Energy, Enzymes, and Metabolism: Chapter 6
1. Enzymes are sensitive to
a. temperature.
b. pH.
c. irreversible inhibitors such as DIPF.
d. allosteric effectors.
e. All of the above
Answer: e
2 End products of biosynthetic pathways often act to block the initial step in that
pathway. This phenomenon is called
a. allosteric inhibition.
b. denaturation.
c. branch pathway inhibition.
d. feedback inhibition.
e. binary inhibition.
Answer: d
3 Competitive and noncompetitive enzyme inhibitors differ with respect to
a. the precise location on the enzyme to which they bind.
b. their pH.
c. their binding affinities.
d. their energies of activation.
e. None of the above
Answer: a
4. During photosynthesis, plants use light energy to synthesize glucose from carbon
dioxide. However, plants do not use up energy during photosynthesis; they merely convert it from light energy to chemical energy. This is an illustration of
a. increasing entropy.
b. chemical equilibrium.
c. the first law of thermodynamics.
d. the second law of thermodynamics.
e. a spontaneous reaction.
Answer: c
i
is –7.3
kcal/mol. What can you conclude from this information?
a. The reaction will never reach equilibrium.
b. The free energy of ADP and phosphate is higher than the free energy of ATP.
c. The reaction requires energy.
d. The reaction is endergonic.
e. The reaction is exergonic.
Answer: e
6. The enzyme α-amylase increases the rate at which starch is broken down into smaller
oligosaccharides. It does this by
a. decreasing the equilibrium constant of the reaction.
b. increasing the change in free energy of the reaction.
c. decreasing the change in free energy of the reaction.
d. increasing the change in entropy of the reaction.
e. lowering the activation energy of the reaction.
Answer: e
7. The enzyme glyceraldehyde 3-phosphate dehydrogenase catalyzes the reaction
glyceraldehyde 3-phosphate → 1,3-diphosphoglycerate. The region of the enzyme where
glyceraldehyde 3-phosphate binds is called the
a. transition state.
b. groove.
c. catalyst.
d. active site.
e. energy barrier.
Answer: d
8. The enzyme glucose oxidase binds the six-carbon sugar glucose and catalyzes its
conversion to glucono-1,4-actone. Mannose is also a six-carbon sugar, but glucose
oxidase cannot bind mannose. The specificity of glucose oxidase is based on the
a. free energy of the transition state.
b. activation energy of the reaction.
c. change in free energy of the reaction.
d. three-dimensional shape and structure of the active site.
e. rate constant of the reaction.
Answer: d
9. In glycolysis, the exergonic reaction 1,3-diphosphoglycerate → 3-phosphoglycerate is
coupled to the reaction ADP + Pi → ATP. Which of the following is most likely to be
true about the reaction ADP + Pi →ATP?
a. The reaction never reaches equilibrium.
b. The reaction is spontaneous.
c. There is a large decrease in free energy.
d. The reaction is endergonic.
e. Temperature will not affect the rate constant of the reaction.
Answer: d
10. Trypsin and elastase are both enzymes that catalyze hydrolysis of peptide bonds. But
trypsin only cuts next to lysine and elastase only cuts next to alanine. Why?
a. Trypsin is a protein, and elastase is not.
b. ∆G for the two reactions is different.
c. The shape of the active site for the two enzymes is different.
d. One of the reactions is endergonic, and the other is exergonic.
e. Hydrolysis of lysine bonds requires water; hydrolysis of alanine bonds does not.
Answer: c
11. The enzyme catalase has a ferric ion tightly bound to the active site. The ferric ion is
called a(n)
a. side chain.
b. enzyme.
c. coupled reaction.
d. prosthetic group.
e. substrate.
Answer: d
12. How does a noncompetitive inhibitor inhibit binding of a substrate to an enzyme?
a. It binds to the substrate.
b. It binds to the active site.
c. It lowers the activation energy.
d. It increases the ∆G of the reaction.
e. It changes the shape of the active site.
Answer: e
13. Binding of substrate to the active site of an enzyme is
a. reversible.
b. irreversible.
c. noncompetitive.
d. coupled.
e. allosteric.
Answer: a
14. The presence in a system of energy that is unusable for the purpose of doing work is
related to the system’s
a. temperature.
b. entropy.
c. work.
d. thermodynamics.
e. equilibrium.
Answer: b
15. The molecules that are acted on by an enzyme are called
a. products.
b. substrates.
c. carriers.
d. prosthetics.
e. effectors.
Answer: b
16. The sum total of all the chemical reactions in a living structure is called its
a. energetics.
b. activity.
c. digestive power.
d. entropy.
e. metabolism.
Answer: e
17. The statement “Enzymes are highly specific” means that certain
a. enzymes are found in certain cells.
b. reactions involving certain substrates are catalyzed by certain enzymes.
c. enzymes require certain concentrations of substrates.
d. reactions with certain activation energies are catalyzed by certain enzymes.
e. concentrations of substrates work with certain enzymes.
Answer: b
18. Competitive inhibitors of enzymes work by
a. fitting into the active site.
b. fitting into a site other than the active site.
c. altering the shape of the enzyme.
d. changing the enzyme into an inactive form.
e. increasing the activation energy of the enzyme-catalyzed reaction.
Answer: a
19. Denatured enzymes are the same as
a. ribozymes.
b. abzymes.
c. isozymes.
d. destroyed enzymes.
e. coenzymes.
Answer: d
20 A type of enzyme inhibitor that binds within the enzyme’s active site is termed
a. allosteric.
b. noncompetitive.
c. competitive.
d. extracompetitive.
e. None of the above
Answer: c
21. The process that involves an end product acting as an inhibitor of an earlier step in a
metabolic pathway is called
a. feedback activation.
b. feedback inhibition.
c. positive feedback.
d. concerted activation.
e. competitive inhibition.
Answer: b
22. What can never be created or destroyed?
a. Entropy
b. Energy
c. Free energy
d. Thermal energy
e. Potential energy
Answer: b
23. When ATP loses a phosphate to form ADP,
a. free energy is released.
b. energy is consumed.
c. the reaction ends.
d. chemical energy is converted to light energy.
e. ribose loses an oxygen to become deoxyribose.
Answer: a
24. Which of the following statements about enzymes is false?
a. An enzyme has no shape..
b. Enzymes lower the activation energy.
c. Enzymes are highly specific.
d. An enzyme may orient substrates, induce strain, or temporarily add chemical groups.
e. Most enzymes are much smaller than their substrates.
Answer: e
25. Enzymes are highly sensitive to pH and temperature because
a. changes in the environment raise their activation energy.
b. changes in temperature and pH readily break their hydrogen bonds.
c. of their three-dimensional structure and side chains.
d. at extreme temperatures and pH levels, coenzymes add chemical groups to the
substrate.
e. extremes of temperature and pH level change the ionization rate.
Answer: c