The last thing I wanna talk about here
are the classification of enzymes.
Enzymes, according to a systematic scheme that has been
developed by the EC commission, The Enzyme Commission,
have broken all reactions that
enzymes catalyze into 6 categories.
And this 6 category scheme is used
to organize and name all
enzymes that are in biology.
The first category scheme
is that of an oxidoreductase,
that is an oxidation and a reduction is happening
in the reaction that is catalyzed
by the first category of enzymes.
In this case you can see
malate which is shown on the left
that is being oxidized. It is
donating its electrons to NAD
to form oxaloacetate and NADH.
So oxidoreductases will always have
transfers of electrons and it will always
have an electron carrier involved.
You can see the NAD and the NADH here.
The second category of enzymes
are those called transferases.
And transferases grab a part of one molecule
and move it to another. So we can see here for
example that we are starting with glucose.
We are taking a phosphate off of ATP
and we are putting it onto
glucose. This enzyme hexokinase
catalyzes the first reaction in
glycolysis and it's a transferase.
The next reaction involves hydrolases
and as the name is suggest
these enzymes use water to break bonds.
So we can see in this schematic reaction
here, a molecule on the left
that has a peptide bond is actually
combining with water to break that peptide bond.
That's what happens with
the serine protease for example.
Water is being used to split a peptide bond.
In the fourth category we have enzymes called lyases.
And a lyase is an enzyme that uses a non-hydrolytic
meaning no water, non-oxidative way of breaking bonds.
So on the left we see for example isocitrate.
The enzyme isocitrate lyase which is found in plants
breaks this 6 carbon molecule
into a 2 carbon piece called glyoxylate
and 4 carbon piece called succinate;
because, water is not involved and because
there is no oxidation involved
this reaction is a lyase.
The 5th category of enzyme is an isomerase.
And isomerases are enzymes
that catalyze rearrangements
without doing other anything else to the
structure of the molecule that they are acting on.
So in this case we see another reaction
from glycolysis the enzyme converts
glucose-6-phosphate, which is a sugar with
a phosphate on it, to fructose-6-phosphate,
which is the different sugar
with the phosphate on it.
But all that is happened has been simply
the rearrangement of the molecule.
That's an isomerase.
The last category of reactions are those
of ligases. And ligases are molecules
that put things together. So
instead of breaking things apart
ligases are making covalent
bonds to join things together.
So in this case we are
seeing ATP energy being used
to join urea and bicarbonate
to make urea-1-carboxylate.
Ligases join things together.
Well, we have seen in the reactions here
that enzymes have some pretty amazing
abilities in terms of flexibility for catalyzing reactions,
flexibility as they affect the mechanism
that they use to catalyze things
and we have also learned about the different
categories of enzymes that are there.
In other lectures I will talk about the
ways that enzymes become inhibited.