Lecture 2. Basic Enzyme Kinetics

Question 1

What conditions do study-state studies involve and why?

Answer 1

[S] > > [E] so that v can be measured over a reasonable period

Question 2

What does v represent?

Answer 2

The steady-state rate of reaction

Question 3

Within the steady-state what is v proportional to?

Answer 3

[E]

Question 4

What is the relationship between v and [S] at low [S] and [E] is constant?

Answer 4

v is proportional to [S]

Question 5

What is the relationship between v and [S] at high [S] and [E] is constant?

Answer 5

v becomes constant

Question 6

When enzyme becomes saturated at high [S], what is rate?

Answer 6

Vmax

Question 7

Enzyme, substrate and product model

Answer 7

E + S ⇌ ES → E + P

Question 8

What does ka represent?

Answer 8

E + S → ES

Question 9

What does kd represent?

Answer 9

ES → E + S

Question 10

Dissociation constant equation

Answer 10

K = [E][S]/[ES] = kd/ka

Question 11

What in most cases the slowest step in the model?

Answer 11

ES → E + P

Question 12

What is the Michaelis-Menten equation?

Answer 12

v = (Vmax x [S])/(Km + [S])

Question 13

What is the value of Km when v equals half of Vmax?

Answer 13

Km = [S]

Question 14

What is Vmax?

Answer 14

The maximum velocity and shows how fast the enzyme can work

Question 15

What is Km?

Answer 15

The Michaelis constant

Question 16

What is Km a measure of?

Answer 16

Affinity and shows the [S] range over which the enzyme works

Question 17

What is enzyme efficiency represented as?

Answer 17

kcat/Km

Question 18

What are the units for enzyme efficiency?

Answer 18

s⁻¹M⁻¹

Question 19

Does Vmax vary with [E]?

Answer 19

Yes

Question 20

What happens to Km and Vmax when one enzyme accepts two different substrates under identical conditions and [E] is the same?

Answer 20

Vmax stays the same but Km may vary

Question 21

What are the axes for the Lineweaver-Burk plot?

Answer 21

x axis = 1/[S]
y axis = 1/v

Question 22

On a Lineweaver-Burk plot, what does the y-intercept represent?

Answer 22

1/Vmax

Question 23

On a Lineweaver-Burk plot, what does the x-intercept represent?

Answer 23

-1/Km

Question 24

On a Lineweaver-Burk plot, what does the gradient represent?

Answer 24

Km/Vmax