Question 1

Considering the active site of serine protease enzymes, a fair generalization is that:

Accepted Answer

A)  Nearly all of the amino acid R-groups of the protein must directly participate in catalysis. 
B)  All of the amino acid residues which are involved in the active site are adjacent because they are located on the same short stretch of the polypeptide chain. 
C)  The conformation of the active site region does not exist at all until the substrate is bound to the enzyme. 
D)  The amino acid residues which form the active site are in close proximity because of the specific three-dimensional shape the protein adopts in its native state. 
E)  Only one amino acid residue is involved in the active site. 
A)  Nearly all of the amino acid R-groups of the protein must directly participate in catalysis. 
B)  All of the amino acid residues which are involved in the active site are adjacent because they are located on the same short stretch of the polypeptide chain. 
C)  The conformation of the active site region does not exist at all until the substrate is bound to the enzyme. 
D)  The amino acid residues which form the active site are in close proximity because of the specific three-dimensional shape the protein adopts in its native state. 
E)  Only one amino acid residue is involved in the active site.

Question 2

Which of the following represents a covalent modification of an enzyme which can be reversed

Accepted Answer

A)  zymogen to enzyme. 
B)  change in enzyme activity with pH. 
C)  phosphorylation of a serine -OH. 
D)  allosteric modification. 
E)  competitive inhibition. 
A)  zymogen to enzyme. 
B)  change in enzyme activity with pH. 
C)  phosphorylation of a serine -OH. 
D)  allosteric modification. 
E)  competitive inhibition.

Question 3

What is the condition under which an enzyme is defined as having a "ping-pong" mechanism?

Accepted Answer

A)  Enzyme (or enzyme/prosthetic group) is modified by substrate 
B)  The enzyme has a dissociable coenzyme 
C)  The first substrate on and the last product off show competitive binding 
D)  The reaction is bimolecular 
E)  The two substrates bind in a random order 
A)  Enzyme (or enzyme/prosthetic group) is modified by substrate 
B)  The enzyme has a dissociable coenzyme 
C)  The first substrate on and the last product off show competitive binding 
D)  The reaction is bimolecular 
E)  The two substrates bind in a random order

Question 4

A competitive inhibitor

Accepted Answer

A)  forms an irreversible complex with the active site of an enzyme 
B)  forms an irreversible complex with a site on an enzyme other than the active site. 
C)  decreases the maximal velocity of the reaction catalyzed by an enzyme. 
D)  competes with the substrate for the active site of an enzyme. 
E)  lowers the Km for the substrate. 
A)  forms an irreversible complex with the active site of an enzyme 
B)  forms an irreversible complex with a site on an enzyme other than the active site. 
C)  decreases the maximal velocity of the reaction catalyzed by an enzyme. 
D)  competes with the substrate for the active site of an enzyme. 
E)  lowers the Km for the substrate.

Question 5

Magnesium functions intracellularly as

Accepted Answer

A)  an activator for certain enzymes. 
B)  an osmotic element. 
C)  a structural part of mitochondria. 
D)  a structural part of the cell membrane. 
E)  a generalized enzyme inhibitor. 
A)  an activator for certain enzymes. 
B)  an osmotic element. 
C)  a structural part of mitochondria. 
D)  a structural part of the cell membrane. 
E)  a generalized enzyme inhibitor.

Question 6

What happens when substrate concentration is much higher than Km?

Accepted Answer

A)  Equilibrium is reached 
B)  Km is increased 
C)  The rate is equal to Kcat [E] 
D)  The rate is linear 
E)  The reaction cannot continues 
A)  Equilibrium is reached 
B)  Km is increased 
C)  The rate is equal to Kcat [E] 
D)  The rate is linear 
E)  The reaction cannot continues

Question 7

The diagram above shows all the possible reaction steps for a reaction where an inhibitor is present. Which numbered steps are possible in the presence of a competitive inhibitor?

Accepted Answer

A)  1, 2, 3, 4, 5 
B)  1, 2, 3, 4, 6 
C)  1, 2, 3, 6, 7 
D)  1, 4, 5, 8, 9 
E)  (1, 4, 5, 8, 9) 
A)  1, 2, 3, 4, 5 
B)  1, 2, 3, 4, 6 
C)  1, 2, 3, 6, 7 
D)  1, 4, 5, 8, 9 
E)  (1, 4, 5, 8, 9)

Question 8

How many binding constants would there be for a tetrameric enzyme where each monomer can bind substrate in the Monod Wyman Changeux model of allosterism?

Accepted Answer

A)  1 
B)  2 
C)  3 
D)  4 
E)  5 
A)  1 
B)  2 
C)  3 
D)  4 
E)  5

Question 9

Why is the imidazole R-group of histidine a particularly versatile amino acid side chain in terms of its involvement in enzymatic reaction mechanisms?

Accepted Answer

A)  It is strongly involved in specific acid-base catalysis. 
B)  It acts as a strong electrophile. 
C)  It disrupts H-bonds and stabilizes exposed peptide residues. 
D)  It acts as a strong nucleophile as well as a general acid or base. 
E)  It contains a high energy phosphate bond. 
A)  It is strongly involved in specific acid-base catalysis. 
B)  It acts as a strong electrophile. 
C)  It disrupts H-bonds and stabilizes exposed peptide residues. 
D)  It acts as a strong nucleophile as well as a general acid or base. 
E)  It contains a high energy phosphate bond.

Question 10

Induced fit

Accepted Answer

A)  is a conformational change brought about by the binding of substrate to an allosteric site. 
B)  is also known as cooperative binding and requires enzymes with more than one subunit. 
C)  occurs when cholesterol becomes embedded in the lipid bilayer of the plasma membrane. 
D)  is the change in the absorption spectrum of an enzyme upon formation of ES complex. 
E)  is a conformational change evoked by binding of substrate to the active site of an enzyme. 
A)  is a conformational change brought about by the binding of substrate to an allosteric site. 
B)  is also known as cooperative binding and requires enzymes with more than one subunit. 
C)  occurs when cholesterol becomes embedded in the lipid bilayer of the plasma membrane. 
D)  is the change in the absorption spectrum of an enzyme upon formation of ES complex. 
E)  is a conformational change evoked by binding of substrate to the active site of an enzyme.

Question 11

Which is LEAST likely to be characteristic of a regulated enzyme in a metabolic pathway?

Accepted Answer

A)  catalyzes the slowest step of the pathway 
B)  has a short half-life in vivo 
C)  concentration is hormonally regulated 
D)  activity under allosteric control 
E)  catalyzes a physiologically reversible reaction 
A)  catalyzes the slowest step of the pathway 
B)  has a short half-life in vivo 
C)  concentration is hormonally regulated 
D)  activity under allosteric control 
E)  catalyzes a physiologically reversible reaction

Question 12

Specific activity of an enzyme refers to

Accepted Answer

A)  the ratio of units of enzyme activity (initial rate in the presence of excess substrate) to the weight of protein in a given preparation. 
B)  the catalytic activity of an enzyme under Vmax conditions. 
C)  the amount of enzyme transforming 1 mole of substrate per second under standard conditions. 
D)  the ratio of the activity of an enzyme in an unknown sample to that of a standard or known sample under identical conditions. 
E)  the activity of an enzyme under specific conditions of first-order kinetics. 
A)  the ratio of units of enzyme activity (initial rate in the presence of excess substrate) to the weight of protein in a given preparation. 
B)  the catalytic activity of an enzyme under Vmax conditions. 
C)  the amount of enzyme transforming 1 mole of substrate per second under standard conditions. 
D)  the ratio of the activity of an enzyme in an unknown sample to that of a standard or known sample under identical conditions. 
E)  the activity of an enzyme under specific conditions of first-order kinetics.

Question 13

High concentrations of substrate overcome reversible inhibition by a transition-state analog because

Accepted Answer

A)  only the substrate has the inherent ability to bind at the active-site. 
B)  the substrate has a greater inherent affinity for the active-site. 
C)  transition-state analogs show noncompetitive kinetics. 
D)  the substrate will react with the transition-state analog. 
E)  The transition-state analog is a competitive inhibitor. 
A)  only the substrate has the inherent ability to bind at the active-site. 
B)  the substrate has a greater inherent affinity for the active-site. 
C)  transition-state analogs show noncompetitive kinetics. 
D)  the substrate will react with the transition-state analog. 
E)  The transition-state analog is a competitive inhibitor.

Question 14

For an enzyme-substrate pair, a graph of reaction rate versus substrate concentration gives an S-shaped curve. From these data which of the following is the most likely conclusion?

Accepted Answer

A)  The enzyme conforms closely to Michaelis-Menten kinetics. 
B)  The enzyme contains more than one kind of polypeptide chain. 
C)  At high concentrations, the substrate is an inhibitor of the reaction. 
D)  More than one binding site for the substrate is present in each enzyme subunit. 
E)  The enzyme is subject to product inhibition. 
A)  The enzyme conforms closely to Michaelis-Menten kinetics. 
B)  The enzyme contains more than one kind of polypeptide chain. 
C)  At high concentrations, the substrate is an inhibitor of the reaction. 
D)  More than one binding site for the substrate is present in each enzyme subunit. 
E)  The enzyme is subject to product inhibition.

Question 15

The Lineweaver-Burk plot gives

Accepted Answer

A)  1/Vmax as the intercept at 1/S = 0. 
B)  Km/Vmax as the intercept at 1/S = 0. 
C)  1/Km as the intercept at 1/S = 0. 
D)  Vmax/Km as the intercept at 1/S = 0. 
E)  none of the above. 
A)  1/Vmax as the intercept at 1/S = 0. 
B)  Km/Vmax as the intercept at 1/S = 0. 
C)  1/Km as the intercept at 1/S = 0. 
D)  Vmax/Km as the intercept at 1/S = 0. 
E)  none of the above.

Question 16

Creatine kinase (CK) activity is used as an early indicator and the LDH activity is used as an delayed indicator of myocardial infarction. This difference in time of appearance in serum is influenced by

Accepted Answer

A)  molecular mass 
B)  half-life of the enzyme in blood 
C)  association of the enzyme with cellular components 
D)  all of the above 
E)  none of the above 
A)  molecular mass 
B)  half-life of the enzyme in blood 
C)  association of the enzyme with cellular components 
D)  all of the above 
E)  none of the above

Question 17

An enzyme transition state inhibitor

Accepted Answer

A)  would probably bind much more tightly than a normal substrate. 
B)  probably would be a noncompetitive inhibitor of an enzyme. 
C)  would probably bind much less tightly than a normal substrate. 
D)  would have a Ki about equal to the Km for the substrate. 
A)  would probably bind much more tightly than a normal substrate. 
B)  probably would be a noncompetitive inhibitor of an enzyme. 
C)  would probably bind much less tightly than a normal substrate. 
D)  would have a Ki about equal to the Km for the substrate.

Question 18

Enzymes that contain aspartate or glutamate at the active site would most likely be involved in what type of catalysis?

Accepted Answer

A)  Induced fit 
B)  Destabilization 
C)  Acid Base Catalysis 
D)  Covalent catalysis 
E)  none of the above 
A)  Induced fit 
B)  Destabilization 
C)  Acid Base Catalysis 
D)  Covalent catalysis 
E)  none of the above

Question 19

If an inorganic ion such as Mg2+ is required for enzyme activity, it is usually described as a

Accepted Answer

A)  coenzyme 
B)  prosthetic group 
C)  holoenzyme 
D)  cofactor 
E)  apoenzyme 
A)  coenzyme 
B)  prosthetic group 
C)  holoenzyme 
D)  cofactor 
E)  apoenzyme

Question 20

Allosteric control of enzyme action requires

Accepted Answer

A)  a cofactor derived from a vitamin. 
B)  a metal ion. 
C)  the conversion of one form of the enzyme to another by the action of proteolytic enzymes. 
D)  a conformational change in an enzyme that changes its catalytic activity. 
E)  an effector that is the product of the enzymatic reaction and which competes for the active site of the enzyme. 
A)  a cofactor derived from a vitamin. 
B)  a metal ion. 
C)  the conversion of one form of the enzyme to another by the action of proteolytic enzymes. 
D)  a conformational change in an enzyme that changes its catalytic activity. 
E)  an effector that is the product of the enzymatic reaction and which competes for the active site of the enzyme.

Exam 10: Enzymes: Classification, Kinetics, and Control

Considering the active site of serine protease enzymes, a fair generalization is that:

Which of the following represents a covalent modification of an enzyme which can be reversed

What is the condition under which an enzyme is defined as having a "ping-pong" mechanism?

A competitive inhibitor

Magnesium functions intracellularly as

What happens when substrate concentration is much higher than Km?

The diagram above shows all the possible reaction steps for a reaction where an inhibitor is present. Which numbered steps are possible in the presence of a competitive inhibitor?

How many binding constants would there be for a tetrameric enzyme where each monomer can bind substrate in the Monod Wyman Changeux model of allosterism?

Why is the imidazole R-group of histidine a particularly versatile amino acid side chain in terms of its involvement in enzymatic reaction mechanisms?

Induced fit

Which is LEAST likely to be characteristic of a regulated enzyme in a metabolic pathway?

Specific activity of an enzyme refers to

High concentrations of substrate overcome reversible inhibition by a transition-state analog because

For an enzyme-substrate pair, a graph of reaction rate versus substrate concentration gives an S-shaped curve. From these data which of the following is the most likely conclusion?

The Lineweaver-Burk plot gives

Creatine kinase (CK) activity is used as an early indicator and the LDH activity is used as an delayed indicator of myocardial infarction. This difference in time of appearance in serum is influenced by

An enzyme transition state inhibitor

Enzymes that contain aspartate or glutamate at the active site would most likely be involved in what type of catalysis?

If an inorganic ion such as Mg2+ is required for enzyme activity, it is usually described as a

Allosteric control of enzyme action requires

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

Filters

If an inorganic ion such as Mg²⁺ is required for enzyme activity, it is usually described as a