Biochemistry Exam 2 Chapter 10

Front 1

An Apoenzyme is
A) The enzyme containing its prosthetic group
B) An enzyme minus its prosthetic group
C) A cofactor that is very tightly bound to the enzyme
D) A cofactor that is very tightly bound to the enzyme
E) A small molecule required for activity

Back 1

B) An enzyme minus its prosthetic group

Front 2

Vmax does NOT change in
A) Sequential mechanisms
B) Noncompetitive inhibition.
C) Ping pong mechanisms.
D) Competitive inhibition
E) Noncompetitive inhibition

Back 2

D) Competitive inhibition

Front 3

Which statements about the two different models proposed to explain enzyme specificity is CORRECT.
A) The substrate changes shape when enzyme binds in the Lock and Key Model.
B) The enzyme undergoes a covalent modification when bound to substrate in the Lock and Key Model.
C) The active site of the enzyme alternates in conformation between opened and closed in the Induced Fit Model.
D) The enzyme changes conformation after binding the substrate in the Induced Fit Model.
E) The product structure is altered after it has bound to the enzyme in the Induced Fit Model.

Back 3

D) The enzyme changes conformation after binding the substrate in the Induced Fit Model.

Front 4

First order reactions
A) are independent of the substrate concentration.
B) have rates of reactions that are constant.
C) are observed at high substrate concentrations
D) have rates of reactions that are inversely proportional to the substrate concentration.
E) have rates of reactions that are directly proportional to the substrate concentration.

Back 4

E) have rates of reactions that are directly proportional to the substrate concentration.

Front 5

Competitive inhibitors
A) covalently modify the enzyme.
B) bind to allosteric sites on the enzymes
C) lower the maximum velocity of the reaction
D) increase the Km of the enzyme for the substrate
E) increases the maximum velocity of the reaction.

Back 5

D) increase the Km of the enzyme for the substrate

Front 6

All of the following statements about allosteric effectors are correct EXCEPT:
A) they can change either the Km or the Vmax of the reaction
B) they cause a conformational change in the enzyme
C) they bind at the substrate-binding site
D) they may decrease the enzyme’s affinity for its substrate
E) they may increase the enzyme’s affinity for its substrate

Back 6

C) they bind at the substrate-binding site

Front 7

What is the purpose of pyrophosphatase in biochemical reactions? PPi + H2O --propophosphatase--> 2 Pi
A) as a symport transporter for phosphate
B) as a pore forming agent
C) as an inhibitor of PGP
D) as a flippase to move aminophospholipids
E) to help drive unfavorable reactions

Back 7

E) to help drive unfavorable reactions

Front 8

True/False
An apoenzyme is a term given to an enzyme having a required cofactor or required coenzyme bound to the enzyme.

Back 8

False

Front 9

True/False
In a first order reaction, the rate of product formation is dependent on the concentration of only one reactant.

Back 9

True

Front 10

True/False
Metal ions, such as copper, iron and manganese are cofactors that bind to the enzyme and participate in catalysis by donating or accepting electrons due to their empty D orbitals.

Back 10

True

Front 11

True/False
Most allosteric enzymes are oligomeric and binding of an activator or inhibitor to a single substrate can change the conformation of the other subunits thus impacting substrate binding affinity.

Back 11

False

Front 12

True/False
The difference between the “Lock and Key” model vs. the “Induced fit model for substrate binding is the ability of the substrate to change conformation upon binding to the enzyme.

Back 12

False

Front 13

True/False
Aspartic acid and glutamic acid, which have a pKa of approximately 4, usually participate in Acid-Base Catalysis because they can readily donate and except protons at physiological pH.

Back 13

False

Front 14

Which of the following statements are not assumptions for the development of the Michaelis-Menten Rate Expression
A. The kon and the koff for the substrate are equal.
B. At [S] in which there is no free enzyme ([E]total= [ES]), the rate of product formation is equal to k3.
C. The rate of association, k1, of the substrate to the enzyme is equal to the rate of dissociation, k2, of the substrate from the enzyme.
D. The Michaelis Constant, KM, is mathematically expressed as (k2+k3)/k1.
E. A and C

Back 14

E. A and C

Front 15

Which of the following are not general characteristics of enzymes?
A. EX complexes are often held together by disulfide bonds –S-S-.
B. Enzymes increase reaction rates by lowering the activation energy barrier.
C.ES complexes are held together by noncovalent interactions (hydrogen bonds, hydrophobic interactions, ionic bond).
D.Enzymes usually are substrate specific.
E.The catalytic activity of some enzymes can be regulated.
F.All enzymes show allosteric properties.
G. A and F

Back 15

G. A and F

Front 16

Which of the statements about a transition state analog is false?
A. It usually is a strong inhibitor of the enzyme.
B. It fits better into the active site than the substrate.
C. It is a stable molecule and has a structure similar to the presumed transitions state.
D. It would probably function as a noncompetitive inhibitor of the enzyme.

Back 16

D.It would probably function as a noncompetitive inhibitor of the enzyme.

Front 17

Which statement is true regarding the action of an enzyme?
A. An enzyme usually binds the substrate more tightly than the transition state.
B. An enzyme usually binds the product more tightly than the transition state.
C. An enzyme stabilizes the transition state for the reaction more than the Enzyme-substrate (ES) complex.
D. An enzyme usually binds S and P with equal affinity.

Back 17

C. An enzyme stabilizes the transition state for the reaction more than the Enzyme-substrate (ES) complex.

Front 18

A reaction whose rate is not dependent on the concentration of reactions is termed a _________order reaction. The rate constant has the units _______________.

Back 18

Zero
Molar or moles/Unit time

Front 19

A reaction whose rate is dependent on the concentration of reactant is termed a ____________ order reaction. The rate constant has the units ____________________.

Back 19

First
1/unit time or time-1

Front 20

3.A reaction involving two reactants with one reactant being in far excess of the second reactant such that the change in the concentration of the reactant in excess is negligible yields a type of ordered reaction that is termed _________________.

Back 20

pseudofirst order

Front 21

3.In a multisubstrate enzyme catalyzed reaction where product formation is dependent on the order of substrate binding, the type of reaction mechanism is termed a _____________reaction mechanism whereas product formation is independent of the order of substrate binding is termed a _____________ reaction mechanism.

Back 21

sequential
random

Front 22

True/False
An enzyme increases the reaction rate of a chemical reaction by lowering the overall free energy of the reaction.

Back 22

False

Front 23

True/False
In a single substrate enzyme catalyzed reaction the fact that the reaction rate is dependent on the concentration of substrate and enzyme makes it a second order reaction.

Back 23

False

Front 24

True/False
Cofactors are inorganic ions that bind to an enzyme stabilize the electron configuration of the substrate thus facilitating catalysis.

Back 24

True

Front 25

True/False
An enzyme in which its coenzyme or cofactor has been removed is called a holoenzyme.

Back 25

False

Front 26

True/False
Derivation of the Michaelis Menten Equation for an enzyme catalyzed reaction is based on the first assumption that the rate of enzyme-substrate complex formation is equal to the rate of enzyme-substrate complex degradation.

Back 26

True

Front 27

True/False
The second assumption for the Michaelis Menten Equation Derivation is that all of the enzyme is bound by substrate (i.e., all the enzyme active sites are saturated with substrate) and there is no unbound enzyme.

Back 27

True

Front 28

True/False
The Km is the product of the rate of association plus the rate of dissociation of the substrate to the enzyme divided by the rate of conversion of the enzyme substrate complex to enzyme plus product.

Back 28

False

Front 29

True/False
If all of the enzyme is bound by substrate, then the rate of product formation will be maximal, i.e. v=Vmax=k3[ES].

Back 29

True

Front 30

True/False
Methotrexate, a drug that impacts amino acid synthesis and nucleic acid synthesis is most effective because it is an allosteric effector of dihyrofolate reductase resulting in a reduction in the Vmax and having no effect on binding of folate to the enzyme.

Back 30

False

Front 31

A _______________ order reaction proceeds at the rate proportional to the concentration of one reactant and the half-life (t ½) = 0.693/k.

Back 31

first

Front 32

A ________________ order rate constant k has the units of M-1 s-1 and the half life (t ½ )= 2.303/k([A0]-B0])

Back 32

second

Front 33

_______________ is a type of enzyme in which the coenzyme and/or cofactor have been removed.

Back 33

apoenzyme

Front 34

______________________ is a type of inhibition when the amount of product exceeds the amount of substrate.

Back 34

Product inhibition

Front 35

True/False
Enzyme catalyzed reactions will change the overall free energy of the reaction.

Back 35

False

Front 36

True/False
Enzyme catalyzed reactions will change the free energy of activation of the reaction.

Back 36

True

Front 37

True/False
In enzyme-catalyzed reactions, the enzyme doesn’t change the equilibrium constant, and it just change the rate at which the reaction reach equilibrium.

Back 37

True

Front 38

True/False
A transition state analog is a type of enzyme inhibitor that binds to an allosteric binding site on the enzyme.

Back 38

False

Front 39

True/False
In an acid/based catalyzed reaction, if the pH is above the pK of the conjugate acid donor, the rate of the reaction is decreased.

Back 39

True

Front 40

True/False
In covalent catalysis, the enzyme becomes covalently modified with one of the reactants.

Back 40

True

Front 41

True/False
A Ping-Pong reaction mechanism refers to a dual substrate enzyme catalyzed reaction where product formation is independent of the order of substrate binding to the enzyme.

Back 41

False

Front 42

True/False
One way an allosteric activator can increase the rate of product formation is to increase the on-rate (kon) and decreases the off-rate (koff) of a substrate.

Back 42

True

Front 43

Which of the following is NOT related to rate accelerations derived from the binding of substrate to enzyme?
A. Decrease off rate for enzyme substrate binding.
B. reduction of entropy
C. acid-base catalysis
D. enzyme-substrate specificity

Back 43

B. reduction of entropy

Front 44

The Serine protease reaction mechanism involves:
A. acid – base catalysis only
B. covalent catalysis only
C. metal ion catalysis only
D. acid-base and covalent catalysis
E. acid – base, covalent and metal ion catalysis

Back 44

D. acid-base and covalent catalysis

Front 45

Which of the following are "broad themes used in discussing enzyme reaction mechanisms"?
A. Proximity stabilization
B. Transition state stabilization
C. Acid-base catalysis
D. Covalent catalysis
E. All of the above

Back 45

E. All of the above

Front 46

In enzyme-catalyzed reactions, which of the following change?
A. overall free energy between reactants and products.
B. free energy of activation
C. reaction equilibrium constant
D. transition state
E. the reaction rate
F. initial state
G. B and E

Back 46

F. B and E

Front 47

_________________ is a term given to an enzyme having a required cofactor or required coenzyme bound to the enzyme.

Back 47

Holoenzyme

Front 48

In a _______________ order reaction, the rate of product formation is dependent on the concentration of only one reactant.

Back 48

First

Front 49

____________ are cofactors that bind to the enzyme and participate in catalysis by donating or accepting electrons due to their empty D orbitals.

Back 49

Metal Ions

Front 50

True/False
An allosteric activator decreases the Km of an enzyme catalyzed reaction.

Back 50

True

Front 51

True/False
The rate of product formation in a zero order reaction is independent of reactant concentrations.

Back 51

True

Front 52

True/False
The KM of an enzyme catalyzed reaction is equal to the concentration of substrate that yields the maximum reaction velocity.

Back 52

False

Front 53

True/False
A competitive inhibitor could reduce the Km of the enzyme reaction but does not affect the maximum velocity of the reaction.

Back 53

True

Front 54

True/False
A non-competitive enzyme inhibitor binds to a site on the enzyme other than the active.

Back 54

True

Front 55

True/False
Ribonuclease cleavage of RNA is an example of a substrate strain mechanism of for enzyme catalysis.

Back 55

False

Front 56

True/False
Hydrolysis of a peptide bond in a protein by chymotrypsin is an example of covalent catalysis.

Back 56

True

Front 57

An enzyme catalyzed chemical reaction
a.) increases the rate of the reaction by decreasing the energy of activation.
b.) is first order in the at low substrate concentration and is zero order at substrate concentrations that approach saturation.
c.) may require a metal ion to be bound to the enzyme or substrate for catalysis.
d.) is affected by pH and temperature.
e.) All of the above

Back 57

e.) All of the above

Front 58

Which of the following assumptions is INCORRECT for transforming the enzyme rate equation into a Michaelis-Menton Equation:
a.) The [ES] complex is in a steady state, i.e. the [ES] concentration remains constant.
b.) There is no free enzyme, i.e. all the enzyme is bound by the substrate
c.) The rate of the product formation is equal to Vmax=k3[ES]
d.) The kon and the koff for the substrate are equal.
e.) None of the above

Back 58

d.) The kon and the koff for the substrate are equal.

Front 59

In all enzymes, the active site:
a. Contains the substrate-binding site
b. Is contiguous which the substrate binding site in the primary sequence
c. Lies in a region of the primary sequence distant from the substrate binding site
d. contains a metal ion as a prosthetic group
e. contains the amino acid side chains involved in catalyzing the reaction

Back 59

e. contains the amino acid side chains involved in catalyzing the reaction

Front 60

Although enzymic catalysis is reversible, a given reaction may appear irreversible:
A. if the products are thermodynamically far more stable than the reactants
B. under equilibrium conditions
C. if a product accumulates
D. at high enzyme concentrations
E. at high temperature

Back 60

A. if the products are thermodynamically far more stable than the reactants

Front 61

Metal cations may do all of the following except:
a. donate electron pairs to functional groups found in the primary structure of the enzyme
b. serve as Lewis acids in enzymes
c. participate in oxidation-reduction processes
d. stabilize the active conformation of an enzyme
e. form chelates with the substrate, with the chelate being the true substrate

Back 61

a. donate electron pairs to functional groups found in the primary structure of the enzyme

Front 62

If the plasma activity of an intracellular enzyme is abnormally high all of the following may be a valid explanation except:
a. the rate of removal of the enzyme from plasma may be depressed
b. tissue damage may have occurred
c. the enzyme may have been activated
d. determination of the isoenzyme distribution may yield useful information
e. the rate of synthesis of the enzyme may have increased

Back 62

e. the rate of synthesis of the enzyme may have increased

Front 63

All of the following are correct about allosteric effectors except:
a. they may increase the enzyme's affinity for its substrate
b. they may decrease the enzyme's affinity for its substrate
c. they bind at the substrate-binding site
d. they cause a conformational change in the enzyme
e. they can change either Km or the Vmax of the reaction

Back 63

c. they bind at the substrate-binding site

Front 64

Most allosteric enzymes:
a. are monomers
b. have more than one subunit
c. exhibit only homotropic interactions
d. exhibit only heterotropic interactions
e. bind the allosteric effector with no effect on binding other ligands

Back 64

b. have more than one subunit.
Most are oligomers