Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

CHE 541 > 13 - Enzyme Kinetics II > Flashcards

13 - Enzyme Kinetics II Flashcards

1
Q

How is product change over time usually measured?

A

Through absorbance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is an example of measuring product change?

A

Beta-galactosidase: cleave into galactose and a red absorbance molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the Michaelis Menten curve?

A

v0 vs S

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

For increasing E, how does vmax change?

A

Vmax is proportional to E (vmax = kcatE)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

For increasing E, how does Km change?

A

Km is independent of E

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How come Km and kcat do not change with more E or S?

A

They are inherent properties of the enzyme

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What properties does Km describe?

A

Relative binding affinity, conversion from S –> P

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does a low Km mean?

A

High affinity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the Lineweaver-Burk plot?

A

A linear form of the Michaelis Menten equation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the equation for the Lineweaver-Burk plot?

A

1/v0 = Km/(vmax*S) + 1/vmax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is plotted in a Lineweaver-Burk plot?

A

1/v0 vs 1/S

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the slope of a Lineweaver-Burk plot?

A

Km/vmax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the y-intercept of a Lineweaver-Burk plot?

A

1/vmax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the problem with the Lineweaver-Burk plot?

A

It can be inaccurate for low S (reciprocal)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the Hanes-Woolf plot?

A

Multiply the Lineweaver-Burke plot by [S] to remove reciprocal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is inhibition?

A

Prevention of catalytic reaction (slow or halt)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the two classes of inhibition?

A

Reversible and irreversible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is an example of an irreversible inhibitor?

A

Asprin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How does asprin work?

A

It transfers a group to the active site to prevent activity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is an example of a reversible inhibitor?

A

Ibuprofin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How does ibuprofin work?

A

It is at equilibrium between the enzyme (bound and unbound)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Which type of inhibition is modifying the enzyme?

A

Irreversible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What time scale is needed for irreversible inhibition?

A

Life time of enzyme

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What type of inhibition is a Kd process?

A

Reversible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What time scale is needed for reversible inhibition?

A

Therapeutic window (peaks)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is Ki?

A

Dissociation constant for inhibitors to free enzyme

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What are the three types of reversible inhibitors?

A

Competitive, noncompetitive, and uncompetative

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is a competitive inhibitor?

A

Bind to free enzyme

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is an uncompetitive inhibitor?

A

Bind to ES complex (or subsequent species, ES –> E + P)

30
Q

What is a noncompetitive inhibitor?

A

Interferes with both processes (mixed) (E and ES)

31
Q

What happens during competitive inhibition?

A

I resembles S but cannot undergo reaction, so I and S compete with E (decreases ES)

32
Q

What happens at very high S for competitive inhibition and why?

A

The reaction will reach vmax, because it will outcompete

33
Q

What kinetic parameters change with competitive inhibition?

A

Km

34
Q

What kinetic parameters do not change in competitive inhibition?

A

vmax

35
Q

What happens when I increases for a competitive inhibitor?

A

Apparent Km increases

36
Q

What does a competitive inhibitor look like in a Lineweaver-Burk plot?

A

At increasing inhibitors, the lines will intersect at the y-axis (higher slopes)

37
Q

How can you determine Ki for a competitive inhibitor?

A

Plot Km(app) vs. I, and the x-intercept is -Ki

38
Q

What happens during uncompetitive inhibition?

A

S and I bind at the same time to different sites of the enzyme, affecting catalytic function (not substrate binding)

39
Q

What are some mechanisms of uncompetitive inhibition?

A

May cause structural distortion in active site, making enzyme less competent, or may prevent product disassociation

40
Q

What kinetic parameters change with an uncompetitive inhibitor?

A

vmax, Km

41
Q

What kinetic parameters do not change with uncompetitive inhibitor?

A

vmax/Km (ratio)

42
Q

What does an uncompetitive inhibitor look like in a Lineweaver-Burk plot?

A

At increasing I, there will be parallel lines (larger y intercept)

43
Q

How can you determine Ki from an uncompetitive inhibitor?

A

Plot S/vo vs. I at increasing S levels, and they will intersect at -Ki’

44
Q

What does Ki’ represent?

A

Dissociation constant of I from the ESI complex

45
Q

What type of inhibition can allosteric be?

A

Uncompetitive or noncompetitive

46
Q

How can the mechanism of inhibition be determined?

A

Through kinetic assays

47
Q

What happens during noncompetitive inhibition?

A

I binds whether or not the substrate is bound (not active site) (interferes with both processes)

48
Q

What kinetic parameters change with noncompetitive inhibition?

A

vmax, Km

49
Q

What kinetic parameters do not change in noncompetitive inhibition?

A

None

50
Q

What does noncompetitive inhibition look like in a Lineweaver plot?

A

At increasing I, the lines will intersect left of the y-axis (increasing slopes)

51
Q

How can Ki and Ki’ be determined for a noncompetitive inhibitor if Ki = Ki’?

A

Plot S/vo vs I at increasing S, and they will intersect at -Ki

52
Q

How can Ki and Ki’ be determined for a noncompetitive inhibitor if Ki does not equal Ki’?

A

Need two plots (1/vo vs. I and S/vo vs. I at increasing S levels) to determine parameters (where lines intersect)

53
Q

What is the problem with Ki?

A

It is a lot of work to calculate Ki for every inhibitor

54
Q

What is the IC50%?

A

The I that gives 50% inhibition at a specific enzyme and substrate concentration

55
Q

What is the advantage of the IC50%?

A

It is quick and easy to calculate

56
Q

If E and S are kept constant, what is IC50% a measure of?

A

Relative ability to inhibit enzyme

57
Q

How can IC50% be calculated?

A

Plot vi/vo vs log(I), and find the I value where vi/vo = 0.5

58
Q

What is the relationship between Ki and IC50%?

A

If Km and type of inhibition are known, the Cheng and Prusoff relationships can be used to calculate Ki from IC50%

59
Q

What is the goal in drug discovery?

A

Want high affinity

60
Q

What is the problem with high affinity inhibitors?

A

Difficult to ensure E &laquo_space;I

61
Q

What happens to IC50% if the affinity is very high?

A

The potency can be underestimated

62
Q

When does problems with IC50% occur?

A

When Ki is close or less to [E]

63
Q

How come [E] cannot be dropped too much?

A

Need to detect the reaction with a certain level of E

64
Q

What is critical for tight binding inhibition?

A

The ratio of apparent Ki/Etot

65
Q

What happens if Ki/Etot > 10?

A

Not tight binding, IC50% = Ki apparent

66
Q

What happens if Ki/Etot is between 10 and 10^-2?

A

IC50% = Ki(app) + 0.5Etot

67
Q

When happens if Ki/Etot < 0.01?

A

Dissociation is negligible, and Ki(app) cannot be determined (IC50% = 0.5Etot)

68
Q

What is slow onset inhibition?

A

The binding of inhibitor to enzyme converts into a final complex

69
Q

What is the formula for slow onset inhibition?

A

E + I –> EI –> EI*

70
Q

What is the slow step for slow onset inhibition?

A

Structural reorganization (low koff, EI –> EI*)

71
Q

What is koff for slow onset inhibition?

A

How rapidly the enzyme-inhibitor complex dissasociates

72
Q

How some slow onset inhibitors are good drugs?

A

They dissociate slowly from the target enzyme, enzyme remains inhibited when drug concentration decreases, and have long residence time (slow dissociation)

CHE 541 (20 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions