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1. Chemical Reactions:The Catalase Reaction An enzyme-catalyzed reaction between two molecules of hydrogen peroxide. Nome Baker, Ph.D. 2009 Gnomus @ IMSLI
2. Bridge No. 1: A video review of the students experiments involving catalase Hyperlink to a demo video that will show students doing simple experiments that all students should do before beginning this activity.
3. Bridge No. 2: Web research. How many uses of hydrogen peroxide in humans, plants, & animals can you find?
4. Find the card. Find the card that shows the reaction that took place in your experiment:
2 H2O2 ? 2 H2O + O2
Hint: Models of the molecules are shown using special symbols for each element.
5. Key to symbols used: Each Answer Card shows molecular structures and uses different symbols for the various atoms in each molecule.
This is the key to the elements shown:
6. Does this card show the reactant molecules in this reaction?2 H2O2 ? 2 H2O + O2
7. Not quite. Look again. The reactants are two molecules of hydrogen peroxide (H2O2): 2 H2O2 ? 2 H2O + O2
8. Your right! . Neither molecule shown is hydrogen peroxide (H2O2). One kind of molecule is H2O; the other is a gas you breathe (O2). Which molecule is the gas and which one water?
9. Does this card show hydrogen peroxide (H2O2) as the product of a catalyzed reaction?
10. Your right! Good! You know the difference now between the reactants and the products of a reaction.
11. Careful! Look out! In this reaction (H2 + O2 ? H2O2), hydrogen peroxide is the product of a reaction catalyzed by a metal.
In the main reaction that you are learning about, hydrogen peroxide molecules are the reactants in an enzyme-catalyzed reaction.
12. Find a card showing two hydrogen peroxide molecules reacting to form water and oxygen:2 H2O2 ? 2 H2O + O2
13. Does this card show this reaction:2 H2O2 ? 2 H2O + O2 ?
14. How could Card A2 be right?Youre looking for a card with this reaction: 2 H2O2 ? 2 H2O + O2
15. Your right. Thats wrong!Youre looking for a card with this reaction: 2 H2O2 ? 2 H2O + O2
16. Does Card A3 show this reaction: 2 H2O2 ? 2 H2O + O2?
17. Your right. Youve found the card with this reaction: 2 H2O2 ? 2 H2O + O2
18. Take another look! 2 H2O2 ? 2 H2O + O2 You are looking for two H2O2 (= HOOH) molecules reacting to form two H2O (= HOH) molecules and one oxygen O2 (= OO) molecule.
Make sure that you can find them on this card before you go on to the next card.
19. Compare these two different enzyme-catalyzed reactions:
20. Cards A2 and A4 show similar reactions. In each one an O atom from H2O2 removes two H atoms from a molecule to form two molecules of water.
21. Build models of these reactions. Use beads or beans or candy or cards (representing different atoms and molecules) to make models of these two enzyme-catalyzed reactions:
2 H2O2 ? 2 H2O + O2
H2O2 + RH2 ? 2 H2O + R
22. How the enzyme catalase works
23. Click on the card that shows the enzyme ready to catalyze the reaction.
24. Can you see why this is a late stage in the series?
25. Youre right! This represents the enzyme before any reactants are attached to it and also how the enzyme might look after all the products have left it free to be used again.
26. Can you see why this is a later stage in the series?
27. True, this is an early stage in the reaction, but try to find a card that shows an even earlier stage.
28. This is the first step in the reaction. A hydrogen peroxide molecule is shown binding to the enzyme, catalase. 2 H2O2 ? 2 H2O + O2
29. Two molecules of hydrogen peroxide have to bind to the enzyme for the reaction to occur.
30. At last! The reaction has taken place and the enzyme will be ready to act again as soon as the products of the reaction leave their binding sites.
31. This is the first and last step in the sequence. The enzyme, catalase, is ready to act again.
32. Reviewing the reaction: Youve now put your model in the correct order: A6 A8 A7- A5 (and back to A6).
33. Now can you explain why bubbles form when you pour hydrogen peroxide on a cut? First you need to know:
Blood forms at the site of the wound.
Blood contains red blood cells.
Red blood cells contain the enzyme catalase.
34. Acknowledgment Special thanks to the invaluable assistance of Ms. Nicole Ng and Ms. Asya Grigorieva in designing this unit.
We are indebted to Dr. Ruth Dusenbery and to Dr. George W. Gagnon for their thoughtful criticisms and suggestions.
This work was greatly influenced by the input from various middle school teachers, most notably by that of Mr. Alan Lee.
35. An brief addendum follows You may end the slide show now. The next three slides are incomplete and are planned for the use of teachers.
36. Students summary: [Link to the Learning Record. Response may be written and/or verbal as a presentation to the class. ] Review the catalase reaction using Cards A5 A8 in the correct order to describe the catalase reaction in your own words. Try to include the following:
What is the equation (write it) that describes the reaction?
What are the reactants? .the products of the reaction?
What is the gas that forms when you add hydrogen peroxide to a fresh wound (e.g., a cut)?
What is an enzyme and what does it do?
Are any atoms lost during the reaction? If so, which?
37. Review As a further review and as reinforcement of the concepts being taught, look at the video (insert link) of the experiment that you (the student) did in preparation for the lesson. You may also do the experiment [insert link] again--or for the first time if youve never done it.
Review the wrong Answer Cards. What lessons can be learned from those (e.g., balanced equations, catalysts).
Review the Learning Aims. (Insert Link)
Insert link to an interactive test (concepts learned). [Test to be constructed.]
38. Lesson Aims and Major Concepts; Understand the following: In a chemical reaction all of the atoms in the reactants appear in the products of the reaction.
Chemical formulas and equations are used to describe a chemical reaction .
A specific chemical equation describes your earlier, hands-on experiments in which oxygen molecules were the product you could observe.
[Reminder: Students should perform hands-on experiments involving hydrogen peroxide and catalase-containing tissues before and/or after this lesson.] [Insert link to lesson plans for suggested experiments.]