Question 1

Which factor has NOT been shown to play a role in determining the specificity of protein kinases?

Accepted Answer

A)  disulfide bonds near the phosphorylation site 
B)  primary sequence at phosphorylation site 
C)  protein quaternary structure 
D)  protein tertiary structure 
E)  residues near the phosphorylation site 
A)  disulfide bonds near the phosphorylation site 
B)  primary sequence at phosphorylation site 
C)  protein quaternary structure 
D)  protein tertiary structure 
E)  residues near the phosphorylation site

Question 2

Cells can develop a resistance to drugs by increasing the cellular concentration of the enzyme that that drug inhibits. If a cell increases its concentration of a given enzyme to 10 times the normal amount, which parameters listed below will be increased ten-fold?
Km
KI
[S]
Vmax
v0 when [S] = Km
kcat
Catalytic efficiency

Accepted Answer

If a cell increases its concentration of

Question 3

Which statement is TRUE of the binding energy derived from enzyme-substrate interactions?

Accepted Answer

A)  It cannot provide enough energy to explain the large rate accelerations brought about by enzymes. 
B)  It is sometimes used to hold two substrates in the optimal orientation for reaction. 
C)  It is the result of covalent bonds formed between enzyme and substrate. 
D)  Most of it is derived from covalent bonds between enzyme and substrate. 
E)  Most of it is used up simply binding the substrate to the enzyme. 
A)  It cannot provide enough energy to explain the large rate accelerations brought about by enzymes. 
B)  It is sometimes used to hold two substrates in the optimal orientation for reaction. 
C)  It is the result of covalent bonds formed between enzyme and substrate. 
D)  Most of it is derived from covalent bonds between enzyme and substrate. 
E)  Most of it is used up simply binding the substrate to the enzyme.

Question 4

Fifteen $\mu$g of an enzyme of Mr 30,000 working at Vmax catalyzes the conversion of 60 $\mu$mol of substrate into product in 3 min. What is the enzyme's turnover number?

Accepted Answer

The turnover number, also known as k_cat

Question 5

The difference in (standard) free energy content, $\Delta$G'°, between substrate S and product P may vary considerably among different reactions. What is the significance of these differences?

Accepted Answer

The significance of the differences in s

Question 6

Which statement about allosteric control of enzymatic activity is FALSE?

Accepted Answer

A)  Allosteric effectors give rise to sigmoidal V0 versus [S] kinetic plots. 
B)  Allosteric proteins are generally composed of several subunits. 
C)  An effector may either inhibit or activate an enzyme. 
D)  Binding of the effector changes the conformation of the enzyme molecule. 
E)  Heterotropic allosteric effectors compete with substrate for binding sites. 
A)  Allosteric effectors give rise to sigmoidal V0 versus [S] kinetic plots. 
B)  Allosteric proteins are generally composed of several subunits. 
C)  An effector may either inhibit or activate an enzyme. 
D)  Binding of the effector changes the conformation of the enzyme molecule. 
E)  Heterotropic allosteric effectors compete with substrate for binding sites.

Question 7

In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitor will alter the:

Accepted Answer

A)  curvature of the plot. 
B)  intercept on the l/[S] axis. 
C)  intercept on the l/V axis. 
D)  pK of the plot. 
E)  Vmax. 
A)  curvature of the plot. 
B)  intercept on the l/[S] axis. 
C)  intercept on the l/V axis. 
D)  pK of the plot. 
E)  Vmax.

Question 8

Methanol (wood alcohol) is highly toxic because it is converted to formaldehyde in a reaction catalyzed by the enzyme alcohol dehydrogenase:
NAD+ + methanol $\rightarrow$ NADH + H+ + formaldehyde
Part of the medical treatment for methanol poisoning is to administer ethanol (ethyl alcohol) in amounts large enough to cause intoxication under normal circumstances. Explain this in terms of what you know about examples of enzymatic reactions.

Accepted Answer

The administration of ethanol in the tre

Question 9

The concept of "induced fit" refers to the fact that:

Accepted Answer

A)  enzyme specificity is induced by enzyme-substrate binding. 
B)  enzyme-substrate binding induces an increase in the reaction entropy, thereby catalyzing the reaction. 
C)  enzyme-substrate binding induces movement along the reaction coordinate to the transition state. 
D)  substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation. 
E)  when a substrate binds to an enzyme, the enzyme induces a loss of water (desolvation) from the substrate. 
A)  enzyme specificity is induced by enzyme-substrate binding. 
B)  enzyme-substrate binding induces an increase in the reaction entropy, thereby catalyzing the reaction. 
C)  enzyme-substrate binding induces movement along the reaction coordinate to the transition state. 
D)  substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation. 
E)  when a substrate binds to an enzyme, the enzyme induces a loss of water (desolvation) from the substrate.

Question 10

For serine to work effectively as a nucleophile in covalent catalysis in chymotrypsin a nearby amino acid, histidine, must serve as general base catalyst. Briefly describe, in words, how these two amino acids work together.

Accepted Answer

Serine and histidine work together in co

Question 11

The Lineweaver-Burk plot is used to:

Accepted Answer

A)  determine the equilibrium constant for an enzymatic reaction. 
B)  extrapolate for the value of reaction rate at infinite enzyme concentration. 
C)  illustrate the effect of temperature on an enzymatic reaction. 
D)  solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration. 
E)  solve, graphically, for the ratio of products to reactants for any starting substrate concentration. 
A)  determine the equilibrium constant for an enzymatic reaction. 
B)  extrapolate for the value of reaction rate at infinite enzyme concentration. 
C)  illustrate the effect of temperature on an enzymatic reaction. 
D)  solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration. 
E)  solve, graphically, for the ratio of products to reactants for any starting substrate concentration.

Question 12

Enzymes differ from other catalysts in that only enzymes:

Accepted Answer

A)  are not consumed in the reaction. 
B)  display specificity toward a single reactant. 
C)  fail to influence the equilibrium point of the reaction. 
D)  form an activated complex with the reactants. 
E)  lower the activation energy of the reaction catalyzed. 
A)  are not consumed in the reaction. 
B)  display specificity toward a single reactant. 
C)  fail to influence the equilibrium point of the reaction. 
D)  form an activated complex with the reactants. 
E)  lower the activation energy of the reaction catalyzed.

Question 13

Sometimes the difference in (standard) free-energy content, $\Delta$G'°, between a substrate S and a product P is very large, yet the rate of chemical conversion, S $\rightarrow$ P, is quite slow. Why?

Accepted Answer

The difference in standard free-energy c

Question 14

Which protein polymerizes into a gel-like matrix after it is activated to assist in blood clotting?

Accepted Answer

A)  trypsinogen 
B)  fibrinogen 
C)  prothrombin 
D)  thrombin 
E)  warfarin 
A)  trypsinogen 
B)  fibrinogen 
C)  prothrombin 
D)  thrombin 
E)  warfarin

Question 15

Draw and label a reaction coordinate diagram for an uncatalyzed reaction, S $\rightarrow$  P, and the same reaction catalyzed by an enzyme, E.

Accepted Answer

A reaction coordinate diagram for an unc

Question 16

A complex organic molecule that is necessary for enzyme function but is NOT permanently associated with the enzyme is a:

Accepted Answer

A)  prosthetic group. 
B)  cofactor. 
C)  holofactor. 
D)  coenzyme. 
E)  metal ion. 
A)  prosthetic group. 
B)  cofactor. 
C)  holofactor. 
D)  coenzyme. 
E)  metal ion.

Question 17

Penicillin and related drugs inhibit the enzyme _____; this enzyme is produced by _____.

Accepted Answer

A)  $\beta$-lacamase; bacteria 
B)  transpeptidase; human cells 
C)  transpeptidase; bacteria 
D)  lysozyme; human cells 
E)  aldolase; bacteria 
A)  $\beta$-lacamase; bacteria 
B)  transpeptidase; human cells 
C)  transpeptidase; bacteria 
D)  lysozyme; human cells 
E)  aldolase; bacteria

Question 18

The benefit of measuring the initial rate of a reaction V0 is that, at the beginning of a reaction:

Accepted Answer

A)  [ES] can be measured accurately. 
B)  changes in [S] are negligible, so [S] can be treated as a constant. 
C)  changes in Km are negligible, so Km can be treated as a constant. 
D)  V0 = Vmax. 
E)  varying [S] has no effect on V0. 
A)  [ES] can be measured accurately. 
B)  changes in [S] are negligible, so [S] can be treated as a constant. 
C)  changes in Km are negligible, so Km can be treated as a constant. 
D)  V0 = Vmax. 
E)  varying [S] has no effect on V0.

Question 19

Binding energy between an enzyme and a substrate contributes to catalysis in which way?

Accepted Answer

A)  Binding energy provides the enzyme specificity for the substrate. 
B)  Binding energy contributions allow for entropy reduction in the substrate-enzyme complex. 
C)  Binding energy compensates for energy changes as a result of desolvation of the substrate. 
D)  Binding energy contributes to the process of induced fit between the substrate and the enzyme. 
E)  All of the answers are correct. 
A)  Binding energy provides the enzyme specificity for the substrate. 
B)  Binding energy contributions allow for entropy reduction in the substrate-enzyme complex. 
C)  Binding energy compensates for energy changes as a result of desolvation of the substrate. 
D)  Binding energy contributes to the process of induced fit between the substrate and the enzyme. 
E)  All of the answers are correct.

Question 20

Which statement is TRUE of enzyme catalysts?

Accepted Answer

A)  They bind to substrates but are never covalently attached to substrate or product. 
B)  They increase the equilibrium constant for a reaction, thus favoring product formation. 
C)  They increase the stability of the product of a desired reaction by allowing ionizations, resonance, and isomerizations not normally available to substrates. 
D)  They lower the activation energy for the conversion of substrate to product. 
E)  To be effective, they must be present at the same concentration as their substrates. 
A)  They bind to substrates but are never covalently attached to substrate or product. 
B)  They increase the equilibrium constant for a reaction, thus favoring product formation. 
C)  They increase the stability of the product of a desired reaction by allowing ionizations, resonance, and isomerizations not normally available to substrates. 
D)  They lower the activation energy for the conversion of substrate to product. 
E)  To be effective, they must be present at the same concentration as their substrates.

Exam 6: Enzymes

Which factor has NOT been shown to play a role in determining the specificity of protein kinases?

Which statement is TRUE of the binding energy derived from enzyme-substrate interactions?

Fifteen μ\muμ g of an enzyme of Mr 30,000 working at Vmax catalyzes the conversion of 60 μ\muμ mol of substrate into product in 3 min. What is the enzyme's turnover number?

The difference in (standard) free energy content, Δ\DeltaΔ G'°, between substrate S and product P may vary considerably among different reactions. What is the significance of these differences?

Which statement about allosteric control of enzymatic activity is FALSE?

In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitor will alter the:

The concept of "induced fit" refers to the fact that:

For serine to work effectively as a nucleophile in covalent catalysis in chymotrypsin a nearby amino acid, histidine, must serve as general base catalyst. Briefly describe, in words, how these two amino acids work together.

The Lineweaver-Burk plot is used to:

Enzymes differ from other catalysts in that only enzymes:

Sometimes the difference in (standard) free-energy content, Δ\DeltaΔ G'°, between a substrate S and a product P is very large, yet the rate of chemical conversion, S →\rightarrow→ P, is quite slow. Why?

Which protein polymerizes into a gel-like matrix after it is activated to assist in blood clotting?

Draw and label a reaction coordinate diagram for an uncatalyzed reaction, S →\rightarrow→ P, and the same reaction catalyzed by an enzyme, E.

A complex organic molecule that is necessary for enzyme function but is NOT permanently associated with the enzyme is a:

Penicillin and related drugs inhibit the enzyme _____; this enzyme is produced by _____.

The benefit of measuring the initial rate of a reaction V0 is that, at the beginning of a reaction:

Binding energy between an enzyme and a substrate contributes to catalysis in which way?

Which statement is TRUE of enzyme catalysts?

The Foundations of Biochemistry

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Amino Acids, Peptides, and Proteins

The Three-Dimensional Structure of Proteins

Protein Function

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DNA-Based Information Technologies

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Principles of Metabolic Regulation

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Amino Acid Oxidation and the Production of Urea

Oxidative Phosphorylation and Photophosphorylation

Carbohydrate Biosynthesis in Plants and Bacteria

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Hormonal Regulation and Integration of Mammalian Metabolism

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Fifteen $\mu$ g of an enzyme of M_r 30,000 working at V_max catalyzes the conversion of 60 $\mu$ mol of substrate into product in 3 min. What is the enzyme's turnover number?

The difference in (standard) free energy content, $\Delta$ G'°, between substrate S and product P may vary considerably among different reactions. What is the significance of these differences?

Sometimes the difference in (standard) free-energy content, $\Delta$ G'°, between a substrate S and a product P is very large, yet the rate of chemical conversion, S $\rightarrow$ P, is quite slow. Why?

Draw and label a reaction coordinate diagram for an uncatalyzed reaction, S $\rightarrow$ P, and the same reaction catalyzed by an enzyme, E.

Penicillin and related drugs inhibit the enzyme _; this enzyme is produced by _.

The benefit of measuring the initial rate of a reaction V₀ is that, at the beginning of a reaction: