West Los Angeles College » Chemistry » Chem 221 - Biochemistry for Science Majors » Fall 2021

Chem 221 - Biochemistry for Science Majors » Fall 2021 » L8 Enzymes Part 1 of 3

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Question #1

Enzymes shift the position of the equilibrium to the right.

A. FALSE

B. TRUE

Question #2

Reactions that are not very spontaneous based on ΔG°’ can be made more spontaneous by adjusting the initial concentrations of reactants and products.

A. TRUE

B. FALSE

Question #3

The equilibrium position (Keq) is a function only of the free-energy difference (ΔG) between reactants and products.

A. TRUE

B. FALSE

Question #4

ΔG°’ = + 20.3 kcal mol-1 means that the reaction is non spontaneous in vivo.

A. FALSE

B. TRUE

Question #5

A reaction with a positive standard free energy change is exergonic.

A. TRUE

B. FALSE

Question #6

The in vivo initial concentrations of reactants and products are usually different from the in vitro initial concentrations of reactants and products.

A. FALSE

B. TRUE

Question #7

When the equilibrium constant is lesser than 1 the standard free energy change of a reaction is negative.

A. TRUE

B. FALSE

Question #8

The ΔG of a reaction is depends on the molecular mechanism of the transformation.

A. TRUE

B. FALSE

Question #9

The value of the ΔG of a reaction depends on the value of the free energy of the reactants and the value of the free energy of the products.

A. FALSE

B. TRUE

Question #10

Spontaneous reactions are exergonic and have a positive free energy change.

A. FALSE

B. TRUE

Question #11

In the induced-fit model of enzyme action, the enzyme active site ________.

A. adjusts shape to adapt to the shape of the substrate

B. stays the same shape during substrate binding

C. uses an inhibitor to adjust its shape for the substrate

D. uses a cofactor to change the shape of a substrate

E. stays the same shape while causing a change in the shape of the substrate

Question #12

The function of the enzyme-substrate complex is to provide an alternative reaction pathway that ________.

A. changes the concentration of the substrate

B. changes the possible product formed

C. lowers the energy of the products

D. lowers the activation energy for the reaction

E. lowers the energy of the substrate

Question #13

The transition state is the point of low energy between the reactants and products.

A. FALSE

B. TRUE

Question #14

The higher the rate of the reaction, the higher is the activation energy.

A. FALSE

B. TRUE

Question #15

Lowering the activation energy means that more energy is needed to convert it into a product and the reaction proceeds at a faster rate

A. TRUE

B. FALSE

Question #16

The active site contains the amino-acid residues that directly participate in the breaking and making of bonds in substrate and product.

A. FALSE

B. TRUE

Question #17

The amino acid residues that are involved in the reaction that forms a product are called:

A. amino acid residue

B. catalytic residues

C. active residues

D. enzymatic residues

Question #18

Some enzymes require the presence of a non-protein substance if they are to catalyze a reaction. Which of the following terms is the best general term for such a substance?

A. prosthetic group

B. cofactor

C. co-enzyme

D. modulator

Question #19

When a piece of liver is dropped into hydrogen peroxide, the peroxide bubbles vigorously as the hydrogen peroxide (H2O2) decomposes into water (H2O) and oxygen (O2). However, if the liver is cooked first, the reaction fails to occur. The reason for this is

A. heating kills the germs that cause the bubbling

B. heating removes the water and oxygen from the liver

C. heating damages the enzyme in liver that breaks down hydrogen peroxide

D. reactions take place faster at lower temperatures

Question #20

Compared to an uncatalyzed reaction, an enzyme-catalyzed reaction ________.

A. uses less substrate

B. requires more energy

C. produces more product per second

D. produces different products

E. requires a higher temperature

Question #21

Most enzymes are ________.

A. insoluble proteins

B. fibrous proteins

C. secondary structure proteins

D. globular proteins

E. substrate proteins

Question #22

Which of the following statements is FALSE with respect to an enzyme's ability to catalyze a reaction?

A. An enzyme binds reactants such that they are positioned correctly and can attain their transition-state alignment.

B. An enzyme allows the reaction to go through a less stable transition state than would normally be the case.

C. An enzyme provides a reaction surface and a suitable environment for the reaction to take place.

Question #23

Which of these are advantages of lowering the activation energy?

A. it allows chemicals to react that otherwise wouldn't

B. it allows reactions to proceed more quickly

C. it allows reactions to proceed at an acceptable temperature

D. it changes the optimum pH of the enzyme

Question #24

Choose the correct statement

A. A certain amount of energy must always be added to the system or no reaction will take place.

B. In chemical reaction, products cannot be formed after the activation energy has been overcome

C. During a chemical reaction, reactants must absorb some energy and go through a more stable intermediate state before they become products.

D. Enzymes usually double the rate of a reaction.

Question #25

Choose the correct statement

A. The structural adaptation that occurs between protein and inhibitor is called induced fit.

B. When an enzyme binds to a substrate it stresses and destabilizes the bonds in the substrate.

C. The shape of the active site cannot be modified by the binding of substrate.

D. Enzymes have a rigid shape

E. The active site of enzymes has a rigid shape

Question #26

Keq is related to thermodynamics, while delta G is related to kinetics.

A. FALSE

B. TRUE

Question #27

Which of the following enzyme groups can catalyze oxidation reactions?

A. dehydrogenases

B. hydrolases

C. isomerases

D. phosphorylases

Question #28

Enzymes differ from inorganic catalysts in that they are highly specific. Which property of an enzyme is responsible for this specificity?

A. The absence of metallic ions in an enzyme.

B. The high molecular mass of enzymes.

C. The surface configuration of enzymes.

D. The insoluble nature of enzymes.

Question #29

ΔG°’ = - 30.5 kcal mol-1 means that the reaction is spontaneous in vivo.

A. FALSE

B. TRUE

Question #30

Which one of the following conditions is least likely to denature an enzyme?

A. an extreme pH

B. heavy metal ions

C. a low temperature

D. a high temperature

Question #31

Which of the following kinetic parameters remains the same for S --> P, whether the reaction is enzyme-catalyzed or uncatalyzed?

A. Keq

B. Rate

Question #32

Which type of enzyme catalyzes the conversion of a dipeptide into two separate amino acids?

A. hydrolase

B. dehydrogenase

C. oxidoreductase

D. decarboxylase

Question #33

Enzymes are potent catalysts because they:

A. drive reactions to completion while other catalysts drive reactions to equilibrium

B. are consumed in the reactions they catalyze

C. lower the activation energy for the reactions they catalyze

D. are very specific and can prevent the conversion of products back to substrates

E. increase the equilibrium constants for the reactions they catalyze

Question #34

Which of the following statements is false?

A. For S → P, a catalyst shifts the reaction equilibrium to the right.

B. After a reaction, the enzyme involved becomes available to catalyze the reaction again.

C. A reaction may not occur at a detectable rate even though it has a favorable equilibrium.

D. Lowering the temperature of a reaction will lower the reaction rate.

E. Substrate binds to an enzyme's active site.

Question #35

The criterion of spontaneity of a reaction in vivo is ΔG°’ not ΔG.

A. TRUE

B. FALSE

Question #36

Enzymes are classified by the:

A. Size of the enzyme

B. Rate of reaction

C. Type of reaction they catalyze

D. Size of the substrate

Question #37

Consider a biochemical reaction A → B, which is catalyzed by A–B dehydrogenase. Which of the following statements is true?

A. The free energy change (ΔG) of the catalyzed reaction is the same as for the uncatalyzed reaction.

B. A component of the enzyme is transferred from A to B.

C. The reaction will be most favorable at 0°C.

D. The reaction will proceed until the enzyme concentration decreases.

Question #38

Which of these statements is true:

A. Hydrolases catalyze the formation of a compound from two molecules using the addition of water.

B. Lyases catalyze the formation of a single molecule from two products (without hydrolysis)

C. Transferases catalyze the movement of a functional group within molecule.

D. Ligases catalyze synthesis reactions often using energy derived from the breakdown of ATP

Question #39

A coenzyme is differentiated from the broader class of cofactors because it is _____

A. metal

B. All of these answers are correct.

C. organic

D. inorganic

Question #40

An enzyme accelerates the forward and reverse reactions by the same factor.

A. TRUE

B. FALSE

Question #41

Which of the following is true of enzymes? I. They increase the rate of reaction by stabilizing the transition state II. They raise activation energy to shift the equilibrium to favor the products III. They lower activation energy by altering the products of a reaction

A. II and III

B. III only

C. I only

D. I and III

Question #42

Which statement about enzymes is false?

A. Enzyme change the relative energy of the initial and final states of a reaction

B. Enzymes use covalent and non covalent interactions to accelerate reaction

C. Enzymes lower the activation energy of a reaction

D. Enzymes can increase the rate of a reaction by a factor of 10 to the 15th power

Question #43

Enzymes increase the equilibrium constant for the reaction, thus favoring product formation.

A. TRUE

B. FALSE

Question #44

Enzymes increase the rate at which substrate is converted to product

A. TRUE

B. FALSE

Question #45

Enzymes ensure that the product is more thermodynamically stable than the substrate

A. FALSE

B. TRUE

Question #46

A. FALSE

B. TRUE

Question #47

When the standard free energy change of a reaction is negative, the equilibrium constant is greater than 1.

A. TRUE

B. FALSE

Question #48

Enzymes ensure that all substrate is converted to product

A. FALSE

B. TRUE

Question #49

Which one of the following statements is true of enzyme catalysts?

A. Their catalytic activity is independent of pH.

B. To be effective, they must be present at the same concentration as their substrate.

C. They are generally equally active on D and L isomers of a given substrate.

D. They can increase the rate for a given reaction by a thousand fold or more.

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