1. An Introduction to Metabolism
Chapter 8
An Introduction to Metabolism
Questions prepared by
Jung Choi
Georgia Institute of Technology

2. Living Organisms and Order
How do living organisms create macromolecules, organelles, cells, tissues, and complex higher-order structures?
The laws of thermodynamics do not apply to living organisms.
Living organisms create order by using energy from the sun.
Living organisms create order locally, but the energy transformations generate waste heat that increases the entropy of the universe.
Answer: c
This question relates to Concept 8.1. 2

3. Free Energy, Enthalpy, and Entropy
When sodium chloride (table salt) crystals dissolve in water, the temperature of the solution decreases. This means that, for dissociation of Na+ and Cl– ions,
the change in enthalpy (H) is negative.
the change in enthalpy (H) is positive, but the change in entropy is greater.
the reaction is endergonic, because it absorbs heat.
the reaction must be coupled to an exergonic reaction.
the reaction cannot occur spontaneously.
Answer: b
This question relates to Concept 8.2. 3

4. Life and Chemical Equilibrium
Are most chemical reactions at equilibrium in living cells?
yes no
only the exergonic reactions
all reactions except those powered by ATP hydrolysis
Answer: b
This question relates to Concept 8.2. At equilibrium, the free energy change is zero, and no work can be done. A cell at equilibrium is dead! 4

5. Free Energy
A reaction has a ∆G of 5.6 kcal/mol. Which of the following would most likely be true?
The reaction could be coupled to power an endergonic reaction with a G of 8.8 kcal/mol.
The reaction would result in a decrease in entropy (S) and an increase in the energy content (H) of the system.
The reaction would result in an increase in entropy (S) and a decrease in the energy content (H) of the system.
The reaction would result in products with a greater free- energy content than in the initial reactants.
Answer: c
This question relates to Concepts 8.2 and 8.3. 5

6. The hydrolysis of ATP: ATP  H2O → ADP  Pi is exergonic, with a G of 7.3 kcal/mol under standard conditions. What is the source of the 7.3 kcal/mol released in this reaction?
breaking the terminal phosphate bond in ATP
the increase in entropy from breaking apart ATP
both the energy released from breaking the terminal phosphate bond and the increase in entropy
the difference between the potential energy in the bonds of ATP and the water molecule, minus the potential energy in the bonds of ADP and Pi
Answer: d 6

7. Rate of a Chemical Reaction
The oxidation of glucose to CO2 and H2O is highly exergonic: G = –636 kcal/mole. Why doesn’t glucose spontaneously combust?
The glucose molecules lack the activation energy at room temperature.
There is too much CO2 in the air.
CO2 has higher energy than glucose.
The formation of six CO2 molecules from one glucose molecule decreases entropy.
The water molecules quench the reaction.
Answer: a
This question relates to Concept 8.4. 7

8. Enzymes
Firefly luciferase catalyzes the reaction luciferin  ATP ↔ adenyl-luciferin  pyrophosphate then the next reaction occurs spontaneously: adenyl-luciferin  O2 → oxyluciferin  H2O  CO2  AMP  light What is the role of luciferase?
Luciferase makes the G of the reaction more negative.
Luciferase lowers the transition energy of the reaction.
Luciferase alters the equilibrium point of the reaction.
Luciferase makes the reaction irreversible.
all of the above
Answer: b
This question relates to Concept 8.4. 8

9. Enzyme-Catalyzed Reactions
In the energy diagram below, which of the lettered energy changes would be the same in both the enzyme-catalyzed and uncatalyzed reactions? a b c d e
Answer: c
This question relates to Concept 8.4. 9

10. This figure could represent the rate of
an enzyme- catalyzed reaction
facilitated diffusion
active transport
any of the above
Answer: d
Concept: 8.4
Protein-mediated reactions, including transport across a membrane, will reach saturation when all available enzyme molecules or transport proteins are fully occupied by substrate. 10

11. If this is an enzyme-catalyzed reaction, how can the rate of this reaction be increased beyond the maximum velocity in this figure?
Increase the substrate concentrations.
Increase the amount of enzyme.
Increase the amount of energy.
any of the above
There is no way to increase the rate of the reaction any further.
Answer: b
Concept 8.4 11

12. Enzyme Inhibitors
Vioxx and other prescription nonsteroidal anti-inflammatory drugs (NSAIDs) are potent inhibitors of the cycloxygenase-2 (COX-2) enzyme. High substrate concentrations reduce the efficacy of inhibition by these drugs. These drugs are
competitive inhibitors.
noncompetitive inhibitors.
allosteric regulators.
prosthetic groups.
feedback inhibitors.
Answer: a
This question relates to Concepts 8.4 and 8.5.
Sources
Copeland et al. Mechanism of Selective Inhibition of the Inducible Isoform of Prostaglandin G/H Synthase 1994, PNAS 91:
Chan et al. Rofecoxib [Vioxx, MK-0966; 4-(4'-Methylsulfonylphenyl)-3-phenyl-2-(5H)-furanone]: A Potent and Orally Active Cyclooxygenase-2 Inhibitor. Pharmacological and Biochemical Profiles 1999, Pharmacology 290: 12

13. Enzyme Regulation
Adenosine monophosphate (AMP) activates the enzyme phosphofructokinase (PFK) by binding at a site distinct from the substrate binding site. This is an example of
cooperative activation.
allosteric activation.
activation by an enzyme cofactor.
coupling exergonic and endergonic reactions.
Answer: b
This question relates to Concept 8.5. 13

14. Which enzymes may translocate from the cytoplasm to associate with the cytoplasmic face of the plasma membrane in response to a signal?
ion channels
active transport proteins
phospholipid hydrolases
aTP synthases
motor proteins
Answer: c
Concept 8.5 14