Section 2.5 Chemical Reactions and Energy
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AP Biology Unit 3 – Biochemistry and Cell Structure Reading Guide – Chapters 2.5; 3.2 – 3.4
Chapters 2.5 and 3.2 – 3.5 Thermodynamics and Enzymes ______
SECTION 2.5 CHEMICAL REACTIONS AND ENERGY
1. Explain what happens when a chemical reaction occurs.
1. Define the following terms: a. Energy
b. Kinetic energy
c. Potential energy
2. Define: a. Metabolism
b. Anabolism
c. Catabolism
3. Why are catabolic and anabolic reactions often linked in living organisms?
State the Laws of Thermodynamics: First Law Second Law
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4. What is free energy?
5. Organisms cannot use heat energy to drive their energy-requiring processes. Does this mean that the heat released by metabolism is of no use to them?
6. Below is the Gibbs free energy equation:
G = H - TS where H = enthalpy (the heat of the system) T = temperature S = entropy
a. If a reaction gains heat it is an endothermic reaction. If the reaction gives off heat, it is an exothermic reaction. This alone DOES NOT determine the spontaneity of a reaction, what actually determines if a reaction is spontaneous in terms of G?
7. In the equation G = H – TS, which part of the equation represents:
a. Change in enthalpy?
b. Change in total energy?
c. Change in free energy?
d. Endothermic reaction?
e. Exothermic reaction?
f. Change in entropy?
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8. Define in terms of G: a. Exergonic reaction
b. Endergonic reaction
9. What is required for an endergonic reaction to occur?
10. What does it mean for a chemical reaction to be spontaneous?
11. Using the concept of entropy, state when a reaction will occur spontaneously.
12. Explain why highly ordered living organisms do not violate the Second Law of Thermodynamics.
13. If a chemical reaction is reversible, explain how the concentration of substrates and products influences chemical equilibrium.
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14. Complete the following chart: Graph A Graph B
Is G positive or negative Exergonic or endergonic Spontaneous Yes or No Uphill or Downhill Reaction Products have more or less energy than reactants
For the following questions, see p101-102 of your text. 15. What is the source of energy in cells used to drive endergonic reactions?
16. Describe the structure of ATP.
17. Why is ATP called a high-energy compound? How does ATP ‘store energy’?
18. Draw the ATP cycle below. What type of chemical reaction occurs when ATP is converted to ADP? How many kcal are produced in this reaction? (Note: This is the G of the reaction!)
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19. What is a coupled reaction? How does a coupled reaction drive an endergonic one? (Use the figure to help explain.)
SECTIONS 3.3 – 3.4 20. What is an enzyme?
21. To the right is an example of a reaction curve. Label the axes, the energy of activation, energy of substrates, and 1 energy of products. a. Which line represents an uncatalyzed chemical reaction? 2
b. Which line represents an enzyme-catalyzed chemical reaction?
22. Explain how the energy of activation is related to the RATE of a chemical reaction.
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23. How does an enzyme enhance the RATE of a chemical reaction? Identify the reaction curve for an enzyme-catalyzed reaction on the curve above. What parts of this reaction does an enzyme NOT alter?
24. What is the primary way that enzyme lowers the energy of activation?
25. Define: a. Active site
b. Induced fit model of enzyme action
26. Describe what is occurring at each step in the catalytic cycle of an enzyme.
enzyme
active site
enzyme
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27. Shown is a progress curve for an enzyme-catalyzed reaction. The point at which substrate was added to an enzyme solution is indicated with an arrow. Describe what this graph is telling you – describe the axes and what the slope of the line means during the initial phase (A), linear phase (B) and the plateau (C). Discuss in terms of both the RATE of product formation and how each of
these phases relate to the enzyme cycle diagramed above.
t] C
uc d
B
ro [P A
Time
28. Why is the formation of the enzyme-substrate complex important in speeding up the reaction?
29. What types of amino acids do you think you might find in an enzyme active site?
30. How does the active site dictate the specificity of an enzyme? (both in the substrates it acts on and the product it helps form)
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31. Describe how each factor affects the RATE of an enzyme-catalyzed reaction, diagram the reaction curve and explain each diagram:
a. Substrate concentration
b. Enzyme concentration
c. Temperature
d. pH
32. Explain the role of cofactors and coenzymes.
33. Why is it important that metabolic pathways are regulated?
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34. Describe how each of these scenarios can inhibit enzyme activity: a. Competitive inhibition
b. Noncompetitive inhibition
c. Feedback (also called product) inhibition
d. Allosteric inhibition
35. Most of the time, inhibition is reversible. What happens if an inhibitor is irreversible? Give some examples of irreversible enzyme inhibitors.
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