Deck 8: Energy, Enzymes, and Metabolism

Question 1

Coenzymes differ from enzymes in that coenzymes are

A) only active outside the cell.
B) polymers of amino acids.
C) smaller molecules, such as vitamins.
D) specific for one reaction.
E) always carriers of high-energy phosphate.

Answer 1

C

Question 2

Which statement about temperature effects is not true?

A) Raising the temperature may reduce the activity of an enzyme.
B) Raising the temperature may increase the activity of an enzyme.
C) Raising the temperature may denature an enzyme.
D) Some enzymes are stable at the boiling point of water.
E) All enzymes have the same optimal temperature.

Answer 2

E

Question 3

In a chemical reaction,

A) the rate depends on the value of G.
B) the rate depends on the activation energy.
C) the entropy change depends on the activation energy.
D) the activation energy depends on the value of G.
E) the change in free energy depends on the activation energy.

Answer 3

B

Question 4

What can never be created or destroyed?

A) Entropy
B) Energy
C) Free energy only
D) Thermal energy only
E) Potential energy only

Question 5

Which of the following represents potential energy?

A) Chemical bonds
B) Concentration gradient
C) Electric charge imbalance
D) Both a and b
E) All of the above

Question 6

Which statement about enzyme inhibitors is not true?

A) A competitive inhibitor binds the active site of the enzyme.
B) An allosteric inhibitor binds a site on the active form of the enzyme.
C) A noncompetitive inhibitor binds a site other than the active site.
D) Noncompetitive inhibition cannot be completely overcome by the addition of more substrate.
E) Competitive inhibition can be completely overcome by the addition of more substrate.

Question 7

The molecule ATP is

A) a component of most proteins.
B) high in energy because of the presence of adenine.
C) required for many energy-transforming biochemical reactions.
D) a catalyst.
E) used in some exergonic reactions to provide energy.

Question 8

Lactose intolerance is due to the

A) inability to hydrolyze polysaccharides.
B) body's ability to digest lactose but inability to absorb the resulting products.
C) gaseous side products produced in the small intestine.
D) inability to produce the enzyme lactase.
E) inability to oxidate luciferase.

Question 9

How does the second law of thermodynamics apply to organisms?

A) As energy transformations occur, free energy increases and unusable energy decreases.
B) To maintain order, life requires a constant input of energy.
C) The potential energy of ATP is converted to kinetic energy such as muscle contractions.
D) Reactions occur only with an input of energy.
E) It does not apply to organisms; the complexity of organisms contradicts the second law.

Question 10

The active site of an enzyme

A) never changes shape.
B) forms no chemical bonds with substrates.
C) determines, by its structure, the specificity of the enzyme.
D) looks like a lump projecting from the surface of the enzyme.
E) changes the $\Delta$ G of the reaction.

Question 11

Which statement about enzymes is not true?

A) They usually consist of proteins.
B) They change the rate of the catalyzed reaction.
C) They change the G of the reaction.
D) They are sensitive to heat.
E) They are sensitive to pH.

Question 12

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.

Question 13

Water held back by a dam represents what kind of energy?

A) Hydroelectric
B) Irrigation
C) Potential
D) Kinetic
E) At times, all of the above

Question 14

In an enzyme-catalyzed reaction,

A) a substrate does not change.
B) the rate decreases as substrate concentration increases.
C) the enzyme can be permanently changed.
D) strain may be added to a substrate.
E) the rate is not affected by substrate concentration.

Question 15

The first law of thermodynamics states that the total energy in the universe is

A) decreasing.
B) increasing.
C) constant.
D) being converted to free energy.
E) being converted to matter.

Question 16

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 process 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.

Question 17

A change in free energy is related to a change in

A) temperature.
B) entropy.
C) pressure.
D) Both a and b
E) All of the above

Question 18

Which statement about thermodynamics is true?

A) Free energy is used up in an exergonic reaction.
B) Free energy cannot be used to do work.
C) The total amount of energy can change after a chemical transformation.
D) Free energy can be kinetic but not potential energy.
E) Entropy has a tendency to increase.

Question 19

In any system, the total energy includes usable and unusable energy. The unusable energy is a measure of the disorder of the system and is referred to as

A) free energy.
B) entropy.
C) enthalpy.
D) thermodynamics.
E) equilibrium.

Question 20

Which statement about the feedback inhibition of enzymes is not true?

A) It is usually exerted through allosteric effects.
B) It is directed at the enzyme that catalyzes the commitment step in a metabolic pathway.
C) It affects the rate of reaction, not the concentration of enzyme.
D) It acts by permanently modifying the active site.
E) It is an example of reversible inhibition.

Question 21

Fireflies

A) release a considerable amount of energy as heat.
B) light up to signal danger.
C) use ATP to begin luciferin oxidation.
D) are constantly converting light energy into chemical energy.
E) have a short life cycle due to rapid depletion of ATP.

Question 22

In a chemical reaction, transition-state species have free energies that are

A) lower than either the reactants or the products.
B) higher than either the reactants or the products.
C) lower than the reactants, but higher than the products.
D) higher than the reactants, but lower than the products.
E) lower than the reactants, but the same as the products.

Question 23

In glycolysis, the exergonic reaction 1,3-diphosphoglycerate $\to$ 3-phosphoglycerate is coupled to the reaction ADP + P_i $\to$ ATP. Which of the following is most likely to be true about the reaction ADP + P_i $\to$ 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.

Question 24

Which of the following statements about the exergonic hydrolysis of maltose to glucose is true?

A) The reaction requires the input of free energy.
B) The free energy of glucose is larger than the free energy of maltose.
C) The reaction is not spontaneous.
D) The reaction releases free energy.
E) At equilibrium, the concentration of maltose is higher than the concentration of glucose.

Question 25

If $\Delta$ G of a chemical reaction is negative and the change in entropy is positive, you can conclude that the reaction

A) requires energy.
B) is endergonic.
C) is exergonic.
D) will not reach equilibrium.
E) decreases the disorder in the system.

Question 26

When ADP gains a phosphate to form ATP,

A) free energy is released by the loss of a phosphate.
B) energy is consumed.
C) the reaction ends.
D) chemical energy is converted to light energy.
E) ribose loses an oxygen to become deoxyribose.

Question 27

The rate of a chemical reaction in a cell is the measure of how

A) often the reaction occurs.
B) quickly the reaction reaches equilibrium.
C) much energy must be added for the reaction to occur.
D) much activation energy is required for the reaction to occur.
E) easily the reaction is inhibited.

Question 28

Which of the following statements about enzymes is false?

A) An enzyme changes shape when it binds to a substrate.
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.

Question 29

An RNA molecule that has enzyme activity is called

A) RNAse.
B) ribonuclease.
C) an allosteric enzyme.
D) a regulatory enzyme.
E) a ribozyme.

Question 30

The standard free energy change for the hydrolysis of ATP to ADP + P_i is -7.3 kcal/mol. From this information, one can conclude that the

A) reaction will never reach equilibrium.
B) free energy of ADP and phosphate is higher than the free energy of ATP.
C) reaction requires energy.
D) reaction is endergonic.
E) reaction is exergonic.

Question 31

Knowing the change in free energy ( $\Delta$ G) of a reaction tells us

A) the equilibrium point of the reaction.
B) the rate of the reaction.
C) how fast equilibrium will be reached.
D) the optimum temperature for the reaction.
E) the activation energy.

Question 32

Chemical equilibrium

A) is a dynamic state.
B) represents a state of negative energy change.
C) represents a state of positive energy change.
D) cannot exist in nature.
E) is a state in which $\Delta$ G = 0.

Question 33

Which of the following statements about ATP is true?

A) The hydrolysis of ATP is exergonic.
B) ATP consists of adenine bonded to deoxyribose.
C) ATP releases a relatively small amount of energy when hydrolyzed.
D) An active cell requires about 100 molecules of ATP per second.
E) On average, ATP is consumed within one second of its formation.

Question 34

Which of the following is an example of an exergonic reaction?

A) The beating cilia of a protozoan
B) Cellular respiration
C) Phagocytosis
D) Receptor-mediated endocytosis
E) The Na⁺- K⁺ pump

Question 35

If the enzyme phosphohexoisomerase is added to a 0.3 M solution of fructose 6-phosphate, and the reaction is allowed to proceed to equilibrium, the final concentrations are 0.2 M glucose 6-phosphate and 0.1 M fructose 6-phosphate. These data give an equilibrium constant of 2. What is the equilibrium constant if the initial concentration of fructose 6-phosphate is 3 M?

A) 2
B) 3
C) 5
D) 10
E) 20

Question 36

ATP can phosphorylate many different molecules. This means that ATP can

A) receive phosphate groups.
B) donate phosphate groups.
C) convert molecules to nucleic acids.
D) store a large amount of energy when hydrolyzed.
E) All of the above

Question 37

Phosphorylation of ADP to ATP is endergonic, whereas the hydrolysis of ATP to ADP is exergonic. The two reactions are therefore said to be

A) substrates.
B) endergonic.
C) kinetic.
D) activated.
E) coupled.

Question 38

A readily reversible reaction, in which reactants and products have almost the same free energies, is indicated by a

A) slightly negative $\Delta$ G.
B) change in free energy.
C) negative $\Delta$ G.
D) $\Delta$ G near zero.
E) large positive $\Delta$ G.

Question 39

What is a transition state?

A) The place where a substrate molecule binds to an enzyme
B) A reactant with high potential energy
C) The combination of a substrate and an enzyme
D) The state at which the bonds of reactants are unstable
E) The active site where reactants are oriented

Question 40

Luciferin and luciferase are added to soft drinks because

A) they enhance the taste.
B) they act as preservatives.
C) they detect bacterial contamination by "lighting up."
D) luciferase speeds up the release of monosaccharides.
E) they hydrolyze disaccharides.

Question 41

The enzyme sucrase increases the rate at which sucrose is broken down into glucose and fructose. Sucrase works by

A) increasing the amount of free energy of the reaction.
B) lowering the activation energy of the reaction.
C) decreasing the equilibrium constant of the reaction.
D) supplying energy to speed up the reaction.
E) changing the shape of the active site.

Question 42

An active site is

A) the part of the substrate that binds with an enzyme.
B) the part of the enzyme that binds with a substrate.
C) the site where energy is added to an enzyme catalyst.
D) the site where enzymes are found in cells.
E) None of the above

Question 43

The statement "enzymes are highly specific" means that certain

A) enzymes are found in certain cells.
B) reactions involving certain substrates are catalyzed by specific 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.

Question 44

In the presence of alcohol dehydrogenase, the rate of reduction of acetaldehyde to ethanol increases as the concentration of acetaldehyde is increased. Eventually, the rate of the reaction reaches a maximum, at which point further increases in the concentration of acetaldehyde have no effect. Why?

A) All the alcohol dehydrogenase molecules are bound to acetaldehyde molecules.
B) At high concentrations of acetaldehyde, the activation energy of the reaction increases.
C) At high concentrations of acetaldehyde, the activation energy of the reaction decreases.
D) The enzyme is no longer specific for acetaldehyde.
E) At high concentrations of acetaldehyde, the change in free energy of the reaction decreases.

Question 45

The ability of an enzyme to change shape when it binds to its substrate is called

A) induced fit.
B) enzyme flex.
C) the lock-and-key paradox.
D) substrate-induced active site shaping.
E) enzyme retrofit.

Question 46

The enzyme glyceraldehyde 3-phosphate dehydrogenase catalyzes the reaction glyceraldehyde 3-phosphate $\to$ 1,3-diphosphoglycerate. The binding of the glyceraldehyde 3-phosphate to the enzyme creates a(n)

A) transition state.
B) activation groove.
C) catalyst.
D) enzyme-substrate complex.
E) energy barrier.

Question 47

Enzymes of the acid-base catalysis type contain

A) a metal ion bound to a side chain.
B) a prosthetic group.
C) a coenzyme.
D) acidic or basic amino acid side chains (R groups) in the active site.
E) a covalently activated active site.

Question 48

In some cases, a substrate-enzyme complex is stabilized by

A) hydrogen bonds.
B) covalent bonds.
C) ionic attractions.
D) hydrophobic interactions.
E) All of the above

Question 49

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.

Question 50

The hydrolysis of sucrose to glucose and fructose is exergonic. However, if sucrose is dissolved in water and the solution is kept overnight at room temperature, there is no detectable conversion to glucose and fructose. Why?

A) The change in free energy of the reaction is positive.
B) The activation energy of the reaction is high.
C) The change in free energy of the reaction is negative.
D) This is a condensation reaction.
E) The free energy of the products is higher than the free energy of the reactants.

Question 51

The presence of a catalyst affects the

A) amount of activation energy required.
B) overall energy change, or $\Delta$ G.
C) energy of the reactants.
D) energy of the products.
E) free energy of the transition state.

Question 52

Binding of substrate to the active site of an enzyme is

A) reversible.
B) irreversible.
C) noncompetitive.
D) coupled.
E) allosteric.

Question 53

Which of the following determines the rate of a reaction?

A) $\Delta$ S
B) $\Delta$ G
C) $\Delta$ H
D) The activation energy
E) The overall change in free energy

Question 54

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) $\Delta$ 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.

Question 55

The enzyme $\alpha$ -amylase increases the rate at which starch is broken down into smaller oligosaccharides by _______ of the reaction.

A) decreasing the equilibrium constant
B) increasing the change in free energy
C) decreasing the change in free energy
D) increasing the change in entropy
E) lowering the activation energy

Question 56

Which of the following is an enzyme?

A) Manganese dioxide
B) Hemoglobin
C) Catalase
D) Hydrogen peroxide
E) Malathion

Question 57

Which of the following statements about enzymes is true?

A) Enzymes are proteins.
B) Enzymes have a specific amino acid sequence.
C) Enzymes are highly specific.
D) Enzymes lower the energy barrier.
E) All of the above

Question 58

Enzymes catalyze a reaction by _______ the substrates.

A) orienting
B) inducing strain in
C) adding chemical groups to
D) adding charges to
E) All of the above

Question 59

The molecules that are acted on by an enzyme are called

A) products.
B) substrates.
C) carriers.
D) prosthetics.
E) effectors.

Question 60

The catalysis mechanism used by lysozyme to break down bacterial cell walls is

A) acid-base catalysis.
B) covalent catalysis.
C) metal cofactor redox catalysis.
D) induced strain.
E) unknown.

Question 61

The addition of the competitive inhibitor mevinolin slows the reaction HMG-CoA $\to$ mevalonate, which is catalyzed by the enzyme HMG-CoA reductase. The effects of mevinolin would be overcome and the rate of the reaction increased by

A) adding more mevalonate.
B) adding more HMG-CoA.
C) lowering the temperature of the reaction.
D) adding a prosthetic group.
E) lowering the rate constant of the reaction.

Question 62

The maximum possible rate of an enzyme reaction that is influenced by a competitive inhibitor depends on the concentration of

A) inhibitor.
B) substrate.
C) product.
D) enzyme.
E) free energy.

Question 63

Denatured enzymes are the same as

A) ribozymes.
B) abzymes.
C) isozymes.
D) enzymes that can no longer function.
E) coenzymes.

Question 64

Allosteric inhibitors act by

A) decreasing the number of enzyme molecules.
B) increasing the number of enzyme molecules.
C) decreasing the amount of the inactive form of the enzyme.
D) decreasing the amount of the active form of the enzyme.
E) increasing the amount of substrate.

Question 65

An allosteric inhibitor

A) decreases the concentration of an inactive enzyme.
B) changes the shape of an enzyme.
C) increases the concentration of a product.
D) changes the shape of a substrate.
E) increases the concentration of an enzyme-substrate complex.

Question 66

Many enzymes require ATP and ADP for a reaction to occur. They temporarily bind to and then release from the substrate to participate in other reactions. ATP and ADP are considered

A) a side chain.
B) coenzymes.
C) a coupled reaction.
D) a prosthetic group.
E) cofactors.

Question 67

Enzymatic reactions can become saturated as substrate concentration increases because

A) enzymes have the maximum possible number of hydrogen atoms attached to them.
B) the concentration of substrate reaches a point at which it cannot increase any further.
C) substrates are inhibitors of enzymes.
D) the activation energy of the reaction reaches a point at which it cannot be lowered further.
E) there are a limited number of the enzyme molecules present.

Question 68

Negative feedback in a sequence of chemical reactions involves a chemical that appears _______ in the sequence and _______ reaction.

A) late; inhibits an earlier
B) early; inhibits a later
C) early; activates a later
D) late; activates an earlier
E) late; inhibits a later

Question 69

Which type of inhibitor can be overcome completely by the addition of more substrate?

A) Irreversible
B) Noncompetitive
C) Competitive
D) Prosthetic
E) Isotonic

Question 70

How do competitive and noncompetitive enzyme inhibitors differ?

A) Competitive inhibitors bind to the active site, whereas noncompetitive inhibitors change the shape of the active site.
B) Competitive inhibitors have a higher energy of activation than noncompetitive inhibitors have.
C) They function at different pH values.
D) Noncompetitive enzyme inhibitors contain magnesium, whereas competitive inhibitors contain iron.
E) Noncompetitive enzyme inhibitors are reversible, whereas competitive inhibitors are irreversible.

Question 71

The inhibition of enzyme activity by noncompetitive inhibitors can be reduced

A) by decreasing the concentration of allosteric enzymes.
B) by decreasing the concentration of substrate.
C) by increasing the concentration of competitive inhibitor.
D) by increasing the concentration of substrate.
E) only when they become unbound.

Question 72

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.

Question 73

A noncompetitive inhibitor inhibits binding of a substrate to an enzyme by

A) binding to the substrate.
B) binding to the active site.
C) lowering the activation energy.
D) increasing the $\Delta$ G of the reaction.
E) changing the shape of the active site.

Question 74

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.

Question 75

Which of the following statements about allosteric regulators is true?

A) The plot for allosteric regulators often has a sigmoid curve.
B) All enzymes are allosterically regulated.
C) Enzymes that are allosterically regulated are made of multiple polypeptide subunits.
D) Both the active site and the regulatory site are present on the same subunit.
E) Allosteric regulators bind to the active site, blocking enzyme function.

Question 76

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.

Question 77

Enzymes are sensitive to

A) temperature.
B) pH.
C) irreversible inhibitors such as DIPF.
D) allosteric effectors.
E) All of the above

Question 78

Nerve gases such as Sarin and malathion

A) block specific chemical transformations by inactivating specific enzymes.
B) have reversible effects on animals.
C) are proteins with a primary structure.
D) block the energy coupling cycle of ATP.
E) bond covalently to the active site of the enzyme.

Question 79

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.

Question 80

Environmental conditions that affect enzyme function include

A) temperature.
B) pH.
C) CO₂ concentration.
D) Both a and b
E) All of the above