Enzyme Kinetics

Front 1

When varying the substrate concentration at a fixed concentration of enzyme it is observed that at low concentrations of substrate the reaction is ________,while at high concentrations of substrate the reaction is ________.

Back 1

First order

Zero order

Front 2

True or False

The lower the value of Km, the less tightly the enzyme is bound to the substrate.

Back 2

False

Front 3

To calculate the turnover number of an enzyme you need to know the:

A. initial velocity of the catalyzed reaction at low [S].

B. initial velocity of the catalyzed reaction at [S] >> Km.

C. Km for the substrate.

D. enzyme concentration.

E. both B and D.

Back 3

E

Front 4

Which of the following statements about a plot of V0 vs. [S] for an enzyme that follows Michaelis-Menten kinetics is false?

A. Km is the [S] at which V0 = 1/2 Vmax.

B. The shape of the curve is a hyperbola.

C. The y-axis is a rate term and the units could be something like μmol/min.

D. As [S] increases, the initial velocity of reaction, V0, also increases.

E. At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km.

Back 4

E

Front 5

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:

Back 5

Turnover number

Front 6

What are two essential things to consider when you want to determine the total amount of enzyme in a sample (given that the temperature, ionicstrength, and pH optimum have been determined)?

A. Max velocity is measured and [S]>>Km

B. Maximum velocity is measured and [S]<

C. Initial velocity is measured and [S] << Km

D. Initial velocity is measured and [S] >>Km

E. None of the above

Back 6

D

Front 7

In a first order chemical reaction, the velocity of the reaction is proportional to the ________, while in a zero order reaction, the velocity of the reaction is proportional to the ________.

Back 7

concentration of substrate

amount of enzyme

Front 8

The initial velocity of an enzyme reaction (vo) describes

Back 8

the rate of the reaction at when the substrate and enzyme are first mixed

Front 9

The Lineweaver-Burk plot and other linear transformation of the Michaelis-Menten curve of kinetics are valuable for:

A. determination of Km.

B. determination of Vmax.

C. determination of kcat.

D. determination of types of enzyme inhibition.

E. All of the above

Back 9

E

Front 10

True or False

Increasing the concentration of a classic competitive inhibitor has no effect on the maximum velocity of an enzyme-substrate reaction.

Back 10

True

Front 11

Vmax for an enzyme-catalyzed reaction:

A. generally increases when pH increases.

B. increases in the presence of a competitive inhibitor.

C. is unchanged in the presence of a uncompetitive inhibitor.

D. is about twice the rate observed when the concentration of substrate is equal to the Km.

E. is limited only by the amount of substrate supplied.

Back 11

D

Front 12

The Km and Vmax values of these enzymes for the substrate garbage are as follows:

Enzyme 1; Km = 0.1mmol Vmax = 5.0 mmol/min

Enzyme 2; Km = 0.3 mmol Vmax = 2.0 mmol/min

Enzyme 3; Km = 1.0 mmol Vmax = 5.0 mmol/min

Enzyme 4; Km = 3.0 mmol Vmax = 20.0 mmol/min

Which of the four enzymes is fastest at a saturating ATP concentration and a garbage concentration of 0.01 mmol/L?

Back 12

Enzyme 1

Front 13

The benefit of measuring the initial rate of a reaction, Vo, is that at the beginning of a reaction from substrate [S] to product [P]:

A. changes in [S] and [P] are negligible .

B. [ES] can be measured accurately.

C. Vo = Vmax.

D. changes in Km are negligible, so Km can be treated as a constant.

E. varying [S] has no effect on Vo.

Back 13

A

Front 14

Which of the following is NOT true of enzyme-catalysed reactions?

A. At high substrate concentrations, relative to the Km, the initial rate is independent of the substrate concentration

B.The substrate concentration which gives a half-maximum rate is sometimes a good measure of the binding affinity of the enzyme for the substrate

C. At low substrate concentrations, relative to the Km, the initial rate is proportional to the substrate concentration

D. The maximum rate of reaction is proportional to the concentration of the substrate

E. At high substrate concentration, relative to the Km, the initial rate is proportional to the concentration of the enzyme

Back 14

D

Front 15

In an enzyme reaction involving one enzyme and one substrate, the rate of the reaction depends on

A. substrate concentration.

B. enzyme concentration.

C. both substrate and enzyme concentrations.

D. the enzyme concentration at first and the substrate concentration later on.

Back 15

C

Front 16

In the Lineweaver-Burk plot of an enzyme reaction, the Km is given by the ________.

A. x-intercept

B. y-intercept

C. negative reciprocal of the x-intercept

D. reciprocal of the y-intercept

Back 16

C

Front 17

Alchohol dehydrogenase (ADH) requires NAD+ for catalytic activity. In the reation catalysed by ADH an alcohol is oxidized to an aldehyde as NAD+ is reduced to NADH and dissociates from the enzyme. The NAD+ is functioning as:

A. coenzyme and prosthetic group

B. cofactor

C. apoenzyme

D. coenzyme and cosubstrate

E. heterotropic effector

Back 17

D

Front 18

An enzyme-catalyzed reaction was carried out with the substrate concentration initially 1,000 times greater than the K m for that substrate. After 9 minutes, less than 1% of the substrate had been converted to product, and the amount of product formed in the reaction mixture was 12 mmol. If, in a separate experiment, one-third as much enzyme was used, how long would it take for the same amount (12 mmol) of product to be formed?

Back 18

27 mins

Front 19

The time that is required for an enzyme to convert one substrate molecule into one product molecule is:

A. Km

B. kcat

C. 1/Km

D. 1/kcat

Back 19

D

Front 20

Phosphorylation that changes an enzymeʹs activity is an example of ________.

Back 20

Covalent modifcation

Front 21

Enzymes differ from other catalysts in that enzymes:

A. lower the activation energy of the reaction catalyzed.

B. fail to influence the equilibrium point of the reaction.

C. form an activated complex with the reactants.

D. usually display specificity toward a single reactant.E. are not consumed in the reaction.

Back 21

D

Front 22

In competitive inhibition, an inhibitor:

A. binds at several different sites on an enzyme.

B. binds reversibly at the active site.

C. binds only to the ES complex.

D. binds covalently to the enzyme.

E. lowers the characteristic Vmax of the enzyme.

Back 22

B