Bio-Chemistry Test 2 Practice Questions

the minimum amount of energy required to bring about a chemical reaction is called:
a. activation energy
b. enthalpy reaction
c. free energy
d. standard free energy
e. transition state

a. activation energy

which of the following is not a property of enzymes?
a. capable of being regulated
b. reaction rates high in comparison to uncatalyzed reaction
c. highly specific
d. side products of reactions are rare
e. all of the above are true

e. all of the above are true

within the enzyme is an intricately shaped surface for binding the reactants called the _______________.
a. substrate
b. cofactor
c. active site
d. apoenzyme
e. holoenzyme

c. active site

the lock and key model of enzyme activity proposes that each:
a. enzyme can react with only a single substrate
b. enzyme has a cofactor that promotes the catalytic activity
c. substrate has a specific cofactor that binds it to the enzyme
d. enzyme binds t

d. enzyme binds to a specific substrate because the active site and substrate is complementary to one another

the synthesis of enzymes in response to changing metabolic needs is referred to as:
a. enzyme induction
b. allosteric regulation
c. negative feedback
d. zymogen activation
e. cooperative binding

a. enzyme induction

which of the following is a prosthetic group?
a. NAD+
b. heme
c. none of the above

b. heme

which of the following classes of enzymes catalyze reactions involving the cleavage of bonds by the addition of water?
a. transferase
b. hydrolase
c. lyase
d. ligase
e. isomerase

b. hydrolase

the steady state assumption states that if:
k 1 = the rate constant for ES formation
k 2 = the rate constant for ES dissociation
k 3 = the rate constant for product formation
a. k2 is highly negligible compared with k3
b. the rate of formation of ES is eq

b. the rate of formation of ES is equal to the rate of its degradation over the course of the reaction

in the lineweaver-burke double reciprocal plot, the vertical intercept is equal to _______.
a. 1/[S]
b. 1/V
c. km/Vmax
d. 1/Vmax
e. -1/km

d. 1/Vmax

in competitive inhibition:
a. the Vmax of the reaction is not changed
b. both substrate and inhibitor bind at the same site on the enzyme
c. the km value is shifted to a higher [S]
d. all of the above are correct

d. all of the above are correct

enzyme control is accomplished in which of the following ways?
a. genetic control
b. covalent modification
c. allosteric regulation
d. compartmentation
e. all of the above are correct

e. all of the above are correct

zymogens are a feature of what type of enzymatic control?
a. genetic control
b. covalent modification
c. allosteric regulation
d. compartmentation
e. both b and c are correct

b. covalent modification

regulatory enzymes are a feature of what type of enzymatic control?
a. genetic control
b. covalent modification
c. allosteric regulation
d. compartmentation
e. both b and c are correct

c. allosteric regulation

positive cooperatively is a feature of what type of enzymatic control?
a. genetic control
b. covalent modification
c. allosteric regulation
d. compartmentation
e. both b and c are correct

c. allosteric regulation

segregation of biochemical pathways into different organelles is an example of which type of enzymatic regulation?
a. genetic control
b. covalent modification
c. allosteric regulation
d. compartmentation
e. both b and c are correct

d. compartmentation

enzymes increase the rate of the reaction by:
a. decreasing the rate of the reverse reaction
b. stabilizing the transition state
c. decreasing the activation energy of a reaction
d. increasing the energy released during a reaction
e. all of the above are

c. decreasing the activation energy of a reaction

enzymes act by ____________.
a. decreasing the energy of activation of a reaction
b. increasing the energy of activation of a reaction
c. raising the temperature of a reaction
d. providing a surface to favorably orient the reactants
e. both a and d are co

e. both a and d are correct

metabolons are defined as:
a. multifunction enzymes
b. complexes that channel product molecules from one active site to another
c. metabolic intermediates
d. effector molecules
e. rate of flow of metabolites from one point to another

c. metabolic intermediates

metabolic flux is best described as a:
a. lubrication enzyme that promotes the flow of reactants
b. rate of flow of metabolites from one another in a pathway
c. rate of a reaction
d. promoter molecule
e. both a and d are correct

b. rate of flow of metabolites from one another in a pathway

what is a zymogen (proenzyme)? explain.

a zymogen is an inactive form of an enzyme that is activated by one or more proteolytic cleavages in its sequence. chymotrypsinogen, trypsinogen, and proelastase are all zymogens, becoming chymotrypsin, trypsin and elastase, respectively, after proper cle

explain how a biochemist might discover that a certain enzyme is allosterically regulated?

the enzyme would show kinetics that do not fit the michaelis-menten equation; the plot of V vs [S] would be sigmoidal, not hyperbolic. the enzyme kinetics would be affected by molecules other than the substrate(s).

the scheme S -> T -> U -> V -> W -> X -> Y represents a hypothetical pathway for the metabolic synthesis of Y. the pathway is regulated by feedback inhibition. indicate where the inhibition is most likely to occur and what the likely inhibitor is.

S -> T -> U -> V -> W -> Y (most likely inhibitor)
^ v

why does the pH affect the activity of an enzyme?

the state of ionization of several amino acid chains is affected by pH, and the activity of many enzymes requires that certain of the amino acid residue side chains be in a specific ionization state.

enzymes are potent catalysts because they:
a. are consumed in the reactions they catalyze
b. are very specific and can prevent the conversion of products back to substrates
c. change the equilibrium constants for the reactions they catalyze
d. lower the a

d. lower the activation energy for the reactions they catalyze

which of the following statements is false?
a. a reaction may not occur at a detectable rate even though it has a favorable equilibrium
b. after a reaction, the enzyme involved becomes available to catalyze the reaction again
c. for s -> p, a catalyst shi

c. for s -> p, a catalyst shifts the reaction equilibrium to the right

the concept of "induced fit" refers to the fact that:
a. enzyme specificity is induced by enzyme-substrate binding
b. enzyme substrate binding induces an increase in the reaction entropy, thereby catalyzing the reaction
c. enzyme substrate binding induces

d. substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation

the steady state assumption, as applied to enzyme kinetics, implies:
a. km = ks
b. the enzyme is regulated
c. the ES complex is formed and broken down at equivalent rates
d. the km is equivalent to the cellular substrate concentration
e. the maximum veloc

c. the ES complex is formed and broken down at equivalent rates

which of these statements about enzyme catalyzed reactions is false?
a. at saturating levels of substrate, the rate of an enzyme catalyzed reaction is proportional to the enzyme concentration
b. if enough substate is added, the normal Vmax of a reaction c

c. the activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme catalyzed reaction

for enzymes in which the slowest (rate limiting) step is the reaction:
k2
ES -> P
km becomes equivalent to:
a. Kcat
b. the [S] where V0 = Vmax
c. the dissociation constant, kd, for the Es complex
d. the maximal velocity
e. the turnover number

c. the dissociation constant, kd, for the Es complex

the lineweaver-burke plot is used to:
a. determine the equilibrium constant for an enzymatic reaction
b. extrapolate for the value of reaction rate at infinite enzyme concentration
c. illustrate the effect of temperature on an enzymatic reaction
d. solve,

d. solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration

to calculate the turnover number of an enzyme, you need to know:
a. the enzyme concentration
b. the initial velocity of the catalyzed reaction at [S] >> km
c. the initial velocity of the catalyzed reaction at low [S]
d. the km for the substrate
e. both a

e. both a and b

the number of substrate molecules converted to product in a given unit of time by a single enzyme molecule at saturation is referred to as the:
a. dissociation constant
b. half saturation constant
c. maximum velocity
d. michaelis-menten number
e. turnover

e. turnover number

in competitive inhibition, an inhibitor:
a. binds at several different sites on an enzyme
b. binds covalently to the enzyme
c. binds only to the Es complex
d. binds reversibly at the active site
e. lowers the characteristics Vmax of the enzyme

d. binds reversibly at the active site

Vmax for an enzyme catalyzed reaction:
a. generally increases when pH increases
b. increases in the presence of a competitive inhibitor
c. is limited only by the amount of substrate supplied
d. is twice the rate observed when the concentration of substrat

d. is twice the rate observed when the concentration of substrate is equal to the km

which of the following statements about allosteric control of enzymatic activity is false?
a. allosteric effectors give rise to sigmoidal V0 vs. [S] kinetic plots
b. allosteric proteins are generally composed of several subunits
c. an effector may either

e. heterotropic allosteric effectors compete with substrate for binding sites

allosteric enzymes:
a. are regulated primarily by covalent modification
b. usually catalyze several different reactions within a metabolic pathway
c. usually have more than one polypeptide chain
d. usually have only one active site
e. usually show strict

c. usually have more than one polypeptide chain

for a reaction that can take place with or without catalysis by an enzyme, what would be the effect of the enzyme on the:
(a) standard free energy change of the reaction?
(b) activation energy of the reaction?
(c) initial velocity of the reaction?
(d) equ

(a) no change,
(b) decrease,
(c) increase,
(d) no change

the steady state assumption, as applied to enzyme kinetics, implies:
a. km = ks
b. the enzyme is regulated
c. the ES complex is formed and broken down at equivalent rates
d. the km is equivalent to the cellular substrate concentration
e. the maximum veloc

...