Question 1

A mixture of enzyme and inhibitor is run through a size-exclusion chromatography column.The activity of the enzyme is assessed before and after the chromatography.The enzyme has more activity after the chromatography step.Which of the following is true?
A) The enzyme was not eluted fully from the column.
B) The enzyme was denatured during chromatography.
C) The inhibitor is a reversible inhibitor.
D) The inhibitor is an irreversible inhibitor.

Accepted Answer

The increase in enzyme activity after chromatography suggests that the inhibitor was separated from the enzyme, indicating that it is a reversible inhibitor.

Question 2

Below is a Lineweaver-Burk plot in which the axis labels have been removed.Interpret the plot to determine the v_max. A) 0.2 B) 5 C) 3 D) 0.33

Accepted Answer

The answer of Below is a Lineweaver-Burk plot in which...

Question 3

Acetylcholinesterase is an important enzyme in the nervous system.Acetylcholinesterase activity is blocked by the nerve agent sarin gas,which forms a covalent bond with a Ser in the active site of the enzyme.Sarin gas is a(n)
A) allosteric effector.
B) competitive inhibitor.
C) reversible inhibitor.
D) irreversible inhibitor.

Accepted Answer

Sarin gas forms a covalent bond with the serine residue in the active site of acetylcholinesterase, irreversibly inhibiting the enzyme. Therefore, it is considered an irreversible inhibitor.

Question 4

Which of the following statements are true?
A) ATCase is regulated by feedback inhibition.
B) CTP is an allosteric activator of ATCase.
C) ATP is an allosteric inhibitor of ATCase.
D) GTP is an allosteric inhibitor of ATCase.

Accepted Answer

ATCase (Aspartate transcarbamoylase) is regulated by feedback inhibition, where CTP acts as an allosteric inhibitor, not an activator. ATP is an allosteric activator, not an inhibitor. GTP is not typically involved in the regulation of ATCase.

Question 5

A kinase adds a phosphate group to a target enzyme,altering the catalytic efficiency of the enzyme.This is an example of
A) covalent modification.
B) proteolytic processing.
C) binding of regulatory molecules.
D) feedback inhibition.

Accepted Answer

Addition of a phosphate group by a kinase is an example of covalent modification, where the chemical structure of the enzyme is altered by the addition of a chemical group. This changes the catalytic efficiency of the enzyme. The other options do not involve the addition of a chemical group by a kinase.

Question 6

Which of the following is NOT a primary mechanism that affects catalytic efficiency?
A) binding of regulatory molecules
B) covalent modification
C) proteolytic processing
D) cofactor degradation

Accepted Answer

The binding of regulatory molecules, covalent modification, and proteolytic processing can all affect the structure and function of a catalytic enzyme, ultimately influencing its efficiency. However, cofactor degradation is not a primary mechanism that affects catalytic efficiency, as it refers to the breakdown or loss of a necessary cofactor molecule that is essential for enzyme function.

Question 7

The Lineweaver-Burk plot shows data obtained for an enzyme in the absence and presence of a noncompetitive inhibitor.If the [I] is increased significantly in the experiment,the V_maxapp would __________ and the K_mapp would __________. A) decrease; decrease B) stay the same; decrease C) decrease; stay the same D) stay the same; stay the same

Accepted Answer

The answer of The Lineweaver-Burk plot shows data obtained for...

Question 8

A plot of 1 / v₀ versus 1/[S] is called a __________ plot.Data in this plot have a slope equal to __________. A) Lineweaver-Burk; K_m/v_max B) Lineweaver-Burk; -1/K_m C) Michaelis-Menten; K_m/v_max D) Michaelis-Menten; v_max

Accepted Answer

The Lineweaver-Burk plot is a double-reciprocal plot of enzyme kinetics, and its slope is equal to K_m/v_max.

Question 9

In the formation of an ESI complex,__________ inhibition can result.
A) mixed
B) competitive
C) covalent
D) anticompetitive

Accepted Answer

In the formation of an ESI complex, mixed inhibition can result. In mixed inhibition, the inhibitor can bind to either the enzyme or the enzyme-substrate complex, resulting in a mixed type of inhibition where the inhibitor has different affinities for the enzyme and the enzyme-substrate complex. This type of inhibition results in a decrease in both the Vmax and the Km values.

Question 10

The Lineweaver-Burk plot shows data obtained for an enzyme in the absence and presence of a reversible inhibitor.Which type of inhibitor was used in the experiment? 
A) competitive
B) uncompetitive
C) mixed
D) noncompetitive

Accepted Answer

The answer of The Lineweaver-Burk plot shows data obtained for...

Question 11

Which of the following pairs correctly matches the type of interaction observed between an inhibitor and an enzyme with the type of inhibition?
A) ionic; irreversible
B) covalent; irreversible
C) hydrogen bonding; reversible
D) hydrophobic; irreversible

Accepted Answer

Hydrogen bonding is a reversible type of interaction between an inhibitor and an enzyme. Neither ionic, covalent, nor hydrophobic interactions are necessarily reversible. Of the given answer choices, only option C matches these criteria.

Question 12

When compared with the T state of aspartate transcarbamoylase,the R state A) has dissociated into two C₃R₃complexes. B) has greater separation of the catalytic subunits. C) is bound to CTP. D) has substrate bound in the ATP binding site.

Accepted Answer

In the R state, the catalytic subunits are separated further apart than in the T state. Option A is incorrect because dissociating into two complexes is not a characteristic of the R state. Option C is incorrect because CTP is a negative allosteric regulator that stabilizes the T state. Option D is incorrect because the ATP binding site is present on the regulatory subunits, not the catalytic subunits.

Question 13

An enzyme undergoes a mutation that causes it to lose the ability to be regulated via phosphorylation.Which of the following mutations may lead to this loss of regulation? Assume that the overall structure is not altered by the mutation.
A) Ser Thr
B) Thr Ser
C) Tyr Phe
D) Ser Tyr

Accepted Answer

The answer of An enzyme undergoes a mutation that causes...

Question 14

Which answer correctly classifies the compound with its relationship to aspartate transcarbamoylase?
A) ATP; allosteric inhibitor
B) ATP; allosteric activator
C) CTP; allosteric activator
D) CTP; substrate

Accepted Answer

ATP is an allosteric activator of aspartate transcarbamoylase, enhancing its activity and promoting the synthesis of pyrimidines.

Question 15

The specificity constant is equal to A) [E_t][S] / v₀. B) K_m/ v₀. C) k_cat/ K_m. D) k_cat/ [E_t].

Accepted Answer

The specificity constant (kcat/Km) is the rate constant for the reaction between the enzyme and substrate and represents the efficiency of an enzyme in converting substrate to product. It is calculated as kcat (catalytic constant or turnover number, number of substrate molecules converted to product per unit time by one enzyme molecule) divided by Km (substrate concentration at which the rate of reaction is half of Vmax). Therefore, option C is the correct formula for the specificity constant.

Question 16

A plot of v_o versus [S] for aspartyl transcarbamoylase displays three sigmoidal lines.If the line in the middle represents the enzyme activity in the absence of any allosteric effectors,then the line to the __________ represents the enzyme in the __________ when bound to __________. A) right; R state; CTP B) right; T state; CTP C) left; R state; GTP D) left; T state; GTP

Accepted Answer

The line to the right represents the enzyme in the T state when bound to CTP, which is an allosteric inhibitor, causing decreased enzyme activity.

Question 17

Which type of interaction is more likely to be found between an enzyme and an irreversible inhibitor?
A) covalent bond
B) hydrogen bond
C) ionic interaction
D) van der Waals interaction

Accepted Answer

Irreversible inhibitors form a covalent bond with the enzyme, leading to permanent inactivation.

Question 18

An inhibitor that binds only to the ES complex and not free enzyme is known as a(n)__________ inhibitor.
A) irreversible
B) competitive
C) uncompetitive
D) mixed

Accepted Answer

Uncompetitive inhibitors bind specifically to the ES complex and cannot bind to the free enzyme. This type of inhibition results in a decrease in both the maximum velocity and the apparent affinity of the enzyme for its substrate.

Question 19

An experiment is performed in which the kinetics of an enzyme-catalyzed reaction at different pHs is monitored.It is found that the K_m does not change but that the k_cat increases as the pH goes above 7.Which of the following is true? A) A chemical group within the enzyme that has a pKa of around 7 is likely involved in the catalytic mechanism. B) A chemical group with a pKa of around 7 must be deprotonated in order for substrate to bind. C) A chemical group with a pKa of around 7 must be positively charged in order for the substrate to bind. D) Protons are acting as positive heterotropic allosteric effectors of this enzyme.

Accepted Answer

The fact that only the kcat increases with pH while the KM remains constant suggests that the rate-limiting step in the reaction involves a chemical group whose pKa is near 7, which is likely involved in the catalytic mechanism. This chemical group could be an amino acid residue in the active site of the enzyme, for example, whose protonation state is important for catalyzing the reaction. The other answer choices are not supported by the information given in the problem.

Question 20

A Lineweaver-Burk plot displays parallel lines for an enzyme in the absence and presence of increasing amounts of an inhibitor.The inhibitor in this experiment A) binds both the free enzyme and the ES complex. B) is competitive. C) alters the K_m but not the v_max. D) is uncompetitive.

Accepted Answer

An uncompetitive inhibitor binds only to the enzyme-substrate complex, leading to parallel lines on a Lineweaver-Burk plot as both Vmax and Km are decreased proportionally.

Quiz 7: Enzyme Mechanisms

A mixture of enzyme and inhibitor is run through a size-exclusion chromatography column.The activity of the enzyme is assessed before and after the chromatography.The enzyme has more activity after the chromatography step.Which of the following is true?

Below is a Lineweaver-Burk plot in which the axis labels have been removed.Interpret the plot to determine the v_max.

Acetylcholinesterase is an important enzyme in the nervous system.Acetylcholinesterase activity is blocked by the nerve agent sarin gas,which forms a covalent bond with a Ser in the active site of the enzyme.Sarin gas is a(n)

Which of the following statements are true?

A kinase adds a phosphate group to a target enzyme,altering the catalytic efficiency of the enzyme.This is an example of

Which of the following is NOT a primary mechanism that affects catalytic efficiency?

The Lineweaver-Burk plot shows data obtained for an enzyme in the absence and presence of a noncompetitive inhibitor.If the [I] is increased significantly in the experiment,the V_maxapp would __________ and the K_mapp would __________.

A plot of 1 / v₀ versus 1/[S] is called a plot.Data in this plot have a slope equal to .

In the formation of an ESI complex,__________ inhibition can result.

The Lineweaver-Burk plot shows data obtained for an enzyme in the absence and presence of a reversible inhibitor.Which type of inhibitor was used in the experiment?

Which of the following pairs correctly matches the type of interaction observed between an inhibitor and an enzyme with the type of inhibition?

When compared with the T state of aspartate transcarbamoylase,the R state

An enzyme undergoes a mutation that causes it to lose the ability to be regulated via phosphorylation.Which of the following mutations may lead to this loss of regulation? Assume that the overall structure is not altered by the mutation.

Which answer correctly classifies the compound with its relationship to aspartate transcarbamoylase?

The specificity constant is equal to

A plot of v_o versus [S] for aspartyl transcarbamoylase displays three sigmoidal lines.If the line in the middle represents the enzyme activity in the absence of any allosteric effectors,then the line to the represents the enzyme in the when bound to __.

Which type of interaction is more likely to be found between an enzyme and an irreversible inhibitor?

An inhibitor that binds only to the ES complex and not free enzyme is known as a(n) __________ inhibitor.

An experiment is performed in which the kinetics of an enzyme-catalyzed reaction at different pHs is monitored.It is found that the K_m does not change but that the k_cat increases as the pH goes above 7.Which of the following is true?

A Lineweaver-Burk plot displays parallel lines for an enzyme in the absence and presence of increasing amounts of an inhibitor.The inhibitor in this experiment