Hi. It's Mr. Andersen and welcome to AP Biology Lab 2 walkthrough. This is on
Enzyme Catalysis. So it's basically the enzyme lab. The enzyme that we'll be studying is
something called catalase. Catalase is an enzyme that's found in almost all living things.
And it's job is to breakdown this chemical. This chemical looks a lot like water, but
we've got an extra oxygen. So this is hydrogen peroxide. And so if you ever skinned your
knee when you were growing up and your mom put hydrogen peroxide on it, what you found
is that it started to bubble. And the reason it was bubbling is that this enzyme is found
in almost all living things and it breaks down hydrogen peroxide into water and oxygen
bubbles. And so is it cleaning the wound? Probably not any more than water but it made
me feel good when I was little. The enzyme that we'll be using comes from yeast. So catalase
from yeast in this experiment. Basically we should talk about what an enzyme is. An enzyme
is going to be a biological molecule that acts as a catalyst. A catalyst is going to
be any chemical that speeds up a reaction. But it's not really consumed in the reaction
itself. It's not a reactant or a product. Let me give you an example of that. If you
can drink milk and you don't feel sick, then you have an enzyme that functions called lactase.
Lactase is going to breakdown a disaccharide called lactose. It's a sugar that's found
in milk. So basically the lactose will fit into the enzyme almost like a key in a lock.
It's going to then put a little chemical tug on it. And it's going to break that lactose
down into its two sugars. And so if you look at the enzyme itself, the lactase, it's never
changing its shape. It's just receiving a substrate we call that. Or a molecule that
fits into an enzyme. It breaks it apart and then it waits for another one over and over
and over again. And for things like lactase this can happen millions of times a second.
So it goes really really quickly. And so in this experiment what we're going to use is
catalase. So catalase is an enzyme. What's it breakdown? It essentially breaks down hydrogen
peroxide or H2O2. It's going to take that in as a substrate. And it's going to break
that down into two things. It's going to break that down into H2O and then oxygen or those
little oxygen bubbles. And it happens at the rate of millions of times per second. And
so in this lab basically what we're going to do is we're going to take a little bit
of filter paper. And then we're going to dip it in different concentrations of yeast. We're
going to dip it into a concentration of yeast where there's no yeast. So we call that zero.
And then we're going to increase the concentration of yeast. We'll then take that filter paper
and we're going to drop it into a beaker. But that beaker is going to contain hydrogen
peroxide. Okay what happens now? We're going to put that little dropper. It's going to
sink down to the bottom. And so if there's no yeast on it, what's going to happen? Well
that filter paper is going to sit at the bottom forever. It will never float. Because there's
no enzyme on it. There's no catalase on it to break that hydrogen peroxide into water
and oxygen. So it will sit there forever. But if we add a certain amount of yeast to
it, what we're going to find is now when we put it in the hydrogen peroxide it's going
to start breaking down that hydrogen peroxide into water and bubbles. And so bubbles will
start to build up on that and eventually it will float to the top. And so what we can
do is we can use a stop watch. We can time how long it takes for that piece of paper
to float to the top. And that's going to tell us the rate of the reaction. And so the more
yeast we add, you can imagine the faster it's going to float up to the top. And so here's
the results from one of my students in my class. So basically we increase the concentration.
This is the amount of that enzyme in grams per liter. And then we measured it in floats
per second. This is kind of a weird unit. Why do we measure it in floats per second?
Well it's a rate. And so it has to be over a certain amount of time. And so basically
we're timing the float. How long it takes for one of them to float. We divide it by
the seconds that it takes. And that gives us a rate. And so again if we put it in there
with no yeast what's going to be the rate? Well it will never ever float. So if we take
one float divided by infinite time, that's going to have a rate of zero. But you can
see on here that basically what we're going to get is a curve that looks something like
that. And so if I were to extrapolate a little bit, it's going to eventually go all the way
out like that. Now you might think to yourself, well, we're increasing the amount of yeast.
Why doesn't it keep going linear like that? Well the reason why is that even though we've
increased the number of enzymes, we broke down so much of that hydrogen peroxide that
it doesn't matter anymore. So this would the curve, the results that we would expect. And
so basically what we're doing again, to review, is that we're breaking down hydrogen peroxide
into water and oxygen. This is the chemical formula that you need to know. We're measuring
that rate and we could measure that rate by looking at the number of products. That's
what we're doing in this case. We're measuring the amount of oxygen that's produced. Or we
could measure a decrease in the amount of hydrogen peroxide. But in this lab we only
measured one thing. We measured an increase in the amount of enzyme. And when you're taking
the AP Bio test they could ask you questions about other things. And so what if we increase
the substrate? What's that going to do? Well if we increase the substrate it's going to
be more of it to breakdown. So it's going to increase right away. What about pH? Or
what about temperature? Well let's think about temperature for a second. Let's say we were
to take an enzyme, some enzyme that's found inside us. Let's say lactase. And we were
to measure it at different temperatures. What would happen? Well we'd find a curve that
looks something like this. In other words it's going to increase to a point like that.
And then it's going to decrease. So temperature is an interesting one. We should think about
that for a second. Why is it increasing on this side of this optimal level? Well that's
because the substrates are moving around. They're moving around so molecular motion.
And the higher the temperature is the faster they're going to move around. So they're more
likely to run into an enzyme. Why does it eventually drop off on this side? That's because
eventually that enzyme, since it's a protein, is going to denature. It's going to break
apart. Now the substrate doesn't fit into it. So it doesn't work. And so in humans,
that's going to be around 37 degrees celsius. Because that's the temperature inside our
body. So they're designed to work at that optimal temperature. If we were to look at
bacteria that are growing in a hot pot in Yellowstone Park, we'd find that their curve
is going to be way out here. In other words they're going to have an optimum much closer
to boiling. In other words they've evolved to that specific temperature. If we were to
look at pH then, what would pH do? pH is going to be very similar to a curve that looks like
this. If we were to change the pH from 0 we'll say up to like, I don't know, 14, it's going
to curve like that as well. And then it's going to peak out at a specific pH. And it's
going to be a optimum pH. Now it's not molecular motion on either side. And so it might look
a little bit more like that. It's going to be denaturing of the protein. Either in an
acidic environment or a basic environment. And so now you know a little bit about enzymes,
how we set that up, how we do that lab. And so I hope that's helpful.