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Biochem Exam 2 > Chapter 6 - Enzymes > Flashcards

Chapter 6 - Enzymes Flashcards

1
Q

What does a catalyst do?

A

Increases the rate of a reaction without affecting its equilibrium position

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2
Q

If a reaction is at equilibrium, what effect will the addition of an enzyme have?

A

none

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3
Q

Converting substrate to products requires___ states

A

intermediate

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4
Q

Are intermediates more or less stable than the substrate/product?

A

less stable

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5
Q

Do intermediates have more or less energy than the substrate/product?

A

more energy

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6
Q

How many transition states exist in an enzymatic reaction?

A

ALWAYS more than 1

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7
Q

Theoretically, with a single intermediate we can….

A

speak of THE transition state (although there is always more than 1)

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8
Q

What is the energy of activation?

A

The difference in energy level between the substrate and transition state

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9
Q

The binding of E to S does what to the activation energy?

A

lowers the activation energy

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10
Q

What does the addition of an enzyme do to the transition state (besides lower it)

A

creates an additional hump - the new path involves more steps

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11
Q

What is enzyme activity?

A

the number of moles of substrate converted to product per unit time (moles per second)

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12
Q

What is an assay?

A

The laboratory measurement of enzyme activity

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13
Q

Why does the rate of product formation steadily decrease with time in an enzyme catalyzed reaction?

A
  1. Decrease in substrate concentration
  2. Increase in product formation
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14
Q

Reaction velocity is computed as….

A

ratio of change in conc/change in time

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15
Q

What are the 3 steps in enzyme catalysis?

A
  1. Enzyme binds substrate
  2. Enzyme transforms the substrate into product
  3. Enzyme releases the product
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16
Q

What is the formula for NET enzymatic reaction?

A

s—>p

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17
Q

Which part of an enzymatic reaction is reversible?

A

E+S<—>ES

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18
Q

Which part of an enzymatic reaction is NOT reversible?

A

ES—>E+P

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19
Q

The rate constants are proportionalities between….

A

substrate concentration and reaction rate

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20
Q

What is kf?

A

The forward rate constant for the formation of ES from E+S

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21
Q

What is kr?

A

The reverse rate constant for the formation of E and S from ES

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22
Q

What is kcat?

A

The rate constant for the breakdown of ES to E + P. Represents the affinity looking at ONE ENZYME AND ITS SUBSTRATE

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23
Q

kcat is also known as the…

A

catalytic rate constant

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24
Q

What are the 3 assumptions to relate the enzymatic equation—> to relate vi to substrate conc?

A
  1. Steady state assumption
  2. Enzyme conservation
  3. Vi is expressed as an equation that leads to product formation
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25
Q

What does the steady state assumption presume?

A

The concentration of ES is CONSTANT with time

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26
Q

What does the enzyme conservation assumption presume?

A

Total amount of enzyme (Etot) is constant for the course of the reaction. Can be expressed as [E] +[ES]

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27
Q

The initial velocity assumption can be expressed as an equation:

A

vi=kcat[ES]

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28
Q

The 3 assumptions derives the….

A

Michaelis Menten Equation

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29
Q

What is vmax?

A

The maximum velocity of an enzyme - proportional to Etot

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30
Q

Km is considered a ____constant

A

steady state

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31
Q

The michaelis menten plot shows ___ asymptotes

A

2

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32
Q

The horizontal asymptote represents the….

A

vmax

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33
Q

The vertical asymptote represents the….

A

slope - vmax/km

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34
Q

What are the 2 constants in the Michaelis Menten equation?

A

Vmax, Km

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35
Q

As [S] approaches infinity, what happens to initial velocity?

A

It equals Vmax

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36
Q

As [S] approaches zero, what happens to initial velocity?

A

It equals (vmax/km}*[S]

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37
Q

At km, vi =….

A

1/2 vmax

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38
Q

When a substrate is in its cellular environment, the concentration of the substrate is usually around…

A

Km

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39
Q

Km is the region of concentration that provides…..

A

the greatest capacity for an increase or decrease in velocity

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40
Q

Km values provide an estimate of….

A

intercellular concentrations

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41
Q

Low Km = _____ bonding affinity

A

high/tight

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42
Q

What is the most common means by which enzymes are regulated?

A

reversible inhibition

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43
Q

Most drugs are….

A

reversible inhibitors

44
Q

Will the kcat of a reaction increase when [S] remains the same but # of enzymes increases?

A

NO- kcat will stay the same because it represents the affinity of a single enzyme for its substrate - not the system as a whole

45
Q

Rate of formation of ES=…..

A

rate of breakdown of ES

46
Q

Does an enzyme affect the equilibrium position of a reaction?

A

NO - just affects how fast the reaction will GET to its equilibrium

47
Q

What molecule is used as a substrate in an assay? What happens to it?

A

p-nitrophenylphosphate
The phosphate group is removed by a phosphatase - gives a color change

48
Q

Describe an enzyme assay graph

A

product formation vs time

49
Q

What is the slope of an enzyme assay graph?

A

Vi —- change in [P]/ change in time

50
Q

Initial velocity allows us to characterize enzymatic reactions by varying ___ and ____

A

[S] and [E]

51
Q

What is the Michaelis-Menten equation?

A

vi = Vmax[S]/[Km] + [S]

52
Q

Vmax=……..

A

kcat * [E]tot

53
Q

Vmax is the ___ ____ of the enzyme

A

maximum velocity

54
Q

The michaelis-menten graph is ___ vs ____

A

initial velocity vs substrate concentration

55
Q

When [S] —> infinity….
vi=…..

A

vmax

56
Q

When [S]=0…..
vi=…..

A

(vmax/km) [S]

57
Q

What is the slop of the michaelis menten graph

A

vmax/km

58
Q

in cells, [s] is close to the value of…..

A

km

59
Q

If the km for an enzyme is 1mM, what is a reasonable estimate for the intracellular glucose concentration?

A

1mM because in cells, [S] is very close to km value

60
Q

Are reversible inhibitors able to bind to different forms of an enzyme?

A

yes

61
Q

There are ____ types of reversible inhibition. What are they?

A

3 types…
1. Competitive
2. Anti (un) competitive
3. Mixed inhibition

62
Q

In competitive inhibition, where does the inhibitor bind?

A

to the active site of the FREE ENZYME ONLY

63
Q

In anti (un) competitive inhibition, where does the inhibitor bind?

A

the inhibitor binds to the ES complex ONLY

64
Q

In mixed inhibition, where does the inhibitor bind?

A

to E AND ES forms

65
Q

A competitive inhibitor is most effective at ____[S]

A

low [S]

66
Q

Do competitive inhibitors change km, vmax, neither, or both?

A

ONLY change km

67
Q

Un(anti) competitive inhibition is most effective at…….why?

A

at HIGH [S] because it only binds to ES form

68
Q

Does un(anti) competitive inhibition change vmax?

A

yes

69
Q

When an inhibitor mimics the transition state, what kind of inhibitor is it?

A

competitive

70
Q

Vmax = ____ * ______

A

kcat * [E]tot

71
Q

km=….

A

(Kr + kcat) / kf

72
Q

What is the plot of 1/vi called?

A

the lineweaver-burk plot

73
Q

What is the lineweaver-burk plot used for?

A

inhibition studies

74
Q

In which inhibition do the 3 lines of the lineweaver-burk plot meet in the middle?

A

competitive inhibition

75
Q

In which inhibitition are the 3 lines of the lineweaver-burk plot all parallel and not touching?

A

un(anti) competitive inhibition

76
Q

In which inhibition are the 3 lines of the lineweaver-burk plot meeting at the initial velocity and spreading out from there?

A

mixed inhibition (noncompetitive)

77
Q

Allosteric enzymes usually display ____ behavior. What does this mean?

A

cooperativity behavior
Binding substrate alters the ability of the enzyme to bind further substrate molecules and is reflected in a steadily increasing velocity

78
Q

Inhibitors of cooperative enzymes shift the curve to the _____

A

right - decrease the effect of substrate on vi

79
Q

The michaelis-menten graph of allosteric enzymes, a _____ shape is seen

A

sigmoidal

80
Q

Give some examples of irreversible inhibitors

A

aspirin, penicillin, prilosec,

81
Q

If acetylcholine cannot be hydrolyzed (because of irreversible inhibition) what happens?

A

Acetylcholine is a neurotransmitter that signals muscle contraction. If it cannot be hydrolyzed, the signal remains high and muscles go into uncontrolled contraction. Death is likely

82
Q

Give 2 examples of enzyme mechanisms

A

-Acid-Base catalysis
-Nucleophilic substitution

83
Q

Fractional saturation =….

A

[ES]/[E]tot

84
Q

given km and substrate concentration, how can you find fractional saturation?

A

substrate conc/ substrate conc+ km

85
Q

When [S] is very high, the ES concentration is approximately equal to….

A

total enzyme conc

86
Q

Is the rate of an enzyme reaction proportional to the substrate concentration

A

NO - they are not directly proportional. At vmax, the rate doesnt change even if [S] increases

87
Q

Do enzymes and substrates recognize each other with complete complementarity?

A

NO - the enzyme adjusts itself and substrate. INDUCED FIT

88
Q

When the enzyme adjusts itself to fit with the substrate, what happens?

A

A LOT of energy is released - causing the activation energy to be lowered

89
Q

list 3 ways an enzyme accelerates a reaction

A

-speeding up both the forward and backward reactions

-lowering the activation energy

-Binding tightly to the transition state

90
Q

Is an enzyme reusable?

A

YES

91
Q

What parameter is best to evaluate an enzyme’s activity at a high substrate concentration?

A

vmax

92
Q

What parameter is best to evaluate an enzyme’s activity at LOW substrate concentration?

A

vmax/km

93
Q

What is the unit of Km?

A

M

94
Q

When choosing your driver who has been drinking, do you want them to have a high or low kcat value?

A

HIGH - break down the acetaldehyde faster

95
Q

Km is a ___

A

constant

96
Q

k=….

A

kcat[S]/km+[S]

97
Q

3 michaelis menten assumptions during derivation (poll everywhere)

A
  1. [S] not changing
  2. steady state - [ES] not changing
  3. E[t] not changing
98
Q

kcat=….

A

vmax/[E]tot

99
Q

Does km depend on enzyme or substrate concentration?

A

NO - IT IS A CONSTANT

100
Q

Un (anti) competitive inhibitor changes ___ and ___ at the same ratio

A

kcat and km

101
Q

Do NON competitive inhibitors change kcat?

A

YES

102
Q

Do NON competitve inhibitors change km?

A

NO

103
Q

What is usually the slowest step in a pathway?

A

the first step

104
Q

WHAT IS THE TRUE DEFINITION OF KM

A

km=kcat + kr/ kf

105
Q

do all enzymes catalyze reactions?

A

YES

106
Q

Uncompetitive inhibitors change…

A

km and vmax

Biochem Exam 2 (7 decks)

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