Chapter 8 Multiple Choice Practice

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Chapter 8 Multiple Choice Practice
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. Which of the following statements is a logical consequence of the second law of thermodynamics?
a. If the entropy of a system increases, there must be a corresponding decrease in the
b.
c.
d.
e.
____
entropy of the universe.
If there is an increase in the energy of a system, there must be a corresponding
decrease in the energy of the rest of the universe.
Every energy transfer requires activation energy from the environment.
Every chemical reaction must increase the total entropy of the universe.
Energy can be transferred or transformed, but it cannot be created or destroyed.
2. The mathematical expression for the change in free energy of a system is
G
HT
S.
Which of the following is (are) correct?
a.
S is the change in enthalpy, a measure of randomness.
b.
H is the change in entropy, the energy available to do work.
c.
G is the change in free energy.
d. T is the temperature in degrees Celsius.
____
3. Which of the following is true for all exergonic reactions?
a. The products have more total energy than the reactants.
b. The reaction proceeds with a net release of free energy.
c. Some reactants will be converted to products.
d. A net input of energy from the surroundings is required for the reactions to
proceed.
e. The reactions are nonspontaneous.
____
4. Chemical equilibrium is relatively rare in living cells. Which of the following could be an example
of a reaction at chemical equilibrium in a cell?
a. a reaction in which the free energy at equilibrium is higher than the energy content
at any point away from equilibrium
b. a chemical reaction in which the entropy change in the reaction is just balanced by
an opposite entropy change in the cell's surroundings
c. an endergonic reaction in an active metabolic pathway where the energy for that
reaction is supplied only by heat from the environment
d. a chemical reaction in which both the reactants and products are only used in a
metabolic pathway that is completely inactive
e. There is no possibility of having chemical equilibrium in any living cell.
____
5. Which of the following best describes enthalpy (H)?
a. the total kinetic energy of a system
b. the heat content of a chemical system
c. the system's entropy
d. the cell's energy equilibrium
e. the condition of a cell that is not able to react
____
6. A number of systems for pumping across membranes are powered by ATP. Such ATP-powered
pumps are often called ATPases although they don't often hydrolyze ATP unless they are
simultaneously transporting ions. Small increases in calcium ions in the cytosol trigger a number of
different intracellular reactions, so the cells must keep the calcium concentration quite low. Muscle
cells also transport calcium from the cytosol into the membranous system called the sarcoplasmic
reticulum (SR). If a muscle cell cytosol has a free calcium ion concentration of 10–7 in a resting cell,
while the concentration in the SR can be 10–2, then how is the ATPase acting?
a. The ATP must be powering an inflow of calcium from the outside of the cell into
the SR.
b. ATP must be transferring Pi to the SR to enable this to occur.
c. ATPase activity must be pumping calcium from the cytosol to the SR against the
concentration gradient.
d. The calcium ions must be diffusing back into the SR along the concentration
gradient.
e. The route of calcium ions must be from SR to the cytosol, to the cell's
environment.
____
7. Sucrose is a disaccharide, composed of the monosaccharides glucose and fructose. The hydrolysis of
sucrose by the enzyme sucrase results in
a. bringing glucose and fructose together to form sucrose.
b. the release of water from sucrose as the bond between glucose and fructose is
broken.
c. breaking the bond between glucose and fructose and forming new bonds from the
atoms of water.
d. production of water from the sugar as bonds are broken between the glucose
monomers.
e. utilization of water as a covalent bond is formed between glucose and fructose to
form sucrase.
____
8. Reactants capable of interacting to form products in a chemical reaction must first overcome a
thermodynamic barrier known as the reaction's
a. entropy.
b. activation energy.
c. endothermic level.
d. heat content.
e. free-energy content.
____
9. Which of the following statements regarding enzymes is true?
a. Enzymes decrease the free energy change of a reaction.
b. Enzymes increase the rate of a reaction.
c. Enzymes change the direction of chemical reactions.
d. Enzymes are permanently altered by the reactions they catalyze.
e. Enzymes prevent changes in substrate concentrations.
Refer to Figure 8.1 to answer the following questions.
Figure 8.1
____ 10. Which curve represents the behavior of an enzyme taken from a bacterium that lives in hot springs at
temperatures of 70°C or higher?
a. curve 1
b. curve 2
c. curve 3
d. curve 4
e. curve 5
____ 11. Which curve was most likely generated from analysis of an enzyme from a human stomach where
conditions are strongly acid?
a. curve 1
b. curve 2
c. curve 3
d. curve 4
e. curve 5
____ 12. Increasing the substrate concentration in an enzymatic reaction could overcome which of the
following?
a. denaturization of the enzyme
b. allosteric inhibition
c. competitive inhibition
d. saturation of the enzyme activity
e. insufficient cofactors
Use the following information to answer the following questions.
Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited
by malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase.
Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid.
____ 13. What is the purpose of using malonic acid in this experiment?
a. It is a competitive inhibitor.
b. It blocks the binding of fumarate.
c. It is a noncompetitive inhibitor.
d. It is able to bind to succinate.
e. It replaces the usual enzyme.
The following questions are based on the reaction A + B  C + D shown in Figure 8.2.
Figure 8.2
____ 14. Which of the following terms best describes the reaction?
a. endergonic
b. exergonic
c. anabolic
d. allosteric
e. nonspontaneous
____ 15. Which of the following represents the
a. a
b. b
c. c
d. d
e. e
G of the reaction?
____ 16. Which of the following would be the same in an enzyme-catalyzed or noncatalyzed reaction?
a. a
b. b
c. c
d. d
e. e
____ 17. Which of the following represents the activation energy required for the enzyme-catalyzed reaction?
a. a
b. b
c. c
d. d
e. e
____ 18. Assume that the reaction has a G of -5.6 kcal/mol. Which of the following would be true?
a. The reaction could be coupled to power an endergonic reaction with a G of +6.2
kcal/mol.
b. The reaction could be coupled to power an exergonic reaction with a
G of +8.8
kcal/mol.
c. The reaction would result in a decrease in entropy (S) and an increase in the total
energy content (H) of the system.
d. The reaction would result in an increase in entropy (S) and a decrease in the total
energy content (H) of the system.
e. The reaction would result in products (C + D) with a greater free-energy content
than in the initial reactants (A + B).
____ 19. Which of the following is likely to lead to an increase in the concentration of ATP in a cell?
a. an increase in a cell's anabolic activity
b. an increase in a cell's catabolic activity
c. an increased influx of cofactor molecules
d. an increased amino acid concentration
e. the cell's increased transport of materials to the environment
____ 20. Among enzymes, kinases catalyze phosphorylation, while phosphatases catalyze removal of
phosphate(s). A cell's use of these enzymes can therefore function as an on-off switch for various
processes. Which of the following is probably involved?
a. the change in a protein's charge leading to a conformational change
b. the change in a protein's charge leading to cleavage
c. a change in the optimal pH at which a reaction will occur
d. a change in the optimal temperature at which a reaction will occur
e. the excision of one or more peptides
____ 21. Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity?
a. cessation of all enzyme formation
b. compartmentalization of enzymes into defined organelles
c. exporting enzymes out of the cell
d. connecting enzymes into large aggregates
e. hydrophobic interactions
____ 22. Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as ____
is to ____.
a.
b.
c.
d.
e.
exergonic; spontaneous
exergonic; endergonic
free energy; entropy
work; energy
entropy; enthalpy
____ 23. Which of the following metabolic processes can occur without a net influx of energy from some
other process?
a. ADP + P i  ATP + H2O
b. C6H12O6 + 6 O2  6 CO2 + 6 H2O
c. 6 CO2 + 6 H2O  C6H12O6 + 6 O2
d. amino acids  protein
e. glucose + fructose  sucrose
____ 24. If an enzyme is added to a solution where its substrate and product are in equilibrium, what would
occur?
a. Additional product would be formed.
b. Additional substrate would be formed.
c. The reaction would change from endergonic to exergonic.
d. The free energy of the system would change.
e. Nothing; the reaction would stay at equilibrium.
____ 25. Some bacteria are metabolically active in hot springs because
a. they are able to maintain a cooler internal temperature.
b. high temperatures make catalysis unnecessary.
c. their enzymes have high optimal temperatures.
d. their enzymes are completely insensitive to temperature.
e. they use molecules other than proteins or RNAs as their main catalysts.
Chapter 8 Multiple Choice Practice
Answer Section
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