Question 1

Which of the following amino acid residues are often involved in proton transfers in enzyme-catalyzed reactions?

Accepted Answer

A)  Histidine, aspartate, serine, and cysteine 
B)  Serine, tyrosine, arginine, and cysteine 
C)  Glutamine, asparagine, lysine, and tyrosine 
D)  Histidine, aspartate, lysine, and serine 
E)  Histidine, aspartate, glutamate, arginine, and lysine 
A)  Histidine, aspartate, serine, and cysteine 
B)  Serine, tyrosine, arginine, and cysteine 
C)  Glutamine, asparagine, lysine, and tyrosine 
D)  Histidine, aspartate, lysine, and serine 
E)  Histidine, aspartate, glutamate, arginine, and lysine E

Question 2

Which of the following statements BEST describes the Michaelis-Menton constant KM?

Accepted Answer

A)  It is numerically equal to the affinity between the enzyme and its substrate. 
B)  It is numerically equal to the substrate concentration required to reach half maximal velocity for an enzyme-catalyzed reaction. 
C)  It is a measure of the rate of a catalytic process. 
D)  It is a measure of enzyme efficiency. 
E)  It has units of concentration. 
A)  It is numerically equal to the affinity between the enzyme and its substrate. 
B)  It is numerically equal to the substrate concentration required to reach half maximal velocity for an enzyme-catalyzed reaction. 
C)  It is a measure of the rate of a catalytic process. 
D)  It is a measure of enzyme efficiency. 
E)  It has units of concentration. B

Question 3

A graph of initial velocity vs substrate concentration will be ________ for an enzyme that obeys Michaelis-Menton kinetics.

Accepted Answer

hyperbolic

Question 4

The equilibrium state of a biochemical reaction is approached ________ in the presence of a catalyst.

Accepted Answer

The answer of The equilibrium state of a biochemical reaction...

Question 5

Which of the following statements about the proposed mechanisms of action for hen egg white lysozyme does NOT support either model?

Accepted Answer

A)  Glycosidic bond cleavage occurs by general acid/base catalysis. 
B)  A covalent intermediate is formed between an active site aspartate and C1 of the substrate. 
C)  A water molecule is deprotonated, which then attacks C1 of the substrate. 
D)  The active site aspartic acid changes between being protonated and deprotonated. 
E)  The active site glutamic acid changes between being protonated and deprotonated. 
A)  Glycosidic bond cleavage occurs by general acid/base catalysis. 
B)  A covalent intermediate is formed between an active site aspartate and C1 of the substrate. 
C)  A water molecule is deprotonated, which then attacks C1 of the substrate. 
D)  The active site aspartic acid changes between being protonated and deprotonated. 
E)  The active site glutamic acid changes between being protonated and deprotonated.

Question 6

The ________ hypothesis suggests that an enzyme can induce distortion of the substrate or the substrate can induce conformational changes in the enzyme that stabilize the transition state.

Accepted Answer

The answer of The ________ hypothesis suggests that an enzyme...

Question 7

The equilibrium constant for a first-order ________ reaction is equivalent to the ratio of the rate constant for the forward and reverse reactions.

Accepted Answer

The answer of The equilibrium constant for a first-order ________...

Question 8

Metal ions are often required for catalytic efficiency but they may not remain permanently bound to the protein or take part in the catalytic process.

Accepted Answer

A) True 
 B)False

Question 9

Which of the following statements about inhibitors of enzyme-catalyzed reactions is TRUE?

Accepted Answer

A)  An uncompetitive inhibitor typically affects KM but not kcat. 
B)  A competitive inhibitor does not affect Vmax. 
C)  An uncompetitive inhibitor will always bind at the active site. 
D)  A competitive inhibitor binds irreversibly to the enzyme at the active site. 
E)  Reversible inhibitors bind to either free enzyme or the enzyme-substrate complex but not both. 
A)  An uncompetitive inhibitor typically affects KM but not kcat. 
B)  A competitive inhibitor does not affect Vmax. 
C)  An uncompetitive inhibitor will always bind at the active site. 
D)  A competitive inhibitor binds irreversibly to the enzyme at the active site. 
E)  Reversible inhibitors bind to either free enzyme or the enzyme-substrate complex but not both.

Question 10

Catalysts affect the thermodynamic f of a chemical reaction.

Accepted Answer

A) True 
 B)False

Question 11

Electrostatic catalysis proceeds via covalent bonding interactions.

Accepted Answer

A) True 
 B)False

Question 12

A second-order reaction:

Accepted Answer

A)  occurs when one substrate is converted into one product. 
B)  is characterized by two molecules coming together to form a product. 
C)  is the rate-limiting step of a reaction. 
D)  has a rate constant with units of (time)-1. 
E)  only occurs in multistep processes. 
A)  occurs when one substrate is converted into one product. 
B)  is characterized by two molecules coming together to form a product. 
C)  is the rate-limiting step of a reaction. 
D)  has a rate constant with units of (time)-1. 
E)  only occurs in multistep processes.

Question 13

Pyruvate carboxylase is an example of the ligase class of enzymes.

Accepted Answer

A) True 
 B)False

Question 14

Proteolytic cleavage is an example of an ________ post-translational modification.

Accepted Answer

The answer of Proteolytic cleavage is an example of an...

Question 15

Covalent modification can either activate or inhibit enzymes.

Accepted Answer

A) True 
 B)False

Question 16

The lock and key model of substrate binding and enzymatic catalysis explains:

Accepted Answer

A)  the release of product. 
B)  substrate specificity. 
C)  formation of a transition state. 
D)  the catalytic mechanism. 
E)  structural changes that occur on substrate binding. 
A)  the release of product. 
B)  substrate specificity. 
C)  formation of a transition state. 
D)  the catalytic mechanism. 
E)  structural changes that occur on substrate binding.

Question 17

Protein kinases add a phosphoryl group to the -OH group of a ________, ________, or ________ residue of the target protein.

Accepted Answer

serine, ty

Question 18

Serine proteases make use of covalent catalysis as well as electrostatic stability of the transition state to achieve rate enhancement.

Accepted Answer

A) True 
 B)False

Question 19

A Lineweaver-Burk plot for a first order enzyme-catalyzed reaction gives values of 1/KM = 2.5 × 104 (M)-1 and 1/Vmax of 1.25 × 10-2 (µmolL-1 sec-1)-1. Calculate the rate constant k.

Accepted Answer

The answer of A Lineweaver-Burk plot for a first order...

Question 20

In an enzyme-catalyzed reaction, the lifetime of the transition state is similar to the vibrational frequencies of covalent bonds.

Accepted Answer

A) True 
 B)False

Exam 8: Enzymes: Biological Catalysts

Which of the following amino acid residues are often involved in proton transfers in enzyme-catalyzed reactions?

Which of the following statements BEST describes the Michaelis-Menton constant KM?

A graph of initial velocity vs substrate concentration will be ________ for an enzyme that obeys Michaelis-Menton kinetics.

The equilibrium state of a biochemical reaction is approached ________ in the presence of a catalyst.

Which of the following statements about the proposed mechanisms of action for hen egg white lysozyme does NOT support either model?

The ________ hypothesis suggests that an enzyme can induce distortion of the substrate or the substrate can induce conformational changes in the enzyme that stabilize the transition state.

The equilibrium constant for a first-order ________ reaction is equivalent to the ratio of the rate constant for the forward and reverse reactions.

Metal ions are often required for catalytic efficiency but they may not remain permanently bound to the protein or take part in the catalytic process.

Which of the following statements about inhibitors of enzyme-catalyzed reactions is TRUE?

Catalysts affect the thermodynamic f of a chemical reaction.

Electrostatic catalysis proceeds via covalent bonding interactions.

A second-order reaction:

Pyruvate carboxylase is an example of the ligase class of enzymes.

Proteolytic cleavage is an example of an ________ post-translational modification.

Covalent modification can either activate or inhibit enzymes.

The lock and key model of substrate binding and enzymatic catalysis explains:

Protein kinases add a phosphoryl group to the -OH group of a ________, ________, or ________ residue of the target protein.

Serine proteases make use of covalent catalysis as well as electrostatic stability of the transition state to achieve rate enhancement.

A Lineweaver-Burk plot for a first order enzyme-catalyzed reaction gives values of 1/KM = 2.5 × 104 (M)-1 and 1/Vmax of 1.25 × 10-2 (µmolL-1 sec-1)-1. Calculate the rate constant k.

In an enzyme-catalyzed reaction, the lifetime of the transition state is similar to the vibrational frequencies of covalent bonds.

Biochemistry and the Language of Chemistry

The Chemical Foundation of Life: Weak Interactions in an Aqueous Environment

The Energetics of Life

Nucleic Acids

Introduction to Proteins: the Primary Level of Protein Structure

The Three-Dimensional Structure of Proteins

Protein Function and Evolution

Carbohydrates: Sugars, Saccharides, Glycans

Lipids, Membranes, and Cellular Transport

Chemical Logic of Metabolism

Carbohydrate Metabolism: Glycolysis, Gluconeogenesis, Glycogen Metabolism, and the Pentose Phosphate Pathway

The Citric Acid Cycle

Electron Transport, Oxidative Phosphorylation, and Oxygen Metabolism

Photosynthesis

Lipid Metabolism

Interorgan and Intracellular Coordination of Energy Metabolism in Vertebrates

Amino Acid and Nitrogen Metabolism

Nucleotide Metabolism

Mechanisms of Signal Transduction

Genes, Genomes, and Chromosomes

DNA Replication

DNA Repair, Recombination, and Rearrangement

Transcription and Post-Transcriptional Processing

Information Decoding: Translation and Post-Translational Protein Processing

Regulation of Gene Expression

Filters

Protein kinases add a phosphoryl group to the -OH group of a , , or residue of the target protein.