Question 1

The Km

Accepted Answer

A)  is always a function of rate constants. 
B)  can always be interpreted as a dissociation constant for the ES complex. 
C)  cannot be calculated from experimental data. 
D)  changes in response to noncompetitive inhibitors. 
E)  changes whenever Vmax is changed experimentally. 
A)  is always a function of rate constants. 
B)  can always be interpreted as a dissociation constant for the ES complex. 
C)  cannot be calculated from experimental data. 
D)  changes in response to noncompetitive inhibitors. 
E)  changes whenever Vmax is changed experimentally.

Question 2

Which of the following could be a positive allosteric effector of an enzyme?

Accepted Answer

A)  a competitive inhibitor 
B)  a noncompetitive inhibitor 
C)  a compound, other than the substrate, which binds to the active site 
D)  a compound, other than the substrate, which binds to the enzyme but not to the active site 
E)  a coenzyme which is essential for the activity of the enzyme 
A)  a competitive inhibitor 
B)  a noncompetitive inhibitor 
C)  a compound, other than the substrate, which binds to the active site 
D)  a compound, other than the substrate, which binds to the enzyme but not to the active site 
E)  a coenzyme which is essential for the activity of the enzyme

Question 3

When enzyme rate, the constraint on the ratio of k cat/Km must be kept in mind. Which values of the two constants, respectively, will give the greatest enzyme rate at a given substrate concentration?

Accepted Answer

A)  1 s -1 / 10-6 M 
B)  102 s -1 / 10-4 M 
C)  103 s -1 / 10-3 M 
D)  104 s -1 / 10-2 M 
E)  105 s -1 / 10-1 M 
A)  1 s -1 / 10-6 M 
B)  102 s -1 / 10-4 M 
C)  103 s -1 / 10-3 M 
D)  104 s -1 / 10-2 M 
E)  105 s -1 / 10-1 M

Question 4

If one wished to diagnose myocardial infarction, one would best measure isoenzymes of

Accepted Answer

A)  creatine kinase. 
B)  lactate dehydrogenase. 
C)  alkaline phosphatase. 
D)  all of the above. 
A)  creatine kinase. 
B)  lactate dehydrogenase. 
C)  alkaline phosphatase. 
D)  all of the above.

Question 5

Enzyme cofactors

Accepted Answer

A)  can be only inorganic ions or compounds. 
B)  combine with the protein moiety of the enzyme to form an apoenzyme. 
C)  are not know to combine simultaneously with both enzyme and substrate. 
D)  can act only by helping to maintain the native conformation of the enzyme protein. 
E)  may participate in the catalytic mechanism of an enzyme, providing a reactive group not found in the side chains of the common amino acids. 
A)  can be only inorganic ions or compounds. 
B)  combine with the protein moiety of the enzyme to form an apoenzyme. 
C)  are not know to combine simultaneously with both enzyme and substrate. 
D)  can act only by helping to maintain the native conformation of the enzyme protein. 
E)  may participate in the catalytic mechanism of an enzyme, providing a reactive group not found in the side chains of the common amino acids.

Question 6

Standard free energy of a reaction can be used for all of the following EXCEPT

Accepted Answer

A)  predict the direction in which a reaction will proceed under standard conditions of temperature, concentrations and pH. 
B)  predict free energy changes for reactions given the concentrations of reactants and products that are unequal to 1 M. 
C)  predict the rate of a chemical reaction. 
D)  predict the standard free energy change of the reaction at pH 7. 
E)  predict the equilibrium constant for a reaction. 
A)  predict the direction in which a reaction will proceed under standard conditions of temperature, concentrations and pH. 
B)  predict free energy changes for reactions given the concentrations of reactants and products that are unequal to 1 M. 
C)  predict the rate of a chemical reaction. 
D)  predict the standard free energy change of the reaction at pH 7. 
E)  predict the equilibrium constant for a reaction.

Question 7

In the case of non-competitive inhibition, the inhibitor may bind to which of the following?

Accepted Answer

A)  only free enzyme 
B)  only enzyme-substrate complex 
C)  both free enzyme and enzyme?substrate complex 
D)  only to substrate 
E)  only to the substrate binding site of the enzyme 
A)  only free enzyme 
B)  only enzyme-substrate complex 
C)  both free enzyme and enzyme?substrate complex 
D)  only to substrate 
E)  only to the substrate binding site of the enzyme

Question 8

How does cAMP modulate protein kinase A activity?

Accepted Answer

A)  It binds to a site on the C subunit to activate it 
B)  It binds to the R subunit leading to a conformation change 
C)  It causes association of the R and C subunits 
D)  It causes phosphorylation of the C subunit to release the R subunit 
E)  It competes with the R subunit for the active site of the C subunit 
A)  It binds to a site on the C subunit to activate it 
B)  It binds to the R subunit leading to a conformation change 
C)  It causes association of the R and C subunits 
D)  It causes phosphorylation of the C subunit to release the R subunit 
E)  It competes with the R subunit for the active site of the C subunit

Question 9

Stereospecificity may be explained by

Accepted Answer

A)  the catalytic constant. 
B)  reversibility of formation of the enzyme-substrate complex. 
C)  three point attachment. 
D)  competitive inhibitors. 
E)  saturation. 
A)  the catalytic constant. 
B)  reversibility of formation of the enzyme-substrate complex. 
C)  three point attachment. 
D)  competitive inhibitors. 
E)  saturation.

Question 10

What is one good reason why initial velocities are employed in enzyme assays?

Accepted Answer

A)  Substrate inhibition is minimized. 
B)  Substrate activation is minimized. 
C)  Errors in technique are minimized. 
D)  Product inhibition is minimized. 
E)  The sensitivity of the assay is increased. 
A)  Substrate inhibition is minimized. 
B)  Substrate activation is minimized. 
C)  Errors in technique are minimized. 
D)  Product inhibition is minimized. 
E)  The sensitivity of the assay is increased.

Question 11

The kinetics of a typical Michaelis-Menten enzyme shows what order dependence of substrate concentration at very high substrate concentrations?

Accepted Answer

A)  zero 
B)  first 
C)  second 
D)  third 
E)  mixed 
A)  zero 
B)  first 
C)  second 
D)  third 
E)  mixed

Question 12

What is the chemical difference between NAD and NADP?

Accepted Answer

A)  NADP has an additional phosphoryl group at position #2' on the pentose adjacent to adenine. 
B)  NAD has a nicotinic acid moiety rather than nicotinamide. 
C)  NADP has an additional phosphoryl group at position #3' on the pentose adjacent to nicotinamide. 
D)  NADP has an additional phosphoryl grouping as an acyl phosphate on the nicotinic acid moiety. 
E)  Chemically, they are identical. 
A)  NADP has an additional phosphoryl group at position #2' on the pentose adjacent to adenine. 
B)  NAD has a nicotinic acid moiety rather than nicotinamide. 
C)  NADP has an additional phosphoryl group at position #3' on the pentose adjacent to nicotinamide. 
D)  NADP has an additional phosphoryl grouping as an acyl phosphate on the nicotinic acid moiety. 
E)  Chemically, they are identical.

Question 13

Which of the following statements relative to the maximum velocity (Vmax) of an enzyme catalyzed reaction (assayed under conditions of excess substrate) is correct?

Accepted Answer

A)  Vmax is equal to twice the Km. 
B)  Vmax is directly proportional to the concentration of the substrate. 
C)  Vmax is reached when the concentration of the enzyme-substrate complex is equal to the original concentration of the enzyme. 
D)  Vmax is reached if an enzyme concentration is used that is at least ten times higher than the Km. 
E)  Vmax is independent of the enzyme concentration. 
A)  Vmax is equal to twice the Km. 
B)  Vmax is directly proportional to the concentration of the substrate. 
C)  Vmax is reached when the concentration of the enzyme-substrate complex is equal to the original concentration of the enzyme. 
D)  Vmax is reached if an enzyme concentration is used that is at least ten times higher than the Km. 
E)  Vmax is independent of the enzyme concentration.

Question 14

Which of the amino acids below is unlikely to be involved in the reaction mechanism at the active site of an enzyme?

Accepted Answer

A)  alanine 
B)  serine 
C)  cysteine 
D)  histidine 
E)  aspartic acid 
A)  alanine 
B)  serine 
C)  cysteine 
D)  histidine 
E)  aspartic acid

Question 15

The intercept on the vertical axis (Y-axis) on a Lineweaver-Burk plot is equal to

Accepted Answer

A)  1/Km. 
B)  1/Vmax. 
C)  -1/Km. 
D)  -1/Vmax. 
E)  Vmax. 
A)  1/Km. 
B)  1/Vmax. 
C)  -1/Km. 
D)  -1/Vmax. 
E)  Vmax.

Question 16

When the substrate concentration is equal to Km for a given enzyme and substrate you would expect which of the following?

Accepted Answer

A)  Vo = Vmax 
B)  Vo = Vmax/2 
C)  Vo = Vmax/3 
D)  Vo = Vmax/4 
E)  Vo = Vmax/10 
A)  Vo = Vmax 
B)  Vo = Vmax/2 
C)  Vo = Vmax/3 
D)  Vo = Vmax/4 
E)  Vo = Vmax/10

Question 17

Hydrolysis of high energy phosphate bonds associated with enzymatic linking of two molecules is catalyzed by what group of enzymes?

Accepted Answer

A)  Oxidoreductases 
B)  Hydrolases 
C)  Lyases 
D)  Isomerases 
E)  Ligases 
A)  Oxidoreductases 
B)  Hydrolases 
C)  Lyases 
D)  Isomerases 
E)  Ligases

Question 18

A measurement of cooperativity is the

Accepted Answer

A)  energy of activation. 
B)  maximum velocity. 
C)  inhibition constant. 
D)  Hill coefficient. 
E)  Arrhenius coefficient. 
A)  energy of activation. 
B)  maximum velocity. 
C)  inhibition constant. 
D)  Hill coefficient. 
E)  Arrhenius coefficient.

Question 19

In the case of an enzyme displaying a sigmoid relationship between velocity and substrate concentration, it can be concluded that

Accepted Answer

A)  the binding of one substrate molecule hinders the binding of others. 
B)  the enzyme contains only one binding site for substrate. 
C)  substrate binds more easily at low concentrations than at high concentrations. 
D)  the enzyme must contain at least four subunits. 
E)  the enzyme displays cooperativity in terms of substrate binding. 
A)  the binding of one substrate molecule hinders the binding of others. 
B)  the enzyme contains only one binding site for substrate. 
C)  substrate binds more easily at low concentrations than at high concentrations. 
D)  the enzyme must contain at least four subunits. 
E)  the enzyme displays cooperativity in terms of substrate binding.

Exam 10: Enzymes: Classification, Kinetics, and Control

The Km

Which of the following could be a positive allosteric effector of an enzyme?

When enzyme rate, the constraint on the ratio of k cat/Km must be kept in mind. Which values of the two constants, respectively, will give the greatest enzyme rate at a given substrate concentration?

If one wished to diagnose myocardial infarction, one would best measure isoenzymes of

Enzyme cofactors

Standard free energy of a reaction can be used for all of the following EXCEPT

In the case of non-competitive inhibition, the inhibitor may bind to which of the following?

How does cAMP modulate protein kinase A activity?

Stereospecificity may be explained by

What is one good reason why initial velocities are employed in enzyme assays?

The kinetics of a typical Michaelis-Menten enzyme shows what order dependence of substrate concentration at very high substrate concentrations?

What is the chemical difference between NAD and NADP?

Which of the following statements relative to the maximum velocity (Vmax) of an enzyme catalyzed reaction (assayed under conditions of excess substrate) is correct?

Which of the amino acids below is unlikely to be involved in the reaction mechanism at the active site of an enzyme?

The intercept on the vertical axis (Y-axis) on a Lineweaver-Burk plot is equal to

When the substrate concentration is equal to Km for a given enzyme and substrate you would expect which of the following?

Hydrolysis of high energy phosphate bonds associated with enzymatic linking of two molecules is catalyzed by what group of enzymes?

A measurement of cooperativity is the

In the case of an enzyme displaying a sigmoid relationship between velocity and substrate concentration, it can be concluded that

Eukaryotic Cell Structure

DNA and RNA: Composition and Structure

Protein I: Composition and Structure

DNA Replication, Recombination, and Repair

RNA: Transcription and Rna Processing

Protein Synthesis: Translation and Posttranslational Modifications

Recombinant Dna and Biotechnology

Regulation of Gene Expression

Protein II: Structure-Function Relationships in Protein Families

The Cytochromes P450 and Nitric Oxide Synthases

Biological Membranes: Structure and Membrane Transport

Fundamentals of Signal Transduction

Bioenergetics and Oxidative Metabolism

Carbohydrate Metabolism I: Major Metabolic Pathways and Their Control

Carbohydrate Metabolism II: Special Pathways and Glycoconjugates

Lipid Metabolism I: Synthesis, Storage, and Utilization of Fatty Acids and Triacylglycerols

Lipid Metabolism II: Pathways of Metabolism of Special Lipids

Amino Acid Metabolism

Purine and Pyrimidine Nucleotide Metabolism

Metabolic Interrelationships

Biochemistry of Hormones

Molecular Cell Biology

Cell Cycle, Programmed Cell Death, and Cancer

Digestion and Absorption of Basic Nutritional Constituents

Digestion and Absorption of Basic Nutritional Constituents

Principles of Nutrition I and II

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