Deck 6: Enzymes: the Catalysts of Life

Question 1

As new enzymes are discovered,the EC system for naming enzymes is to be used.The names are to be based on which of the following criteria?

A)the name of the substrate
B)a description of substrate function
C)an indication of the size of the substrate
D)the six major classes of enzyme function
E)the size of the enzyme

Answer 1

D

Question 2

The active site for carboxypeptidase

A)contains amino acids that are contiguous to one another along the primary sequence of the protein.
B)uses iron as the prosthetic group.
C)involves only 6 out of a total of 307 amino acids.
D)contains a glutamate residue at position 69.
E)is formed by the interaction of two polypeptide chains.

Answer 2

C

Question 3

The site on an enzyme that will bind the substrate is called the

A)prosthetic group.
B)catalyst.
C)active site.
D)metastable site.
E)activation site.

Answer 3

C

Question 4

The equation A-PO₄ + B → A + B-PO₄ would be catalyzed by which of the following classes of enzymes?

A)transferases
B)oxidoreductases
C)hydrolases
D)ligases
E)isomerases

Question 5

Which of the following is an example of a prosthetic group?

A)a zinc ion
B)a glycine residue
C)a polypeptide chain
D)a nickel catalyst
E)carboxypeptidase A

Question 6

An enzyme

A)decreases the rate of a reaction.
B)binds substrates in a manner that facilitates the formation of product.
C)changes the position of the equilibrium of the reaction.
D)does not change the rate at which the equilibrium is achieved.
E)is always a protein.

Question 7

An enzyme is active in the stomach of an animal but quickly loses its activity when it leaves the stomach.This example illustrates that enzymes are

A)specific to the organs in which they are produced.
B)inactivated by movement.
C)sensitive to changes in pH.
D)inactivated by inhibitors in the small intestine.
E)consumed by the quantities of substrate in the small intestine.

Question 8

A competitive inhibitor will affect the ________ of an enzymatic reaction.

A)Km
B)Vmax
C)S
D)P
E)both choices A and B

Question 9

An organism that is labeled a cryophile is capable of

A)growth at 4°C.
B)growth in hydrothermal vents.
C)synthesizing liquid nitrogen.
D)producing large quantities of liquid hydrogen.
E)both choices C and D

Question 10

A noncompetitive inhibitor will affect the ________ of an enzymatic reaction.

A)Km
B)Vmax
C)S
D)P
E)both choices A and B

Question 11

An enzyme influences the structure of which of the following?

A)substrate
B)product
C)transition state
D)cofactor
E)intermediate

Question 12

All of the following are examples of irreversible enzyme inhibitors except

A)herbicides.
B)pesticides.
C)monoamine oxidase inhibitors.
D)aspirin.
E)natural poisons.

Question 13

Substrate activation may involve

A)a change in enzyme conformation induced by substrate binding.
B)accepting protons from the enzyme.
C)formation of temporary covalent bonds.
D)donation of protons to the enzyme.
E)all of the above

Question 14

According to the EC system,which is not one of the major groups of enzymes?

A)proteases
B)hydrolases
C)oxidoreductases
D)transferases
E)ligases

Question 15

All of the following are associated with substration activation except

A)bond distortion.
B)proton transfer.
C)electron transfer.
D)intramolecular hydrogen bonding.
E)neutron transfer.

Question 16

The work of James B.Sumner was to

A)discover ribozymes.
B)prove that enzymes were carbohydrates.
C)isolate the insulin hormone.
D)originate the term ferments to describe enzymes.
E)crystallize urease, the first enzyme isolated.

Question 17

Which of the following is an enzyme?

A)iron
B)histidine
C)carboxypeptidase A
D)ATP
E)N-acetylmuramic acid

Question 18

The equation AB + H₂O → A + B would be catalyzed by which of the following classes of enzymes?

A)oxidoreductases
B)transferases
C)hydrolases
D)ligases
E)isomerases

Question 19

Which of the following best describes a metastable state?

A)This state is composed of the difference in activation energy of a catalyzed versus an uncatalyzed reaction.
B)The metastable state is formed by transient complexes with the substrate.
C)The metastable state is created by the prosthetic group of the enzyme.
D)This state changes the position of the equilibrium but not the rate.
E)The metastable state is a state of the substrate in which the reaction can proceed but typically requires a catalyst.

Question 20

A sick person often has a fever,which can inhibit the growth of bacteria because

A)bacteria reproduce more rapidly at higher body temperature.
B)enzymes do not function as well at temperatures other than the optimal temperature.
C)the higher temperature increases the activity of lyases.
D)sweating removes prosthetic groups from biological enzymes.
E)fever blocks synthesis of proteins in the bacterial nucleus.

Question 21

Why is the Lineweaver-Burk plot important in enzyme kinetics?

A)It is a single-reciprocal plot.
B)It illustrates enzyme specificity.
C)It reveals the presence of prosthetic groups in enzymes.
D)It makes it easier to determine Vmax.
E)It is nonlinear.

Question 22

Which of the following is not true of the enzyme-substrate interaction?

A)Many enzymes are extremely specific regarding a substrate.
B)Many enzymes cannot recognize a stereoisomer of their substrate.
C)Some enzymes accept any of a whole group of substrates.
D)Carboxypeptidase recognizes any of the amino acids from the carboxyl end of a polypeptide.
E)Cells are often able to carry out metabolic activity with only a handful of enzymes.

Question 23

The Michaelis constant

A)can be determined using the Lineweaver-Burk plot.
B)is equal to twice the Vmax.
C)is equal to the substrate concentration at Vmax/2.
D)both choices A and C
E)choices A, B, and C

Question 24

An example of an irreversible inhibitor is

A)a competitive inhibitor.
B)acetylcholinesterase.
C)a noncompetitive inhibitor.
D)penicillin.
E)isoleucine.

Question 25

The type of inhibitor that binds to the enzyme (E)but not to the enzyme-substrate (ES)complex is a(n)________ inhibitor.

A)competitive
B)noncompetitive
C)uncompetitive
D)coenzyme
E)mixed-type

Question 26

Of the following,which is used to inhibit specific enzymes in the treatment of many bacterial and viral diseases?

A)substrate analogues
B)noncompetitive inhibitors
C)intercalating agents
D)nitrous oxide
E)X-rays

Question 27

Covalent modification

A)can activate an enzyme.
B)affects the activity of an enzyme by adding or removing a chemical group.
C)can involve the addition of phosphate groups.
D)produces modifications that can sometimes be reversed.
E)all of the above

Question 28

An allosteric inhibitor

A)increases the rate of substrate binding.
B)binds and activates the high-affinity state of the enzymes.
C)is identical to the active site.
D)binds at the regulatory site.
E)is converted to an activator by the enzyme.

Question 29

A linear relationship between Vmax and enzyme concentration would be expected when

A)[S] << Km.
B)[S] >> Km.
C)[S] = Km.
D)both choices A and B
E)both choices B and C

Question 30

The induced-fit model

A)was proposed by Hans Buchner.
B)involves a conformational change in the shape of the enzyme.
C)is also called the lock-and-key model.
D)states that enzyme-substrate interactions are rigid.
E)proposes that very strong covalent bonds are formed upon substrate binding.

Question 31

Saturation can be defined as

A)denaturation of an enzyme.
B)the inability to increase reaction velocity beyond a finite upper limit.
C)inhibition of enzyme function by blocking the active site.
D)the substrate concentration at which velocity reaches one-half maximum velocity.
E)a characteristic of all uncatalyzed reactions.

Question 32

Enzyme regulation may occur by several methods.Which of the following is not a means of enzyme regulation?

A)substrate-level phosphorylation
B)feedback inhibition
C)allosteric regulation
D)covalent modification
E)saturation

Question 33

Which of the following does accurately describe the Lineweaver-Burk plot?

A)It is a double-reciprocal plot.
B)The y intercept is equal to 1/Vmax.
C)The x intercept is -1/Km.
D)It is a linear plot.
E)Its slope is the same as the Eadie-Hofstee plot.

Question 34

A competitive inhibitor

A)binds at a site other than the active site.
B)irreversibly binds and inactivates the enzyme.
C)cannot be processed by the enzyme.
D)does not inhibit enzyme activity but does lower substrate concentration.
E)binds to and inactivates the substrate.

Question 35

In the Eadie-Hofstee plot,

A)the x axis shows substrate concentration.
B)the y intercept is Vmax.
C)the slope can be used to determine Km.
D)the y axis shows v/[S].
E)both choices C and D

Question 36

The equation v = Vmax [S]/(Km + [S])is part of which of the following plots?

A)Michaelis-Menten
B)Lineweaver-Burk
C)Eadie-Hofstee
D)both choices A and B
E)none of the above

Question 37

Which of the following variables is part of the Michaelis-Menten equation?

A)kcat
B)Km
C)Vmax
D)[S]
E)v

Question 38

All of the following are examples of ribozymes or ribozyme activity except

A)peptidyl transferase.
B)autocatalytic RNAs.
C)ribonuclease P.
D)intron removal from pre-rRNA.
E)zymogen.

Question 39

Which of the following is/are means whereby a catalyst can lower the activation energy of a reaction?

A)decreasing the number of reactive molecules
B)altering the temperature within the cell to one appropriate for reactions to proceed
C)quantum tunneling
D)inefficient collisions
E)permanently binding substrates

Question 40

Mixed type inhibitors will affect the ________ of an enzymatic reaction.

A)Km
B)Vmax
C)S
D)P
E)both choices A and B

Question 41

________ inhibitors bind the enzyme at a location other than the active site but still interfere with product formation.

Question 42

________ are a class of enzymes responsible for the movement of functional groups from one molecule to another.

Question 43

A nonprotein component of an enzyme that is usually a metal ion or small organic molecule is called a(n)________.

Question 44

A noncompetitive inhibitor will

A)bind to free enzyme.
B)bind to free product.
C)decrease Vmax.
D)decrease Km.
E)both choices A and C

Question 45

Two specific coenzymes we need to obtain from our diet are niacin and ________,as our bodies cannot synthesize them.

Question 46

________ is a mechanism of lowering the activation energy barrier in some reactions,as with the detoxification of hydrogen peroxide.

Question 47

The ________ is the minimum energy required before two molecules can be successful in producing a reaction.

Question 48

Nonprotein catalysts are known as ________.

Question 49

Azidothymidine (AZT)is a(n)________ used in the treatment of AIDS and targets the enzyme reverse transcriptase.

Question 50

The ________ velocity of an enzymatic reaction is the velocity at substrate concentration.

Question 51

________ inhibitors bind reversibly at the active site of an enzyme.

Question 52

________ is the turnover number for a given enzyme.

Question 53

Enzyme activity may be regulated by several means.Can you identify the mode of regulation for each of the following examples?
a.When glucose is converted to glucose-6-phosphate by hexokinase,the accumulation of glucose-6-phosphate inhibits the reaction.
b.A foreign substance is added to the reaction in part a above.This substance binds to hexokinase and prevents its ability to catalyze the reaction.
c.An inactive form of an enzyme becomes active after being phosphorylated.
d.Pepsinogen becomes pepsin after being released into the lumen of the stomach.
e.In a series of enzymatic reactions,it is found that the product of the last reaction inhibits the first enzyme in the series of reactions.

Question 54

The site on an enzyme that is designated for the substrate bind is called the ________.

Question 55

________ is the class of enzymes able to convert a substrate to its mirror image.

Question 56

Inhibitors of enzymes can be either reversible or irreversible.The most common reversible inhibitors are competitive or noncompetitive.Based on what you know about enzyme inhibitors,can you determine the type of inhibition discussed in these examples?
a.Diisopropyl fluorophosphate binds to acetylcholinesterase and permanently inactivates the enzyme.Paralysis results.
b.An inhibitor binds to the active site of an enzyme but disassociates and leaves the enzyme active.
c.A toxin binds to an enzyme.The enzyme then binds the substrate.No product is produced.The toxin may disassociate and allow for product formation.
d.Vitamin K is a coenzyme involved in blood clotting.An anticoagulant drug binds at the site of vitamin K and prevents clotting.Clotting resumes after the drug has been discontinued.
e.Aspirin binds to prostaglandin synthetase and permanently stops its ability to produce prostaglandin.