Biology 12

Chapter 2 Enzymes and Energy • MHR 47

3.Your experimental design should use a control and

test one variable at a time. Will you be collecting

quantitative or qualitative data?

4.Write a numbered procedure for your experiment

that lists each step, and prepare a list of materials

that includes the amounts you will require.

Checking the Plan

1.What will be your independent variable? What will

be your dependent variable? How will you set up

your control?

2.How will you determine peroxidase activity? How

will you measure the amount of oxygen produced?

Have you designed a table for collecting data?

3.Will you conduct more than one trial? How long will

you allow each trial to run?

4.How will you analyze your data?

5.Before beginning the experiment, have your teacher

check your plan.

Data and Observations

Conduct your experiments, record your data, and
complete your data table. Design and complete a chart
to present your results.

Analyze

1.What do these laboratory procedures indicate about

the activity of peroxidase?

2.Make graphs showing the relationship between

temperature and oxygen produced and between

pH and oxygen produced.

3.How does the presence of HCl affect the activity

of peroxidase?

4.How does the presence of NaOH affect the activity

of peroxidase?

Conclude and Apply

5.Do your data support or reject your hypotheses?

6.At what temperature did peroxidase work best? at

what pH?

7.What was the purpose of using control samples?

8.If you have ever used hydrogen peroxide as an

antiseptic to treat a cut or scrape, you know that it

foams as soon as it touches an open wound. How

can you account for this observation?

Exploring Further

9.You may wish to use hydrogen peroxide to test for

the presence of peroxidase in other foods, such as

pieces of other vegetables or of meat. Which food

shows the greatest peroxidase activity? How could

you explain differences in enzyme activity among

different foods?

If you have access to Probeware, do the activity

“Enzymes and Rates of Reaction.”

Probeware

Enzyme Inhibitors and

Allosteric Regulation

In addition to the environmental factors of pH and
temperature, various substances can inhibit the
actions of enzymes. Inhibitorsare chemicals that
bind to specific enzymes. This results in a change
in the shape of the enzyme that causes the enzyme
to shut down its activity. In cells, enzyme inhibition
is usually reversible; that is, the inhibitor is not
permanently bound to the enzyme. Inhibition of

enzymes can also be irreversible. For example,

hydrogen cyanide, a powerful toxin, is an inhibitor

for the essential enzyme cytochrome coxidase.

Toxins, such as hydrogen cyanide, typically bind

(either covalently or non-covalently) so strongly

with an enzyme that the enzyme cannot bind

with its substrate. Some poisons that result in

irreversible enzyme inhibition do not combine with

the enzyme; instead, they destroy enzyme activity by

chemically modifying critical amino acid R-groups.

Other toxins, such as venom from the Malayan

pit viper (Calloselasma rhodostoma) (shown in

Figure 2.9 on the next page), are enzyme inhibitors

that can help people overcome the effects of a

stroke. Strokes are caused by blood clots in the

brain, which can result in mental and physical

debilitation. A substance called ANCROD, derived

To learn more about the function of enzymes, go to your

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