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. FALSE

B. TRUE

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. 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. FALSE

B. TRUE

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. stays the same shape during substrate binding

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

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

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

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

Question #12

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

A. lowers the energy of the substrate

B. changes the possible product formed

C. changes the concentration of the substrate

D. lowers the activation energy for the reaction

E. lowers the energy of the products

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. 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. TRUE

B. FALSE

Question #17

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

A. active residues

B. enzymatic residues

C. catalytic residues

D. amino acid residue

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. 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 removes the water and oxygen from the liver

B. heating kills the germs that cause the bubbling

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. produces different products

B. produces more product per second

C. requires more energy

D. uses less substrate

E. requires a higher temperature

Question #21

Most enzymes are ________.

A. substrate proteins

B. secondary structure proteins

C. insoluble proteins

D. globular proteins

E. fibrous 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 reactions to proceed at an acceptable temperature

B. it changes the optimum pH of the enzyme

C. it allows reactions to proceed more quickly

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

Question #24

Choose the correct statement

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

B. Enzymes usually double the rate of a reaction.

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

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. The active site of enzymes has a rigid shape

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

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

D. Enzymes have a rigid shape

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

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. hydrolases

B. dehydrogenases

C. phosphorylases

D. isomerases

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 high molecular mass of enzymes.

B. The insoluble nature of enzymes.

C. The absence of metallic ions in an enzyme.

D. The surface configuration 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. an extreme pH

B. a low temperature

C. heavy metal ions

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. dehydrogenase

B. decarboxylase

C. hydrolase

D. oxidoreductase

Question #33

Enzymes are potent catalysts because they:

A. lower the activation energy for the reactions they catalyze

B. increase the equilibrium constants for the reactions they catalyze

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

D. are consumed in the reactions they catalyze

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

Question #34

Which of the following statements is false?

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

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

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

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

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

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. Type of reaction they catalyze

B. Rate of reaction

C. Size of the substrate

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. The reaction will proceed until the enzyme concentration decreases.

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

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

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

Question #38

Which of these statements is true:

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

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

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

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

Question #39

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

A. organic

B. All of these answers are correct.

C. inorganic

D. metal

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 and III

B. III only

C. I only

D. II and III

Question #42

Which statement about enzymes is false?

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

B. Enzymes lower the activation energy of a reaction

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

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

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

Enzymes are consumed in the reactions they catalyze.

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. 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. Their catalytic activity is independent of pH.

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

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

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

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