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2ND SEM BIOCHEMISTRY > PPT Enzyme Kinetics - Dr. Bonleon > Flashcards

PPT Enzyme Kinetics - Dr. Bonleon Flashcards

1
Q

The quanititative measurement of the rates of enzyme-catalyzed reactions.

A

Enzyme kinetics

*Systematic study of factors that affect these rate.

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2
Q

Permit the reconstruction of the number and order of the individual steps which enzymes transform SUBSTRATE to PRODUCTS.

A

Enzyme Kinetics

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3
Q

Identify potential drugs that selectively enhance or inhibit the rates of specific enzyme-catalyzed processes.

A

Enzyme kinetics

*Reveal details of the catalytic mechanism

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4
Q

Lists the initial chemical species (SUBSTRATES) present and the new chemical species (PRODUCTS) formed for a particular reaction.

A

Balanced chemical equation

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5
Q

All in their correct proportions.

A

Stoichiometry

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6
Q

By kinetic and chemical modification, the central questions about enzymes:

A
  1. How do they work?

2. How do they catalyze reactions

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7
Q

A typical overall enzyme-catalyzed reaction involving a single substrate and a single product.

A

Enzyme kinetics

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8
Q

Reaction occurs in both directions

A

Double arrows

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9
Q

___________ provide an alternate, energetically favorable reaction pathway different from the uncatalyzed reaction.

A

Enzymes

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10
Q

_____________ chemically facilitates CATALYSIS.

A

Active site

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11
Q

Direction in which a chemical reaction will tend to proceed.

A

Gibbs free energy

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12
Q

Concentrations of reactant and products that will be present in equilibrium.

A

Gibbs free energy

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13
Q

🔼Gp - 🔼Gs =

A

🔼G or Gibbs free energy

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14
Q

Free energy that accompanies transition from the standard state, one-molar concentrations of S & P, to equilibrium.

A

🔼G0

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15
Q

🔼G0 : 🔼G0 at a standard state of 10-7 M protons at pH ______.

A

7

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16
Q

If the free energy of the product is LOWER than that of the substrates.

A

Negative

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17
Q

Direction LEFT TO RIGHT.

A

Negative

*Spontaneous

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18
Q

________ & ________ of free energy change determine how FAR the reaction will proceed.

A

Sign and magnitude

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19
Q

Independent of the mechanism of reaction.

A

🔼G0

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20
Q

🔼G0 provide information only about the ___________ & ___________ state of the reaction.

A

Direction and equilibrium

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21
Q

Provides no information concerning the rates of reaction.

A

🔼G0

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22
Q

We can use the sign of 🔼G0 to figure out whether a reaction is spontaneous in the forward direction, backward direction or if the reaction is at ______________.

A

Equilibrium

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23
Q

Virtually all chemical reactions have an energy barrier separating the reactants and the products.

A

Barrier : free energy of activation

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24
Q

Energy difference between that of the reactant and a high-energy intermediate that occurs during the formation of the product.

A

Free energy of activation

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25
Q

Sufficient energy needed for molecules to react.

A

Rate of reaction

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26
Q

Energy to overcome the energy barrier of the transition state.

A

Rate of reaction

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27
Q

Only a small portion of the molecules may possess enough energy to achieve the transition state between reactants and products.

A

No enzymes

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28
Q

Determined by the number of energized molecules.

A

Rate of reaction

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29
Q

The _______ the free energy of activation, the more molecules have sufficient energy to pass through the TRANSITION STATE = the FASTER the rate of reaction.

A

Lower

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30
Q

A reaction may be looked at as passing from one valley, representing __________, over a mountain pass to another valley, the ___________.

A

Stable reactants

Products

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31
Q

The pass between them is called the ______________, the state from which the molecules may with equal probability go ahead to products or back to reactants.

A

Transition state

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32
Q

Energy must be put into a reaction to raise the reactants to the top of the pass, the transition state; this energy is called the _______________.

A

Free energy of activation or activation energy

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33
Q

The role of the catalyst is to find A LOWER PASS over the mountain range, a pathway with a _____________.

A

Lower activation energy

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34
Q

An alternative way of looking at the role of a catalyst is that is ___________ the transition state.

A

Stabilizes

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35
Q

Provides the enzyme allowing a reaction to proceed rapidly under conditions prevailing in the cell.

A

Alternate reaction pathway

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36
Q

Condition of Alternate reaction pathway:

A

Lower free energy of activation

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37
Q

Enzyme does not change the free energies of the reactants or products and doe not change the equilibrium of the reaction.

A

Alternate reaction pathway

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38
Q

For 2 molecules to react they must approach within BOND-FORMING DISTANCE of one another (collide).

A

Kinetic theory or Collision theory

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39
Q

For two molecules to react they must possess SUFFICIENT KINETIC ENERGY to overcome the energy barrier for reaching the transition state.

A

Kinetic theory or Collision theory

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40
Q

Anything which INCREASES the frequency or energy of collision between the substrates will INCREASEZ the rate of reaction in which they participate.

A

Kinetic theory

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41
Q

Factors that affect the reaction rate:

A

Temperature and reactant concentration

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42
Q

Raising the ambient temperature __________ the kinetic energy of molecules.

A

increases

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43
Q

If the concentrations of BOTH A and B are DOUBLED, the probability of collision will ________.

A

Increase fourfold

44
Q

If concentrations of EITHER A and B are doubled, the probability of collision will _________.

A

Double

45
Q

At equilibrium, the overall concentrations of reactants and products remain constant.

A

Keq: ratio of rate constants

46
Q

The rate of conversion of substrates to products therefore equals the rate at which products are converted to substrates.

A

Keq: ratio of rate constants

47
Q

___________ is a ratio of the reaction rate constants.

A

Equilibrium constant

48
Q

Reaction rates of the forward and back reactions are equal

A

Equilibrium

49
Q

No net change in the concentration of S & P.

A

Equilibrium

*Dynamic state

50
Q

Individual S & P molecules are continually being interconverted.

A

Equilibrium

51
Q

The environment of the active site _______ 🔼Gf by stabilizing the transition state intermediates.

A

Lowers

52
Q

______________ suitably positioned to transfer protons to and from the developing transition state intermediate.

A

Acid-base groups

*Suitably positioned charged groups or metal ions that stabilize developing charges.

53
Q

Imposition of ___________ on S that their geometry approaches that of the transition state.

A

Steric strain

54
Q

Factors that affect the rate of enzyme-catalyzed reactions:

A

Temperature and hydrogen ion concentration

55
Q

________ temperature will INCREASE rate of both catalyzed and non-catalyed reactions by increasing kinetic energy & collision frequency of the reacitng molecules.

A

Increase

56
Q

_________ can also increase the kinetic energy of the enyzme to the point that exceeds the energy barrier for disrupting their noncovalent interactions that maintain the enzyme’s 3D structure __________.

A

Heat

Denaturation

57
Q

Loss of catalytic activity.

A

Denaturation

58
Q

Enzymes from humans generally exhibit stability at temperatures up to _______ to ________.

A

45 - 55C

Clinical importance: FEVER or HYPOTHERMIA

59
Q

Intracellular enzymes exhibit optimal activity at pH:

A

5-9

60
Q

Reflects balance between denaturation at high or low pH.

A

Hydrogen ion concentration

61
Q

Residues involved must be in the appropriate state of protonation for the reaction to proceed.

A

Acid-base catalysis

62
Q

Most common charged groups:

A
  1. Negative carboxylate groups

2. Protonated amines

63
Q

Gain or loss of critical charged groups adversely affect substrate binding and thus will __________ or _________ catalysis.

A

Retard or abolish

64
Q

Catalytic activity may require that an amino group of the enzyme may be in the __________ form.

A

Protonated form

65
Q

At __________ ph, the group is DEPROTONATED thus DECREASING the rate of reaction.

A

Alkaline

66
Q

Extremes of pH

A

Denaturation

67
Q

Structure of catalytically active protein molecule depends on the _____________ of the amino acid side chains.

A

ionic character

68
Q

Effect of enzyme concentration on reaction velocity

A

Michaelis-Menten kinetic theory

69
Q

Michaelis-Menten kinetic theory: If the substrate concentration is held CONSTANT, velocity of the reaction is __________ to the enzyme concentration.

A

Proportional

70
Q

Effect of substrate concentration on reaction velocity:

[S] is _______, v is 1st order with respect to substrate.

A

Low

71
Q

Effect of substrate concentration on reaction velocity:

[S] is HIGH, reaction is ____________ (independent of S)

A

Zero order

72
Q

Effect of substrate concentration on reaction velocity:

Mid-[S], reaction is __________ (proportionality is changing).

A

Mixed-order

73
Q

At LOW VALUES of S, the initial velocity Vi rises almost ________ with increasing S.

A

Linearly

74
Q

But as S INCREASES, the gains in Vi level off forming a ____________.

A

Rectangular hyperbola

75
Q

The substrate concentration that produces a Vi that is one-half of Vmax is designated the ____________.

A

Michaelis-Menten constant

76
Q

________ is roughly an inverse measure of the affinity or strength of binding between the enzyme and its substrate.

A

Km

77
Q

The LOWER the Km, the _______ the affinity (so the lower the concentration of substrate needed to achieve a given rate).

A

Greater

78
Q

Used because it is difficult to estimate Vmax from the position of the asymptote (plot of a rectangular hyperbola).

A

Lineweaver-Burk linear plot

79
Q

Plotting the reciprocals of the SAME DATA POINTS yields a “double reciprocal” or _____________. This provides a more precise way to determine Vmax and Km.

A

Lineweaver-Burk plot

80
Q

Is determined by the point where the line crosses the 1/V1 = 0 axis so the [S] is infinite.

A

Vmax

81
Q

Km = Vmax times the slope of line. This is easily determined from the intercept of ________.

A

X-axis

82
Q

[S] is very _______ compared with [E] where when all E are bound, there is still an excess of S.

A

Large

83
Q

Rate of breakdown of ES = rate of formation of ES

A

Steady state assumption

84
Q

Characteristic of an enzyme and its substrate.

A

Km

85
Q

Reflects the affinity of the enzyme for that substrate.

A

Km

86
Q

Numerically equal to the substrate concentration at which the reaction velocity =

A

1/2 vmax

87
Q

Does not vary with the concentration of the enzyme.

A

Km

88
Q

High affinity of the enzyme for the substrate.

A

Small Km

89
Q

Lower concentration of the substrate is needed to half-saturate the enzyme.

A

Small Km

90
Q

Low affinity of enzyme for substrate because a high concentration of substrate is needed to half-saturate the enzyme.

A

Large Km

91
Q

Rate of reaction is DIRECTLY PROPORTIONAL to the enzyme concentration.

A

Velocity-enzyme concentration

92
Q

If enzyme concentration is HALVED, the initial rate of reaction and Vmax is reduced to half that of the original.

A

Velocity-enzyme concentration

93
Q

Inhibitors compete directly with substrate for binding to the active site (i.e catalytic site).

A

Competitive inhibition

94
Q

Overcome by raising the concentration of the substrate.

A

Competitive inhibition

95
Q

Inhibitors bind only to the ES complex at a site distinct from the active site (i.e the allosteric site).

A

Uncompetitive inhibition

96
Q

Inhibitors bind both to the free enzyme and to the ES complex at the allosteric site, which is distinct from the active site.

A

Noncompetitive inhibition

97
Q

Bind covalently so tightly to the active site that the enzyme is inactivated irreversibly.

A

Irreversible competitive inhibitors

98
Q

Does not obey the Michaelis-Menten kinetics.

A

Irreversible competitive inhibitors

99
Q

Substrate analogs that possess a highly reactive group that is not present on the natural substrate.

A

Affinity labels

100
Q

The active site is PERMANENTLY BLOCKED from the substrate because the group reacts covalently with amino acid residue.

A

Affinity labels

101
Q

The reside modified - not necessarily involved in catalysis.

A

Affinity labels

102
Q

Substrate analogs that are transformed by the catalytic action of the enzyme.

A

Mechanism-based or suicide inhibitors

103
Q

Product of this reaction is HIGHLY REACTIVE which combines covalently with amino acid residue in the active site resulting to ENZYME INACTIVATION.

A

Mechanism - based or suicide inhibitors

104
Q

Substrate analogs whose structures closely resemble the transition state of the natural substrate.

A

Transition state analogs

105
Q

Do not covalently modify the enzyme but bind the active site so tightly that they irreversibly inactivate it.

A

Transtition state analogs

106
Q

Provide pharmacologic agents and research tolls for study of mechanism of enzyme action.

A

Enzyme inhibition

107
Q

Highly toxic, naturally-occuring and man made compounds.

A

Irreversible enzyme inhibitors

2ND SEM BIOCHEMISTRY (33 decks)

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