Biology Assignment B

Enzymes I:

Demonstration and Worksheet

LEARNING GOALS

By the end of this unit, you should be able to do the following:

1. Identify the substrates and products of the enzyme tyrosinase.

2. Describe why fruits turn brown when cut and how this relates to the

enzyme tyrosinase.

3. Explain how factors such as concentration, pH, and temperature affect

the speed of an enzyme reaction, including the concept of denaturing.

4. Identify the Independent, Dependent, and Control Variables in your

experiment.

MATERIALS NEEDED

Tablespoon and cup measures

Knife and cutting board

3 small plates or bowls

Blender or grater

Mesh strainer or colander

Coffee filters

Kitchen timer, stopwatch, or regular watch

1 pot for boiling

1 head of red cabbage

2 regular potatoes

2 apples

2 bananas

1/4 cup apple juice, tea, lemonade, or other non-carbonated liquid (not milk)

1/4 cup lemon juice or white vinegar

1/4 cup ammonia

Demonstration with a worksheet. You do not need to fill out an

experiment tracking sheet for this lab.

You must take pictures of the experiments for your worksheet. You must

have a card with your name visible in the picture.

ENZYMES

Preparation of Foods

For each of these experiments, you will need to cut "fresh" slices of an

apple, potato, and banana. DO NOT cut them all at once as they will begin

to brown. Cut them as needed for each experiment. When using an piece of

food that has already been cut and exposed to the air, "reset" the food slices

by cutting a thin slice off of any exposed side. Now you should see white,

fresh produce.

Place a section of an apple, banana, and potato in the refrigerator

now. Place a section of apple, banana, and potato in the freezer now. Begin

boiling a pot of water now. You will use these in later experiments. Keep

all other food samples at room temperature unless otherwise noted.

Each experiment will require observing the food slices for 2 hours. Feel free

to begin the next section of the experiment while this is going on.

Examples of “apple browning.” The apple on the left has no browning at all

(though it has changed texture due to cooking). The apple on the right has

slight browning (note the weak brown “veins”). The apple in the middle has

significant browning (note the strong brown “veins”).

Experiment #1 - Enzymes Require Substrates (Tyrosinase)

The substrates for the enzyme tyrosinase are catechol and oxygen. Since

fruits contain both tyrosinase and catechol, we cannot test to see if catechol

is required for this reaction. We can however exclude oxygen from the

reaction to prove that it is needed.

1. Cut two fresh slices of banana, apple, and potato.

2. Fill a bowl with water. Place one slice of each food into the water

and set one slice of each aside on a plate. Make sure the water

covers the foods in the bowl.

3. Observe the slices every 30 minutes for 2 hours and record your

results.

4. Set the slices on a piece of paper and label the two groups as

"oxygen" and "no oxygen." Take pictures and paste them into the

worksheet.

Conclusions - Did the reaction occur when the foods were submerged under

water?

Experiment #2 - Enzyme Denaturation by pH (Tyrosinase)

You will now show that extreme pH values can denature (inactivate) the

enzyme tyrosinase. First you must make pH paper to identify common acids

and bases around the house.

1. Blend or grate 1/2 of a red (or purple) cabbage head. Add 1/4 cup of

water either before blending or after grating.

2. Place the cabbage shreds in a bowl and microwave until steaming

hot. (Microwave times will vary between 1 and 3 minutes.)

3. Pour the cabbage juice through a mesh strainer or colander and

capture the liquid. Throw away the pulp.

4. Pour the strained cabbage juice through a coffee filter and capture

the liquid.

5. Cut a coffee filter into 1 inch squares and soak them in the cabbage

juice for 5 minutes. Allow them to dry.

The paper will change colors depending on the pH of the liquid placed on

it. Neutral pH (7) will not change the color, though it will make the color

seem darker due to the wetness. Weak bases (9-10) will give a blue color

and strong bases (12-14) will give a green color. Weak acids (3-5) will give

a violet or red color and strong acids (1-2) will give a pink color.

1. Place a drop of water, a drop of the ammonia and a drop of the lemon

or white vinegar each onto a separate pH test paper. Determine the

pH of each solution and take a picture of the three test papers with

labels for the worksheet.

Conclusions - What was the pH of each of your solutions? (Note, the pH

paper is not an enzyme reaction. This is simply a test to see which of your

solutions are acid, base, or neutral.)

1. Cut three fresh slices each of apple, banana, and potato. Soak one

slice of each food in each of the three solutions for 5 minutes.

2. Pull the slices out of solution and set them on a plate. Observe the

slices every 30 minutes for 2 hours and record your results.

3. Set the slices on a piece of paper and label the three groups as "acid,"

"neutral," and "base." Take pictures and paste them into the

worksheet.

Conclusions - What is the effect of an acid or base on the tyrosinase

reaction?

Experiment #3 - Enzyme Denaturation by Temperature (Tyrosinase)

1. Cut one fresh slice of each food and boil for 10 minutes.

2. Cut fresh slices of food from the room temperature samples, the

refrigerated samples, and the frozen samples. (Remember to slice off

any portion of the fruit that was exposed prior to this point.)

3. Place the room temperature and boiled apple slices on a plate

together. Leave the chilled slices in the refrigerator and the frozen

slices in the freezer.

4. Observe the slices every 30 minutes for 2 hours and record your

results.

5. Set the slices on a piece of paper and label the four groups as

"frozen," "chilled," "room temp," and "boiled." Take pictures and

paste them into the worksheet.

Conclusions - What is the effect of changing the temperature on the

tyrosinase reaction? Did some temperatures fully denature the enzyme vs. .

NEXT STEP

The next item in the module is the worksheet. Paste your pictures into this

sheet, answer the questions, and submit through the Assignment found in

this module. Be prepared to answer quiz questions about enzymes in

general and specifically about tyrosinase.