Deck 6: Enzymes

Question 1

The minimum amount of energy required to bring about a chemical reaction is called __________.

A) activation energy
B) enthalpy of reaction
C) free energy
D) standard free energy
E) transition state

Answer 1

A

Question 2

Which of the following is not a property of enzymes?

A) Capable of being regulated
B) Reaction rates high in comparison to uncatalyzed reaction
C) Highly specific
D) Side products of reactions are rare.
E) All of the above are correct.

Answer 2

E

Question 3

Consider the following reaction diagram. Which letter indicates the transition state?

A) A
B) B
C) C
D) D
E) E

Answer 3

C

Question 4

In contrast to inorganic catalysts, enzymes have an intricately shaped surface called the __________.

A) substrate
B) cofactor
C) active site
D) apoenzyme
E) holoenzyme

Question 5

The lock and key model of enzyme activity proposes that each __________.

A) enzyme can react with only a single substrate
B) enzyme has a cofactor that promotes the catalytic activity
C) substrate has a specific cofactor that binds it to the enzyme
D) enzyme binds a specific substrate because the active site and substrate have complementary structures.
E) Both A and B are correct.

Question 6

The synthesis of enzymes in response to changing metabolic needs is referred to as __________.

A) enzyme induction
B) allosteric regulation
C) negative feedback
D) zymogen activation
E) cooperative binding

Question 7

Which of the following is a coenzyme?

A) NADP⁺
B) Zn⁺⁺
C) Cu⁺⁺
D) Insulin
E) Oxytocin

Question 8

Alcohol dehydrogenase without NAD⁺ is called a __________.

A) apoenzyme
B) holoenzyme
C) substrate
D) cofactor
E) coenzyme

Question 9

The term synthetase is included in which class of enzymes?

A) Ligases
B) Hydrolases
C) Transferases
D) Lyases
E) Isomerases

Question 10

Which of the following is not a type of oxidoreductase?

A) Peroxidase
B) Hydroxylase
C) Reductase
D) Dehydrogenase
E) Peptidase

Question 11

Which of the following classes of enzymes catalyze reactions involving the cleavage of bonds by the addition of water?

A) Transferase
B) Hydrolase
C) Lyase
D) Ligase
E) Isomerase

Question 12

Consider the following reaction data.
Alanylanine + water $\rightarrow$ alanine
$\begin{array}{lll}\text { [alanylanine] } & {[\text { water] }} & \text { Rate } \\0.1 & 0.1 & 1 \times 10^{-4} \\0.2 & 0.1 & 2 \times 10^{-4} \\0.1 & 0.2 & 2 \times 10^{-4} \\0.2 & 0.2 & 4 \times 10^{-4}\end{array}$ The reaction is __________ order overall.

A) zero
B) first
C) second
D) third
E) fourth

Question 13

The steady state assumption states that if
K₁ = the rate constant for ES formation
K₂ = the rate constant for ES dissociation
K₃ = the rate constant for product formation

A) k₂ is highly negligible compared with k₃
B) The rate of formation of ES is equal to the rate of its degradation over the course of the reaction.
C) The rate of formation of ES exceeds the rate of degradation over the course of the reaction.
D) k₃ is negligible when compared to k₂.
E) Product concentration at the beginning of the reaction is low.

Question 14

The expression of the Michaelis constant is equal to

A) (K₂ + K₃)/K₁
B) (K₂ + K_1./K₃
C) (K₁ + K₂)/K₃
D) (K₃ + K₁) + K₃
E) (K₂/K₁) + K₃
Where
K₁ = the rate constant for ES formation
K₂ = the rate constant for ES dissociation
K₃ = the rate constant for product formation

Question 15

Specific activity is defined as __________.

A) enzyme concentration that converts 1 $\mu$ mole of substrate to product per minute.
B) enzyme concentration that converts 1 mole of substrate to product per minute
C) the number of I.U. per mg of protein
D) the number of I. U. per gram of protein
E) enzyme concentration that converts 1 mm of substrate to product per minute.

Question 16

In the Lineweaver-Burk double reciprocal plot the slope is equal to __________.

A) 1/[S]
B) 1/V
C) K_m/V_max
D) 1/V_max
E) -1/K_m

Question 17

In the Lineweaver-Burk double reciprocal plot the vertical intercept is equal to __________.

A) 1/[S]
B) 1/V
C) K_m/V_max
D) 1/V_max
E) -1/K_m

Question 18

In the Lineweaver-Burk double reciprocal plot the horizontal intercept is equal to __________.

A) 1/[S]
B) 1/V
C) K_m/V_max
D) 1/V_max
E) -1/K_m

Question 19

In competitive inhibition, increasing the concentration of substrate __________

A) decreases the overall rate of the reaction
B) increases the overall rate of the reaction
C) is without effect
D) the observed effect depends on the inhibitor
E) competitive inhibitors do not affect the rate of the reaction

Question 20

Which of the following amino acids is capable of acting as a general acid or general base at physiological pH?

A) Glycine
B) Histidine
C) Tyrosine
D) Tryptophan
E) Proline

Question 21

Which of the following amino acids can participate in covalent catalysis?

A) Tryptophan
B) Alanine
C) Serine
D) Histidine
E) Both C and D are correct.

Question 22

Which of the following is a feature of transition metals that makes them efficient cofactors?

A) Have a high concentration of positive charge
B) Can act as a Lewis acid
C) Have directed valences
D) Can exist as a variety of valence states
E) All of the above are correct.

Question 23

NADPH and NADH are coenzymes found in which class of enzymes?

A) Dehydrogenases
B) Ligases
C) Hydrolases
D) Transferases
E) Both C and D are correct.

Question 24

Which of the following is not present in the active site of alcohol dehydrogenase?

A) Zn⁺⁺
B) Histidine
C) Cysteine
D) NAD⁺
E) Proline

Question 25

Enzyme control is accomplished in which of the following ways?

A) Genetic control
B) Covalent modification
C) Allosteric regulation
D) Compartmentation
E) All of the above are correct.

Question 26

Zymogens are a feature of what type of enzymatic control?

A) Genetic control
B) Covalent modification
C) Allosteric regulation
D) Compartmentation
E) Both B and C are correct.

Question 27

Regulatory enzymes are a feature of what type of enzymatic control?

A) Genetic control
B) Covalent modification
C) Allosteric regulation
D) Compartmentation
E) Both B and C are correct.

Question 28

Positive cooperativity is a feature of what type of enzymatic control?

A) Genetic control
B) Covalent modification
C) Allosteric regulation
D) Compartmentation
E) Both B and C are correct.

Question 29

Segregation of biochemical pathways into different organelles in an example of which type of enzymatic regulation?

A) Genetic control
B) Covalent modification
C) Allosteric regulation
D) Compartmentation
E) Both B and C are correct.

Question 30

Catalysts are effective because they __________.

A) decrease the rate of the reverse reaction
B) stabilize the transition state
C) decrease the activation energy of a reaction
D) increase the energy released during a reaction
E) Both B and C are correct.

Question 31

Enzymes act by __________.

A) decreasing the energy of activation of a reaction
B) increasing the energy of activation of a reaction
C) raising the temperature of a reaction
D) providing a surface to favorably orient the reactants
E) Both A and D are correct.

Question 32

Enzyme studies are best carried out in __________.

A) dilute aqueous solution
B) highly concentrated solutions of the enzyme
C) highly concentrated solutions of the substrate
D) the presence of an inert crowding agent
E) the presence of a membrane

Question 33

Alcohol dehydrogenase is an example of which of the following classes of enzymes?

A) Oxidoreductases
B) Transferase
C) Hydrolase
D) Lyase
E) Isomerase

Question 34

Which of the following is not an assumption of the law of mass action?

A) Forward reaction is linear.
B) Reverse reaction is linear.
C) System is homogenous.
D) Interacting molecules move randomly and independently of each other.
E) All are assumptions of the law of mass action.

Question 35

Metabolons are defined as __________.

A) multifunction enzymes
B) complexes that channel product molecules from one active site to another
C) metabolic intermediates
D) effector molecules
E) rate of flow of metabolites from one point to another

Question 36

Metabolic flux is best defined as a __________.

A) lubrication enzyme that promotes the flow of reactants
B) rate of flow of metabolites from one point to another in a pathway
C) rate of a reaction
D) promoter molecule
E) Both A and D are correct.

Question 37

An enzyme without it cofactor is called __________.

A) coenzyme
B) apoenzyme
C) holoenzyme
D) noncatalytic
E) isoenzyme

Question 38

Which of the following amino acids cannot actively participate in a catalytic site?

A) Serine
B) Threonine
C) Tyrosine
D) Glycine
E) Glutamine

Question 39

In addition to serine and aspartate which of the following amino acids is a member of the serine triad?

A) Threonine
B) Tyrosine
C) Glutamine
D) Histidine
E) Glycine

Question 40

Which of the following is not an important metal in biological systems?

A) Na⁺
B) K⁺
C) Mg⁺⁺
D) Cu⁺⁺
E) Ba⁺⁺

Question 41

The major site of alcohol detoxification is __________.

A) intestine
B) kidney
C) pancreas
D) liver
E) stomach

Question 42

The main enzyme used to detoxify alcohol in humans is __________.

A) ADH1
B) ADH2
C) ADH3
D) ADH4
E) All of the above are correct.

Question 43

Consider the following diagram. What constitutes the activation energy for the forward reaction?

A) C-A
B) C-E
C) E-A
D) C-B
E) E-D

Question 44

Which of the following statements is not true of enzymes?

A) Increase the reaction rate
B) Obey the laws of thermodynamics
C) Catalyze the forward reaction only
D) Do not affect the position of equilibrium
E) Not consumed by the reaction

Question 45

Hexokinase is an example of which class of enzymes?

A) Hydrolase
B) Lyase
C) Isomerase
D) Transferase
E) Ligase

Question 46

Pyruvate carboxylase is an example of which class of enzymes?

A) Oxidoreductase
B) Transferase
C) Hydrolase
D) Ligase
E) Lyase

Question 47

What is meant by the term activation energy?

Question 48

Describe the term coenzyme. Give two examples.

Question 49

What is meant by the term turnover number?

Question 50

What is a noncompetitive inhibitor?

Question 51

What is a reaction intermediate?

Question 52

What is a proenzyme ?

Question 53

List four important properties of enzymes.

Question 54

Describe negative feedback inhibition.

Question 55

What properties of transition metals make them useful as enzyme cofactors?

Question 56

Explain why enzyme kinetics measurement are made at the start of a reaction.

Question 57

Describe the relationship between the law of mass action, solute concentration and effective concentration.

Question 58

Catalysts are believed to lower the activation energy of the transition state in a chemical reaction. How do they accomplish this task?

Question 59

Transition metals can act as Lewis acids. Explain.

Question 60

Is a reaction mechanism altered by the presence of a catalyst? Explain.

Question 61

Explain the difference between the energy of reaction and energy of activation.

Question 62

Mercuric ion and methyl alcohol are inhibitors of alcohol dehydrogenase. Explain.

Question 63

Describe the difference between reversible and irreversible inhibitors. Give an example of each.

Question 64

List three enzymatic dyads.

Question 65

How does an enzyme attain catalytic perfection?

Question 66

Water is often excluded from the active site of enzymes. Under these circumstances an amino nitrogen becomes much more nucleophilic. Explain.

Question 67

Can an activity coefficient ever be greater than one?

Question 68

Why do many enzymes require cofactors?

Question 69

Is catalytic perfection a function of concentration?

Question 70

Freeze drying is a useful technique for isolating enzymes. If the pH is not carefully controlled, however, the enzyme frequently becomes denatured. Explain.

Question 71

An enzyme is a large complex molecule much of which is seemingly uninvolved in the enzyme's catalytic function. Would it be possible to eliminate excess polypeptide segments and still retain activity?

Question 72

Some enzymes exist in the body as an inactive form (proenzymes) that are activated only when needed. What advantage do inactive precursors provide?

Question 73

Most enzymes are amino acid polymers. Would the replacement of the nitrogen in the peptide bond and side chains with oxygen be possible?

Question 74

How does aspirin inhibit the perception of pain?

Question 75

Catalase has a K_m of 25 mM and a k_cat of 4×10⁷sec^-1 with H₂O₂ as a substrate. Carbonic anhydrase has a K_m of 26mM and a k_cat of 4×10⁵ sec^-1. What does this data tell you about these two enzymes?

Question 76

The k_m and k_cat for fumarase the enzyme that catalyzes the conversion of fumarate to malate are 5×10^-6M and 8×10² s-1respectively. What does the data tell you about the operation of this enzyme in the citric acid cycle?

Question 77

Consider the following reaction along with its rate information
A + B $\rightarrow$ C
$\begin{array}{lll}{[\mathrm{A}](\mathrm{mM})} & {[\mathrm{B}](\mathrm{mM})} & \text { Rate }(\mathrm{mM} / \mathrm{s}) \\0.05 & 0.05 & 2 \times 10^{7} \\0.10 & 0.05 & 4 \times 10^{7} \\0.05 & 0.1 & 4 \times 10^{7} \\0.1 & 0.1 & 8 \times 10^{7}\end{array}$ What is the overall rate expression for this reaction? What is the order of the reaction?

Question 78

Consider the following data for an enzyme-catalyzed hydrolysis reaction in the presence and absence of inhibitor I using a Michaelis-Menton plot determine K_m for both inhibited and uninhibited reactions

Question 79

The table represents a specific substrate concentrations for an enzyme that displays classical Michaelis-Menten kinetics. Two sets of inhibitor data are also included. Determine the K_m and V_max for the uninhibited enzyme.