate is the 3-phosphate.
Cells can easily convert glyceraldehyde
When it does that, the end product
is two molecules from glycolysis.
So I said something was wrong
with fructose metabolism.
This looks like we are simply feeding
glycolysis like we were before.
Why would there be a problem? Well, we
don't know the answer of that question
but I have an idea about it that
I want to share with you here.
If we look at glycolysis what I have shown
in the first few reactions in glycolysis,
glucose going to glucose-6-phosphate
catalyzed by hexokinase. So in each case the enzyme
that does the reaction is shown in orange
and the molecule is shown in green.
Now if we consider what I just described,
which is the molecule involving fructokinase
and fructoaldolase, we have bypassed
the first set of reactions in glycolysis.
Why was that important? We just produced
The reason that's important,
is if you remember from glycolysis,
we bypass two enzymes that play
roles in regulating glycolysis.
Now, Houston, we might have a problem.
Because what will happen is without regulation,
this pathway, that's feeding it, can make
abundant intermediates of dihydroxyacetone
phosphate and glyceraldehyde-3-phosphate
under conditions with a cell
might not normally do that.
Now yes it is the case that this reaction might occur in
the consumption of too much sugar in the first place
so it's a good reason perhaps
not to drink too much sugar.
But now if we are starting to feed glycolysis
when it normally would not be fed
here is what can happen, okay?
Bypass the regulatory enzyme, we
get to the last half of glycolysis
and things are coming down the pike that wouldn't normally
come down the pike, the cell would normally shut it off.
But now this sugar metabolism is force-feeding glycolysis.
So, that what
could happen? Again, this is my
idea, this isn't anybody's proof.
What could happen with this,
is we produce excess pyruvate.
Why is excess pyruvate a problem? Well, pyruvate
turns out to be a precursor of acetyl-CoA
and when you have plenty of energy and
when you have plenty of acetyl-CoA
what you make, a fatty acids.
And when you make fatty acids, you make fat.
Some people think and there
is pretty good evidence,
that high fructose corn syrup
correlates with obesity.
So my advice to you be careful with
the carbs that you are taking in.