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BIO1332 - Biochemistry > Enzyme Kinetics > Flashcards

Enzyme Kinetics Flashcards

1
Q

What is the difference between kinetics and thermodynamics?

A
  • Kinetics: how fast the reaction

- Thermodynamics: does the reaction happen or how far does it proceed

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2
Q

Why is the rate of biological reactions important?

A
  • Most cellular chemicals are unstable, rely on rate of their breakdown
  • Some disease are cause by imbalances in rate at which a reaction takes place
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3
Q

What does change in G of a reaction equal to?

A

free energy of the products (final) - the free energy of the reactants (initial)

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4
Q

Does change in G provide information about the rate of reaction?

A

No

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5
Q

What is change in G independent on?

A

Path of the transformation

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6
Q

What is the rate of reaction dependent on?

A

Free energy of activation

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7
Q

What is the sign for free energy of activation?

A

change in G double daggers

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8
Q

if change in G reaction < 0 for a spontaneous reaction, how is it possible to reach a transition state that is at a higher value of G?

A

Have to consider individual molecule properties rather than bulk properties that change in G refers to

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9
Q

Will a mixture of molecules have all the same amount of energy as one another?

A

No

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10
Q

How is the distribution of energy of molecules shown?

A

On a Maxwell-Boltzmann distribution

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11
Q

Define activation energy:

A

Energy that a molecule requires to overcome the transition state free energy barrier

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12
Q

How many molecules can overcome the activation energy?

A

Only a certain proportion of molecules in a mixture

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13
Q

What does the Arrhenius equation show?

A

Rate of reaction is related to activation energy

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14
Q

What is the Arrhenius equation?

A

k = Ae^-(change in G double dagger/RT)

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15
Q

What is k in the Arrhenius equation?

A

Rate constant

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16
Q

What is T in the Arrhenius equation?

A

Temperature in kelvin

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17
Q

What is A in the Arrhenius equation?

A

Pre-exponential factor (constant for each chemical reaction that defines the rate due to frequency of collisions the correct orientation)

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18
Q

What is change in g double dagger in the Arrhenius equation?

A

Activation energy for the reaction in joules

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19
Q

What is R in the Arrhenius equation?

A

universal gas constant

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20
Q

How to speed up a chemical reaction?

A
  • Increase the temperature
  • Increase the pressure
  • Change the pH
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21
Q

What are enzymes?

A

Macromolecules whose function is to increase the rate of reactions

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22
Q

How do enzymes generally increase the rate of reaction?

A

By reducing the transition state energy for a reaction

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23
Q

What are the general properties of an enzyme?

A
  • Catalytic
  • Specific
  • Fast
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24
Q

What is meant by catalytic in terms of enzymes?

A

Enzyme ends in the state that it started

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25
What is meant by specific in terms of enzymes?
Change the rate of a limited set of reactions
26
What is meant by fast in terms of enzymes?
Most reactions need to be speeded up by many orders of magnitude
27
Why are enzymes made of proteins?
- 20 amino acids offer a wide range of difference on shape (SPECIFIC) - Very different chemical properties (SPEED) - Good at accommodating different reactants so proteins itself is not changed in the reaction (CATALYTIC)
28
What do enzymes for form with substrates?
Enzyme-substrate complexes
29
What substrate does enzyme cytochrome P450 bound to?
Camphor
30
What doe enzymes decrease?
The activation energy
31
How is the transition state barrie reduced?
- Stabilise the unfavourable intermediated | - Make possible a less favourable reaction
32
What are the unfavourable intermediates?
- Charge-charge interactions - Hydrogen bonding - Protecting hydrophobic groups
33
How do you make a less favourable reaction?
- Provide acid/base-like conditions - Allow oxidation/reduction - Provide a small vacuum - Provide an attacking group (covalent catalysis) - Provide a metal ion
34
What is the reaction kinetics in terms of S and P with no enzyme?
An equilibrium of S to P
35
What is the reaction kinetics in terms of S and P with an enzyme?
Equilibrium of E + S to ES to EP to E + P
36
What is rate constant?
Constant temperature, elementary reaction is proportional to the frequency with the reacting molecules come together
37
What should you assume for enzyme kinetics??
- Release of product is vert fast | - Reverse reaction is sufficiently slow that we can ignore it
38
When applying the enzyme kinetics assumptions we can use what equation?
Michaelis-Menten equation
39
What is the Michaelis-Menten equation?
Vo = Vmax ([S]/Km + [S])
40
What is Vmax in the Michaelis-Menten equation?
Maximal rate
41
What is [S] in the Michaelis-Menten equation?
Substrate concentration
42
What is Km in the Michaelis-Menten equation?
Michaelis constant
43
What is Vo in the Michaelis-Menten equation?
Reaction velocity
44
What is the x-axis label of the Michaelis-Menten?
Substrate concentration
45
What is the y-axis label of the Michaelis-Menten?
Reaction velocity
46
Do Km values of enzymes a little or wide range?
Wide range
47
What range does Km lie between?
10^-1 and 10^7M
48
What does Km range depend on?
Substrate and conditions such as pH
49
What is Km?
Concentration of substrate at which hall the active sites are filled
50
What does Km provide?
A measure of the substrate concentration required for significant catalysis to occur
51
What does Km provide for in vivo?
Approximation of the substrate concentration
52
What does Km measure other than substrate concentration?
The strength of the ES complex
53
What does a high Km indicate?
Weak ES binding
54
What does a low Km indicate?
Strong ES binding
55
When does Km indicate the affinity of the ES complex?
When k-1 is much greater than k2
56
What does Vmax show?
The turnover number
57
What is another work for turnover number?
Kcat
58
What must you have to calculate the Michaelis-Menten constants?
- Obtain at least 5 values of [S] - Values of [S] should be both sides of the Km for a good result - Constants of enzyme then can be calculated
59
How do you calculate the Michaelis-Menten constants?
-Proper statical package and non linear regression to solve equation OR -Rearrange the equation to give a linear equation
60
What is the rearrange equation of Michaelis-Menten equation to present y = mx + c?
1/v = ((Km/Vmax)*(1/[x]) + 1/Vmaz
61
What is the consequence of Michaelis-Menten equation?
When the substrate concentration drops, so does the rate
62
How can you solve the problems of when the substrate concentration drops, so does the rate relating to the Michaelis-Menten equation?
Record initial rate | or use stopped assay
63
How will kinetics differ?
- Enzyme is affect by concentration of some other compounds - Reaction is more complicated - Enzyme has multiple subunits - Law of mass action do not apply
64
What is Kcat/Km?
A measure of catalytic efficiency
65
What does Kcat/Km take into account?
Rate of catalysis and strength of ES
66
What is the x-axis of the line weaver-burk plot?
1/[S]
67
What is the y-axis of the line weaver-burk plot?
1/V
68
What is the x-axis intercept of the line weaver-burk plot?
-1/Km
69
What is the y-axis intercept of the line weaver-burk plot?
1/Vmax
70
What is the slope of the line weaver-burk plot?
Km/Vmax
71
What is the x-axis of the Hanes-woolf plot?
[S]
72
What is the y-axis of the Hanes-woolf plot?
[S]/V
73
What is the x-axis intercept of the Hanes-woolf plot?
-Km
74
What is the y-axis intercept of the Hanes-woolf plot?
Km/Vmax
75
What is the slope of the Hanes-woolf plot?
1/Vmax
76
Can enzymes tightly bind to either substrate of products?
No - bad for catalysis
77
When can enzymes tightly bind?
During transition state

BIO1332 - Biochemistry (19 decks)

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