Deck 6: Basic Concepts of Enzyme Action

Question 1

A reaction can occur spontaneously only if ΔG is __________________.

Answer 1

negative

Question 2

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

Answer 2

equilibrium

Question 3

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) apoenzymes
b) hydrolyases
c) active site
d) transition state
e) spontaneous
f) induced fit
g) energy
h) prosthetic group
i) lock and key
j) substrate(s)
k) oxidoreductases
l) equilibria
A tightly bound cofactor might be called a(n) ____________.

Answer 3

h

Question 4

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) apoenzymes
b) hydrolyases
c) active site
d) transition state
e) spontaneous
f) induced fit
g) energy
h) prosthetic group
i) lock and key
j) substrate(s)
k) oxidoreductases
l) equilibria
Enzymes that transfer electrons are called ____________.

Question 5

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) apoenzymes
b) hydrolyases
c) active site
d) transition state
e) spontaneous
f) induced fit
g) energy
h) prosthetic group
i) lock and key
j) substrate(s)
k) oxidoreductases
l) equilibria
Enzymes will decrease the energy of activation but do not change the ____________ of a chemical reaction.

Question 6

Organic cofactors are referred to as __________________.

Question 7

The total change of free energy in a reaction depends on __________________ and __________________.

Question 8

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) apoenzymes
b) hydrolyases
c) active site
d) transition state
e) spontaneous
f) induced fit
g) energy
h) prosthetic group
i) lock and key
j) substrate(s)
k) oxidoreductases
l) equilibria
An endergonic reaction requires an input of ____________ to proceed.

Question 9

Competitive inhibitors which mimic the substrate while in the transition state are called __________________ inhibitors.

Question 10

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) apoenzymes
b) hydrolyases
c) active site
d) transition state
e) spontaneous
f) induced fit
g) energy
h) prosthetic group
i) lock and key
j) substrate(s)
k) oxidoreductases
l) equilibria
Enzymes that cleave molecules by the addition of water are called ____________.

Question 11

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

Question 12

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) apoenzymes
b) hydrolyases
c) active site
d) transition state
e) spontaneous
f) induced fit
g) energy
h) prosthetic group
i) lock and key
j) substrate(s)
k) oxidoreductases
l) equilibria
Which model is most appropriate to explain an enzyme binding to its substrate?

Question 13

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) apoenzymes
b) hydrolyases
c) active site
d) transition state
e) spontaneous
f) induced fit
g) energy
h) prosthetic group
i) lock and key
j) substrate(s)
k) oxidoreductases
l) equilibria
____________: The site on the enzyme where the reaction occurs.

Question 14

The difference in values for ∆G and ∆G°′ is in the __________________.

Question 15

An enzyme which has been stripped of the small molecules needed for activity is called an __________________.

Question 16

An enzyme which loosely binds substrate will have a __________________ level of specificity.

Question 17

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) apoenzymes
b) hydrolyases
c) active site
d) transition state
e) spontaneous
f) induced fit
g) energy
h) prosthetic group
i) lock and key
j) substrate(s)
k) oxidoreductases
l) equilibria
A reaction that is exergonic will be ____________.

Question 18

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) apoenzymes
b) hydrolyases
c) active site
d) transition state
e) spontaneous
f) induced fit
g) energy
h) prosthetic group
i) lock and key
j) substrate(s)
k) oxidoreductases
l) equilibria
____________: The substance that the enzyme binds and converts to a product.

Question 19

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) apoenzymes
b) hydrolyases
c) active site
d) transition state
e) spontaneous
f) induced fit
g) energy
h) prosthetic group
i) lock and key
j) substrate(s)
k) oxidoreductases
l) equilibria
Enzymes that do not have the required cofactor bound are called ____________.

Question 20

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

Question 21

What is the relation between an enzyme-catalyzed reaction and the transition state of a reaction?

Question 22

What is the difference between prosthetic groups and coenzymes

Question 23

The Gibbs free energy of activation is:

A) the difference between the substrate and the transition state.
B) the difference between the substrate and the product.
C) the difference between the product and the transition state.
D) All of the above.
E) None of the above.

Question 24

An enzyme will specifically bind its substrate because of:

A) a tight lock-and-key binding mechanism.
B) a high number of hydrophobic amino acids in the center of the protein.
C) a large number of weak interactions at the active site.
D) additional nonprotein cofactors.
E) None of the above.

Question 25

The active site of an enzyme:

A) is a series of amino acids which bind the enzyme.
B) is a linear sequence of amino acids that react with each other.
C) binds covalently to the substrate.
D) allows water to enter into the active site and thereby solvate the substrate.
E) None of the above.

Question 26

Examples of cofactors include:

A) Zn+2, Mg+2, and Ni+2.
B) biotin and thiamine pyrophosphate.
C) pyridoxal phosphate and coenzyme A.
D) B and C.
E) A, B, and C.

Question 27

How do enzymes facilitate the formation of the transition state?

Question 28

At equilibrium, the Gibbs free energy is:

A) a positive value.
B) neutral.
C) a negative value.
D) zero.
E) one.

Question 29

The rate of a reaction, or how quickly a reaction will proceed, is best determined by:

A) ∆R
B) ∆G‡
C) ∆G°′
D) ∆H
E) None of the above.

Question 30

How is the substrate bound to the active site?

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 above.
E) None of the above.

Question 32

You believe a substrate fits into a cleft like a key into a lock, but your roommate does not. Who is right?

Question 33

The free energy of activation is:

A) the amount of chemical energy available in the transition state.
B) the difference in free energy between the substrate and the product.
C) the free energy gained by adding a catalyst.
D) the difference in free energy between the transition state and the substrate.
E) All of the above.

Question 34

The relationship between ∆G°′ and ∆G is best described as:

A) determined by the temperature.
B) described by changes in Keq.
C) differing from standard state to physiological or actual concentrations of reactants and products.
D) dependent on the reaction mechanism of the reaction.
E) differing only in terms of the types of reactions used for each value.

Question 35

A cofactor is best defined as:

A) another protein.
B) a covalently bound inorganic molecule.
C) a small molecule that holds the substrate in the active site.
D) a molecule responsible for most of the catalytic activity of the enzyme.
E) None of the above

Question 36

The molecular structure that is short-lived and neither substrate nor product is known as the:

A) substrate analog.
B) transition state.
C) free-energy stabilization state.
D) catalysis state.
E) equilibrium intermediate.

Question 37

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 above.
E) None of the above.

Question 38

For the two reactions (a) A → B ∆G°′ = 2 kJ mol−1, and (b) X → Y ∆G°′ = −3.5 kJ mol−1 , which of the following statements is correct?

A) Reaction (a) is not spontaneous at cellular concentrations.
B) Reaction (b) will react very quickly.
C) Reaction (a) is a more thermodynamically favorable reaction than is (b).
D) Neither reaction is reversible.
E) None of the above.

Question 39

Which of the following statements is most correct?

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

Question 40

Why does the amount of product level off as time increases?

A) The reaction has reached equilibrium; that is, the forward and reverse reactions are occurring at a fixed rate.
B) There is a product inhibition of the enzyme.
C) The reaction runs out of reaction materials.
D) The enzyme has finished accelerating the reaction.
E) None of the above.

Question 41

If the cellular concentrations of ATP, ADP, and Pi are 8, 1, and 8 mM, respectively, is the above reaction at equilibrium in the cell?

Question 42

Explain why paper is stable at room temperature in the presence of oxygen (O2).

Question 43

Why does this not happen in living organisms?

Question 44

How does a rigid, lock-and key-model for substrate binding not fit with the formation of the transition state?

Question 45

How is free energy useful for understanding enzyme function?

Question 46

If Keq = 1, what is the ∆G°′? If Keq > 1, what is the ∆G°′? If Keq < 1, what is the ∆G°′?

Question 47

What might be the cause of this? Assume the structure of the protein is retained.

Question 48

What are transition-state analogs?

Question 49

What would you suspect is the reason for this?

Question 50

What would be the most likely outcome of enzyme function?