Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity?

1. connecting enzymes into large aggregates
2. hydrophobic interactions
3. localization of enzymes into specific organelles or membranes
4. exporting enzymes out of the cell

C

Which of the following represents the activation energy required for the enzyme-catalyzed reaction in the figure?

1. a
2. b
3. c
4. d

B

The mathematical expression for the change in free energy of a system is ΔG =ΔH - TΔS. Which of the following is (are) correct?

1. ΔH is the change in entropy, the energy available to do work.
2. T is the temperature in degrees Celsius.
3. ΔG is the change in free energy.
4. ΔS is the change in enthalpy, a measure of randomness.

C

Which of the following is true when comparing an uncatalyzed reaction to the same reaction with a catalyst?

1. The catalyzed reaction will have higher activation energy.
2. The catalyzed reaction will consume all of the catalyst.
3. The catalyzed reaction will be slower.
4. The catalyzed reaction will have the same ∆G.

D

For living organisms, which of the following is an important consequence of the first law of thermodynamics?

1. The entropy of an organism decreases with time as the organism grows in complexity.
2. The energy content of an organism is constant.
3. The organism ultimately must obtain all of the necessary energy for life from its environment.
4. Organisms grow by converting energy into organic matter.

C

Which of the following in the figure would be the same in either an enzyme-catalyzed or a noncatalyzed reaction?

1. a
2. b
3. c
4. d

D

Which of the following is the most correct interpretation of the figure?

1. Energy from catabolism can be used directly for performing cellular work.
2. ADP + i are a set of molecules that store energy for catabolism.
3. i acts as a shuttle molecule to move energy from ATP to ADP.
4. ATP is a molecule that acts as an intermediary to store energy for cellular work.

D

Which temperature and pH profile curves on the graphs were most likely generated from analysis of an enzyme from a human stomach where conditions are strongly acid?

1. curves 2 and 4
2. curves 1 and 5
3. curves 3 and 4
4. curves 1 and 4

D

Which H+ ion has just passed through the inner mitochondrial membrane by diffusion?

1. hydrogen ion A
2. hydrogen ion B
3. hydrogen ion C
4. hydrogen ion D

D

For the enzyme- catalyzed reaction shown in the figure, if the initial reactant concentration is 1.0 micromolar, which of these treatments will cause the greatest increase in the rate of the reaction?

1. cooling the reaction by 10°C
2. doubling the activation energy needed
3. increasing the concentration of reactants to 10.0 micromolar, while reducing the concentration of enzyme by 1/2
4. doubling the enzyme concentration

D

How might a change of one amino acid at a site, distant from the active site of an enzyme, alter an enzyme's substrate specificity?

1. by changing the enzyme's pH optimum
2. by changing the shape of an enzyme
3. by changing the enzyme's stability
4. An amino acid change away from the active site cannot alter the enzyme's substrate specificity.

B

Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as _____.

1. an allosteric activator of the enzyme
2. a coenzyme derived from a vitamin
3. a noncompetitive inhibitor of the enzyme
4. a cofactor necessary for enzyme activity

D

In a biological reaction, succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, a substance that resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the amount of succinate molecules to those of malonic acid reduces the inhibitory effect if malonic acid. Select the correct identification of the molecules described in the reaction.

1. Fumarate is the product, and malonic acid is a noncompetitive inhibitor in the reaction.
2. Succinate is the substrate, and fumarate is the product in the reaction.
3. Succinate dehydrogenase is the enzyme, and malonic acid is the substrate in the reaction.
4. Succinate dehydrogenase is the enzyme, and fumarate is the substrate in the reaction.

B

Which of the following is true of metabolism in its entirety in all organisms?

1. Metabolism uses all of an organism's resources.
2. Metabolism depends on a constant supply of energy from food.
3. Metabolism consists of all the energy transformation reactions in an organism.
4. Metabolism manages the increase of entropy in an organism.

C

A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. What is substance X?

1. the product
2. an intermediate
3. an allosteric inhibitor
4. a substrate

D

According to the induced fit hypothesis of enzyme catalysis, _____.

1. some enzymes change their structure when activators bind to the enzyme
2. the binding of the substrate depends on the shape of the active site
3. the active site creates a microenvironment ideal for the reaction
4. the binding of the substrate changes the shape of the enzyme's active site

D

You have isolated a previously unstudied protein, identified its complete structure in detail, and determined that it catalyzes the breakdown of a large substrate. You notice it has two binding sites. One of these is large, apparently the bonding site for the large substrate; the other is small, possibly a binding site for a regulatory molecule. What do these findings tell you about the mechanism of this protein?

1. It is probably an enzyme that works through allosteric regulation.
2. It is probably a cell membrane transport protein–like an ion channel.
3. It is probably a structural protein that is involved in cell-to-cell adhesion.
4. It is probably an enzyme that works through competitive inhibition.

A

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?

1. 0 kcal/mol
2. -40 kcal/mol
3. +20 kcal/mol
4. -20 kcal/mol

D

Which of the following is a statement of the first law of thermodynamics?

1. Energy cannot be transferred or transformed.
2. The entropy of the universe is decreasing.
3. Energy cannot be created or destroyed.
4. The entropy of the universe is constant.

C

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. Based on this information, which of the following is correct?

1. Succinate dehydrogenase is the enzyme, and malonic acid is the substrate.
2. Succinate is the substrate, and fumarate is the product.
3. Fumarate is the product, and malonic acid is a noncompetitive inhibitor.
4. Succinate dehydrogenase is the enzyme, and fumarate is the substrate.

B

Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's _____.

1. equilibrium point
2. activation energy
3. free-energy content
4. entropy

B

The active site of an enzyme is the region that _____.

1. is involved in the catalytic reaction of the enzyme
2. is inhibited by the presence of a coenzyme or a cofactor
3. binds noncompetitive inhibitors of the enzyme
4. binds allosteric regulators of the enzyme

A

You have discovered an enzyme that can catalyze two different chemical reactions. Which of the following is most likely to be correct?

1. Two types of allosteric regulation occur: The binding of one molecule activates the enzyme, while the binding of a different molecule inhibits it.
2. The enzyme contains α-helices and β-pleated sheets.
3. The enzyme is subject to competitive inhibition and allosteric regulation.
4. Either the enzyme has two distinct active sites or the reactants involved in the two reactions are very similar in size and shape.

D

Protein kinases are enzymes that transfer the terminal phosphate from ATP to an amino acid residue on the target protein. Many are located on the plasma membrane as integral membrane proteins or peripheral membrane proteins. What purpose may be served by their plasma membrane localization?

1. They can more readily encounter and phosphorylate other membrane proteins.
2. They flip back and forth across the membrane to access target proteins on either side.
3. Membrane localization lowers the activation energy of the phosphorylation reaction.
4. ATP is more abundant near the plasma membrane.

A

When 10,000 molecules of ATP are hydrolyzed to ADP and i in a test tube, about half 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?

1. Reactant and product concentrations in the test tube are different from those in the cell.
2. Cells are open systems, but a test tube is an isolated system.
3. Cells are less efficient at heat production than nonliving systems.
4. The reaction in cells must be catalyzed by enzymes, but the reaction in a test tube does not need enzymes.

A

The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as _____.

1. metabolic inhibition
2. feedback inhibition
3. noncooperative inhibition
4. allosteric inhibition

B

Which of the following involves a decrease in entropy?

1. condensation reactions
2. hydrolysis reactions
3. reactions that separate monomers
4. depolymerization reactions

A

In solution, why do hydrolysis reactions occur more readily than condensation reactions?

1. Hydrolysis decreases entropy and is exergonic.
2. Hydrolysis raises G, or Gibbs free energy.
3. Hydrolysis increases entropy and is endergonic.
4. Hydrolysis increases entropy and is exergonic.

D

Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?

1. anabolism (anabolic pathways)
2. dehydration
3. metabolism
4. catabolism (catabolic pathways)

D

Why is ATP an important molecule in metabolism?

1. Its terminal phosphate group contains a strong covalent bond that, when hydrolyzed, releases free energy.
2. It provides energy coupling between exergonic and endergonic reactions.
3. Its terminal phosphate bond has higher energy than the other two phosphate bonds.
4. Its hydrolysis provides an input of free energy for exergonic reactions.

B

Catabolic pathways _____.

1. are endergonic
2. supply energy, primarily in the form of ATP, for the cell's work
3. are spontaneous and do not need enzyme catalysis
4. combine molecules into more energy-rich molecules

B

A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. With respect to the enzyme that converts X to Y, substance A functions as _____.

1. an intermediate
2. a competitive inhibitor
3. the substrate
4. an allosteric inhibitor

D

When ATP releases some energy, it also releases inorganic phosphate. What happens to the inorganic phosphate in the cell?

1. It is used only to regenerate more ATP.
2. It enters the nucleus and affects gene expression.
3. It is secreted as waste.
4. It may be used to form a phosphorylated intermediate.

D

The lock-and-key analogy for enzymes applies to the specificity of enzymes _____.

1. interacting with water
2. as they form their tertiary and quaternary structure
3. interacting with ions
4. binding to their substrate

D

Which of the following types of reactions would decrease the entropy within a cell?

1. anabolic reactions
2. digestion
3. catabolic reactions
4. hydrolysis

A

Increasing the substrate concentration in an enzymatic reaction could overcome which of the following?

1. competitive inhibition
2. insufficient cofactors
3. the need for a coenzyme
4. allosteric inhibition

A

A system at chemical equilibrium….

1. releases energy at a steady rate
2. consumes energy at a steady rate
3. can do no work
4. has zero kinetic energy

C

Biological systems use free energy based on empirical data that all organisms require a constant energy input. The first law of thermodynamics states that energy can be neither created nor destroyed. For living organisms, which of the following statements is an important consequence of this first law?

1. The energy content of an organism is constant except for when its cells are dividing.
2. Organisms are unable to transform energy from the different states in which it can exist.
3. The organism must ultimately obtain all the necessary energy for life from its environment.
4. The entropy of an organism decreases with time as the organism grows in complexity.

C