A system at chemical equilibrium
A) consumes energy at a steady rate.
B) releases energy at a steady rate.
C) consumes or releases energy, depending on whether it is exergonic or endergonic.
D) has zero kinetic energy.
E) can do no work.

Answer: E

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) The reaction goes only in a forward direction: all reactants will be converted to products, but no products will be converted to reactants.
D) A net input of energy from the surroundings is required for the reactions to proceed.
E) The reactions are rapid.

Answer: B

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 not being produced or used in any active metabolic pathway
E) no possibility of having chemical equilibrium in any living cell

Answer: D

A chemical reaction that has a positive ΔG is correctly described as
A) endergonic.
B) endothermic.
C) enthalpic.
D) spontaneous.
E) exothermic.

Answer: A

Why is ATP an important molecule in metabolism?
A) Its hydrolysis provides an input of free energy for exergonic reactions.
B) It provides energy coupling between exergonic and endergonic reactions.
C) Its terminal phosphate group contains a strong covalent bond that, when hydrolyzed, releases free energy.
D) Its terminal phosphate bond has higher energy than the other two.
E) It is one of the four building blocks for DNA synthesis.

Answer: B

When 10,000 molecules of ATP are hydrolyzed to ADP and Pi in a test tube, about twice as much heat is liberated as when a cell hydrolyzes the same amount of ATP. Which of the following is the best explanation for this observation?
A) Cells are open systems, but a test tube is a closed system.
B) Cells are less efficient at heat production than nonliving systems.
C) The hydrolysis of ATP in a cell produces different chemical products than does the reaction in a test tube.
D) The reaction in cells must be catalyzed by enzymes, but the reaction in a test tube does not need enzymes.
E) Reactant and product concentrations in the test tube are different from those in the cell.

Answer: E

Which of the following is most similar in structure to ATP?
A) a pentose sugar
B) a DNA nucleotide
C) an RNA nucleotide
D) an amino acid with three phosphate groups attached
E) a phospholipid

Answer: C

Which of the following statements is true concerning catabolic pathways?
A) They combine molecules into more energy-rich molecules.
B) They supply energy, primarily in the form of ATP, for the cell's work.
C) They are endergonic.
D) They are spontaneous and do not need enzyme catalysis.
E) They build up complex molecules such as protein from simpler compounds.

Answer: B

When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?
A) It is used to power yet more cellular work.
B) It is used to store energy as more ATP.
C) It is used to generate ADP from nucleotide precursors.
D) It is lost to the environment.
E) It is transported to specific organs such as the brain.

Answer: D

When ATP releases some energy, it also releases inorganic phosphate. What purpose does this serve (if any) in the cell?
A) The phosphate is released as an excretory waste.
B) The phosphate can only be used to regenerate more ATP.
C) The phosphate can be added to water and excreted as a liquid.
D) The phosphate may be incorporated into any molecule that contains phosphate.
E) It enters the nucleus to affect gene expression.

Answer: D

What is the difference (if any) between the structure of ATP and the structure of the precursor of the A nucleotide in RNA?
A) The sugar molecule is different.
B) The nitrogen-containing base is different.
C) The number of phosphates is three instead of one.
D) The number of phosphates is three instead of two.
E) There is no difference.

Answer: E

Which of the following statements is true about enzyme-catalyzed reactions?
A) The reaction is faster than the same reaction in the absence of the enzyme.
B) The free energy change of the reaction is opposite from the reaction that occurs in the absence of the enzyme.
C) The reaction always goes in the direction toward chemical equilibrium.
D) Enzyme-catalyzed reactions require energy to activate the enzyme.
E) Enzyme-catalyzed reactions release more free energy than noncatalyzed reactions.

Answer: A

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) equilibrium point.
E) free-energy content.

Answer: B

A solution of starch at room temperature does not readily decompose to form a solution of simple sugars because
A) the starch solution has less free energy than the sugar solution.
B) the hydrolysis of starch to sugar is endergonic.
C) the activation energy barrier for this reaction cannot be surmounted.
D) starch cannot be hydrolyzed in the presence of so much water.
E) starch hydrolysis is nonspontaneous.

Answer: C

Which of the following statements regarding enzymes is true?
A) Enzymes increase the rate of a reaction by making the reaction more exergonic.
B) Enzymes increase the rate of a reaction by lowering the activation energy barrier.
C) Enzymes increase the rate of a reaction by reducing the rate of reverse reactions.
D) Enzymes change the equilibrium point of the reactions they catalyze.
E) Enzymes make the rate of a reaction independent of substrate concentrations.

Answer: B

During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a ∆G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the ∆G for the new reaction?
A) -40 kcal/mol
B) -20 kcal/mol
C) 0 kcal/mol
D) +20 kcal/mol
E) +40 kcal/mol

Answer: B

Note: Enzymes never change the value of ∆G

The active site of an enzyme is the region that
A) binds allosteric regulators of the enzyme.
B) is involved in the catalytic reaction of the enzyme.
C) binds noncompetitive inhibitors of the enzyme.
D) is inhibited by the presence of a coenzyme or a cofactor.

<p>Answer: B</p> <span>According to the induced fit hypothesis of enzyme catalysis, which of the following is correct?&nbsp;</span><br><span>A) The binding of the substrate depends on the shape of the active site.&nbsp;</span><br><span>B) Some enzymes change their structure when activators bind to the enzyme.&nbsp;</span><br><span>C) A competitive inhibitor can outcompete the substrate for the active site.&nbsp;</span><br><span>D) The binding of the substrate changes the shape of the enzyme's active site.&nbsp;</span><br><span>E) The active site creates a microenvironment ideal for the reaction.</span>

According to the induced fit hypothesis of enzyme catalysis, which of the following is correct?
A) The binding of the substrate depends on the shape of the active site.
B) Some enzymes change their structure when activators bind to the enzyme.
C) A competitive inhibitor can outcompete the substrate for the active site.
D) The binding of the substrate changes the shape of the enzyme's active site.
E) The active site creates a microenvironment ideal for the reaction.

Answer: D

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

Answer: C

Which of the following is true of enzymes?
A) Nonprotein cofactors alter the substrate specificity of enzymes.
B) Enzyme function is increased if the 3-D structure or conformation of an enzyme is altered.
C) Enzyme function is independent of physical and chemical environmental factors such as pH and temperature.
D) Enzymes increase the rate of chemical reaction by lowering activation energy barriers.
E) Enzymes increase the rate of chemical reaction by providing activation energy to the substrate.

Answer: D

Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as a(n)
A) competitive inhibitor of the enzyme.
B) noncompetitive inhibitor of the enzyme.
C) allosteric activator of the enzyme.
D) cofactor necessary for enzyme activity.
E) coenzyme derived from a vitamin.

Answer: D

Some of the drugs used to treat HIV patients are competitive inhibitors of the HIV reverse transcriptase enzyme. Unfortunately, the high mutation rate of HIV means that the virus rapidly acquires mutations with amino acid changes that make them resistant to these competitive inhibitors. Where in the reverse transcriptase enzyme would such amino acid changes most likely occur in drug-resistant viruses?
A) in or near the active site
B) at an allosteric site
C) at a cofactor binding site
D) in regions of the protein that determine packaging into the virus capsid
E) such mutations could occur anywhere with equal probability

Answer: A

When you have a severe fever, what grave consequence may occur if the fever is not controlled?
A) destruction of your enzymes' primary structure
B) removal of amine groups from your proteins
C) change in the tertiary structure of your enzymes through denaturing
D) removal of the amino acids in active sites of your enzymes
E) binding of your enzymes to inappropriate substrates

Answer: C

How does a noncompetitive inhibitor decrease the rate of an enzyme reaction?
A) by binding at the active site of the enzyme
B) by changing the shape of the enzyme's active site
C) by changing the free energy change of the reaction
D) by acting as a coenzyme for the reaction
E) by decreasing the activation energy of the reaction

Answer: B

The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as
A) metabolic inhibition.
B) feedback inhibition.
C) allosteric inhibition.
D) noncooperative inhibition.
E) reversible inhibition.

Answer: B

Which of the following statements describes enzyme cooperativity?
A) A multienzyme complex contains all the enzymes of a metabolic pathway.
B) A product of a pathway serves as a competitive inhibitor of an early enzyme in the pathway.
C) A substrate molecule bound to an active site of one subunit promotes substrate binding to the active site of other subunits.
D) Several substrate molecules can be catalyzed by the same enzyme.
E) A substrate binds to an active site and inhibits cooperation between enzymes in a pathway.

Answer: C

Allosteric enzyme regulation is usually associated with
A) lack of cooperativity.
B) feedback inhibition.
C) activating activity.
D) an enzyme with more than one subunit.
E) the need for cofactors.

Answer: D

Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity?
A) cessation of cellular protein synthesis
B) localization of enzymes into specific organelles or membranes
C) exporting enzymes out of the cell
D) connecting enzymes into large aggregates
E) hydrophobic interactions

Answer: B

An important group of peripheral membrane proteins are enzymes such as the phospholipases that cleave the head groups of phospholipids. What properties must these enzymes exhibit?
A) resistance to degradation
B) independence from cofactor interaction
C) water solubility
D) lipid solubility
E) membrane-spanning domains

Answer: C

Note: If the phospholipid heads are hydrophilic, the enzyme must also be hydrophilic

How might an amino acid change at a site distant from the active site of the enzyme alter the enzyme's substrate specificity?
A) by changing the enzyme's stability
B) by changing the enzyme's location in the cell
C) by changing the shape of the protein
D) by changing the enzyme's pH optimum
E) an amino acid change away from the active site cannot alter the enzyme's substrate specificity

Answer: C

This question is based on the reaction A + B ↔ C + D shown in the figure.

Which of the following terms best describes the forward reaction in Figure 8.1?
A) endergonic, ∆G > 0
B) exergonic, ∆G < 0
C) endergonic, ∆G < 0
D) exergonic, ∆G > 0
E) chemical equilibrium, ∆G = 0

Answer: B

This question is based on the reaction A + B ↔ C + D shown in the figure.

Which of the following represents the ΔG of the reaction in Figure 8.1?
A) a
B) b
C) c
D) d
E) e

Answer: D

This question is based on the reaction A + B ↔ C + D shown in the figure.

Which of the following in Figure 8.1 would be the same in either an enzyme-catalyzed or a noncatalyzed reaction?
A) a
B) b
C) c
D) d
E) e

Answer: D

This question is based on the reaction A + B ↔ C + D shown in the figure.

Which of the following represents the activation energy needed for the enzyme-catalyzed reverse reaction, C + D → A + B, in Figure 8.1?
A) a
B) b
C) c
D) d
E) e

Answer: A