Brainscape's Knowledge GenomeTM

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


See full index

BMS02 > Enzyme Kinetics > Flashcards

Enzyme Kinetics Flashcards

1
Q

What is enzyme kinetics?

A

The study of the rate of an enzyme-catalysed reaction and how that rate varies with different conditions

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

What is the rate of a reaction?

A

Decrease in substrate concentration/increase in product concentration

Per unit time

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

Describe the rate-concentration graph of a typical enzyme with saturation hyperbolic kinetics

A

Michaelis-Menten

Low substrate concentration = linear/first order as rate is proportional to [substrate]

High substrate concentration= zero order as rate is independent of [substrate]

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

What is Vmax?

A

The maximum velocity of a reaction that occurs at infinite substrate concentration

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

What is the Michaelis-Menten reaction model?

A

E + S —> ES —> E + P

With rate constants

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

What assumptions do we make when using the Michaelis-Menten reaction model?

A

[S] is much greater than [E] so only a small amount of substrate bound at any one time

[ES] does not change with time (formation = breakdown into E+S/P) - steady state approximation

Initial velocities used so [P] is small so E + P —> ES can be ignored (k-2)

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

What equation is used to find the rate of a reaction?

A

V0 = (Vmax.[S]) / (Km+[S])

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

What does the substrate concentration represent when V0 = Vmax/2?

A

Km

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

How do you calculate Km using rate constants?

A

Km = (K2 + K-1) / K1

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

When is Km approximately the Kd for ES?

A

When K2 is very small/rate-limiting

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

What does Km represent when K2 is rate-limiting?

A

Measurement of affinity of enzyme for its substrate in the ES complex (Kd)

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

What does a low Km mean?

A

High affinity of enzyme for substrate

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

What is Kcat?

A

Turnover number

Number of substrate molecules converted to product in a given unit of time on a single enzyme molecule when saturated with substrate

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

What is the equation relating Vmax, Kcat and [E]t?

A

Vmax = Kcat.[E]t

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

What does a high Kcat mean?

A

Reaction can occur faster (higher Vmax)

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

What is the specificity constant?

A

Number used to quantify catalytic efficiency of enzymes

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

How do you calculate the specificity constant?

A

Specificity constant = Kcat / Km

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

What does a high specificity constant show?

A

Enzyme is very efficient

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

What is the Lineweaver-Burk equation?

A

1/V0 = Km/Vmax . 1/[S] + 1/Vmax

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

What are on the axes of a Michaelis-Menten graph?

A

X = [S]

Y = initial reaction velocity

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

What are on the axes of a Lineweaver-Burk plot?

A

X = 1/[S]

Y = 1/V0

22
Q

How do you find 1/Vmax on a Lineweaver-Burk plot?

A

Y-intercept

23
Q

How do you find -1/Km on a Lineweaver-Burk plot?

A

X-intercept

24
Q

What does the y-intercept represent on a Lineweaver-Burk plot?

A

1/Vmax

25
Q

What does the x-intercept represent on a Lineweaver-Burk plot?

A

-1/Km

26
Q

How can you calculate the gradient of a Lineweaver-Burk plot?

A

Km/Vmax

27
Q

What is an example of a competitive inhibitor?

A

Malonate inhibiting succinate dehydrogenase

28
Q

How does a competitive inhibitor work?

A

Similar chemical structure to substrate

Binds to active site of enzyme but does not activate/react

29
Q

What value does a competitive inhibitor affect?

A

Km = [S] must increase to outcompete inhibitor

Vmax unaffected as inhibitor can be surmounted

30
Q

What value does a non-competitive inhibitor affect?

A

Vmax = turnover of substrate prevented and effect cannot be surmounted

(Km unaffected as inhibitor does not affect affinity of enzyme for its substrate)

31
Q

What do ACE inhibitors do in the body?

A

Inhibit ACE (angiotensin converting enzyme)

So no angiotensin II produced

So no periphery vasoconstriction

Blood pressure does not increase

32
Q

What is an example of an ACE inhibitor?

A

Captopril

33
Q

What is a competitive reversible inhibitor of acetylcholine-esterase?

A

Neostigmine

34
Q

What is a competitive irreversible inhibitor of acetylcholine-esterase?

A

Diisopropyl fluorophosphate/dyflos

35
Q

How does neostigmine work?

A

Competitive reversible inhibitor of acetylcholine-esterase

Forms covalent bond with Ser (of catalytic triad)

Bond is hydrolysed over time

36
Q

How does diisopropyl fluorophosphate work?

A

Competitive irreversible inhibitor of acetylcholine-esterase

Bonds covalently with no spontaneous hydrolysis

37
Q

What can be used to reactivate AChE after using diisopropyl fluorophosphate?

A

Pralidoxime

38
Q

What are neostigmine and diisopropyl fluorophosphate used to treat?

A

Alzheimer’s disease

39
Q

How can enzyme activity be regulated?

A

Allosteric regulators with allosteric enzymes

Covalent modification by other enzymes

Induction/repression of enzyme synthesis

40
Q

What kind of graph represents the enzyme activity of an allosteric enzyme?

A

Sigmoid

41
Q

What is an example of allosteric inhibition?

A

ATP and citrate on phosphofructokinase

42
Q

What is an example of allosteric activation?

A

Phosphoenol pyruvate (PEP) and fructose-1,6-bisphosphate on pyruvate kinase

43
Q

What residues are usually (de)phosphorylated in covalent modifications?

A

Ser

Thr

Tyr

His

44
Q

How is covalent modification used to activate and inactivate glycogen phosphorylase?

A

Phosphorylase kinase phosphorylates Ser 14 using ATP to activate

Phosphorylase phosphatase dephosphorylates Ser 14 to inhibit

45
Q

What are some types of covalent modification of enzymes?

A

Phosphorylation

Adenylylation/Uridylylation of Tyr

ADP ribosylation (Arg, Gln, Cys)

Methylation (Glu)

Acetylation (Lys)

46
Q

What happens in adenylylation/uridylylation?

A

ATP or UDP —> PPi

Tyrosine residues

47
Q

What happens in ADP ribosylation?

A

Arg, Gln, Cys

NAD —> nicotinamide

48
Q

What happens in methylation?

A

Glu

S-adenosyl-methionine —> S-adenosyl-homocysteine

49
Q

What happens in acetylation?

A

Lys on histones

Increased transcription

50
Q

What is an example of induction of enzyme synthesis?

A

High blood glucose stimulates insulin release

Insulin increases rate of synthesis of key enzymes involved in glucose metabolism (glucokinase, phosphofructokinase, pyruvate kinase)

BMS02 (10 decks)

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