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Molecules to Cells - Practicals > Enzyme Kinetics > Flashcards

Enzyme Kinetics Flashcards

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1
Q

What is enzyme kinetics ?

A

The study of the rates of enzyme catalysed reactions

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2
Q

What is measured in enzyme kinetics ?

A

The reaction rate is measured and the effects of varying the conditions of the reactions investigated

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3
Q

What does studying enzyme kinetics reveal ?

A
  1. The catalytic mechanism of an enzyme
  2. The enzymes role in metabolism
  3. How the enzyme activity is controlled
  4. How a drug or poison might inhibit the enzyme
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4
Q

What type of relationship is there between the rate of an enzyme catalysed reaction and the concentration of substrate at a fixed concentration of enzyme ?

A

Hyperbolic relationship

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5
Q

At low substrate concentrations what happens to the rate of reaction with increasing substrate concentration ?

A

Steep increase

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6
Q

What is the rate at which product can be formed limited by ?

A

The concentration of the substrate available

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7
Q

What is the initial rate of the enzyme-catalysed reaction to the concentration of substrate ?

A

Directly proportional

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8
Q

What is a first order reaction ?

A

The steep increase at the beginning of the curve

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9
Q

What happens to the enzyme as the concentration of the substrate increases ?

A

The enzyme becomes saturated with substrate

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10
Q

What happens as soon as the catalytic site is empty ?

A

More substrate is available to bind and undergo reaction

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11
Q

What happens at the high concentrations of substrate while the substrate continues to increase ?

A

Decreased enzyme response

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12
Q

When is the maximum velocity achieved ?

A

At substrate saturation

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13
Q

What is a zero order reaction ?

A

Proceeds at a constant rate

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14
Q

At maximum velocity, what does the rate of formation of the product depend on ?

A

The activity of the enzyme itself. Adding more substrate will not affect the rate of reaction to any significant effect

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15
Q

What is the hyperbolic relationship between substrate concentration and initial velocity also known as ?

A

Michaelis Menten equation

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16
Q

What is the michaelis constant ?

A

Km

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17
Q

What does the michaelis constant equal ?

A

The substrate concentration resulting in half the Vmax

18
Q

What is the michaelis constant express as ?

A

In terms of substrate concentration in moles per litre

19
Q

What is the michaelis constant independent of ?

A

Enzyme concentration

20
Q

What does the Km value for mammalian enzymes usually fall between ?

A

10 micromolar to 1 minimolar

21
Q

What is the dissociation constant of the enzyme substrate constant ?

A

Ks

22
Q

What is the affinity constant of the enzyme for the substrate ?

A

1/Ks

23
Q

What does Km provide a measure of ?

A

The affinity of an enzyme for the substrate

24
Q

What does a large Km indicate ?

A

A low affinity for substrate

25
Q

What does a low Km indicate ?

A

A high affinity for substrate

26
Q

What are enzyme inhibitors ?

A

Molecules that interact in some way with the enzyme to prevent it from working in its normal manner

27
Q

What are enzyme inhibitors normally ?

A

Poisons and drugs

28
Q

What is a competitive inhibitor ?

A

Competes with the substrate for binding at the enzyme active site - prevents substrate binding.

29
Q

What does the competitive inhibitor have in its structure ?

A

A chemical structure similar to the substrate

30
Q

How is an enzyme inhibitor complex formed ?

A

A competitive inhibitor reacts reversibly with the enzyme

31
Q

What is the inhibitor constant ?

A

Ki

32
Q

What is Ki defined as ?

A

The dissociation constant of the enzyme inhibitor complex

33
Q

What does the competitive inhibitor do to the Km value of the enzyme for substrate ?

A

Increases the Km- Requires a higher substrate concentration to achieve Vmax

34
Q

What is uncompetitive inhibition ?

A

When an inhibitor binds to the enzyme substrate complex and renders the enzyme catalytically inactive

35
Q

What do plots of 1/initial velocity against 1/substrate concentration measured at different concentrations of an uncompetitive inhibitor give ?

A

A series of parallel lines

36
Q

What is non-competitive inhibition ?

A

Occurs when the inhibitor binds at a site different from the active site

37
Q

How does binding at a site other than the active site effect enzymes ?

A

Reduces the enzymes ability to convert substrates into products in the active site

38
Q

What happens when noncompetitive inhibitors are added into a reaction ?

A

The Vmax reduces as the enzyme can no longer function as well as it could in the absence of the inhibitor

39
Q

Does the km for a noncompetitive inhibitor change during this reaction ?

A

No - stays the same

40
Q

Why does the Km not change in noncompetitive inhibition ?

A

The enzyme can still bind the substrate but just isnt catalyzing the reaction well

Molecules to Cells - Practicals (5 decks)

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