Need for Speed

Imagine a world without enzymes. Bread wouldn’t rise. Seeds wouldn’t sprout. Your tasty lunch wouldn’t digest; it would sit in your stomach for weeks … EXACTLY! Life is not possible without enzymes. ALL reactions and processes within an organism depend on enzyme activity.

The challenge is helping students understand that enzymes are essential in order for reactions to occur at a speed that promotes normal function within the organism. However, since each enzyme only interacts with a specific substrate to catalyze a specific reaction, one effective learning strategy is to get students to consider the impact of a specific enzyme deficiency on an organism. For example, Carolina’s Inquiries in Science®: Synthesizing Macromolecules Kit includes the activity “Investigate How an Enzyme Decomposes Hydrogen Peroxide,” which focuses on how the concentration of the enzyme catalase affects the decomposition rate of the substrate hydrogen peroxide (H₂O₂). A great approach to this exploration is having students consider what happens if an organism’s cells completely lack the enzyme catalase.

During this investigation, students test various concentrations of catalase prepared by homogenizing potato cubes. (Irish potatoes are rich in catalase.) Prepare a potato homogenate.

1. Cut whole potato into cubes.
2. Measure an equal volume of water to the weight of potato cubes (e.g., 25 g of potatoes: 25 mL of distilled water) into a blender.
3. Homogenize for approximately 30 seconds.
4. Filter mixture through cheesecloth into a beaker.
5. Place beaker of homogenate on ice and keep it there throughout experiment.

Another good source for catalase is beef liver. (The liver is the decomposition site of many toxins found in the blood.) Prepare the liver homogenate in the same manner as above using fresh or frozen liver.

Decomposing hydrogen peroxide with catalase

The success of this activity depends on 2 things:

1. Ensuring that your catalase solution is fresh and keeping it so in an ice bath throughout the experiment (The bath keeps proteases from denaturing the enzyme once the cells are lysed.)
2. Using only fresh H₂O₂

Here’s a twist

Baker’s yeast is an alternative source of catalase. Here’s a great demonstration to show your students how catalase in yeast breaks down H₂O₂:

1. Add a few grains of baker’s yeast to an Erlenmeyer flask.
2. Pour fresh H₂O₂ into the flask.
3. Watch bubbles rapidly develop. (BEWARE: The bubbles will overflow.)
4. Explain to your students that bubbles are the result of catalase breaking down H₂O₂ into H₂O and O₂.

Germinating seeds and amylase

During seed germination, stored starch supplies energy to the developing embryo. This occurs as amylase, a digestive enzyme, breaks down the starch into sugars in the seeds. It’s a great activity to emphasize temperature as a factor affecting the rate of enzymatic activity.

Procedure

1. Soak seeds/beans in distilled water overnight. (good choices: pinto beans, corn, lima beans, broad beans)
2. Boil half the seeds/beans for 10 to 15 minutes.
3. Transfer both boiled and non-boiled seeds to moistened paper towel; allow 24 to 48 hours for germination.
4. Melt starch agar (or prepare starch agar solution) and fill petri dishes halfway. Allow mixture to set and cool (about 20 to 30 minutes).
5. Using a wax pencil, divide the petri dish lid in half. Label the left side “boiled” and the right side “normal/control.”
6. Cut seeds/beans in half longitudinally with a razor blade. Using sterile forceps, place 4 halves facing down on the appropriate side of the dish.
7. Place petri dish lid over bottom, and let seeds incubate 24 to 48 hours.
8. Discard the seeds, without contaminating the inside of the petri dish.
9. Using a disposable pipette, flood the empty petri dish with iodine.
10. Pour off the iodine, rinse the dish with distilled water, and record results.

Analysis

Iodine in the presence of starch yields a blue/black color. Dark areas occur where boiled seeds touched the dish because the high boiling temperatures denatured the amylase. The dish is clear on the side that held the non-boiled seeds since amylase in those seeds digested the starch.