Deck 8: Enzymes: Basic Concepts and Kinetics

Question 1

Allosteric enzymes can be identified because the plot of initial velocity, V₀, versus substrate concentration, S, is not hyperbolic but __________________ -shaped.

Answer 1

sigmoidal or "S"

Question 2

Enzymes accelerate the rate of a chemical reaction by __________________ the activation energy of the reaction.

Answer 2

lowering

Question 3

The Circe effect enhances what aspect of enzyme catalysis?

A) catalysis of substrate to product
B) binding of substrate
C) removal of product(s) from active site
D) prevention of enzyme inhibition
E) None of the answers is correct.

Answer 3

B

Question 4

A tightly bound cofactor for an enzyme is often called a(n) _____.

A) prosthetic group
B) coenzyme
C) allosteric activator
D) inorganic cofactor
E) None of the answers is correct.

Question 5

A(n) _____ requires an input of energy to proceed.

A) reaction at equilibrium
B) irreversible reaction
C) spontaneous reaction
D) exergonic reaction
E) endergonic reaction

Question 6

What term describes an enzyme without its required cofactor?

A) holoenzyme
B) coenzyme
C) isozyme
D) apoenzyme
E) None of the answers is correct.

Question 7

Organic cofactors are referred to as __________________.

Question 8

When ΔG for a system is zero, the system is at ______________________.

Question 9

What term is used to describe the dynamic recognition of the substrate when binding to an enzyme occurs?

A) allosteric modulation
B) transition state enhancement
C) sequential binding
D) induced fit
E) None of the answers is correct.

Question 10

Compounds that resemble the transition state of a catalyzed reaction and inhibit enzyme activity are called ____________________________.

Question 11

The k_cat is often referred to as the _____.

A) turnover number
B) Michaelis constant
C) dissociation constant
D) rate constant
E) None of the answers is correct.

Question 12

The straight-line kinetic plot of 1/ V₀ versus 1/S is called a ________________________.

Question 13

Most known enzymes are proteins; however, some ___________ molecules have been shown to possess catalytic activity.

Question 14

What type of enzymes often display sigmoidal plots of activity versus substrate concentration?

A) holoenzymes
B) monomeric enzymes
C) allosteric enzymes
D) Michaelis-Menten enzymes
E) isozymes

Question 15

If a reaction is exergonic at specific reactant concentrations, it is considered _____.

A) at equilibrium
B) nonspontaneous
C) spontaneous
D) irreversible
E) None of the answers is correct.

Question 16

The site on an enzyme where the reaction that is catalyzed by the enzyme occurs is the _____.

A) binding site
B) substrate site
C) allosteric site
D) regulatory site
E) active site

Question 17

A reaction can occur spontaneously only if ΔG is __________________.

Question 18

The difference between the standard-state free energy, ΔGº, and the biochemical standard-state free energy is that ΔGº′ refers to the standard free-energy change at ________.

Question 19

A __________________ inhibitor often has a structure similar to the substrate and often reversibly binds to the active site of the enzyme but can be displaced by substrate.

Question 20

What term describes the substance that is bound by an enzyme and converted to product?

A) inhibitor
B) substrate
C) coenzyme
D) prosthetic group
E) cofactor

Question 21

Multiple substrate enzyme reactions are divided into two classes which are called

A) sequential displacement and double displacement.
B) double displacement and concerted displacement.
C) sequential displacement and concerted displacement.
D) sequential displacement and double as well as sequential displacement and concerted displacement are correct.
E) None of the answers is correct.

Question 22

The K_M is

A) equal to the product concentration at initial reaction conditions.
B) equal to the substrate concentration when the reaction rate is half its maximal value.
C) proportional to the standard free energy.
D) All of the answers are correct.
E) None of the answers is correct.

Question 23

What type(s) of inhibition can be reversed?

A) competitive
B) noncompetitive
C) mixed
D) All of the answers are correct.
E) None of the answers is correct.

Question 24

Five K_M values are given for the binding of substrates to a particular enzyme. Which has the strongest affinity when k ₁ is greater than k₂?

A) 150 mM
B) 0.15 mM
C) 150 $\mu$ M
D) 1.5 nM
E) 15000 pM

Question 25

The formula K'_eq = 10 ^{- $\Delta$ G ° ' /1.36} indicates the relationship between

A) the free energy and the equilibrium constant.
B) the reaction equilibrium and the isomerization rate.
C) the equilibrium constant and standard free energy.
D) All of the answers are correct.
E) None of the answers is correct.

Question 26

How is the substrate bound to the active site?

Question 27

Riboflavin is a water-soluble organic substance that is not synthesized by humans. Metabolically, it is chemically converted into a substance called flavin adenine dinucleotide, which is required by succinate dehydrogenase. Which of the following statements is most correct?

A) Riboflavin is a coenzyme.
B) Flavin adenine dinucleotide is a vitamin.
C) Succinate dehydrogenase is a coenzyme.
D) Flavin adenine dinucleotide is a coenzyme. Succinate dehydrogenase is a vitamin.

Question 28

In this type of inhibition, the inhibitor can only bind to the ES complex to form an ESI complex.

A) competitive
B) noncompetitive
C) mixed
D) uncompetitive
E) None of the answers is correct.

Question 29

Examples of cofactors include

A) Zn²⁺, Mg²⁺, and Ni²⁺.
B) biotin and thiamine pyrophosphate.
C) pyridoxal phosphate and coenzyme A.
D) biotin and thiamine pyrophosphate and pyridoxal phosphate and coenzyme A
E) All of the answers are correct.

Question 30

Give an example of a reaction catalyzed by a hydrolase.

Question 31

Which of the following is true?

A) Enzymes force reactions to proceed in only one direction.
B) Enzymes alter the equilibrium of the reaction.
C) Enzymes alter the standard free energy of the reaction.
D) All of the answers are correct.
E) None of the answers is correct.

Question 32

When substrate concentration is much greater than K_M, the rate of catalysis is almost equal to

A) K_d.
B) k_cat / K_M.
C) V_max.
D) All of the answers are correct.
E) None of the answers is correct.

Question 33

What conclusion can be drawn concerning an inhibitor if the V_max is the same in the presence and absence of the inhibitor?

A) The inhibitor binds to the substrate.
B) The inhibitor can be overcome with sufficiently high concentrations of substrate.
C) The inhibitor reacts with a critical residue of the enzyme.
D) The inhibitor binds to the same active site as the substrate.
E) The K_M is smaller in the presence of inhibitor.

Question 34

There are six basic categories of enzymes. List the categories, and define the type of reaction.

Question 35

Which of the following is true under the following conditions: the enzyme concentration is 5 nM, the substrate concentration is 5 mM, and the K_M is 5 $\mu$ 0M?

A) The enzyme is saturated with substrate.
B) Most of the enzyme does not have substrate bound.
C) There is more enzyme than substrate.
D) All of the answers are correct.
E) None of the answers is correct.

Question 36

The Gibbs-free energy of activation is the difference between the

A) substrate and the transition state.
B) substrate and the product.
C) product and the transition state.
D) All of the answers are correct.
E) None of the answers is correct.

Question 37

When the k_cat / K_M ratio is at its upper limit, it is referred to as

A) Circe limits.
D) All of the answers are correct.
B) Michaelis rate.
E) None of the answers is correct.
C) kinetic perfection.

Question 38

You believe a substrate fits rigidly into a cleft like a key into a lock, but your roommate believes that the structure of the enzyme adapts to the substrate. Who is right?

Question 39

In many enzyme assays, the natural substrate and product are not used. Why?

Question 40

What is the common strategy by which catalysis occurs?

A) increasing the probability of product formation
B) shifting the reaction equilibrium
C) stabilization of transition state
D) All of the answers are correct.
E) None of the answers is correct.

Question 41

What is an affinity label?

Question 42

In an enzymatic reaction in a test tube, the reaction will eventually reach equilibrium. Why does this not happen in living organisms?

Question 43

. What is the upper limit of k_cat / K_M?

Question 44

How are the types of inhibition kinetically distinguishable?

Question 45

Explain what an abzyme is and give an example.

Question 46

How do the intermediate steps in multisubstrate enzyme mechanisms differ?

Question 47

What are transition-state analogs?

Question 48

What is the Michaelis-Menten equation? Define all parameters.

Question 49

. Enzyme populations are studied with the use of ensemble methods. How would the data differ from a single-enzyme study?

Question 50

What does V_max indicate?