Question 1

The allosteric enzyme ATCase is regulated by CTP,which binds to the T-state of ATCase.CTP is a:

Accepted Answer

A) positive regulator. 
B) negative regulator. 
C) co-factor. 
D) competitive inhibitor. 
E) coenzyme. 
A) positive regulator. 
B) negative regulator. 
C) co-factor. 
D) competitive inhibitor. 
E) coenzyme. B

Question 2

One of the enzymes involved in glycolysis,aldolase,requires Zn2+ for catalysis.Under conditions of zinc deficiency,when the enzyme may lack zinc,it would be referred to as the:

Accepted Answer

A) apoenzyme. 
B) coenzyme. 
C) holoenzyme. 
D) prosthetic group. 
E) substrate. 
A) apoenzyme. 
B) coenzyme. 
C) holoenzyme. 
D) prosthetic group. 
E) substrate. A

Question 3

A small molecule that decreases the activity of an enzyme by binding to a site other than the catalytic site is termed a(n):

Accepted Answer

A) allosteric inhibitor. 
B) alternative inhibitor. 
C) competitive inhibitor. 
D) stereospecific agent. 
E) transition-state analog. 
A) allosteric inhibitor. 
B) alternative inhibitor. 
C) competitive inhibitor. 
D) stereospecific agent. 
E) transition-state analog. A

Question 4

How does the total enzyme concentration affect turnover number and Vmax?

Accepted Answer

The turnover number,k_cat,is t

Question 5

When 10 $\mu$g of an enzyme of Mr 50,000 is added to a solution containing its substrate at a concentration one hundred times the Km,it catalyzes the conversion of 75 $\mu$mol of substrate into product in 3 min.What is the enzyme's turnover number?

Accepted Answer

Because the velocity measured occurs far

Question 6

An enzyme follows Michaelis-Menten kinetics.Indicate (with an "x")which of the kinetic parameters at the left would be altered by the following factors.Give only one answer for each.

Accepted Answer

(a)K_m; (b)

Question 7

Penicillin and related drugs inhibit the enzyme ;this enzyme is produced by .

Accepted Answer

A) ($\beta$-lacamase;bacteria) 
B) transpeptidase;human cells 
C) transpeptidase;bacteria 
D) lysozyme;human cells 
E) aldolase;bacteria 
A) ($\beta$-lacamase;bacteria) 
B) transpeptidase;human cells 
C) transpeptidase;bacteria 
D) lysozyme;human cells 
E) aldolase;bacteria

Question 8

Allosteric enzymes:

Accepted Answer

A) are regulated primarily by covalent modification. 
B) usually catalyze several different reactions within a metabolic pathway. 
C) usually have more than one polypeptide chain. 
D) usually have only one active site. 
E) usually show strict Michaelis-Menten kinetics. 
A) are regulated primarily by covalent modification. 
B) usually catalyze several different reactions within a metabolic pathway. 
C) usually have more than one polypeptide chain. 
D) usually have only one active site. 
E) usually show strict Michaelis-Menten kinetics.

Question 9

Which of the following statements about a plot of V0 vs.[S] for an enzyme that follows Michaelis-Menten kinetics is false?

Accepted Answer

A) As [S] increases,the initial velocity of reaction V0 also increases. 
B) At very high [S],the velocity curve becomes a horizontal line that intersects the y-axis at Km. 
C) Km is the [S] at which V0 = 1/2 Vmax. 
D) The shape of the curve is a hyperbola. 
E) The y-axis is a rate term with units of $\mu$m/min. 
A) As [S] increases,the initial velocity of reaction V0 also increases. 
B) At very high [S],the velocity curve becomes a horizontal line that intersects the y-axis at Km. 
C) Km is the [S] at which V0 = 1/2 Vmax. 
D) The shape of the curve is a hyperbola. 
E) The y-axis is a rate term with units of $\mu$m/min.

Question 10

The steady state assumption,as applied to enzyme kinetics,implies:

Accepted Answer

A) Km = Ks. 
B) the enzyme is regulated. 
C) the ES complex is formed and broken down at equivalent rates. 
D) the Km is equivalent to the cellular substrate concentration. 
E) the maximum velocity occurs when the enzyme is saturated. 
A) Km = Ks. 
B) the enzyme is regulated. 
C) the ES complex is formed and broken down at equivalent rates. 
D) the Km is equivalent to the cellular substrate concentration. 
E) the maximum velocity occurs when the enzyme is saturated.

Question 11

A transition-state analog:

Accepted Answer

A) is less stable when binding to an enzyme than the normal substrate. 
B) resembles the active site of general acid-base enzymes. 
C) resembles the transition-state structure of the normal enzyme-substrate complex. 
D) stabilizes the transition state for the normal enzyme-substrate complex. 
E) typically reacts more rapidly with an enzyme than the normal substrate. 
A) is less stable when binding to an enzyme than the normal substrate. 
B) resembles the active site of general acid-base enzymes. 
C) resembles the transition-state structure of the normal enzyme-substrate complex. 
D) stabilizes the transition state for the normal enzyme-substrate complex. 
E) typically reacts more rapidly with an enzyme than the normal substrate.

Question 12

The difference in (standard)free energy content,$\Delta$G'°,between substrate S and product P may vary considerably among different reactions.What is the significance of these differences?

Accepted Answer

The difference in free energy content be

Question 13

The role of the metal ion (Mg2+)in catalysis by enolase is to:

Accepted Answer

A) act as a general acid catalyst. 
B) act as a general base catalyst. 
C) facilitate general acid catalysis. 
D) facilitate general base catalysis. 
E) stabilize protein conformation. 
A) act as a general acid catalyst. 
B) act as a general base catalyst. 
C) facilitate general acid catalysis. 
D) facilitate general base catalysis. 
E) stabilize protein conformation.

Question 14

Penicillin and related antibiotics contain a 4-membered $\beta$-lactam ring.Explain why this feature is important to the mechanism of action of these drugs.

Accepted Answer

The strained 4-membered ring i

Question 15

For enzymes in which the slowest (rate-limiting)step is the reaction

Km becomes equivalent to:

Accepted Answer

A) kcat. 
B) the [S],where V0 = Vmax. 
C) the dissociation constant,Kd,for the ES complex. 
D) the maximal velocity. 
E) the turnover number. 
A) kcat. 
B) the [S],where V0 = Vmax. 
C) the dissociation constant,Kd,for the ES complex. 
D) the maximal velocity. 
E) the turnover number.

Question 16

For serine to work effectively as a nucleophile in covalent catalysis in chymotrypsin a nearby amino acid,histidine,must serve as general base catalyst.Briefly describe,in words,how these two amino acids work together.

Accepted Answer

The serine is a polar hydroxyl,with the

Question 17

A good transition-state analog:

Accepted Answer

A) binds covalently to the enzyme. 
B) binds to the enzyme more tightly than the substrate. 
C) binds very weakly to the enzyme. 
D) is too unstable to isolate. 
E) must be almost identical to the substrate. 
A) binds covalently to the enzyme. 
B) binds to the enzyme more tightly than the substrate. 
C) binds very weakly to the enzyme. 
D) is too unstable to isolate. 
E) must be almost identical to the substrate.

Question 18

For a reaction that can take place with or without catalysis by an enzyme,what would be the effect of the enzyme on the:
(a)standard free energy change of the reaction?
(b)activation energy of the reaction?
(c)initial velocity of the reaction?
(d)equilibrium constant of the reaction?

Accepted Answer

(a)no change; 
(b)de

Question 19

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

The velocity of 20 @#LAT-DLM&mol/min is essentiall

Question 20

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.

Exam 6: Enzymes

The allosteric enzyme ATCase is regulated by CTP,which binds to the T-state of ATCase.CTP is a:

One of the enzymes involved in glycolysis,aldolase,requires Zn2+ for catalysis.Under conditions of zinc deficiency,when the enzyme may lack zinc,it would be referred to as the:

A small molecule that decreases the activity of an enzyme by binding to a site other than the catalytic site is termed a(n):

How does the total enzyme concentration affect turnover number and Vmax?

When 10 μ\muμ g of an enzyme of Mr 50,000 is added to a solution containing its substrate at a concentration one hundred times the Km,it catalyzes the conversion of 75 μ\muμ mol of substrate into product in 3 min.What is the enzyme's turnover number?

An enzyme follows Michaelis-Menten kinetics.Indicate (with an "x")which of the kinetic parameters at the left would be altered by the following factors.Give only one answer for each.

Penicillin and related drugs inhibit the enzyme ;this enzyme is produced by .

Allosteric enzymes:

Which of the following statements about a plot of V0 vs.[S] for an enzyme that follows Michaelis-Menten kinetics is false?

The steady state assumption,as applied to enzyme kinetics,implies:

A transition-state analog:

The difference in (standard)free energy content, Δ\DeltaΔ G'°,between substrate S and product P may vary considerably among different reactions.What is the significance of these differences?

The role of the metal ion (Mg2+)in catalysis by enolase is to:

Penicillin and related antibiotics contain a 4-membered β\betaβ -lactam ring.Explain why this feature is important to the mechanism of action of these drugs.

For enzymes in which the slowest (rate-limiting)step is the reaction Km becomes equivalent to:

For serine to work effectively as a nucleophile in covalent catalysis in chymotrypsin a nearby amino acid,histidine,must serve as general base catalyst.Briefly describe,in words,how these two amino acids work together.

A good transition-state analog:

For a reaction that can take place with or without catalysis by an enzyme,what would be the effect of the enzyme on the: (a)standard free energy change of the reaction? (b)activation energy of the reaction? (c)initial velocity of the reaction? (d)equilibrium constant of the reaction?

How is trypsinogen converted to trypsin?

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

Recombinant Dna Technology

Lipids

Biological Membranes and Transport

Biosignaling

Principles of Bioenergetics

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

Integration and Hormonal Regulation of Mammalian Metabolism

Genes and Chromosomes

Dna Metabolism

Rna Metabolism

Protein Metabolism

Regulation of Gene Expression

Filters

One of the enzymes involved in glycolysis,aldolase,requires Zn²⁺ for catalysis.Under conditions of zinc deficiency,when the enzyme may lack zinc,it would be referred to as the:

How does the total enzyme concentration affect turnover number and V_max?

When 10 $\mu$ g of an enzyme of M_r 50,000 is added to a solution containing its substrate at a concentration one hundred times the K_m,it catalyzes the conversion of 75 $\mu$ mol of substrate into product in 3 min.What is the enzyme's turnover number?

Which of the following statements about a plot of V₀vs.[S] for an enzyme that follows Michaelis-Menten kinetics is false?

The difference in (standard)free energy content, $\Delta$ G'°,between substrate S and product P may vary considerably among different reactions.What is the significance of these differences?

The role of the metal ion (Mg²⁺)in catalysis by enolase is to:

Penicillin and related antibiotics contain a 4-membered $\beta$ -lactam ring.Explain why this feature is important to the mechanism of action of these drugs.

For enzymes in which the slowest (rate-limiting)step is the reaction K_m becomes equivalent to: