Question 1

Justify how an enzyme that catalyzes a hydrolysis reaction does not contradict the concept that enzyme active sites are microenvironments that exclude excess water.

Accepted Answer

An enzyme that catalyzes a hydrolysis re

Question 2

Define the term zymogen.

Accepted Answer

Zymogen is the inactive precur

Question 3

The activity of an enzyme is monitored as a function of temperature.At low temperature very little activity is seen; the activity peaks as the temperature increases and then dramatically decreases to zero as higher temperatures are attained.Explain why the activity drops off completely at higher temperatures.

Accepted Answer

The higher temperature destabi

Question 4

Which of the following is true of the induced-fit model of enzyme catalysis but NOT of the lock and key model of enzyme catalysis?

Accepted Answer

A)  It was proposed by Emil Fischer. 
B)  It involves weak interactions of a substrate with an enzyme. 
C)  It involves a conformational change of the enzyme. 
D)  It involves noncovalent interactions of the substrate with the enzyme. 
A)  It was proposed by Emil Fischer. 
B)  It involves weak interactions of a substrate with an enzyme. 
C)  It involves a conformational change of the enzyme. 
D)  It involves noncovalent interactions of the substrate with the enzyme.

Question 5

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

Accepted Answer

A)  binding of regulatory molecules 
B)  covalent modification 
C)  proteolytic processing 
D)  cofactor degradation 
A)  binding of regulatory molecules 
B)  covalent modification 
C)  proteolytic processing 
D)  cofactor degradation

Question 6

When a nucleophile present in the enzyme attacks an electrophilic substrate to form an enzyme-substrate intermediate,this is an example of __________ catalysis.

Accepted Answer

A)  covalent 
B)  acid-base 
C)  metal ion 
D)  hydrophobic 
A)  covalent 
B)  acid-base 
C)  metal ion 
D)  hydrophobic

Question 7

Given the following data for lactate dehydrogenase,calculate the specificity constant.

Accepted Answer

The specificity cons

Question 8

The substrate binding pocket of __________ is best at accommodating substrates with small side chains.

Accepted Answer

A)  elastase 
B)  chymotrypsin 
C)  enolase 
D)  trypsin 
A)  elastase 
B)  chymotrypsin 
C)  enolase 
D)  trypsin

Question 9

The specificity constant is equal to

Accepted Answer

A)  [Et][S] / v0. 
B)  Km / v0. 
C)  kcat / Km. 
D)  kcat / [Et]. 
A)  [Et][S] / v0. 
B)  Km / v0. 
C)  kcat / Km. 
D)  kcat / [Et].

Question 10

For a reaction of Q + R   P,the rate constant

Accepted Answer

A)  is equal to [Q][R] / [P]. 
B)  has units of s-1. 
C)  is a second-order rate constant. 
D)  is equal to [P] / [Q][R]. 
A)  is equal to [Q][R] / [P]. 
B)  has units of s-1. 
C)  is a second-order rate constant. 
D)  is equal to [P] / [Q][R].

Question 11

Explain the two ways that catalytic efficiency of enzymes can be controlled within a cell.

Accepted Answer

Catalytic efficiency can be co

Question 12

Many medicinal drugs are transition state analogs.They are good drugs because they can interact with the target enzyme active site and are

Accepted Answer

A)  higher in energy than the transition state. 
B)  identical in structure to the transition state. 
C)  stable. 
D)  polar. 
A)  higher in energy than the transition state. 
B)  identical in structure to the transition state. 
C)  stable. 
D)  polar.

Question 13

A reaction coordinate diagram comparing an uncatalyzed reaction with an enzyme-catalyzed reaction can directly illustrate that the enzyme __________,but will not directly illustrate that the enzyme __________.

Accepted Answer

A)  orients the substrates appropriately for the reaction to occur; provides an alternative path for product formation 
B)  provides an alternative path for product formation; stabilizes the transition state 
C)  stabilizes the transition state; orients the substrates appropriately for the reaction to occur 
D)  stabilizes the transition state; provides an alternative path for product formation 
A)  orients the substrates appropriately for the reaction to occur; provides an alternative path for product formation 
B)  provides an alternative path for product formation; stabilizes the transition state 
C)  stabilizes the transition state; orients the substrates appropriately for the reaction to occur 
D)  stabilizes the transition state; provides an alternative path for product formation

Question 14

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

Accepted Answer

A)  Lineweaver-Burk; Km/vmax 
B)  Lineweaver-Burk; -1/Km 
C)  Michaelis-Menten; Km/vmax 
D)  Michaelis-Menten; vmax 
A)  Lineweaver-Burk; Km/vmax 
B)  Lineweaver-Burk; -1/Km 
C)  Michaelis-Menten; Km/vmax 
D)  Michaelis-Menten; vmax

Question 15

When __________ is increased,__________ is activated,which acts on glycogen phosphorylase,leading to a decrease in the activity of the enzyme.

Accepted Answer

A)  glucagon; phosphorylase kinase 
B)  epinephrine; phosphorylase kinase 
C)  insulin; protein phosphatase 1 
D)  glucagon; protein phosphatase 1 
A)  glucagon; phosphorylase kinase 
B)  epinephrine; phosphorylase kinase 
C)  insulin; protein phosphatase 1 
D)  glucagon; protein phosphatase 1

Question 16

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

Accepted Answer

A)  irreversible 
B)  competitive 
C)  uncompetitive 
D)  mixed 
A)  irreversible 
B)  competitive 
C)  uncompetitive 
D)  mixed

Question 17

What is the rate enhancement as a result of the presence of an enzyme if the uncatalyzed rate of the reaction is 1.2   102 mmol/sec and the catalyzed rate is 2.4   104 mmol/sec?

Accepted Answer

A)  0.005 
B)  200 
C)  2.88   106 
D)  2 
A)  0.005 
B)  200 
C)  2.88   106 
D)  2

Question 18

KM is equal to

Accepted Answer

A)  k1 / (k-1 + k2). 
B)  (k-1 + k2) / k1. 
C)  1/2 vmax. 
D)  vmax[S] / v0. 
A)  k1 / (k-1 + k2). 
B)  (k-1 + k2) / k1. 
C)  1/2 vmax. 
D)  vmax[S] / v0.

Question 19

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?

Accepted Answer

A)  competitive 
B)  uncompetitive 
C)  mixed 
D)  noncompetitive 
A)  competitive 
B)  uncompetitive 
C)  mixed 
D)  noncompetitive

Question 20

All of the following are common catalytic reaction mechanisms in enzyme active sites EXCEPT __________ catalysis.

Accepted Answer

A)  acid-base 
B)  covalent 
C)  metal ion 
D)  van der Waals 
A)  acid-base 
B)  covalent 
C)  metal ion 
D)  van der Waals

Exam 7: Enzyme Mechanisms

Justify how an enzyme that catalyzes a hydrolysis reaction does not contradict the concept that enzyme active sites are microenvironments that exclude excess water.

Define the term zymogen.

Which of the following is true of the induced-fit model of enzyme catalysis but NOT of the lock and key model of enzyme catalysis?

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

When a nucleophile present in the enzyme attacks an electrophilic substrate to form an enzyme-substrate intermediate,this is an example of __________ catalysis.

Given the following data for lactate dehydrogenase,calculate the specificity constant.

The substrate binding pocket of __________ is best at accommodating substrates with small side chains.

The specificity constant is equal to

For a reaction of Q + R P,the rate constant

Explain the two ways that catalytic efficiency of enzymes can be controlled within a cell.

Many medicinal drugs are transition state analogs.They are good drugs because they can interact with the target enzyme active site and are

A reaction coordinate diagram comparing an uncatalyzed reaction with an enzyme-catalyzed reaction can directly illustrate that the enzyme __________,but will not directly illustrate that the enzyme __________.

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

When __________ is increased,__________ is activated,which acts on glycogen phosphorylase,leading to a decrease in the activity of the enzyme.

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

What is the rate enhancement as a result of the presence of an enzyme if the uncatalyzed rate of the reaction is 1.2 102 mmol/sec and the catalyzed rate is 2.4 104 mmol/sec?

KM is equal to

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?

All of the following are common catalytic reaction mechanisms in enzyme active sites EXCEPT __________ catalysis.

Principles of Biochemistry

Physical Biochemistry: Energy Conversion,water,and Membranes

Nucleic Acid Structure and Function

Protein Structure

Methods in Protein Biochemistry

Protein Function

Cell Signaling Systems

Glycolysis: a Paradigm of Metabolic Regulation

The Citrate Cycle

Oxidative Phosphorylation

Photosynthesis

Carbohydrate Structure and Function

Carbohydrate Metabolism

Lipid Structure and Function

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Metabolic Integration

Dna Replication, repair, and Recombination

Rna Synthesis, processing, and Gene Silencing

Protein Synthesis, posttranslational Modification, and Transport

Gene Regulation

Filters

A reaction coordinate diagram comparing an uncatalyzed reaction with an enzyme-catalyzed reaction can directly illustrate that the enzyme ,but will not directly illustrate that the enzyme .

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

When is increased, is activated,which acts on glycogen phosphorylase,leading to a decrease in the activity of the enzyme.

What is the rate enhancement as a result of the presence of an enzyme if the uncatalyzed rate of the reaction is 1.2 10² mmol/sec and the catalyzed rate is 2.4 10⁴ mmol/sec?

K_M is equal to