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Section 2-4 Chemical Reactions and Enzymes (pages 49-53)
Key Concepts
• What happens to chemical bonds during chemical reactions?
• How do energy changes affect whether a chemical reaction will occur?
• Why are enzymes important to living things?
Chemical Reactions (page 49)
1. What is a chemical reaction?
2. In the space provided, write a definition for each of the terms
3. Chemical reactions always involve changes in chemical
Energy in Reactions (page 50)
4. What is released or absorbed whenever chemical bonds form or are broken?
5. What do chemical reactions that absorb energy need to occur?
6. Chemists call the energy needed to get a reaction started the
7. Complete the graph of an energy-releasing reaction by indicating where the energy of
the reactants, the energy of the products, and the activation energy should appear.
Course of Reaction
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Enzymes (pages 51-52)
8. What is a catalyst?
9. Proteins that act as biological catalysts are called
10. What do enzymes do?
11. What is part of an enzyme’s name usually derived from?
Enzyme Action (pages 52-53)
12. The reactants of enzyme-catalyzed reactions are known as
13. Why are the active site and the substrates in an enzyme-catalyzed reaction often compared to
a lock and key?
14. The binding together of an enzyme and a substrate forms a(an)
15. How do most cells regulate the activity of enzymes?
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69
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Class
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Energy in Reactions
The graphs below show the amount of energy present during two
chemical reactions. The top graph has been labeled to show the
reactants, products, and activation energy. Recall that activation
energy is the energy needed to start a chemical reaction.
Label the reactants and products on the bottom graph. Then,
draw an arrow to show the activation energy.
Use the graphs to answer the question. Circle the correct
answer.
1. Which type of reaction often occurs spontaneously?
energy-absorbing
energy-releasing
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Enzymes
Many chemical reactions in cells take place on enzymes. The
reactants bind to the enzyme until the reaction is complete.
These reactants are called substrates. When the reaction is
complete, the products are released.
Enzyme
Products
Substrates
Active site
Use the diagram to place the steps below in the correct order.
Products are released.
Substrates bind to enzyme.
Substrates are converted into products.
Use the diagram to answer the questions.
1. Where do the reactants bind to the enzyme?
2. What is the function of enzymes in living things? Circle the
correct answer.
catalyze chemical reactions
inhibit chemical reactions