Question 1

In the mechanism of chymotrypsin,which of the following amino acids found in the active site is correctly defined in terms of its role in the reaction?

Accepted Answer

A) serine: hydrogen bonds with carbonyl oxygen to withdraw electron density from the substrate 
B) histidine: deprotonates aspartic acid to allow a nucleophilic attack to occur 
C) aspartic acid: electrostatic stabilization of histidine to make a stronger base 
D) cysteine: performs a nucleophilic attack on the carbonyl carbon of the substrate 
E) none of the above 
A) serine: hydrogen bonds with carbonyl oxygen to withdraw electron density from the substrate 
B) histidine: deprotonates aspartic acid to allow a nucleophilic attack to occur 
C) aspartic acid: electrostatic stabilization of histidine to make a stronger base 
D) cysteine: performs a nucleophilic attack on the carbonyl carbon of the substrate 
E) none of the above C

Question 2

A plot of enzyme activity with and without an inhibitor present gave the following plot.What type of inhibitor is present? How does this inhibitor function? What changes are seen in Vmax and KM? Draw a line that approximates the result from addition of twice as much inhibitor to the reaction.

Accepted Answer

A competitive inhibitor is present which functions by binding to the active site and competing with the substrate.V_max does not change while K_M appears to increase.Addition of twice the concentration of inhibitor would give the bold line in the plot below.

Question 3

Given the chymotrypsin catalytic triad and the peptide substrate,draw the first tetrahedral intermediate of the chymotrypsin mechanism.

Accepted Answer

The answer of Given the chymotrypsin catalytic triad and the...

Question 4

Below is a curve for the enzyme glycogen phosphorylase without any allosteric effectors present showing velocity as a function of the substrate,orthophosphate (Pi).Draw and label a curve that shows the result of addition of the allosteric activator,AMP.Draw and label a curve that shows the result of addition of the allosteric inhibitor,ATP.Glycogen phosphorylase is activated by phosphorylation.Which of these three curves most resembles what happens when glycogen phosphorylase is phosphorylated?

Accepted Answer

@#IMG-DLM& The curve with AMP

Question 5

In noncompetitive inhibition,which of the following best explains how the inhibitor binds to the enzyme?

Accepted Answer

A) the inhibitor binds to the active site only after the substrate binds 
B) the inhibitor binds to a site other than the active site only before the substrate binds 
C) the inhibitor binds to a site other than the active site only after the substrate binds 
D) the inhibitor binds to a site other than the active site either before or after the substrate binds 
E) none of the above 
A) the inhibitor binds to the active site only after the substrate binds 
B) the inhibitor binds to a site other than the active site only before the substrate binds 
C) the inhibitor binds to a site other than the active site only after the substrate binds 
D) the inhibitor binds to a site other than the active site either before or after the substrate binds 
E) none of the above

Question 6

If an enzyme gave a rate enhancement of 3.4 $\times$ 107 over the noncatalyzed reaction,what is the $\Delta$$\Delta$GS1U1P1$\circ$S1S1P0‡ at 37S1U1P1$\circ$S1S1P0C?

Accepted Answer

A) 5)3 kJ/mol 
B) 45 kJ/mol 
C) 9)5 kJ/mol 
D) 19 kJ/mol 
E) none of the above 
A) 5)3 kJ/mol 
B) 45 kJ/mol 
C) 9)5 kJ/mol 
D) 19 kJ/mol 
E) none of the above

Question 7

Which of the following cofactors is used during the activation and transfer of carbon dioxide?

Accepted Answer

A) nicotinamide adenine dinucleotide (NA
D)  
B) thiamine pyrophosphate 
C) biotin 
D) coenzyme A 
E) tetrahydrofolate 
A) nicotinamide adenine dinucleotide (NA
D)  
B) thiamine pyrophosphate 
C) biotin 
D) coenzyme A 
E) tetrahydrofolate

Question 8

What are the expected changes in kinetics in the presence of a competitive inhibitor?

Accepted Answer

A) Vmax decreases,KM appears to decrease 
B) Vmax does not change,KM appears to decrease 
C) Vmax decreases,KM appears to increase 
D) Vmax does not change,KM appears to increase 
E) Vmax decreases,KM does not change 
A) Vmax decreases,KM appears to decrease 
B) Vmax does not change,KM appears to decrease 
C) Vmax decreases,KM appears to increase 
D) Vmax does not change,KM appears to increase 
E) Vmax decreases,KM does not change

Question 9

The activity of lysozyme is greater than 50% of maximum between pH 3.8 and 6.1 with peak activity occurring around pH 5.Below 3.8 and above 6.1,the activity drops rapidly.Which of the following provides the best explanation for this?

Accepted Answer

A) two histidine residues in the active site must be protonated for enzyme activity 
B) the active site contains an aspartic acid and glutamic acid,both of which must be deprotonated 
C) the active site contains an aspartic acid that must be deprotonated and a glutamic acid that must be protonated 
D) the active site contains a histidine that must be protonated and a glutamic acid that must be deprotonated 
E) none of the above 
A) two histidine residues in the active site must be protonated for enzyme activity 
B) the active site contains an aspartic acid and glutamic acid,both of which must be deprotonated 
C) the active site contains an aspartic acid that must be deprotonated and a glutamic acid that must be protonated 
D) the active site contains a histidine that must be protonated and a glutamic acid that must be deprotonated 
E) none of the above

Question 10

What type of inhibitor would give the results seen in the following plot?

Accepted Answer

A) competitive inhibitor 
B) mixed inhibitor 
C) noncompetitive inhibitor 
D) uncompetitive inhibitor 
E) none of the above 
A) competitive inhibitor 
B) mixed inhibitor 
C) noncompetitive inhibitor 
D) uncompetitive inhibitor 
E) none of the above

Question 11

Which of the following explains why enzymes are extremely effective catalysts?

Accepted Answer

A) an enzyme stabilizes the transition state 
B) enzymes bind very tightly to substrates 
C) enzymes release products very rapidly 
D) an enzyme can convert a normally endergonic reaction into an exergonic reaction 
E) an enzyme lowers the energy of activation only for the forward reaction 
A) an enzyme stabilizes the transition state 
B) enzymes bind very tightly to substrates 
C) enzymes release products very rapidly 
D) an enzyme can convert a normally endergonic reaction into an exergonic reaction 
E) an enzyme lowers the energy of activation only for the forward reaction

Question 12

An enzymatic reaction has a Vmax of 100 $\mu$M/min.At a substrate concentration of 5 $\mu$M,the velocity is 25 $\mu$M/min.What is the KM for the reaction?

Accepted Answer

A) 5 $\mu$M 
B) 10 $\mu$M 
C) 15 $\mu$M 
D) 20 $\mu$M 
E) none of the above 
A) 5 $\mu$M 
B) 10 $\mu$M 
C) 15 $\mu$M 
D) 20 $\mu$M 
E) none of the above

Question 13

What must be true if KM is truly a measure of the affinity of enzyme and substrate?

Accepted Answer

A) kcat must be larger than KM 
B) kcat must be smaller than KM 
C) kcat must be about equal to k1 
D) kcat must be much smaller than k-1 
E) kcat must be much larger than k-1 
A) kcat must be larger than KM 
B) kcat must be smaller than KM 
C) kcat must be about equal to k1 
D) kcat must be much smaller than k-1 
E) kcat must be much larger than k-1

Question 14

Since an enzyme is a catalyst,which of the following must be true?

Accepted Answer

A) an enzyme-catalyzed reaction is always exergonic 
B) enzymes increase the rate of a reaction by providing a completely alternate mechanism to the uncatalyzed reaction 
C) over the course of an enzyme-catalyzed reaction,the enzyme is not changed 
D) in the absence of an enzyme,the reaction that is normally catalyzed by the enzyme will not occur 
E) enzyme-catalyzed reactions never reach equilibrium 
A) an enzyme-catalyzed reaction is always exergonic 
B) enzymes increase the rate of a reaction by providing a completely alternate mechanism to the uncatalyzed reaction 
C) over the course of an enzyme-catalyzed reaction,the enzyme is not changed 
D) in the absence of an enzyme,the reaction that is normally catalyzed by the enzyme will not occur 
E) enzyme-catalyzed reactions never reach equilibrium

Question 15

Which of the following scenarios would result in a relatively low energy of activation?

Accepted Answer

A) an enzyme binds to the substrate with greater affinity than the transition state 
B) an enzyme binds to both substrate and transition state with equal affinity 
C) an enzyme binds to the transition state with greater affinity than the substrate 
D) an enzyme binds only to the transition state 
E) none of the above 
A) an enzyme binds to the substrate with greater affinity than the transition state 
B) an enzyme binds to both substrate and transition state with equal affinity 
C) an enzyme binds to the transition state with greater affinity than the substrate 
D) an enzyme binds only to the transition state 
E) none of the above

Question 16

Which of the following is the most common form of reversible covalent modification for control of enzyme activity?

Accepted Answer

A) acetylation/deacetylation 
B) adenylation/deadenylation 
C) phosphorylation/dephosphorylation 
D) ADP-ribosylation/de-ADP-ribosylation 
E) none of the above 
A) acetylation/deacetylation 
B) adenylation/deadenylation 
C) phosphorylation/dephosphorylation 
D) ADP-ribosylation/de-ADP-ribosylation 
E) none of the above

Question 17

The steady state assumption in enzyme kinetics:

Accepted Answer

A) insures that the product of an enzymatic reaction will always be formed 
B) explains why enzymes are effective catalysts 
C) states that the formation of ES is equal to its breakdown 
D) is based upon the fact that the maximum velocity of an enzyme is very high 
E) none of the above 
A) insures that the product of an enzymatic reaction will always be formed 
B) explains why enzymes are effective catalysts 
C) states that the formation of ES is equal to its breakdown 
D) is based upon the fact that the maximum velocity of an enzyme is very high 
E) none of the above

Question 18

In a Lineweaver-Burke plot,what does the slope represent?

Accepted Answer

A) KM 
B) Vmax 
C) Vmax/KM 
D) KM/Vmax 
E) none of the above 
A) KM 
B) Vmax 
C) Vmax/KM 
D) KM/Vmax 
E) none of the above

Question 19

In the following enzyme reaction scheme,what sort of multi-enzyme kinetics are shown?

Accepted Answer

A) ordered substrate binding with random product release 
B) ordered substrate binding with ordered product release 
C) random substrate binding with ordered product release 
D) random substrate binding with random product release 
E) ping-pong mechanism 
A) ordered substrate binding with random product release 
B) ordered substrate binding with ordered product release 
C) random substrate binding with ordered product release 
D) random substrate binding with random product release 
E) ping-pong mechanism

Question 20

Since the product of the reaction catalyzed by hexokinase,glucose-6-phosphate (G6P),can act as both a competitive and uncompetitive inhibitor,what can be said about the interaction between G6P and hexokinase?

Accepted Answer

A) G6P binds only to active site of the enzyme 
B) G6P binds only to a regulatory site of the enzyme 
C) G6P binds to both the active site and a regulatory site of the enzyme 
D) G6P binds to one of the substrates,ATP,thus preventing ATP from binding to the active site 
E) none of the above 
A) G6P binds only to active site of the enzyme 
B) G6P binds only to a regulatory site of the enzyme 
C) G6P binds to both the active site and a regulatory site of the enzyme 
D) G6P binds to one of the substrates,ATP,thus preventing ATP from binding to the active site 
E) none of the above

Exam 11: Enzymes: Biological Catalysts

In the mechanism of chymotrypsin,which of the following amino acids found in the active site is correctly defined in terms of its role in the reaction?

A plot of enzyme activity with and without an inhibitor present gave the following plot.What type of inhibitor is present? How does this inhibitor function? What changes are seen in Vmax and KM? Draw a line that approximates the result from addition of twice as much inhibitor to the reaction.

Given the chymotrypsin catalytic triad and the peptide substrate,draw the first tetrahedral intermediate of the chymotrypsin mechanism.

In noncompetitive inhibition,which of the following best explains how the inhibitor binds to the enzyme?

If an enzyme gave a rate enhancement of 3.4 ×\times× 107 over the noncatalyzed reaction,what is the Δ\DeltaΔΔ\DeltaΔ G ∘\circ∘ ‡ at 37 ∘\circ∘ C?

Which of the following cofactors is used during the activation and transfer of carbon dioxide?

What are the expected changes in kinetics in the presence of a competitive inhibitor?

The activity of lysozyme is greater than 50% of maximum between pH 3.8 and 6.1 with peak activity occurring around pH 5.Below 3.8 and above 6.1,the activity drops rapidly.Which of the following provides the best explanation for this?

What type of inhibitor would give the results seen in the following plot?

Which of the following explains why enzymes are extremely effective catalysts?

An enzymatic reaction has a Vmax of 100 μ\muμ M/min.At a substrate concentration of 5 μ\muμ M,the velocity is 25 μ\muμ M/min.What is the KM for the reaction?

What must be true if KM is truly a measure of the affinity of enzyme and substrate?

Since an enzyme is a catalyst,which of the following must be true?

Which of the following scenarios would result in a relatively low energy of activation?

Which of the following is the most common form of reversible covalent modification for control of enzyme activity?

The steady state assumption in enzyme kinetics:

In a Lineweaver-Burke plot,what does the slope represent?

In the following enzyme reaction scheme,what sort of multi-enzyme kinetics are shown?

Since the product of the reaction catalyzed by hexokinase,glucose-6-phosphate (G6P),can act as both a competitive and uncompetitive inhibitor,what can be said about the interaction between G6P and hexokinase?

The Scope of Biochemistry

The Matrix 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

Contractile Proteins and Molecular Motors

Carbohydrates: Sugars,saccharides,glycans

Lipids,membranes and Cellular Transport

Chemical Logic of Metabolism

Carbohydrate Metabolism: Glycolysis, gluconeogenesis, glycogen Metabolism, and the Pentose Phosphate Pathway

Citric Acid Cycle and Glyoxylate Cycle

Electron Transport, oxidative Phosphorylation, and Oxygen Metabolism

Photosynthesis

Lipid Metabolism I: Fatty Acids,triacylglycerols,and Lipoproteins

Interorgan and Intracellular Coordination of Energy Metabolism in Vertebrates

Lipid Metabolism Ii: Membrane Lipids, steroids, isoprenoids, and Eicosanoids

Metabolism of Nitrogenous Compounds I: Principles of Biosynthesis, utilization, and Turnover

Metabolism of Nitogenous Compounds Ii: Amino Acids, porphyrins, and Neurotransmitters

Nucleotide Metabolism

Mechanisms of Signal Transduction

Genes,genomes and Chromosomes

Dna Replication

Dna Restructuring: Repair,recombination,rearrangement,amplification

Information Readout: Transcription and Post-Transcriptional Processing

Information Decoding: Translation and Post-Translational Protein Processing

Regulation of Gene Expression

Filters

A plot of enzyme activity with and without an inhibitor present gave the following plot.What type of inhibitor is present? How does this inhibitor function? What changes are seen in V_max and K_M? Draw a line that approximates the result from addition of twice as much inhibitor to the reaction.

If an enzyme gave a rate enhancement of 3.4 $\times$ 10⁷ over the noncatalyzed reaction,what is the $\Delta$ $\Delta$ G^$\circ$^‡ at 37^$\circ$C?

An enzymatic reaction has a V_max of 100 $\mu$ M/min.At a substrate concentration of 5 $\mu$ M,the velocity is 25 $\mu$ M/min.What is the K_M for the reaction?

What must be true if K_M is truly a measure of the affinity of enzyme and substrate?