Question 1

Define the term "suicide inhibitor."

Accepted Answer

A suicide inhibitor, also known as a mec

Question 2

An enzyme's specificity constant (kcat/Km) has a maximum upper limit due to:

Accepted Answer

A)  substrate concentration. 
B)  enzyme concentration. 
C)  the enzyme turnover number. 
D)  diffusion of the enzyme and substrate together. 
E)  the Michaelis constant. 
A)  substrate concentration. 
B)  enzyme concentration. 
C)  the enzyme turnover number. 
D)  diffusion of the enzyme and substrate together. 
E)  the Michaelis constant.

Question 3

Penicillin and related antibiotics contain a four-membered $\beta$-lactam ring. Explain why this feature is important to the mechanism of action of these drugs.

Accepted Answer

The four-membered @#LAT-DLM&-lactam ring in penici

Question 4

A transition-state analog:

Accepted Answer

A)  is less stable when binding to an enzyme than the normal substrate. 
B)  resembles the active site of general acid-base enzymes. 
C)  resembles the transition-state structure of the normal enzyme-substrate complex. 
D)  stabilizes the transition state for the normal enzyme-substrate complex. 
E)  typically reacts more rapidly with an enzyme than the normal substrate. 
A)  is less stable when binding to an enzyme than the normal substrate. 
B)  resembles the active site of general acid-base enzymes. 
C)  resembles the transition-state structure of the normal enzyme-substrate complex. 
D)  stabilizes the transition state for the normal enzyme-substrate complex. 
E)  typically reacts more rapidly with an enzyme than the normal substrate.

Question 5

Which statement is FALSE?

Accepted Answer

A)  A reaction may not occur at a detectable rate even though it has a favorable equilibrium. 
B)  After a reaction, the enzyme involved becomes available to catalyze the reaction again. 
C)  For S $\rightarrow$ P, a catalyst shifts the reaction equilibrium to the right. 
D)  Lowering the temperature of a reaction will lower the reaction rate. 
E)  Substrate binds to an enzyme's active site. 
A)  A reaction may not occur at a detectable rate even though it has a favorable equilibrium. 
B)  After a reaction, the enzyme involved becomes available to catalyze the reaction again. 
C)  For S $\rightarrow$ P, a catalyst shifts the reaction equilibrium to the right. 
D)  Lowering the temperature of a reaction will lower the reaction rate. 
E)  Substrate binds to an enzyme's active site.

Question 6

The enzyme pepsin is produced in the stomach lining initially as a _____, which requires _____ for activation in the stomach.

Accepted Answer

A)  kinase; phosphorylation 
B)  zymogen; irreversible proteolytic cleavage 
C)  proprotein; reversible proteolytic cleavage 
D)  zymogen; ubiquitination 
E)  phosphorylase; irreversible proteolytic cleavage 
A)  kinase; phosphorylation 
B)  zymogen; irreversible proteolytic cleavage 
C)  proprotein; reversible proteolytic cleavage 
D)  zymogen; ubiquitination 
E)  phosphorylase; irreversible proteolytic cleavage

Question 7

Why is the Lineweaver-Burk (double reciprocal) plot (see Box 6, p. 206) more useful than the standard V versus [S] plot in determining kinetic constants for an enzyme? (Your answer should probably show typical plots.)

Accepted Answer

The Lineweaver-Burk plot, also known as

Question 8

The allosteric enzyme ATCase is regulated by CTP, which binds to the T-state of ATCase. CTP is a:

Accepted Answer

A)  positive regulator. 
B)  negative regulator. 
C)  cofactor. 
D)  competitive inhibitor. 
E)  coenzyme. 
A)  positive regulator. 
B)  negative regulator. 
C)  cofactor. 
D)  competitive inhibitor. 
E)  coenzyme.

Question 9

A small molecule that DECREASES the activity of an enzyme by binding to a site other than the catalytic site is termed a(n):

Accepted Answer

A)  allosteric inhibitor. 
B)  alternative inhibitor. 
C)  competitive inhibitor. 
D)  stereospecific agent. 
E)  transition-state analog. 
A)  allosteric inhibitor. 
B)  alternative inhibitor. 
C)  competitive inhibitor. 
D)  stereospecific agent. 
E)  transition-state analog.

Question 10

The role of the metal ion (Mg2+) in catalysis by enolase is to:

Accepted Answer

A)  act as a general acid catalyst. 
B)  act as a general base catalyst. 
C)  facilitate general acid catalysis. 
D)  facilitate general base catalysis. 
E)  stabilize protein conformation. 
A)  act as a general acid catalyst. 
B)  act as a general base catalyst. 
C)  facilitate general acid catalysis. 
D)  facilitate general base catalysis. 
E)  stabilize protein conformation.

Question 11

For the simplified representation of an enzyme-catalyzed reaction shown below, the statement "ES is in steady-state" means that:

Accepted Answer

A)  k2 is very slow. 
B)  k1 = k2. 
C)  k1 = k-1. 
D)  k1[E][S] = k-1[ES] + k2[ES]. 
E)  k1[E][S] = k-1[ES]. 
A)  k2 is very slow. 
B)  k1 = k2. 
C)  k1 = k-1. 
D)  k1[E][S] = k-1[ES] + k2[ES]. 
E)  k1[E][S] = k-1[ES].

Question 12

Why does pH affect the activity of an enzyme?

Accepted Answer

Enzymes are biological catalysts that sp

Question 13

The role of an enzyme in an enzyme-catalyzed reaction is to:

Accepted Answer

A)  bind a transition state intermediate, such that it cannot be converted back to substrate. 
B)  ensure that all of the substrate is converted to product. 
C)  ensure that the product is more stable than the substrate. 
D)  increase the rate at which substrate is converted into product. 
E)  make the free-energy change for the reaction more favorable. 
A)  bind a transition state intermediate, such that it cannot be converted back to substrate. 
B)  ensure that all of the substrate is converted to product. 
C)  ensure that the product is more stable than the substrate. 
D)  increase the rate at which substrate is converted into product. 
E)  make the free-energy change for the reaction more favorable.

Question 14

Which molecule would NOT be effective to administer as an anticoagulant?

Accepted Answer

A)  aspirin 
B)  warfarin 
C)  heparin 
D)  vitamin K 
E)  antithrombin 
A)  aspirin 
B)  warfarin 
C)  heparin 
D)  vitamin K 
E)  antithrombin

Question 15

Which enzymes are NOT among the six internationally accepted classes of enzymes?

Accepted Answer

A)  hydrolases 
B)  ligases 
C)  oxidoreductases 
D)  polymerases 
E)  transferases 
A)  hydrolases 
B)  ligases 
C)  oxidoreductases 
D)  polymerases 
E)  transferases

Question 16

Describe why the Michaelis constant (Km) and the dissociation constant (Kd) should NOT be considered to be the same. Use the rate constant definitions of these terms in your explanation, and also indicate in what case Km and Kd can be considered to be the same.

Accepted Answer

The Michaelis constant (Km) and the diss

Question 17

Explain how a biochemist might discover that a certain enzyme is allosterically regulated.

Accepted Answer

A biochemist might discover that a certa

Question 18

Enzymes that cleave carbon-carbon bonds without the use of water in the chemical reaction are members of which class of enzymes?

Accepted Answer

A)  oxidoreductases 
B)  transferases 
C)  hydrolases 
D)  lyases 
E)  isomerases 
A)  oxidoreductases 
B)  transferases 
C)  hydrolases 
D)  lyases 
E)  isomerases

Question 19

Phenyl-methane-sulfonyl-fluoride (PMSF) inactivates serine proteases by binding covalently to the catalytic serine residue at the active site; this enzyme-inhibitor bond is not cleaved by the enzyme. This is an example of what kind of inhibition?

Accepted Answer

A)  irreversible 
B)  competitive 
C)  noncompetitive 
D)  mixed 
E)  pH inhibition 
A)  irreversible 
B)  competitive 
C)  noncompetitive 
D)  mixed 
E)  pH inhibition

Question 20

Which statement about a plot of V0 versus [S] for an enzyme that follows Michaelis-Menten kinetics is FALSE?

Accepted Answer

A)  As [S] increases, the initial velocity of reaction V0 also increases. 
B)  At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km. 
C)  Km is the [S] at which V0 = 1/2 Vmax. 
D)  The shape of the curve is a hyperbola. 
E)  The y-axis is a rate term with units of $\mu$m/min. 
A)  As [S] increases, the initial velocity of reaction V0 also increases. 
B)  At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km. 
C)  Km is the [S] at which V0 = 1/2 Vmax. 
D)  The shape of the curve is a hyperbola. 
E)  The y-axis is a rate term with units of $\mu$m/min.

Exam 6: Enzymes

Define the term "suicide inhibitor."

An enzyme's specificity constant (kcat/Km) has a maximum upper limit due to:

Penicillin and related antibiotics contain a four-membered β\betaβ -lactam ring. Explain why this feature is important to the mechanism of action of these drugs.

A transition-state analog:

Which statement is FALSE?

The enzyme pepsin is produced in the stomach lining initially as a _____, which requires _____ for activation in the stomach.

Why is the Lineweaver-Burk (double reciprocal) plot (see Box 6, p. 206) more useful than the standard V versus [S] plot in determining kinetic constants for an enzyme? (Your answer should probably show typical plots.)

The allosteric enzyme ATCase is regulated by CTP, which binds to the T-state of ATCase. CTP is a:

A small molecule that DECREASES the activity of an enzyme by binding to a site other than the catalytic site is termed a(n):

The role of the metal ion (Mg2+) in catalysis by enolase is to:

For the simplified representation of an enzyme-catalyzed reaction shown below, the statement "ES is in steady-state" means that:

Why does pH affect the activity of an enzyme?

The role of an enzyme in an enzyme-catalyzed reaction is to:

Which molecule would NOT be effective to administer as an anticoagulant?

Which enzymes are NOT among the six internationally accepted classes of enzymes?

Describe why the Michaelis constant (Km) and the dissociation constant (Kd) should NOT be considered to be the same. Use the rate constant definitions of these terms in your explanation, and also indicate in what case Km and Kd can be considered to be the same.

Explain how a biochemist might discover that a certain enzyme is allosterically regulated.

Enzymes that cleave carbon-carbon bonds without the use of water in the chemical reaction are members of which class of enzymes?

Phenyl-methane-sulfonyl-fluoride (PMSF) inactivates serine proteases by binding covalently to the catalytic serine residue at the active site; this enzyme-inhibitor bond is not cleaved by the enzyme. This is an example of what kind of inhibition?

Which statement about a plot of V0 versus [S] for an enzyme that follows Michaelis-Menten kinetics is FALSE?

The Foundations of Biochemistry

Water

Amino Acids, Peptides, and Proteins

The Three-Dimensional Structure of Proteins

Protein Function

Carbohydrates and Glycobiology

Nucleotides and Nucleic Acids

DNA-Based Information Technologies

Lipids

Biological Membranes and Transport

Biosignaling

Bioenergetics and Biochemical Reaction Types

Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway

Principles of Metabolic Regulation

The Citric Acid Cycle

Fatty Acid Catabolism

Amino Acid Oxidation and the Production of Urea

Oxidative Phosphorylation and Photophosphorylation

Carbohydrate Biosynthesis in Plants and Bacteria

Lipid Biosynthesis

Biosynthesis of Amino Acids, Nucleotides, and Related Molecules

Hormonal Regulation and Integration of Mammalian Metabolism

Genes and Chromosomes

DNA Metabolism

RNA Metabolism

Protein Metabolism

Regulation of Gene Expression

Filters

An enzyme's specificity constant (k_cat/K_m) has a maximum upper limit due to:

Penicillin and related antibiotics contain a four-membered $\beta$ -lactam ring. Explain why this feature is important to the mechanism of action of these drugs.

The enzyme pepsin is produced in the stomach lining initially as a _, which requires _ for activation in the stomach.

The role of the metal ion (Mg²⁺) in catalysis by enolase is to:

Describe why the Michaelis constant (K_m) and the dissociation constant (K_d) should NOT be considered to be the same. Use the rate constant definitions of these terms in your explanation, and also indicate in what case K_m and K_d can be considered to be the same.

Which statement about a plot of V₀versus [S] for an enzyme that follows Michaelis-Menten kinetics is FALSE?