Deck 6: Enzymes: The Catalysts of Life

Question 1

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

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

Answer 1

B

Question 2

The work of James B. Sumner was to

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

Answer 2

A

Question 3

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 inhibitors in the small intestine.
C)sensitive to changes in pH.
D)inactivated by movement.
E)consumed by the quantities of substrate in the small intestine.

Answer 3

C

Question 4

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

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

Question 5

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)choices A, B, and C
E)both A and C

Question 6

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

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

Question 7

Substrate activation may involve

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

Question 8

An allosteric inhibitor

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

Question 9

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)This state changes the position of the equilibrium, but not the rate.
C)The metastable state is formed by transient complexes with the substrate.
D)The metastable state is created by the prosthetic group of the enzyme.
E)The metastable state is a state of the substrate in which the reaction can proceed, but usually will not proceed, without a catalyst.

Question 10

The Eadie- Hofstee plot

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

Question 11

An example of an irreversible inhibitor is

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

Question 12

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

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

Question 13

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

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

Question 14

Which of the following is an enzyme?

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

Question 15

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

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

Question 16

A sick person often runs a fever and this fever can inhibit the growth of bacteria because

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

Question 17

The active site for carboxypeptidase

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

Question 18

Covalent modification

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

Question 19

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

Question 20

Saturation can be defined as

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

Question 21

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

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

Question 22

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

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

Question 23

inhibitors bind reversibly at the active site of an enzyme.

Question 24

Which is not one of the major groups of enzymes according to the EC system?

A)hydrolase
B)oxidoreductase
C)protease
D)transferase
E)ligase

Question 25

The induced- fit model

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

Question 26

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

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

Question 27

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

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

Question 28

A competitive inhibitor

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

Question 29

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

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

Question 30

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

Question 31

The site on an enzyme that is designed for the substrate to bind is called the _.

Question 32

Which of the following does NOT accurately describe the Lineweaver- Burk plot?

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

Question 33

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

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

Question 34

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

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

Question 35

An enzyme

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