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Biochem Exam 2 > Chapter 6 - Enzymes > Flashcards

Chapter 6 - Enzymes Flashcards

(106 cards)

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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
What does the steady state assumption presume?
The concentration of ES is CONSTANT with time
26
What does the enzyme conservation assumption presume?
Total amount of enzyme (Etot) is constant for the course of the reaction. Can be expressed as [E] +[ES]
27
The initial velocity assumption can be expressed as an equation:
vi=kcat[ES]
28
The 3 assumptions derives the....
Michaelis Menten Equation
29
What is vmax?
The maximum velocity of an enzyme - proportional to Etot
30
Km is considered a ____constant
steady state
31
The michaelis menten plot shows ___ asymptotes
2
32
The horizontal asymptote represents the....
vmax
33
The vertical asymptote represents the....
slope - vmax/km
34
What are the 2 constants in the Michaelis Menten equation?
Vmax, Km
35
As [S] approaches infinity, what happens to initial velocity?
It equals Vmax
36
As [S] approaches zero, what happens to initial velocity?
It equals (vmax/km}*[S]
37
At km, vi =....
1/2 vmax
38
When a substrate is in its cellular environment, the concentration of the substrate is usually around...
Km
39
Km is the region of concentration that provides.....
the greatest capacity for an increase or decrease in velocity
40
Km values provide an estimate of....
intercellular concentrations
41
Low Km = _____ bonding affinity
high/tight
42
What is the most common means by which enzymes are regulated?
reversible inhibition
43
Most drugs are....
reversible inhibitors
44
Will the kcat of a reaction increase when [S] remains the same but # of enzymes increases?
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
Rate of formation of ES=.....
rate of breakdown of ES
46
Does an enzyme affect the equilibrium position of a reaction?
NO - just affects how fast the reaction will GET to its equilibrium
47
What molecule is used as a substrate in an assay? What happens to it?
p-nitrophenylphosphate The phosphate group is removed by a phosphatase - gives a color change
48
Describe an enzyme assay graph
product formation vs time
49
What is the slope of an enzyme assay graph?
Vi ---- change in [P]/ change in time
50
Initial velocity allows us to characterize enzymatic reactions by varying ___ and ____
[S] and [E]
51
What is the Michaelis-Menten equation?
vi = Vmax[S]/[Km] + [S]
52
Vmax=........
kcat * [E]tot
53
Vmax is the ___ ____ of the enzyme
maximum velocity
54
The michaelis-menten graph is ___ vs ____
initial velocity vs substrate concentration
55
When [S] ---> infinity.... vi=.....
vmax
56
When [S]=0..... vi=.....
(vmax/km) [S]
57
What is the slop of the michaelis menten graph
vmax/km
58
in cells, [s] is close to the value of.....
km
59
If the km for an enzyme is 1mM, what is a reasonable estimate for the intracellular glucose concentration?
1mM because in cells, [S] is very close to km value
60
Are reversible inhibitors able to bind to different forms of an enzyme?
yes
61
There are ____ types of reversible inhibition. What are they?
3 types... 1. Competitive 2. Anti (un) competitive 3. Mixed inhibition
62
In competitive inhibition, where does the inhibitor bind?
to the active site of the FREE ENZYME ONLY
63
In anti (un) competitive inhibition, where does the inhibitor bind?
the inhibitor binds to the ES complex ONLY
64
In mixed inhibition, where does the inhibitor bind?
to E AND ES forms
65
A competitive inhibitor is most effective at ____[S]
low [S]
66
Do competitive inhibitors change km, vmax, neither, or both?
ONLY change km
67
Un(anti) competitive inhibition is most effective at.......why?
at HIGH [S] because it only binds to ES form
68
Does un(anti) competitive inhibition change vmax?
yes
69
When an inhibitor mimics the transition state, what kind of inhibitor is it?
competitive
70
Vmax = ____ * ______
kcat * [E]tot
71
km=....
(Kr + kcat) / kf
72
What is the plot of 1/vi called?
the lineweaver-burk plot
73
What is the lineweaver-burk plot used for?
inhibition studies
74
In which inhibition do the 3 lines of the lineweaver-burk plot meet in the middle?
competitive inhibition
75
In which inhibitition are the 3 lines of the lineweaver-burk plot all parallel and not touching?
un(anti) competitive inhibition
76
In which inhibition are the 3 lines of the lineweaver-burk plot meeting at the initial velocity and spreading out from there?
mixed inhibition (noncompetitive)
77
Allosteric enzymes usually display ____ behavior. What does this mean?
cooperativity behavior Binding substrate alters the ability of the enzyme to bind further substrate molecules and is reflected in a steadily increasing velocity
78
Inhibitors of cooperative enzymes shift the curve to the _____
right - decrease the effect of substrate on vi
79
The michaelis-menten graph of allosteric enzymes, a _____ shape is seen
sigmoidal
80
Give some examples of irreversible inhibitors
aspirin, penicillin, prilosec,
81
If acetylcholine cannot be hydrolyzed (because of irreversible inhibition) what happens?
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
Give 2 examples of enzyme mechanisms
-Acid-Base catalysis -Nucleophilic substitution
83
Fractional saturation =....
[ES]/[E]tot
84
given km and substrate concentration, how can you find fractional saturation?
substrate conc/ substrate conc+ km
85
When [S] is very high, the ES concentration is approximately equal to....
total enzyme conc
86
Is the rate of an enzyme reaction proportional to the substrate concentration
NO - they are not directly proportional. At vmax, the rate doesnt change even if [S] increases
87
Do enzymes and substrates recognize each other with complete complementarity?
NO - the enzyme adjusts itself and substrate. INDUCED FIT
88
When the enzyme adjusts itself to fit with the substrate, what happens?
A LOT of energy is released - causing the activation energy to be lowered
89
list 3 ways an enzyme accelerates a reaction
-speeding up both the forward and backward reactions -lowering the activation energy -Binding tightly to the transition state
90
Is an enzyme reusable?
YES
91
What parameter is best to evaluate an enzyme's activity at a high substrate concentration?
vmax
92
What parameter is best to evaluate an enzyme's activity at LOW substrate concentration?
vmax/km
93
What is the unit of Km?
M
94
When choosing your driver who has been drinking, do you want them to have a high or low kcat value?
HIGH - break down the acetaldehyde faster
95
Km is a ___
constant
96
k=....
kcat[S]/km+[S]
97
3 michaelis menten assumptions during derivation (poll everywhere)
1. [S] not changing 2. steady state - [ES] not changing 3. E[t] not changing
98
kcat=....
vmax/[E]tot
99
Does km depend on enzyme or substrate concentration?
NO - IT IS A CONSTANT
100
Un (anti) competitive inhibitor changes ___ and ___ at the same ratio
kcat and km
101
Do NON competitive inhibitors change kcat?
YES
102
Do NON competitve inhibitors change km?
NO
103
What is usually the slowest step in a pathway?
the first step
104
WHAT IS THE TRUE DEFINITION OF KM
km=kcat + kr/ kf
105
do all enzymes catalyze reactions?
YES
106
Uncompetitive inhibitors change...
km and vmax

Biochem Exam 2 (7 decks)

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