Chapter 6: Enzyme Kinetics

Question 1

what are enzyme kinetics

Answer 1

the study of the rate of an enzyme-catalyzed reaction

learn about enzyme mechanism

learn about mechanism of inhibition

Question 2

rate is equal to ___ which is…

Answer 2

velocity (Vo) in mol/sec

change in [P] / change in [t]

Question 3

graphing Vo vs. [S]

Answer 3

curve that never reaches Vmax

at some point adding more substrate doesn’t increase rate

graph is linear at low [S] and plateaus at high [S]

Question 4

Michaelis-Menten Equation

Answer 4

Vo = Vmax[S] / (Km + [S])

Question 5

what is the rate limiting step in MM

Answer 5

K2

ES —-> E+P

Vo = K2[ES]

Question 6

what is Km?

Answer 6

a constant of K-1, K2, and K1

Question 7

what happens when [S] &laquo_space;Km

Answer 7

equation becomes Vmax[S] / Km

Question 8

what happens when [S]&raquo_space; Km

Answer 8

Vo = Vmax

Question 9

what happens when [S] = Km

Answer 9

equation becomes Vo = Vmax/2

Question 10

when does Km = [S]?

Answer 10

when 1/2 active sites are filled

Question 11

at 1/2 Vmax…

Answer 11

[S] = Km

Question 12

sometimes K1&raquo_space; K2

Answer 12

ignore k2 in Km calculations

Km ~ K-1/K1

Question 13

Kcat

Answer 13

rate constant for rate-limiting step

Kcat = Vmax/[Et] units s-1

Question 14

do you want a high Kcat?

Answer 14

yes, it’s how fast the enzyme works/second

Question 15

comparing enzymes when [S] &laquo_space;Km

Answer 15

Vo = Kcat/Km x [E][S]

Question 16

Kcat/Km

Answer 16

specificity constant

measure of catalytic efficiency

Question 17

when is an enzyme with high Kcat limited?

Answer 17

by affinity for the substrate

by diffusion speed of E+S —> ES

Question 18

upper limit of Kcat/Km

Answer 18

10^8 to 10^9 m-1s-1

catalytic perfection

Question 19

double reciprocal plot

Answer 19

Lineweaver-Burke 1/Vo = Km / Vmax[S] + 1/Vmax

Question 20

axes, intercepts, and slope in double reciprocal

Answer 20

y-axis = 1/Vo

x-axis = 1/[S]

y-intercept = 1/Vmax

x-intercept = -1/Km

slope = Km/Vmax