Question 1

Nonclassical competitive inhibition involves .

Accepted Answer

A)  binding of the substrate at both the active site and at the inhibitor site 
B)  binding of either the substrate to the active site or the inhibitor to its own binding site thus preventing the other from binding 
C)  binding of the inhibitor to the substrate followed by binding of this complex to the active site 
D)  chemical removal of the substrate from the active site by reaction with the inhibitor 
A)  binding of the substrate at both the active site and at the inhibitor site 
B)  binding of either the substrate to the active site or the inhibitor to its own binding site thus preventing the other from binding 
C)  binding of the inhibitor to the substrate followed by binding of this complex to the active site 
D)  chemical removal of the substrate from the active site by reaction with the inhibitor B

Question 2

In E. coli is an activator and is a negative allosteric modulator of the enzyme phosphofructokinase-1.

Accepted Answer

A)  DFP; phosphoenolpyruvate 
B)  phosphoenolpyruvate; ATP 
C)  ADP; phosphoenolpyruvate 
D)  fructose-6-phosphate; ADP 
A)  DFP; phosphoenolpyruvate 
B)  phosphoenolpyruvate; ATP 
C)  ADP; phosphoenolpyruvate 
D)  fructose-6-phosphate; ADP C

Question 3

Allosteric modulators seldom resemble the substrate or product of the enzyme. What does this observation show?

Accepted Answer

A)  Modulators likely bind at a site other than the active site. 
B)  Modulators always act as activators. 
C)  Modulators bind non-covalently to the enzyme. 
D)  The enzyme catalyzes more than one reaction. 
A)  Modulators likely bind at a site other than the active site. 
B)  Modulators always act as activators. 
C)  Modulators bind non-covalently to the enzyme. 
D)  The enzyme catalyzes more than one reaction. A

Question 4

In an enzyme reaction involving one enzyme and one substrate, the rate of the reaction depends on

Accepted Answer

A)  substrate concentration. 
B)  enzyme concentration. 
C)  both substrate and enzyme concentrations. 
D)  the enzyme concentration at first and the substrate concentration later on. 
A)  substrate concentration. 
B)  enzyme concentration. 
C)  both substrate and enzyme concentrations. 
D)  the enzyme concentration at first and the substrate concentration later on.

Question 5

Which of the following statements is FALSE?

Accepted Answer

A)  The word enzyme is from a Greek word meaning ʺin yeast.ʺ 
B)  Enzymes are always made of protein. 
C)  The first enzyme was crystallized in 1926. 
D)  Enzymes can couple two different reactions. 
A)  The word enzyme is from a Greek word meaning ʺin yeast.ʺ 
B)  Enzymes are always made of protein. 
C)  The first enzyme was crystallized in 1926. 
D)  Enzymes can couple two different reactions.

Question 6

Two curves showing the rate versus substrate concentration are shown below for an enzyme-catalyzed reaction. One curve is for the reaction in the presence of substance X. The other curve is for data in the absence of substance X. Examine the curves and tell which statement below is false.

Accepted Answer

A)  X is an activator of the enzyme. 
B)  The enzyme exhibits non-Michaelis-Menten kinetics. 
C)  X is likely an allosteric modulator. 
D)  X is a competitive inhibitor. 
A)  X is an activator of the enzyme. 
B)  The enzyme exhibits non-Michaelis-Menten kinetics. 
C)  X is likely an allosteric modulator. 
D)  X is a competitive inhibitor.

Question 7

What distinguishes reversible inhibitors from irreversible inhibitors?

Accepted Answer

A)  Reversible inhibitors are not covalently bound to enzymes but irreversible inhibitors are. 
B)  There is an equilibrium between bound and unbound reversible inhibitor. There usually is little back reaction for the binding of an irreversible inhibitor. 
C)  Reversible inhibitors are easier to purify from solutions of enzymes than irreversible inhibitors. 
D)  All of the above 
E)  A and B only 
A)  Reversible inhibitors are not covalently bound to enzymes but irreversible inhibitors are. 
B)  There is an equilibrium between bound and unbound reversible inhibitor. There usually is little back reaction for the binding of an irreversible inhibitor. 
C)  Reversible inhibitors are easier to purify from solutions of enzymes than irreversible inhibitors. 
D)  All of the above 
E)  A and B only

Question 8

The following data were obtained in the presence and absence of inhibitor. What type of inhibition is shown? $\begin{array}{|l|l|l|}
\hline\begin{array}{l}
\text { Substrateconcentration } \
\text { millimolar) }
\end{array} & \begin{array}{l}
\text { Rate withoutinhibitor } \
\mathrm{mmol} / \mathrm{min})
\end{array} & \begin{array}{l}
\text { Rate with inhibitor } \
\mathrm{mmol} / \mathrm{min})
\end{array} \
\hline 0.100 & 2.5 & 1.6 \
\hline 0.200 & 4.2 & 2.9 \
\hline 0.500 & 6.6 & 5.1 \
\hline 0.750 & 7.4 & 6.2 \
\hline 1.000 & 9.9 & 9.8 \
\hline 2.000 & 10.0 & 10.1\
\hline
\end{array}$

Accepted Answer

A)  competitive 
B)  uncompetitive 
C)  noncompetitive 
D)  irreversible 
E)  cannot tell inhibition type from the information given 
A)  competitive 
B)  uncompetitive 
C)  noncompetitive 
D)  irreversible 
E)  cannot tell inhibition type from the information given

Question 9

Select the correct class of enzyme for each of these reactions. A) isomerase
B) ligase
C) lyase
D) transferase
E) oxidoreductase
F) hydrolase
-L-Glutamate + ATP + NH4+
→ L-glutamine + ADP + Pi

Accepted Answer

Question 10

Ethanol CH3CH2OH) is the alcohol found in beverages. It is oxidized in the body to acetaldehyde by the enzyme alcohol dehydrogenase. Methanol CH3OH), also known as wood alcohol, is converted to formaldehyde by the same enzyme. Acetaldehyde is toxic, but formaldehyde is far more toxic to humans, which is why the ingestion of relatively small amounts of methanol can cause blindness or death. One treatment for mild methanol poisoning is the administration of ethanol. Why might a doctor choose this treatment?

Accepted Answer

A)  Ethanol must act as a competitive inhibitor for the alcohol dehydrogenase and therefore slows the formation of formaldehyde. 
B)  Ethanol likely irreversibly binds to alcohol dehydrogenase which prevents the formation of formaldehyde. 
C)  The ethanol is likely an uncompetitive inhibitor and binds to a site other than the active site of the enzyme. 
D)  The doctor has given up on the patient and administers ethanol for sedation. 
A)  Ethanol must act as a competitive inhibitor for the alcohol dehydrogenase and therefore slows the formation of formaldehyde. 
B)  Ethanol likely irreversibly binds to alcohol dehydrogenase which prevents the formation of formaldehyde. 
C)  The ethanol is likely an uncompetitive inhibitor and binds to a site other than the active site of the enzyme. 
D)  The doctor has given up on the patient and administers ethanol for sedation.

Question 11

Protein A has four identical subunits, each of which binds one molecule of ligand Y. The binding of one molecule of Y to one of the subunits induces a conformational change in neighboring subunits that enhances the binding of additional units of Y. This is an example of .

Accepted Answer

A)  negative cooperativity 
B)  competitive activation 
C)  symmetry-driven binding 
D)  the sequential theory 
A)  negative cooperativity 
B)  competitive activation 
C)  symmetry-driven binding 
D)  the sequential theory

Question 12

In a certain enzyme-catalyzed reaction the following steps occur: 1. A phosphate group on substrate A is transferred to a side chain of an active site residue of the enzyme.
2. The dephosphorylated form of substrate A dissociates from the enzyme.
3. Substrate B enters the active site and is phosphorylated with simultaneous regeneration of the enzyme in its original form.
What kind of kinetic mechanism is described?

Accepted Answer

A)  random 
B)  sequential 
C)  ordered 
D)  ping-pong 
A)  random 
B)  sequential 
C)  ordered 
D)  ping-pong

Question 13

The Km values for enzyme reactions such as A + B → C + D

Accepted Answer

A)  cannot be determined using the Lineweaver-Burk plot analysis. 
B)  can be determined by holding one A or 
B)  at high concentration, while varying the concentration of the other substrate). 
C)  can be determined for one substrate and not the other. 
D)  do not indicate the efficiency of the enzyme. 
A)  cannot be determined using the Lineweaver-Burk plot analysis. 
B)  can be determined by holding one A or 
B)  at high concentration, while varying the concentration of the other substrate). 
C)  can be determined for one substrate and not the other. 
D)  do not indicate the efficiency of the enzyme.

Question 14

When there are two substrates in a reaction, the reaction is said to be second order if .

Accepted Answer

A)  the reaction is first order with respect to each substrate concentration 
B)  the maximum rate is independent of either substrateʹs concentration 
C)  the substrate concentrations are equal 
D)  it proceeds at twice the rate upon double the concentrations of both substrates 
A)  the reaction is first order with respect to each substrate concentration 
B)  the maximum rate is independent of either substrateʹs concentration 
C)  the substrate concentrations are equal 
D)  it proceeds at twice the rate upon double the concentrations of both substrates

Question 15

The ʺTʺ state refers to the .

Accepted Answer

A)  inactive conformation of the enzyme 
B)  transition state of the product 
C)  form of the enzyme without the modulator bound at the regulatory site 
D)  denatured form of the enzyme 
A)  inactive conformation of the enzyme 
B)  transition state of the product 
C)  form of the enzyme without the modulator bound at the regulatory site 
D)  denatured form of the enzyme

Question 16

Both reversible and irreversible inhibitors can be separated from solutions of enzymes by dialysis.

Accepted Answer

A) True 
 B)False

Question 17

The expression: Vmax = k2[E]total applies to

Accepted Answer

A)  zero order kinetics of an enzyme-catalyzed reaction. 
B)  first order kinetics of an enzyme-catalyzed reaction. 
C)  second order kinetics of an enzyme-catalyzed reaction. 
D)  only the initial part near time = zero) of an enzyme-catalyzed reaction. 
A)  zero order kinetics of an enzyme-catalyzed reaction. 
B)  first order kinetics of an enzyme-catalyzed reaction. 
C)  second order kinetics of an enzyme-catalyzed reaction. 
D)  only the initial part near time = zero) of an enzyme-catalyzed reaction.

Question 18

Increasing the concentration of a classic competitive inhibitor has no effect on the maximum velocity of an enzyme-substrate reaction.

Accepted Answer

A) True 
 B)False

Question 19

The enymatic rate constant kcat/Km) of orotidine 5ʹ-phosphate decarboxylase is 6 x 107 M-1s-1 and the nonenzymatic rate constant kn) is 3 x 10-16 s-1. What is the value of the enzymeʹs catalytic proficiency?

Accepted Answer

A)  2 x 1023 M-1 
B)  5 x 10-24 M 
C)  12 x 10-9 M-1s-2 
D)  8.3 x 107 Ms2 
E)  Cannot calculate the proficiency without knowing the value of Vmax. 
A)  2 x 1023 M-1 
B)  5 x 10-24 M 
C)  12 x 10-9 M-1s-2 
D)  8.3 x 107 Ms2 
E)  Cannot calculate the proficiency without knowing the value of Vmax.

Question 20

An enzyme is irreversibly inhibited by diisopropylfluorophosphate DFP). What does this show?

Accepted Answer

A)  The enzyme has been denatured by DFP. 
B)  Serine is likely an important residue in the active site. 
C)  DFP is an allosteric modulator of the enzyme. 
D)  DFP is an analog of the enzymeʹs substrate. 
A)  The enzyme has been denatured by DFP. 
B)  Serine is likely an important residue in the active site. 
C)  DFP is an allosteric modulator of the enzyme. 
D)  DFP is an analog of the enzymeʹs substrate.

Exam 5: Properties of Enzymes

Nonclassical competitive inhibition involves .

In E. coli is an activator and is a negative allosteric modulator of the enzyme phosphofructokinase-1.

Allosteric modulators seldom resemble the substrate or product of the enzyme. What does this observation show?

In an enzyme reaction involving one enzyme and one substrate, the rate of the reaction depends on

Which of the following statements is FALSE?

Two curves showing the rate versus substrate concentration are shown below for an enzyme-catalyzed reaction. One curve is for the reaction in the presence of substance X. The other curve is for data in the absence of substance X. Examine the curves and tell which statement below is false.

What distinguishes reversible inhibitors from irreversible inhibitors?

The following data were obtained in the presence and absence of inhibitor. What type of inhibition is shown? Substrateconcentration millimolar) Rate withoutinhibitor /) Rate with inhibitor /) 0.100 2.5 1.6 0.200 4.2 2.9 0.500 6.6 5.1 0.750 7.4 6.2 1.000 9.9 9.8 2.000 10.0 10.1

Select the correct class of enzyme for each of these reactions. A) isomerase B) ligase C) lyase D) transferase E) oxidoreductase F) hydrolase -L-Glutamate + ATP + NH4+ → L-glutamine + ADP + Pi

Protein A has four identical subunits, each of which binds one molecule of ligand Y. The binding of one molecule of Y to one of the subunits induces a conformational change in neighboring subunits that enhances the binding of additional units of Y. This is an example of .

The Km values for enzyme reactions such as A + B → C + D

When there are two substrates in a reaction, the reaction is said to be second order if .

The ʺTʺ state refers to the .

Both reversible and irreversible inhibitors can be separated from solutions of enzymes by dialysis.

The expression: Vmax = k2[E]total applies to

Increasing the concentration of a classic competitive inhibitor has no effect on the maximum velocity of an enzyme-substrate reaction.

The enymatic rate constant kcat/Km) of orotidine 5ʹ-phosphate decarboxylase is 6 x 107 M-1s-1 and the nonenzymatic rate constant kn) is 3 x 10-16 s-1. What is the value of the enzymeʹs catalytic proficiency?

An enzyme is irreversibly inhibited by diisopropylfluorophosphate DFP). What does this show?

Introduction to Biochemistry

Water

Amino Acids and the Primary Structures of Proteins

Proteins: Three-Dimensional Structure and Function

Mechanisms of Enzymes

Coenzymes and Vitamins

Carbohydrates

Lipids and Membranes

Introduction to Metabolism

Glycolysis

Gluconeogenesis, the Pentose Phosphate Pathway, and Glycogen Metabolism

The Citric Acid Cycle

Electron Transport and Oxidative Phosphorylation

Photosynthesis

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Nucleic Acids

Dna Replication, Repair, and Recombination

Transcription and Rna Processing

Protein Synthesis

Recombinant Dna Technology

Filters

Select the correct class of enzyme for each of these reactions. A) isomerase B) ligase C) lyase D) transferase E) oxidoreductase F) hydrolase -L-Glutamate + ATP + NH₄⁺ → L-glutamine + ADP + P_i

The K_mvalues for enzyme reactions such as A + B → C + D

The expression: V_max= k₂[E]_totalapplies to

The enymatic rate constant k_cat/K_m) of orotidine 5ʹ-phosphate decarboxylase is 6 x 10⁷ M^-¹s^-¹and the nonenzymatic rate constant k_n) is 3 x 10^-¹⁶s^-¹. What is the value of the enzymeʹs catalytic proficiency?