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Flashcards in Enzymes (Ross) Deck (22):
1

At what values of ΔGo′ and Keq are the products favored?

ΔGo′ less than 0
Keq greater than 1

2

At what values of ΔGo′ and Keq are the reactants favored?

ΔGo′>0
Keq less than 1

3

What is the equation for Gibb's free energy?

ΔG=ΔGo′+RTlnKeq

4

Name the four different catalytic strategies

Covalent catalysis
General acid-base catalysis
Catalysis by approximation
Metal ion catalysis

5

What is the Michaelis-Menten equation?

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

6

What relation describes the fraction of active sites filled?

[ES]/[E]total=Vo/Vm=[S]/(Km+[S])

7

What are the assumptions of the Michaelis-Menten equation?

•Formation of ES complex
•No back reaction from product buildup i.e. k4=0
•Initial velocities used for analysis
•Steady state assumption for [ES]
•Negligible depletion of substrate i.e. [S]>[E]

8

Define the Michaelis constant Km

Km=(k2+k3)/k1

9

Define the turnover number and what it measures

Turnover number=k3=kcat
Measure of the catalytic ability of the enzyme when the active sites are saturated

10

Define catalytic efficiency

Kcat/Km

11

What is a perfect enzyme?

One whose catalytic efficiency is limited only by the rate of diffusion of the substrate to the enzyme

12

What the characteristics of the Lineweaver-Burk plot?

x-int=-1/Km
y-int=1/Vm
slope=Km/Vm

13

For two-substrate kinetics, name the three types of mechanisms

Ordered sequential
Random sequential
Ping-pong (double replacement)

14

Describe the changes in Vm, Km, and Kcat/Km for competitive inhibitors

Vm stays the same
Km increases
kcat/Vm decreases

15

Describe the changes in Vm, Km, and Kcat/Km for noncompetitive inhibitors

Vm decreases
Km stays the same
kcat/Vm decreases

16

Describe the changes in Vm, Km, and Kcat/Km for uncompetitive inhibitors

Vm decreases
Km decreases
kcat/Vm stays the same

17

Describe the changes in the Lineweaver-Burk plot for competitive inhibitors

Y-intercept stays the same, slope increases

18

Describe the changes in the Lineweaver-Burk plot for noncompetitive inhibitors

X intercept stays the same, slope increases

19

Describe the changes in the Lineweaver-Burk plot for uncompetitive inhibitors

Slope stays the same, line moves higher

20

Describe the effect of irreversible inhibitors on Michaelis-Menten parameters

Vm decreases
Km stays the same

21

Name the three types of irreversible inhibitors

Group-specific reagents
Affinity labels
Suicide inhibitors

22

Why don't allosteric enzymes fit into the Michaelis-Menten model?

Show sigmoidal relationship between velocity and substrate