Question 1

What would be the systematic name for an enzyme that catalyzes the following reaction? alanine + 2-oxoglutarate $\rightarrow$  pyruvate + glutamate

Accepted Answer

A)  alanine:2-oxoglutarate hydrolyase 
B)  alanine:2-oxoglutarate ligase 
C)  alanine:2-oxoglutarate aminotransferase 
D)  glutamate oxidoreductase 
E)  pyruvate:glutamate phosphotransferase 
A)  alanine:2-oxoglutarate hydrolyase 
B)  alanine:2-oxoglutarate ligase 
C)  alanine:2-oxoglutarate aminotransferase 
D)  glutamate oxidoreductase 
E)  pyruvate:glutamate phosphotransferase

Question 2

You measure the initial rate of an enzyme reaction as a function of substrate concentration in the presence and absence of an inhibitor. The following data are obtained:
[S]
V0
-Inhibitor
+Inhibitor
0.0001
33
17
0.0002
50
29
0.0005
71
50
0.001
83
67
0.002
91
80
0.005
96
91
0.01
98
95
0.02
99
98
0.05
100
99
0.1
100
100
0.2
100
100
a) What is the Vmax in the absence of inhibitor?
b) What is the Km in the absence of inhibitor?
c) When [S] = 0.0004, what will V0 be in the absence of inhibitor?
d) When [S] = 0.0004, what will V0 be in the presence of inhibitor?
e) What kind of inhibitor is it likely to be?

Accepted Answer

a) The V in the absence of inhibitor can

Question 3

How does the total enzyme concentration affect turnover number and Vmax?

Accepted Answer

The total enzyme concentration in a reac

Question 4

Enzymes are potent catalysts because they:

Accepted Answer

A)  are consumed in the reactions they catalyze. 
B)  are very specific and can prevent the conversion of products back to substrates. 
C)  drive reactions to completion while other catalysts drive reactions to equilibrium. 
D)  increase the equilibrium constants for the reactions they catalyze. 
E)  lower the activation energy for the reactions they catalyze. 
A)  are consumed in the reactions they catalyze. 
B)  are very specific and can prevent the conversion of products back to substrates. 
C)  drive reactions to completion while other catalysts drive reactions to equilibrium. 
D)  increase the equilibrium constants for the reactions they catalyze. 
E)  lower the activation energy for the reactions they catalyze.

Question 5

Chymotrypsin belongs to a group of proteolytic enzymes called the "serine proteases," many of which have an Asp, His, and Ser residue that are crucial to the catalytic mechanism. The serine hydroxyl functions as a nucleophile. What do the other two amino acids do to support this nucleophilic reaction?

Accepted Answer

Chymotrypsin, as a member of the serine

Question 6

On the enzyme hexokinase, ATP reacts with glucose to produce glucose 6-phosphate and ADP five orders of magnitude faster than ATP reacts with H2O to form phosphate and ADP. The intrinsic chemical reactivity of the -OH group in water is about the same as that of the glucose molecule, and water can certainly fit into the active site. Explain this rate differential in two sentences or less.

Accepted Answer

The rate differential is likely due to t

Question 7

The number of substrate molecules converted to product in a given unit of time by a single enzyme molecule at saturation is referred to as the:

Accepted Answer

A)  dissociation constant. 
B)  half-saturation constant. 
C)  maximum velocity. 
D)  Michaelis-Menten number. 
E)  turnover number. 
A)  dissociation constant. 
B)  half-saturation constant. 
C)  maximum velocity. 
D)  Michaelis-Menten number. 
E)  turnover number.

Question 8

The double-reciprocal transformation of the Michaelis-Menten equation, also called the Lineweaver-Burk plot, is given by 1/V0 = Km /(Vmax[S]) + 1/Vmax
To determine Km from a double-reciprocal plot, you would:

Accepted Answer

A)  multiply the reciprocal of the x-axis intercept by -1. 
B)  multiply the reciprocal of the y-axis intercept by -1. 
C)  take the reciprocal of the x-axis intercept. 
D)  take the reciprocal of the y-axis intercept. 
E)  take the x-axis intercept, where V0 = 1/2 Vmax. 
A)  multiply the reciprocal of the x-axis intercept by -1. 
B)  multiply the reciprocal of the y-axis intercept by -1. 
C)  take the reciprocal of the x-axis intercept. 
D)  take the reciprocal of the y-axis intercept. 
E)  take the x-axis intercept, where V0 = 1/2 Vmax.

Question 9

For enzymes in which the slowest (rate-limiting) step is the reaction   Km becomes equivalent to:

Accepted Answer

A)  kcat. 
B)  the [S], where V0 = Vmax. 
C)  the dissociation constant, Kd, for the ES complex. 
D)  the maximal velocity. 
E)  the turnover number. 
A)  kcat. 
B)  the [S], where V0 = Vmax. 
C)  the dissociation constant, Kd, for the ES complex. 
D)  the maximal velocity. 
E)  the turnover number.

Question 10

Define the terms "cofactor" and "coenzyme."

Accepted Answer

Cofactor and coenzyme are terms used in

Question 11

Which statement about enzyme-catalyzed reactions is FALSE?

Accepted Answer

A)  At saturating levels of substrate, the rate of an enzyme-catalyzed reaction is proportional to the enzyme concentration. 
B)  If enough substrate is added, the normal Vmax of a reaction can be attained even in the presence of a competitive inhibitor. 
C)  The rate of a reaction decreases steadily with time as substrate is depleted. 
D)  The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme-catalyzed reaction. 
E)  The Michaelis-Menten constant Km equals the [S] at which V = 1/2 Vmax. 
A)  At saturating levels of substrate, the rate of an enzyme-catalyzed reaction is proportional to the enzyme concentration. 
B)  If enough substrate is added, the normal Vmax of a reaction can be attained even in the presence of a competitive inhibitor. 
C)  The rate of a reaction decreases steadily with time as substrate is depleted. 
D)  The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme-catalyzed reaction. 
E)  The Michaelis-Menten constant Km equals the [S] at which V = 1/2 Vmax.

Question 12

The turnover number for an enzyme is known to be 5000 min-1. From the following set of data, calculate the Km and the total amount of enzyme present in these experiments.
Substrate
Initial
concentration
velocity
(mM)
($\rightarrow$mol/min)
1
167
2
250
4
334
6
376
100
498
1,000
499
(a) Km = _____. (b) Total enzyme = _____ $\mu$mol.

Accepted Answer

(a) To calculate K_m, we can u

Question 13

Write out the equation that describes the mechanism for enzyme action used as a model by Michaelis and Menten. List the important assumptions used by Michaelis and Menten to derive a rate equation for this reaction.

Accepted Answer

The equation that describes the mechanis

Question 14

When 10 $\mu$g of an enzyme of Mr 50,000 is added to a solution containing its substrate at a concentration one hundred times the Km, it catalyzes the conversion of 75 $\mu$mol of substrate into product in 3 min. What is the enzyme's turnover number?

Accepted Answer

To calculate the enzyme's turnover numbe

Question 15

Treatment of methanol poisoning by using ethanol is an example of what type of enzyme inhibition?

Accepted Answer

A)  mixed inhibition 
B)  uncompetitive inhibition 
C)  competitive inhibition 
D)  noncompetitive inhibition 
E)  suicide inhibition 
A)  mixed inhibition 
B)  uncompetitive inhibition 
C)  competitive inhibition 
D)  noncompetitive inhibition 
E)  suicide inhibition

Question 16

Enzyme X exhibits maximum activity at pH = 6.9. X shows a fairly sharp decrease in its activity when the pH goes much lower than 6.4. One likely interpretation of this pH activity is that:

Accepted Answer

A)  a Glu residue on the enzyme is involved in the reaction. 
B)  a His residue on the enzyme is involved in the reaction. 
C)  the enzyme has a metallic cofactor. 
D)  the enzyme is found in gastric secretions. 
E)  the reaction relies on specific acid-base catalysis. 
A)  a Glu residue on the enzyme is involved in the reaction. 
B)  a His residue on the enzyme is involved in the reaction. 
C)  the enzyme has a metallic cofactor. 
D)  the enzyme is found in gastric secretions. 
E)  the reaction relies on specific acid-base catalysis.

Question 17

The steady state assumption, as applied to enzyme kinetics, implies:

Accepted Answer

A)  Km = Ks. 
B)  the enzyme is regulated. 
C)  the ES complex is formed and broken down at equivalent rates. 
D)  the Km is equivalent to the cellular substrate concentration. 
E)  the maximum velocity occurs when the enzyme is saturated. 
A)  Km = Ks. 
B)  the enzyme is regulated. 
C)  the ES complex is formed and broken down at equivalent rates. 
D)  the Km is equivalent to the cellular substrate concentration. 
E)  the maximum velocity occurs when the enzyme is saturated.

Question 18

What is the difference between general acid-base catalysis and specific acid-base catalysis? (Assume that the solvent is water.)

Accepted Answer

General acid-base catalysis and specific

Question 19

To calculate the turnover number of an enzyme, you need to know:

Accepted Answer

A)  the enzyme concentration. 
B)  the initial velocity of the catalyzed reaction at [S] >> Km. 
C)  the initial velocity of the catalyzed reaction at low [S]. 
D)  the Km for the substrate. 
E)  both the enzyme concentration and the initial velocity of the catalyzed reaction at [S] >> Km. 
A)  the enzyme concentration. 
B)  the initial velocity of the catalyzed reaction at [S] >> Km. 
C)  the initial velocity of the catalyzed reaction at low [S]. 
D)  the Km for the substrate. 
E)  both the enzyme concentration and the initial velocity of the catalyzed reaction at [S] >> Km.

Question 20

Allosteric enzymes:

Accepted Answer

A)  are regulated primarily by covalent modification. 
B)  usually catalyze several different reactions within a metabolic pathway. 
C)  usually have more than one polypeptide chain. 
D)  usually have only one active site. 
E)  usually show strict Michaelis-Menten kinetics. 
A)  are regulated primarily by covalent modification. 
B)  usually catalyze several different reactions within a metabolic pathway. 
C)  usually have more than one polypeptide chain. 
D)  usually have only one active site. 
E)  usually show strict Michaelis-Menten kinetics.

Exam 6: Enzymes

What would be the systematic name for an enzyme that catalyzes the following reaction? alanine + 2-oxoglutarate →\rightarrow→ pyruvate + glutamate

How does the total enzyme concentration affect turnover number and Vmax?

Enzymes are potent catalysts because they:

The number of substrate molecules converted to product in a given unit of time by a single enzyme molecule at saturation is referred to as the:

The double-reciprocal transformation of the Michaelis-Menten equation, also called the Lineweaver-Burk plot, is given by 1/V0 = Km /(Vmax[S]) + 1/Vmax To determine Km from a double-reciprocal plot, you would:

For enzymes in which the slowest (rate-limiting) step is the reaction Km becomes equivalent to:

Define the terms "cofactor" and "coenzyme."

Which statement about enzyme-catalyzed reactions is FALSE?

Write out the equation that describes the mechanism for enzyme action used as a model by Michaelis and Menten. List the important assumptions used by Michaelis and Menten to derive a rate equation for this reaction.

When 10 μ\muμ g of an enzyme of Mr 50,000 is added to a solution containing its substrate at a concentration one hundred times the Km, it catalyzes the conversion of 75 μ\muμ mol of substrate into product in 3 min. What is the enzyme's turnover number?

Treatment of methanol poisoning by using ethanol is an example of what type of enzyme inhibition?

Enzyme X exhibits maximum activity at pH = 6.9. X shows a fairly sharp decrease in its activity when the pH goes much lower than 6.4. One likely interpretation of this pH activity is that:

The steady state assumption, as applied to enzyme kinetics, implies:

What is the difference between general acid-base catalysis and specific acid-base catalysis? (Assume that the solvent is water.)

To calculate the turnover number of an enzyme, you need to know:

Allosteric enzymes:

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

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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

What would be the systematic name for an enzyme that catalyzes the following reaction? alanine + 2-oxoglutarate $\rightarrow$ pyruvate + glutamate

How does the total enzyme concentration affect turnover number and V_max?

The double-reciprocal transformation of the Michaelis-Menten equation, also called the Lineweaver-Burk plot, is given by 1/V₀ = K_m /(V_max[S]) + 1/V_max To determine K_m from a double-reciprocal plot, you would:

For enzymes in which the slowest (rate-limiting) step is the reaction K_m becomes equivalent to:

When 10 $\mu$ g of an enzyme of M_r 50,000 is added to a solution containing its substrate at a concentration one hundred times the K_m, it catalyzes the conversion of 75 $\mu$ mol of substrate into product in 3 min. What is the enzyme's turnover number?