>>Dr. Ketchum: In this video segment, we are only going to be focusing on what an enzyme
catalyzed reaction is and what are the components of this reaction. What we have here is basically
a, a diagram or a schematic of an enzyme catalyzed reaction. So first off what we need to do
is we need to define what each of these components is, and so let’s just begin with the enzyme.
So we’ll go ahead and label these. This is the enzyme. And if you notice on the enzyme,
this particular enzyme actually has two different active sites. Not all enzymes will have two
active sites, not all enzymes will have one active site, okay? They can have more than
one active site, in other words. So you have to have an enzyme for an enzyme catalyzed
reaction. The other thing that you need for an enzyme catalyzed reaction to occur is a
substrate. So here we have an example of a substrate. Okay, so for this enzyme-catalyzed
reaction to occur, you must have an enzyme, you must have a substrate (which we’ll abbreviate
with an “s.”) So when the enzyme and the substrate come together, in other words the
substrate binds to the active side on your enzyme, that will form what’s called the
enzyme substrate complex. And so illustrated here is your enzyme substrate complex. Again,
the substrate has to fit to the active site of the enzyme. If the shape doesn’t fit,
it’s not going to bind, okay?
So once the enzyme substrate complex is formed, now a reaction can occur. So in this particular
example—notice during this catalyzed reaction that a bond is being broken between your substrates.
So when that bond is broken, the substrates now get converted into products. So here we
have two different products. And then if you notice, the enzyme retains its original shape.
And so the enzyme once again is what we call highly conserved. At the end of this reaction,
it has returned to its original confirmation and can be reused. So enzymes can be reused
over and over. The substrate, on the other hand, has been converted into a product. So
in this particular case, let’s look closely at what this substrate is so that we’re
tying this information into previous material. So this substrate is a disaccharide. So you
have two—sugar I should say—carbohydrate monomers. So this is a disaccharide. So in
this disaccharide, we’re going to break the chemical bond holding together these two
sugars, and when we do that, our products are actually called monosaccharides. So question
for you is the following: What kind of chemical reaction is this, anabolic or catabolic? This
would be called a catabolic reaction, because we’re breaking down a biomolecule. We’re
breaking a disaccharide down into a monosaccharide.
Okay. So just to reiterate, okay, the enzyme and the substrate have to come together so
the substrate binds to the active side on the enzyme. Once that happens, then we formed
an enzyme substrate complex. That binding is going to cause a conformational change
in the shape of the enzyme, and you’ll end up turning the substrates into products and
then the enzyme will revert back to its original confirmation so that it can be reused again,
because enzymes are highly conserved. That concludes the segment on what an enzyme catalyzed
reaction is.