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. TRUE

B. FALSE

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. TRUE

B. FALSE

Question #5

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

A. FALSE

B. TRUE

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. TRUE

B. FALSE

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. TRUE

B. FALSE

Question #10

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

A. TRUE

B. FALSE

Question #11

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

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

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

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

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

E. stays the same shape during substrate binding

Question #12

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

A. lowers the energy of the products

B. changes the concentration of the substrate

C. lowers the activation energy for the reaction

D. lowers the energy of the substrate

E. changes the possible product formed

Question #13

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

A. TRUE

B. FALSE

Question #14

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

A. TRUE

B. FALSE

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. FALSE

B. TRUE

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. TRUE

B. FALSE

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. cofactor

B. prosthetic group

C. modulator

D. co-enzyme

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 damages the enzyme in liver that breaks down hydrogen peroxide

B. reactions take place faster at lower temperatures

C. heating removes the water and oxygen from the liver

D. heating kills the germs that cause the bubbling

Question #20

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

A. produces more product per second

B. requires more energy

C. uses less substrate

D. produces different products

E. requires a higher temperature

Question #21

Most enzymes are ________.

A. fibrous proteins

B. substrate proteins

C. insoluble proteins

D. secondary structure proteins

E. globular proteins

Question #22

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

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

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

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

Question #23

Which of these are advantages of lowering the activation energy?

A. it allows reactions to proceed at an acceptable temperature

B. it changes the optimum pH of the enzyme

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

D. it allows reactions to proceed more quickly

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. Enzymes usually double the rate of a reaction.

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

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

Question #25

Choose the correct statement

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

B. The active site of enzymes has a rigid shape

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

D. Enzymes have a rigid shape

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

Question #26

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

A. TRUE

B. FALSE

Question #27

Which of the following enzyme groups can catalyze oxidation reactions?

A. isomerases

B. phosphorylases

C. hydrolases

D. dehydrogenases

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 insoluble nature of enzymes.

C. The surface configuration of enzymes.

D. The high molecular mass of enzymes.

Question #29

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

A. TRUE

B. FALSE

Question #30

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

A. a high temperature

B. a low temperature

C. heavy metal ions

D. an extreme pH

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. dehydrogenase

B. hydrolase

C. decarboxylase

D. oxidoreductase

Question #33

Enzymes are potent catalysts because they:

A. increase the equilibrium constants for the reactions they catalyze

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

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

D. are consumed in the reactions they catalyze

E. lower the activation energy for the reactions they catalyze

Question #34

Which of the following statements is false?

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

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

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

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

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

Question #35

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

A. FALSE

B. TRUE

Question #36

Enzymes are classified by the:

A. Size of the substrate

B. Type of reaction they catalyze

C. Rate of reaction

D. Size of the enzyme

Question #37

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

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

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

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

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

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

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

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

Question #39

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

A. metal

B. organic

C. inorganic

D. All of these answers are correct.

Question #40

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

A. FALSE

B. TRUE

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. I only

B. I and III

C. III only

D. II 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. FALSE

B. TRUE

Question #45

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

A. TRUE

B. FALSE

Question #46

A. TRUE

B. FALSE

Question #47

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

A. FALSE

B. TRUE

Question #48

Enzymes ensure that all substrate is converted to product

A. TRUE

B. FALSE

Question #49

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

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

B. Their catalytic activity is independent of pH.

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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