Resource Information

These resources, while free, are not openly licensed so they may not be altered from the original form.  Here I have supplied a link to the resources and a transcript of the video.  You can use the transcript as a basis to create your own worksheet, quiz, or as an additional resource for students who are differently-abled. I find it most helpful to play the video to the class and stop it every minute or two to further elaborate what Mr. Anderson is explaining.  You can highlight sentences in the transcript you would especially like the students to take notes on, and pause the video while you write the notes on the board.  This demonstrates note-taking skills for the students in real-time.  You can also pause the video as the answers to the worksheet questions appear, to give the students time to answer the questions.  This can also be given as a pre-lecture assignment to be done independently.  This works especially well if students have 1:1 computers and can do the assignment before class.

It also makes an excellent substitute lesson plan.

Enzymes Video Summary

Paul Andersen explains how enzymes are used to break down substrates. The correct shape of the active site allows a key/lock fit between the enzyme and the substrate. The enzyme catalase is used to break down hydrogen peroxide. The importance of cofactors and coenzymes is emphasized. Competitive and allosteric inhibition is also included.

Resource Link:

http://www.bozemanscience.com/048-enyzmes

Education Resources

Enzymes Review Worksheet - Leya Mathew Joykutty
Enzymes Review Worksheet - Winnie Litten

TRANSCRIPT:

"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."