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