Question 1

Which statement is TRUE of enzyme catalysts?

Accepted Answer

A)  Their catalytic activity is independent of pH. 
B)  They are generally equally active on D and L isomers of a given substrate. 
C)  They can increase the equilibrium constant for a given reaction by a thousand fold or more. 
D)  They can increase the reaction rate for a given reaction by a thousand-fold or more. 
E)  To be effective, they must be present at the same concentration as their substrate. 
A)  Their catalytic activity is independent of pH. 
B)  They are generally equally active on D and L isomers of a given substrate. 
C)  They can increase the equilibrium constant for a given reaction by a thousand fold or more. 
D)  They can increase the reaction rate for a given reaction by a thousand-fold or more. 
E)  To be effective, they must be present at the same concentration as their substrate.

Question 2

For the reaction E + S $\rightarrow$ ES $\rightarrow$  P the Michaelis-Menten constant, Km, is actually a summary of three terms. What are they? How is Km determined graphically?

Accepted Answer

The Michaelis-Menten constant, K_m</

Question 3

Which statement BEST describes why niacin is required in the mammalian diet?

Accepted Answer

A)  Niacin is a precursor of nicotinamide adenine dinucleotide (NA
D) , which is a coenzyme required by many oxidoreductase enzymes. 
B)  Niacin is a precursor of flavin adenine dinucleotide (FA
D) , which is a coenzyme required by many ligases. 
C)  Niacin is a precursor of thiamine pyrophosphate, which is a coenzyme required by many transferases. 
D)  Niacin is a component of coenzyme A, which is involved in many transferase reactions. 
E)  Niacin is not actually required in the mammalian diet. 
A)  Niacin is a precursor of nicotinamide adenine dinucleotide (NA
D) , which is a coenzyme required by many oxidoreductase enzymes. 
B)  Niacin is a precursor of flavin adenine dinucleotide (FA
D) , which is a coenzyme required by many ligases. 
C)  Niacin is a precursor of thiamine pyrophosphate, which is a coenzyme required by many transferases. 
D)  Niacin is a component of coenzyme A, which is involved in many transferase reactions. 
E)  Niacin is not actually required in the mammalian diet.

Question 4

Chymotrypsin catalyzes the cleavage of proteins at peptide bonds adjacent to aromatic amino acid residues by using which catalytic mechanism?

Accepted Answer

A)  general acid-base catalysis 
B)  metal ion catalysis 
C)  covalent catalysis 
D)  both general acid-base catalysis and metal ion catalysis 
E)  both general acid-base catalysis and covalent catalysis 
A)  general acid-base catalysis 
B)  metal ion catalysis 
C)  covalent catalysis 
D)  both general acid-base catalysis and metal ion catalysis 
E)  both general acid-base catalysis and covalent catalysis

Question 5

In competitive inhibition, an inhibitor:

Accepted Answer

A)  binds at several different sites on an enzyme. 
B)  binds covalently to the enzyme. 
C)  binds only to the ES complex. 
D)  binds reversibly at the active site. 
E)  lowers the characteristic Vmax of the enzyme. 
A)  binds at several different sites on an enzyme. 
B)  binds covalently to the enzyme. 
C)  binds only to the ES complex. 
D)  binds reversibly at the active site. 
E)  lowers the characteristic Vmax of the enzyme.

Question 6

How is trypsinogen converted to trypsin?

Accepted Answer

A)  A protein kinase-catalyzed phosphorylation converts trypsinogen to trypsin. 
B)  An increase in Ca2+ concentration promotes the conversion. 
C)  Proteolysis of trypsinogen forms trypsin. 
D)  Trypsinogen dimers bind an allosteric modulator, cAMP, causing dissociation into active trypsin monomers. 
E)  Two inactive trypsinogen dimers pair to form an active trypsin tetramer. 
A)  A protein kinase-catalyzed phosphorylation converts trypsinogen to trypsin. 
B)  An increase in Ca2+ concentration promotes the conversion. 
C)  Proteolysis of trypsinogen forms trypsin. 
D)  Trypsinogen dimers bind an allosteric modulator, cAMP, causing dissociation into active trypsin monomers. 
E)  Two inactive trypsinogen dimers pair to form an active trypsin tetramer.

Question 7

Two different enzymes are able to catalyze the same reaction, A $\rightarrow$  B. They both have the same Vmax, but differ their Km the substrate A. For enzyme 1, the Km is 1.0 mM; for enzyme 2, the Km is 10 mM. When enzyme 1 was incubated with 0.1 mM A, it was observed that B was produced at a rate of 0.0020 mmoles/minute. a) What is the value of the Vmax of the enzymes? b) What will be the rate of production of B when enzyme 2 is incubated with 0.1 mM A? c) What will be the rate of production of B when enzyme 1 is incubated with 1 M (i.e., 1000 mM) A?

Accepted Answer

To answer these questions, we need to ap

Question 8

The HIV protease enzyme uses a general acid-base catalysis mechanism to cleave viral polypeptides but does not use a covalent catalysis. This enzyme functions optimally in the pH range of 4-6. Due to the specific amino acids involved in this catalysis, HIV protease is a member of which subclass of proteases?

Accepted Answer

A)  metalloproteases 
B)  serine proteases 
C)  aspartyl proteases 
D)  cysteine proteases 
E)  lysine proteases 
A)  metalloproteases 
B)  serine proteases 
C)  aspartyl proteases 
D)  cysteine proteases 
E)  lysine proteases

Question 9

An enzyme catalyzes a reaction at a velocity of 20 $\mu$mol/min when the concentration of substrate (S) is 0.01 M. The Km for this substrate is 1 × 10-5 M. Assuming that Michaelis-Menten kinetics are followed, what will the reaction velocity be when the concentration of S is (a) 1 × 10-5 M and (b) 1 × 10-6 M?

Accepted Answer

To answer this question, we will use the

Question 10

Which enzyme uses general acid-base catalysis and/or covalent catalysis mechanisms to hydrolyze peptidoglycan?

Accepted Answer

A)  enolase 
B)  lysozyme 
C)  chymotrypsin 
D)  pepsin 
E)  $\beta$ lactamase 
A)  enolase 
B)  lysozyme 
C)  chymotrypsin 
D)  pepsin 
E)  $\beta$ lactamase

Question 11

The enzymatic activity of lysozyme is optimal at pH 5.2 and decreases above and below this pH value. Lysozyme contains two amino acid residues in the active site essential for catalysis: Glu35 and Asp52. The pK value for the carboxyl side chains of these two residues are 5.9 and 4.5, respectively. What is the ionization state of each residue at the pH optimum of lysozyme? How can the ionization states of these two amino acid residues explain the pH-activity profile of lysozyme?

Accepted Answer

At the pH optimum of 5.2, the ionization

Question 12

Michaelis and Menten assumed that the overall reaction for an enzyme-catalyzed reaction could be written as:   Using this reaction, the rate of breakdown of the enzyme-substrate complex can be described by the expression:

Accepted Answer

A)  k1 ([Et] - [ES]). 
B)  k1 ([Et] - [ES])[S]. 
C)  k2 [ES]. 
D)  k-1 [ES] + k2 [ES]. 
E)  k-1 [ES]. 
A)  k1 ([Et] - [ES]). 
B)  k1 ([Et] - [ES])[S]. 
C)  k2 [ES]. 
D)  k-1 [ES] + k2 [ES]. 
E)  k-1 [ES].

Question 13

A double-reciprocal plot of 1/V0 versus 1/[S] for an enzyme in the presence of increasing concentrations of an uncompetitive inhibitor will have lines corresponding to the differentinhibitor concentrations that are BEST described by which statement?

Accepted Answer

A)  The lines will intersect at the x-axis to the left of the y-axis. 
B)  The lines will cross the y-axis and will be parallel to each other. 
C)  The lines will intersect to the left of the y-axis but above the x-axis. 
D)  The lines will intersect below the x-axis, to the right of the y-axis. 
E)  The lines will be parallel to each other but will not cross the y-axis. 
A)  The lines will intersect at the x-axis to the left of the y-axis. 
B)  The lines will cross the y-axis and will be parallel to each other. 
C)  The lines will intersect to the left of the y-axis but above the x-axis. 
D)  The lines will intersect below the x-axis, to the right of the y-axis. 
E)  The lines will be parallel to each other but will not cross the y-axis.

Question 14

Compare the two reaction coordinate diagrams below and select the answer that CORRECTLY describes their relationship. In each case, the single intermediate is the ES complex.

Accepted Answer

A)  (a) describes a strict "lock and key" model, whereas (b) describes a transition-state complementarity model. 
B)  The activation energy for the catalyzed reaction is 5 in (a) and is 7 in (b). 
C)  The activation energy for the uncatalyzed reaction is given by 5 + 6 in (a) and by 7 + 4 in (b). 
D)  The contribution of binding energy is given by 5 in (a) and by 7 in (b). 
E)  The ES complex is given by 2 in (a) and 3 in (b). 
A)  (a) describes a strict "lock and key" model, whereas (b) describes a transition-state complementarity model. 
B)  The activation energy for the catalyzed reaction is 5 in (a) and is 7 in (b). 
C)  The activation energy for the uncatalyzed reaction is given by 5 + 6 in (a) and by 7 + 4 in (b). 
D)  The contribution of binding energy is given by 5 in (a) and by 7 in (b). 
E)  The ES complex is given by 2 in (a) and 3 in (b).

Question 15

If you were attempting to design a new drug for the treatment of a disease by interfering with enzyme activity in the disease-causing organism, which type of inhibitor would likely be the MOST effective?

Accepted Answer

A)  a transition-state analog that is an irreversible inhibitor 
B)  a substrate analog that is a competitive inhibitor 
C)  a transition-state analog that is a competitive inhibitor 
D)  a product analog that is an uncompetitive inhibitor 
E)  a substrate analog that is a mixed inhibitor 
A)  a transition-state analog that is an irreversible inhibitor 
B)  a substrate analog that is a competitive inhibitor 
C)  a transition-state analog that is a competitive inhibitor 
D)  a product analog that is an uncompetitive inhibitor 
E)  a substrate analog that is a mixed inhibitor

Question 16

Blood coagulation involves:

Accepted Answer

A)  a kinase cascade. 
B)  zymogen activation. 
C)  serine proteases. 
D)  both a kinase cascade and zymogen activation. 
E)  both zymogen activation and serine proteases. 
A)  a kinase cascade. 
B)  zymogen activation. 
C)  serine proteases. 
D)  both a kinase cascade and zymogen activation. 
E)  both zymogen activation and serine proteases.

Question 17

Which amino acid is NOT one that may be targeted for phosphorylation to modulate the activity of an enzyme?

Accepted Answer

A)  Tyr 
B)  His 
C)  Ser 
D)  Ala 
E)  Thr 
A)  Tyr 
B)  His 
C)  Ser 
D)  Ala 
E)  Thr

Question 18

A biochemist obtains the following set of data for an enzyme that is known to follow Michaelis-Menten kinetics.
Substrate
Initial
concentration
velocity
($\mu$M)
($\mu$mol/min)
1
49
2
96
8
349
50
621
100
676
1,000
698
5,000
699
(a) Vmax for the enzyme is _____. Explain in one sentence how you determined Vmax.
(b) Km for the enzyme is _____. Explain in one sentence how you determined Km.

Accepted Answer

(a) Vmax for the enzyme is 699 @#LAT-DLM&mol/min.

Question 19

Leucine biosynthesis occurs in a multistep pathway starting from 2-oxovalerate, and the final product of the pathway (leucine) inhibits the first enzyme involved in the biosynthetic pathway through a process called feedback inhibition. This enzyme inhibition occurs, regardless of whether or not the 2-oxovalerate substrate is bound in the active site of the enzyme. Describe what type of inhibitor leucine is and justify your response.

Accepted Answer

Leucine is a non-competitive inhibitor.

Question 20

What is a zymogen (proenzyme)? Explain briefly with an example.

Accepted Answer

A zymogen, also known as a proenzyme, is

Exam 6: Enzymes

Which statement is TRUE of enzyme catalysts?

For the reaction E + S →\rightarrow→ ES →\rightarrow→ P the Michaelis-Menten constant, Km, is actually a summary of three terms. What are they? How is Km determined graphically?

Which statement BEST describes why niacin is required in the mammalian diet?

Chymotrypsin catalyzes the cleavage of proteins at peptide bonds adjacent to aromatic amino acid residues by using which catalytic mechanism?

In competitive inhibition, an inhibitor:

How is trypsinogen converted to trypsin?

Which enzyme uses general acid-base catalysis and/or covalent catalysis mechanisms to hydrolyze peptidoglycan?

Michaelis and Menten assumed that the overall reaction for an enzyme-catalyzed reaction could be written as: Using this reaction, the rate of breakdown of the enzyme-substrate complex can be described by the expression:

A double-reciprocal plot of 1/V0 versus 1/[S] for an enzyme in the presence of increasing concentrations of an uncompetitive inhibitor will have lines corresponding to the differentinhibitor concentrations that are BEST described by which statement?

Compare the two reaction coordinate diagrams below and select the answer that CORRECTLY describes their relationship. In each case, the single intermediate is the ES complex.

If you were attempting to design a new drug for the treatment of a disease by interfering with enzyme activity in the disease-causing organism, which type of inhibitor would likely be the MOST effective?

Blood coagulation involves:

Which amino acid is NOT one that may be targeted for phosphorylation to modulate the activity of an enzyme?

What is a zymogen (proenzyme)? Explain briefly with an example.

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

Lipids

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

For the reaction E + S $\rightarrow$ ES $\rightarrow$ P the Michaelis-Menten constant, K_m, is actually a summary of three terms. What are they? How is K_m determined graphically?

A double-reciprocal plot of 1/V₀ versus 1/[S] for an enzyme in the presence of increasing concentrations of an uncompetitive inhibitor will have lines corresponding to the differentinhibitor concentrations that are BEST described by which statement?