Question 1

Which of the following statements is FALSE?

Accepted Answer

A) Enzymes make reactions 103 to 1020 times faster. 
B) Enzymes lower the amount of energy needed for a reaction. 
C) Enzymes are chemically unchanged during the actual catalytic process. 
D) Enzymes speed up the attainment of a reaction equilibrium. 
E) Enzymes are usually proteins. 
A) Enzymes make reactions 103 to 1020 times faster. 
B) Enzymes lower the amount of energy needed for a reaction. 
C) Enzymes are chemically unchanged during the actual catalytic process. 
D) Enzymes speed up the attainment of a reaction equilibrium. 
E) Enzymes are usually proteins.

Question 2

The time that is required for an enzyme to convert one substrate molecule into one product molecule is

Accepted Answer

A) Km. 
B) kcat. 
C) 1/Km. 
D) 1/kcat. 
A) Km. 
B) kcat. 
C) 1/Km. 
D) 1/kcat.

Question 3

Natural inhibitors often are regulators of metabolic reactions.

Accepted Answer

A) True 
 B)False

Question 4

Examples of multienzyme complexes include

Accepted Answer

A) fatty acid synthase. 
B) tryptophan synthase. 
C) isomerase. 
D) A and B. 
E) All of the above. 
A) fatty acid synthase. 
B) tryptophan synthase. 
C) isomerase. 
D) A and B. 
E) All of the above.

Question 5

Protein A has four identical subunits,each of which binds one molecule of ligand Y.The binding of one molecule of Y to one of the subunits induces a conformational change in neighboring subunits that enhances the binding of additional units of Y.This is an example of ________.

Accepted Answer

A) negative cooperativity 
B) competitive activation 
C) symmetry-driven binding 
D) the sequential theory 
A) negative cooperativity 
B) competitive activation 
C) symmetry-driven binding 
D) the sequential theory

Question 6

Very few catalytic proficiency values are known because many nonenzymatic reaction rates are so slow that they are difficult to measure.

Accepted Answer

A) True 
 B)False

Question 7

Two substances are used to produce a certain biological product in an enzyme-catalyzed reaction.It is found that both substrates must bind to the enzyme,first one,then the other before the product is produced.This is an example of a(n)________.

Accepted Answer

A) linear reaction 
B) ordered sequential reaction 
C) random sequential reaction 
D) ping-pong reaction 
A) linear reaction 
B) ordered sequential reaction 
C) random sequential reaction 
D) ping-pong reaction

Question 8

Which statement is false about regulatory enzymes that are controlled allosterically?

Accepted Answer

A) They are always less active when a modulator is bound to them. 
B) They are often larger than other enzymes. 
C) They have more than one binding site. 
D) They often catalyze the first step in a reaction pathway. 
A) They are always less active when a modulator is bound to them. 
B) They are often larger than other enzymes. 
C) They have more than one binding site. 
D) They often catalyze the first step in a reaction pathway.

Question 9

The Km values for enzyme reactions such as A + B → C + D

Accepted Answer

A) cannot be determined using the Lineweaver-Burk plot analysis. 
B) can be determined by holding one (A or 
B) at high concentration,while varying the concentration of the other substrate. 
C) can be determined for one substrate and not the other. 
D) do not indicate the efficiency of the enzyme. 
A) cannot be determined using the Lineweaver-Burk plot analysis. 
B) can be determined by holding one (A or 
B) at high concentration,while varying the concentration of the other substrate. 
C) can be determined for one substrate and not the other. 
D) do not indicate the efficiency of the enzyme.

Question 10

An enzyme that catalyzes conversions of L-sugars to D-sugars is called a(n)________.

Accepted Answer

A) lyase 
B) hydrolase 
C) synthetase 
D) synthase 
E) isomerase 
A) lyase 
B) hydrolase 
C) synthetase 
D) synthase 
E) isomerase

Question 11

A noncompetitive inhibitor can bind to either the enzyme or the enzyme-substrate complex.

Accepted Answer

A) True 
 B)False

Question 12

Calculate the value of the maximum velocity for an enzyme-catalyzed reaction that follows Michaelis-Menton kinetics if the initial velocity is 6 mM/s at a substrate concentration of 6 mM.The KM for the enzyme system is 2 mM.

Accepted Answer

A) 4.5 mM 
B) 8 mM 
C) 8.75 mM 
D) 12 mM 
E) 66 mM 
A) 4.5 mM 
B) 8 mM 
C) 8.75 mM 
D) 12 mM 
E) 66 mM

Question 13

In E.coli ________ is an activator and ________ is a negative allosteric modulator of the enzyme phosphofructokinase-1.

Accepted Answer

A) DFP;phosphoenolpyruvate 
B) phosphoenolpyruvate;ATP 
C) ADP;phosphoenolpyruvate 
D) fructose-6-phosphate;ADP 
A) DFP;phosphoenolpyruvate 
B) phosphoenolpyruvate;ATP 
C) ADP;phosphoenolpyruvate 
D) fructose-6-phosphate;ADP

Question 14

Interconvertible enzymes ________.

Accepted Answer

A) are those controlled by covalent modification 
B) follow a concerted mechanism to go back and forth between the T and R states 
C) catalyze reactions to covalently modify another enzyme 
D) are allosteric modulators 
A) are those controlled by covalent modification 
B) follow a concerted mechanism to go back and forth between the T and R states 
C) catalyze reactions to covalently modify another enzyme 
D) are allosteric modulators

Question 15

The most common enzyme inhibitors are competitive inhibitors.

Accepted Answer

A) True 
 B)False

Question 16

The expression: Vmax = k2[E]total applies to

Accepted Answer

A) zero order kinetics of an enzyme-catalyzed reaction. 
B) first order kinetics of an enzyme-catalyzed reaction. 
C) second order kinetics of an enzyme-catalyzed reaction. 
D) only the initial part (near time = zero)of an enzyme-catalyzed reaction. 
A) zero order kinetics of an enzyme-catalyzed reaction. 
B) first order kinetics of an enzyme-catalyzed reaction. 
C) second order kinetics of an enzyme-catalyzed reaction. 
D) only the initial part (near time = zero)of an enzyme-catalyzed reaction.

Question 17

Which are correlated with allosteric enzymes that do not follow typical Michaelis-Menten kinetics?

Accepted Answer

A) Cooperative binding of the substrate. 
B) Sigmoidal curves of velocity when S is varied. 
C) Changes in conformation of the enzyme when S binds. 
D) All of the above. 
A) Cooperative binding of the substrate. 
B) Sigmoidal curves of velocity when S is varied. 
C) Changes in conformation of the enzyme when S binds. 
D) All of the above.

Question 18

The assumptions made in calculating the Michaelis-Menten Equation include

Accepted Answer

A) that the formation and decomposition of ES is the same for a period of time. 
B) that the concentration of the substrate is much greater than the concentration of E. 
C) that the value of k-2 can be ignored. 
D) A,B and C. 
E) A and B only. 
A) that the formation and decomposition of ES is the same for a period of time. 
B) that the concentration of the substrate is much greater than the concentration of E. 
C) that the value of k-2 can be ignored. 
D) A,B and C. 
E) A and B only.

Question 19

In a certain enzyme-catalyzed reaction the following steps occur: 1. A phosphate group on substrate A is transferred to a side chain of an active
Site residue of the enzyme.
2. The dephosphorylated form of substrate A dissociates from the enzyme.
3. Substrate B enters the active site and is phosphorylated with simultaneous
Regeneration of the enzyme in its original form.
What kind of kinetic mechanism is described?

Accepted Answer

A) Random. 
B) Sequential. 
C) Ordered. 
D) Ping-pong. 
A) Random. 
B) Sequential. 
C) Ordered. 
D) Ping-pong.

Question 20

The Lineweaver-Burk plot and other linear transformation of the Michaelis-Menten curve of kinetics are valuable for

Accepted Answer

A) determination of Km. 
B) determination of Vmax. 
C) determination of kcat. 
D) determination of types of enzyme inhibition. 
E) All of the above. 
A) determination of Km. 
B) determination of Vmax. 
C) determination of kcat. 
D) determination of types of enzyme inhibition. 
E) All of the above.

Exam 5: Properties of Enzymes

Which of the following statements is FALSE?

The time that is required for an enzyme to convert one substrate molecule into one product molecule is

Natural inhibitors often are regulators of metabolic reactions.

Examples of multienzyme complexes include

Protein A has four identical subunits,each of which binds one molecule of ligand Y.The binding of one molecule of Y to one of the subunits induces a conformational change in neighboring subunits that enhances the binding of additional units of Y.This is an example of ________.

Very few catalytic proficiency values are known because many nonenzymatic reaction rates are so slow that they are difficult to measure.

Two substances are used to produce a certain biological product in an enzyme-catalyzed reaction.It is found that both substrates must bind to the enzyme,first one,then the other before the product is produced.This is an example of a(n)________.

Which statement is false about regulatory enzymes that are controlled allosterically?

The Km values for enzyme reactions such as A + B → C + D

An enzyme that catalyzes conversions of L-sugars to D-sugars is called a(n)________.

A noncompetitive inhibitor can bind to either the enzyme or the enzyme-substrate complex.

Calculate the value of the maximum velocity for an enzyme-catalyzed reaction that follows Michaelis-Menton kinetics if the initial velocity is 6 mM/s at a substrate concentration of 6 mM.The KM for the enzyme system is 2 mM.

In E.coli ________ is an activator and ________ is a negative allosteric modulator of the enzyme phosphofructokinase-1.

Interconvertible enzymes ________.

The most common enzyme inhibitors are competitive inhibitors.

The expression: Vmax = k2[E]total applies to

Which are correlated with allosteric enzymes that do not follow typical Michaelis-Menten kinetics?

The assumptions made in calculating the Michaelis-Menten Equation include

The Lineweaver-Burk plot and other linear transformation of the Michaelis-Menten curve of kinetics are valuable for

Introduction to Biochemistry

Water

Amino Acids and the Primary Structures of Proteins

Proteins: Three-Dimensional Structure and Function

Mechanisms of Enzymes

Coenzymes and Vitamins

Carbohydrates

Lipids and Membranes

Introduction to Metabolism

Glycolysis

Gluconeogenesis, the Pentose Phosphate Pathway, and Glycogen Metabolism

The Citric Acid Cycle

Electron Transport and Atp Synthesis

Photosynthesis

Lipid Metabolism

Amino Acid Metabolism

Nucleotide Metabolism

Nucleic Acids

DNA Replication, repair, and Recombination

Transcription and RNA Processing

Protein Synthesis

Filters

In E.coli is an activator and is a negative allosteric modulator of the enzyme phosphofructokinase-1.