Deck 6: Enzymes: the Catalysts of Life

Question 1

Irreversible enzyme inhibitors

A)bind to the active site of an enzyme through noncovalent bonds.
B)have only a temporary effect on enzyme activity.
C)are often toxic to cells.
D)are not active against ribozymes.
E)are uncommon in nature.

Answer 1

C

Question 2

The active site for many enzymes

A)contains amino acids that are contiguous to one another along the primary sequence of the protein.
B)may require a prosthetic group such as a metal ion.
C)involves amino acids that are brought into close proximity by extensive protein folding.
D)usually depends on only one amino acid.
E)involves amino acids that are brought into close proximity by extensive protein folding and may require a prosthetic group such as a metal ion.

Answer 2

E

Question 3

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.

Answer 3

E

Question 4

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 5

The rate of a reaction catalyzed by an enzymes usually ________ with temperature; however,at temperatures above the optimum range ________.

A)increases; protein denaturation occurs
B)increases; the reaction proceeds without the enzyme
C)decreases; the reaction proceeds without the enzyme
D)increases; the direction of the reaction reverses
E)decreases; prosthetic groups are necessary

Question 6

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 7

Which of the following is a mechanism of substrate activation?

A)bond distortion
B)proton transfer
C)electron transfer
D)neutron transfer
E)bond distortion,proton transfer,and electron transfer

Question 8

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

A)K_m
B)V_max
C)S
D)P
E)both K_m and V_max

Question 9

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)digested in the small intestine.
E)consumed by the quantities of substrate in the small intestine.

Question 10

Ribozymes were discovered ________ protein enzymes,even though they ________.

A)before; only catalyze one type of cellular reaction
B)before; are more heat labile than protein enzymes
C)after; catalyze many important cellular reactions
D)after; are the only catalysts found in bacteria and archaea
E)at the same time as; only catalyze one type of cellular reaction

Question 11

An enzyme reduces the free energy of which of the following?

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

Question 12

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.

Question 13

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

A)K_m
B)V_max
C)S
D)P
E)both K_m and V_max

Question 14

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 hydrogen ion
E)carboxypeptidase A

Question 15

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

Question 16

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 17

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 18

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 these are correct.

Question 19

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 20

Which of the following is an enzyme?

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

Question 21

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

A)K_m
B)V_max
C)S
D)P
E)both K_m and V_max

Question 22

The Michaelis constant

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

Question 23

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 because many are nonspecific.

Question 24

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)denaturing agents
D)allosteric regulation
E)hydrogenases

Question 25

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 26

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 these are correct.

Question 27

The induced-fit model

A)was proposed by Hans Buchner.
B)distorts the shape of the enzyme and the substrate.
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 28

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

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

Question 29

The enzyme carbonic anhydrase catalyzes the formation of carbonic acid from carbon dioxide and water.Imagine that you have two sealed tubes with carbon dioxide gas above a buffer containing water and carbon dioxide.One tube has carbonic anhydrase and the other does not.After 24 hours,both tubes are at equilibrium.Which statement below accurately describes the conditions in the tubes?

A)The tube with carbonic anhydrase will have a lower concentration of carbon dioxide and a higher concentration of carbonic acid than the tube with any enzyme.
B)The tube with carbonic anhydrase will have a higher concentration of carbon dioxide and a lower concentration of carbonic acid than the tube with any enzyme.
C)The tubes will have equal concentrations of carbon dioxide and carbonic acid.
D)The tube with carbonic anhydrase will have a higher concentration of carbonic acid than the tube with any enzyme,but the concentration of carbon dioxide will be the same in both tubes.
E)It is not possible to determine the relative concentrations of the products and reactants without more information about carbonic anhydrase,such as the K_m.

Question 30

Feedback inhibition prevents cells from

A)the harmful effects of enzyme activation by covalent modification of unneeded enzymes.
B)making products that are not needed by inhibiting the activity of enzymes in biosynthetic pathways allosterically.
C)destroying enzymes by proteolytic cleavage when they are needed in biosynthetic pathways.
D)accumulating unnecessary proteins.
E)irreversibly inhibiting critical enzymes.

Question 31

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 32

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 33

An example of an irreversible inhibitor is

A)a competitive inhibitor.
B)angiotensin converting enzyme (ACE)inhibiting drugs.
C)a noncompetitive inhibitor.
D)penicillin.
E)isoleucine.

Question 34

The type of inhibitor that binds to the enzyme active site is a(n)________ inhibitor.

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

Question 35

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 36

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

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

Question 37

A noncompetitive inhibitor will

A)bind to free enzyme.
B)bind to free product.
C)decrease V_max.
D)decrease K_m.
E)bind to free enzyme and decrease V_max.

Question 38

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 39

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 V_max and K_m.
E)It is nonlinear.

Question 40

Which of the following variables is not part of the Michaelis-Menten equation?

A)k_cat
B)K_m
C)V_max
D)[S]
E)v

Question 41

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

Question 42

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

Question 43

Nonprotein catalysts are known as ________.

Question 44

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

Question 45

The site on an enzyme that the substrate binds to is called the ________.

Question 46

________ is the turnover number for a given enzyme.

Question 47

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

Question 48

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

Question 49

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

Question 50

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

Question 51

________ are enzymes able to convert a substrate to its mirror image.

Question 52

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