Hi. It's Mr. Andersen and welcome
to Biology Essentials video 48. This podcast is on enzymes. Enzymes remember are chemicals
that aren't consumed in a reaction but can speed up a reaction. One of the major ones
we'll talk about this year in AP bio is called catalase. Catalase is an enzyme that's found
in almost all living cells, especially eukaryotic cells. But what it does is it breaks down
hydrogen peroxide. Hydrogen peroxide you probably knew growing up, you'd put it on a cut maybe
and it would bubble or you could use it to bleach your hair. That's pretty dilute hydrogen
peroxide. Actually concentrated hydrogen peroxide, this is somebody who's touch 30% hydrogen
peroxide, it damages and kills cells. And so hydrogen peroxide is just produced naturally
in chemical reactions but your cell has to get rid of it before it builds up an appreciable
amounts. And it uses catalase to do that. And so if we were to look at the equation,
so we've got hydrogen peroxide or H2O2 is going to breakdown into two things. One is
water and the other one is O2, oxygen. And so this is not a balanced reaction. So if
I put a 2 there and I put a 2 here, so hydrogens I've got 4, 4. Oxygens I've got 4, so perfect.
So this is a balanced equation. So you've got 2 hydrogen peroxide breaking down into
2 water molecules and 1 oxygen molecule. But it does that using an enzyme. And so in other
words, hydrogen peroxide, let me get my arrows to fit in here is going to feed into catalase
and it's going to break that down into these 2 products, water and oxygen. And it does
that at an incredible rate. I was reading that 40 million hydrogen peroxides will go
into a catalase and be broken down into water and oxygen, 40 million every second. And so
it's incredibly fast at breaking down that hydrogen peroxide into something that it can
use. And so how does it do that? Well that's what I'm going to talk about. And so basically
an enzyme, let me try and draw an enzyme, so if an enzyme looks like this. It's a giant
protein, so if we say it looks like that, it's going to have an area inside it called
the active site. And so the active site, let's see how I could do this, good, so the active
site is basically going to be a part on the enzyme where there's a hole in it. So this
is this giant protein, it's got an active site, and the substrate is going to fit into
to it. And so going back to how do enzymes work, well the active site is going to be
an area within the enzyme, so this would be the enzyme here, and basically the substrate
fits into it. And so what was the example we were just talking about? The enzyme was
catalase. What was the substrate? Substrate is H2O2 or hydrogen peroxide. So that's how
enzymes work. It basically tugs on the substrate and breaks it down. It's very important in
chemical reactions. And sometimes we want to turn on enzymes and sometimes we want to
turn off enzymes. And so in every step of photosynthesis, in every step of cellular
respiration, glycolysis, citric acid cycle, all of those chemical reactions remember have
to have an enzyme that's associated with them that can speed up that reaction. And so it's
really important that we sometimes activate or turn on those enzymes. It's also just as
important that sometimes we turn them off. And so there are two types of inhibition.
Inhibition can either be competitive, that's where a chemical is blocking the active site
or allosteric when we're actually changing the shape or giving it another shape. Chemical
reactions, another important thing that we want to measure with them is the rate of a
chemical reaction. We can do that by either measuring the reactants or the products. So
let me stop talking about what I'm going to talk about and actually talk about it. And
so here is our enzyme. Our enzyme that we talked about is called catalase. So catalase
is going to be a protein. It has a specific shape and so if we go down here to the enzyme,
this would be the enzyme right here, it's going to have an active site. An active site
is the area when the substrate can fit in. And so the substrate is going to be this green
thing in this picture. It'll fit right in here. It fits almost like a key fits a lock.
And so it's going to be a perfect fit between the two. Every chemical reaction is going
to have a different enzyme that breaks that. And so the important part is right here. So
now once we have the enzyme inside the active site, there's going to be a chemical tug.
In other words it's going to pull on that chemical. It's going to lower it's activation
energy so it can actually break apart into its products. And so if this is our H2O2 right
here, there's going to be a tug on those chemicals. Sometimes it will actually change the pH,
sometimes it'll put a mechanical tug on it, but basically what it's going to do is it's
going to make it easier for those chemicals to spontaneously break apart. Now hydrogen
peroxide by itself, H2O2, if you leave it in a bottle for millions and millions of years,
if you come back it's spontaneously going to break down into water and oxygen but that's
going to take years and years and years to do that. And with an enzyme it can happen
in seconds. It's like I said, 40 million hydrogen peroxides can feed through this, create all
of this water and can do that really really quickly. And so enzymes are ready to go and
so we want to control which enzymes are firing at which time and which ones are being released.
And so there's basically a turn on and then there's a turn off. And so how do we turn
enzymes on? Well there's two ways that we can do that. Number 1, we could just not produce
them until they're needed. And so lots of times we won't produce a protein until it's
required and so we do what's called gene regulation, where we don't even code those proteins until
we're ready to use them. But also we can activate them. And so activation is adding something
to an enzyme to actually make it work. And so you don't have to remember the names of
these, but this is succinate dehydrogenase and it's a cool enzyme that's used both in
the citric acid cycle and the electron transport chain. So this is going to be on, it's going
to be embedded in that inner mitochondrial membrane and so it's going to run two specific
reactions. So it's going to convert certain reactants into products. But if you just build
succinate dehydrogenase by itself, it doesn't do anything. It's not going to work. It has
to be activated. And so there are two type of activators. Those that are called cofactors
and those that are called coenzymes. And so if you were to look in here there's going
to be things that have to be added to that enzyme before it can actually function. And
so the two types are cofactors, coenzymes. I came up with some that you might know. Cofactors
are basically going to be small chemicals that are inorganic. What that means is they're
not made up of carbon. And so heme is an example of a co-factor. Heme is also what's found
in blood. It has an iron atom in the middle and so that's why we call it hemoglobin. And
so what it does is it's creating that hemoglobin protein and activating it. And so cofactors
are going to be inorganic. And so in other words they are not containing carbon. And
then we're going to have coenzymes and those are going to be organic. And so they're helping
that enzyme to work. An example of a coenzyme would be thiamine. And so thiamine, another
name for that is vitamin B1. And so vitamins are a required organics that we need inside
our diet and they help enzymes function. And if you don't get enough vitamin B1 in your
body then you die as a result of the neurological issue. And same thing with cofactors. So these
are required for life. But basically what happens is once we have the cofactors and
the coenzymes now we have an enzyme that can actually function. And now it can do what
it's meant to do. But if we remove those cofactors, if we remove those inorganics and those organics
then it will actually come to a stop or it won't function anymore. So that's activation.
That's how we turn enzymes on. But sometimes we want to turn them off. And so let me kind
of get you situated. We've got our enzyme here, we've got our substrate that's going
to fit here so if you think about it as an engineer for a second, how could we stop that
substrate, again 40 million of them coming through the active site in catalase? How do
we slow it down? Well there are two types of inhibition. First on is called competitive
inhibition. Competitive inhibition is when you use an inhibitor, which is another chemical
and you just get that to bond into the active site. So if you have that bonding in the active
site then that substrate can't fit in and so we're going to stop the reaction. So if
we make an inhibitor that bonds to the active site we call that competitive inhibition because
it's competing for the space with the substrate. Now we can also do that non-competitive inhibition
and we usually call that allosteric. Allosteric reaction works the same way. Here we are.
We've got our enzyme. Here's our substrate. It's trying to fit into the active site. We
also have what's called an allosteric site, which is going to be another site on the enzyme
itself. And so one type of allosteric or changing the shape inhibition that we can do is we
can have an inhibitor now that's just going to bond to that allosteric site. When it bonds
to the allosteric site it's covering up the active site and so now there's going to be
no way that that substrate can fit in. But since it's not actually bonding to the active
site we call that allosteric. Allosteric means different shape or different shape of the
enzyme. So that's a type of non-competitive inhibition. Or we can do it this way. So this
would be another type of allosteric inhibition. We can have an inhibitor bond to an allosteric
site, but if you look at the active site in this picture, here's the active site, once
this inhibitor bonds with the allosteric site it now changes the shape of the active site.
Once you've changed the shape of the active site, remember the substrate only fits if
it's like a lock and a key, now it's not going to fit anymore. And so this is another type
of allosteric inhibition. And so we use feedback loops and we use inhibitors and cofactors
and coenzymes to regulate what enzymes are going off at what time. Now when we do the
enzyme lab we are using catalase. And so when we do it in class we're using catalase. It's
an enzyme we use, an enzyme that's found in yeast. We then fill up a beaker with hydrogen
peroxide. We put our little disks of filter paper or chads at the bottom. We dip them
in varying concentrations of the enzyme and we then see how long it takes for them to
float up. And so what we're varying or the independent variable is going to be, the independent
variable is going to be the amount of the enzyme. And the dependent variable is going
to be how long it takes for them to float or the number of floats per second. And so
you can imagine, let me get a better color, if I increase the concentration of the enzyme,
we're going to increase the rate of the reaction. But eventually you can see how it starts to
level off here. Eventually if you have enough of those, let me change to a different color,
eventually it's going to level off. And so when we're measuring reaction rate we could
measure two things. We could measure the products that are created or we could measure the amount
of reactants that are being consumed. In the enzyme lab we're measuring the amount of oxygen
so we're measuring the amount of products that are created. But there's other things
we could measure in this. Not only the concentration of the enzyme, we could measure the temperature,
we could measure the pH. We could measure a lot of different things and remember organisms,
if we were to measure temperature for example the reaction rate's going to increase and
eventually the enzyme is going to denature and so there's going to be an optimum set
point. And since you have an internal temperature of 37 degrees celsius, most of the enzymes
inside your body are prime to work at that specific rate. And so that's enzymes and they
are used to maintain that internal balance and I hope that's helpful.
