- [Dr. Lennon] Hi, BIO
101. This is Dr. Lennon,
your friendly neighborhood
biology professor,
with a primer on how enzymes function
to help you prepare for lab.
We've talked about enzymes
in previous lectures,
so we'll just do a quick review.
Enzymes speed up a
cell's chemical reactions
by lowering energy barriers.
We're gonna talk a little bit about
what an energy barrier is,
but first, let's review
what an enzyme does.
A catalyst is anything that speeds up
a chemical reaction within the cell,
or speeds up the chemical
reaction in general.
An enzyme is a type of
catalyst that is a protein,
so our enzymes are proteins,
which means they are
going to behave in the
way that we discussed
how proteins behave in chapter three.
So flashback, and think
about that for a moment.
We know enzymes are
important in speeding up
chemical reactions within cells,
'cause as I mentioned
in an earlier lecture,
without them it's highly
unlikely that your cells
would survive long enough
for a chemical reaction
to take place.
So they can speed up chemical reactions
at least a billion times.
The enzyme that you're
going to be working with
in lab this week is catalyst,
so I'd encourage you to
refer to your lab handout,
and to make notes as I go
through this quick introduction,
or even sometimes review of enzymes.
Remember when we're talking
about chemical reactions,
this is going to involve the
making and breaking of bonds.
All those chemical bonds
that we talked about
in earlier chapters,
that's what we're referring to now.
What the enzyme does is it
makes the chemical reaction
more likely to proceed.
Now sometimes I think about this
like a match-making website.
You go to the match-making website,
you give it your information,
it searches its database,
and it comes up with some
possible partners for you.
Someone for you to maybe
go out on a date with,
someone with whom you might have
something in common,
you could form a bond;
like a chemical bond.
That (mumbles).
The other option would
be to just go out there
and meet a lot of people, talk to them,
go out on lots and lots of dates,
and eventually you may find someone
with whom you would bond.
So an enzyme is kind of like
that, it's a match-maker.
The idea is you would
eventually find that person,
but it may take longer and it would take
a larger investment of energy.
So an enzyme reduces the
amount of energy and time
it takes for a chemical
reaction to take place.
The energy that we talk about with enzymes
is called activation energy,
or the energy of activation,
and it's usually noted as
EA, energy of activation.
This is the initial energy that's needed
to start a chemical reaction.
It's that initial push
of energy that you need
to get a chemical reaction going.
Another analogy that I like to use is
it's also like a down payment.
So let's say you wanna
buy a house, or a car,
or something else really expensive,
but you need a down payment
in order to buy that item.
What an enzyme does is
it reduces that payment,
the initial payment that you
need to purchase that item,
so that activation energy is
kind of like a down payment.
And regardless, whether we're
talking about match-making,
whether we're talking
about large purchases,
or we're talking about chemical reactions,
reducing the amount of
energy you need initially
allows that reaction, that
purchase, or that match,
to be made more efficiently.
So an enzyme catalyst lowers
the activation energy,
it takes less energy to
get the reaction going,
which means it's more likely to happen.
It happens more quickly,
it happens more easily,
and it actually happens,
'cause you can imagine
if you just couldn't save up
enough for that down payment,
you'd never actually get to buy that item.
Here's kind of a cute illustration
of what we're talking about.
The one we're looking at on the left,
we have kind of two graphs here,
we'll think about them as graphs,
we have the amount of
energy in the system.
On the bottom it's showing you
with and without the enzyme,
so this one is without the enzyme.
We have our reactant,
and then we have this
activation energy barrier.
So you can see this is
kind of a large barrier.
We need to push those reactants
up this amount of energy,
put that amount of energy into the system
in order to get a reaction to take place.
So this is what it would
look like without an enzyme.
This is what it would
look like with an enzyme,
and of course it's going to vary
depending on your type of enzyme,
so this is just a cute, literally example.
So in this example, this is
our activation energy barrier,
and it's greatly reduced by our enzyme,
so it's much more likely
that that reaction
will be able to proceed
forward to get our products.
When you look in your textbook,
or you look in pretty
much any of the literature
about this kind of work,
this is really the kind
of thing that you'll see,
and we'll come back to
this in chapter five.
So if we look at this graph,
we see free energy on the y-axis,
the amount of free energy,
and the progress of the
reaction on the x-axis.
The black line is showing us the course
of the reaction without the enzyme.
So we've got our reactants
at this level of energy,
but we need to add this much energy
in order to get our reaction going.
So without the enzyme,
this is the example of how
much energy we would need.
Once we get to this point,
the reaction will proceed,
and we'll get our products.
We have our enzyme, is shown in red,
and you can see they're
showing us in this example,
it's about a half as much,
so our reactants are starting off
at the same level of energy,
we have to add this much energy
which hey, that might be doable,
to get our reaction going,
and then our reaction will
proceed and we get our products.
So the enzyme doesn't change
what reactants are involved,
nor does it change what
products are involved,
it just changes what's our investment,
and so we're good shoppers,
we don't want to spend any
more energy than we have to.
When you're looking at your enzymes,
you're gonna be looking at
the progress of the reaction
in relation to the amount
of product produced,
so keep that in mind.
This is how these things work.
So the reactant that an
enzyme acts on is called
the enzyme's substrate.
So we're talking about chemical
reactions into reactant,
truly, but it's a
special kind of reactant,
because it's something
that binds to an enzyme,
and that is the substrate.
So if you want to take a
look at your lab handouts,
identify what the substrate
is for the experiment
you're going to be doing in lab this week.
In the reaction, the substrate binds to
the active site of the enzyme.
So there's a special part of the protein
called the active site,
and that protein (mumbles).
Our substrate binds to
our active site and it is
effected by the enzyme.
We'll see this in
picture form in a moment.
The active site can lower
the activation energy
in multiple ways, so it's
gonna be specific for
our enzyme and our substrate.
One of the things that can
happen is it can orient
our substrates correctly.
Another thing that can happen
is it can take our substrate,
and encourage bonds to break or to form.
And the first way that enzymes can work,
is it can provide a
capable micro-environment,
so that just the tiny
environment of our active site
can be a little bit different
from the environment
around the enzyme.
And we learned about amino
acids recently in class,
we learned about some are
charged, some are not charged,
some are polar, some are nonpolar,
some are basic, some are acidic,
and you can envision that
a part of the protein
that is in the active
site has these amino acids
which change the character
of just that area,
so in our active site of
our protein, the catalyst,
we could actually have a different PH,
we could have some charge differences.
Something's different
about the little part
of the enzyme that allows
that chemical reaction
to move forward more easily.
So this is what it looks like.
Here's our enzyme, represented
in this purple blob
kind of thing.
This is a very, very simple
way of thinking about enzymes,
so if this bothers you
because you know it's
harder than this, just
relax and take BIO 201.
Alright, so here's our enzyme,
here are our substrates or
reactants in red and green.
We're gonna speed up
our reaction by lowering
the activation energy, convert
those substrates to products,
which are represented by
the blue and yellow things,
and release them into the environment.
One of the important
parts about this figure
that it's trying to show
you is that it's a cycle.
So our enzymes are going
to go around and around
taking in substrates,
kicking out products,
taking in substrates,
kicking out products,
they are reusable.
Unless they get damaged
or conditions change,
that enzyme will continue
to crank out products.
Now at the bottom here you
see the example of Sucrase
that we watched in class.
If you'd like to watch that
again, ask me (mumbles).
So here's one of the things
that you're going to be
looking at in lab this week.
It's the idea that each enzyme
has an optimal temperature
at which it can function,
and it makes a lot of sense.
So you're gonna be looking
at catalyze enzymes
at different temperatures.
Each group will look at
a different temperature,
you'll compile your data,
and then you'll share
your data and analyze.
If you look on the left, you
see an optimal temperature
for human enzymes.
We've got temperature
along our bottom axis,
you've got rate of
reaction along our y-axis.
When you graph your data,
you're gonna have temperature down here,
and you're going to have mils
of O2 produced per minute,
or rate of reaction in mils
of O2 produced per minute
over here.
So this is what we're lookin' at.
If you look at this enzyme,
this is a typical human enzyme,
and if the optimal temperature
is about 37 degrees,
which happens to be...
Body temperature. I gave
you there a second for those
of you who just wanted to shout it out.
So it makes sense that
this human enzyme functions
best at human body temperature.
Now if you look at the
red one on the right,
this is temperature optimal for
a thermophilic bacterial enzyme.
The optimal temperature here
is about 78 degrees. 77,78,
and if you look at the overlap,
so we want to think about
is would this enzyme
work in the human body?
Look at it, it doesn't even
function at all over here at 37,
so that's really important
to think about, too.
When you look at your, maybe
you go to GNC or CVS Pharmacy,
or something like that, you
look at enzyme supplements,
think about the organisms
from which their enzymes
were isolated and whether
or not that's going to work.
There may be something
interesting for you to discover.
Each enzyme has an optimal temperature,
some of them actually have more than one.
You're going to be exploring
the optimal temperature
for potato catalysts in lab.
You're also gonna be
looking at the effects
of acids and bases on enzymes in lab.
So this is showing you each
enzyme has an optimal PH
in which it can function,
and actually, again,
some of them have more than one,
so in this simple world it's one.
If you look at the curve on the left,
this is a graph of optimal PH for pepsin,
a stomach enzyme.
You can see the optimal PH is about two.
Well, we know our stomach is
acidic, hence stomach acids,
so it makes sense that a stomach enzyme
would have an acidic optimal PH.
Now on the right, we have
the optimal PH for trypsin,
an intestinal enzyme.
It's optimal is about eight,
so your intestines are
actually much more basic
than your stomach, but if
we took this trypsin enzyme,
and we had it in the stomach,
it probably wouldn't function very well.
See, we don't even have any overlap here,
so enzymes do have PH optimum as well.
You will be exploring that a
little bit in lab this week,
so look over the enzyme
section of the textbook,
listen to this video again,
watch this video again,
read over your handout for the lab,
just make sure you're
ready when you come in,
and be sure to ask your
instructor questions
if you have any.
Alright, enjoy learning about enzymes.
