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Biochemistry > Enzyme Kinetics > Flashcards

Enzyme Kinetics Flashcards

1
Q

What assumptions are made about substrate concentration when discussing Michaelis-Menten kinetics?

A
  1. The rapid equilibrium approximation: K1 and K-1 are small compared to Kp
  2. Initial rate/High [S]: [S] represents the free substrate concentration and is assumed to be close to the total substrate concentration because the reaction just began
  3. Initial Rate: The [ES] rapidly became steady because substrate is unlimited and [EP] is tiny
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2
Q

What is Vmax?

A

Vmax is the maximum velocity that would occur when all the enzyme is part of the enzyme-substrate complex

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3
Q

What is kp?

A

The reaction constant between the enzyme-substrate complex and the enzyme + product step

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4
Q

What is k-1?

A

Dissociation constant between the enzyme-substrate complex step and the enzyme + substrate step

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5
Q

What is the steady state assumption?

A

The concentrations of the intermediates of a reaction remain the same even when the concentrations of starting materials and products are changing

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6
Q

What does a high Kcat value signify?

A

Faster product production

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7
Q

What is the specificity constant?

A

Kcat/Km

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8
Q

Why is Kcat/Km the specificity constant?

A

The equation is basically the maximum product production per enzyme over the inverse efficiency of substrate binding.

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9
Q

What is a Lineweaver-Burk plot?

A

The plotting of Michaelis Menten kinetics as a double reciprocal

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10
Q

What can you tell by a Lineweaver-Burk plot?

A
  1. The slope is Km/Vmax
  2. y-intercept is 1/Vmax
  3. x-intercept is -1/Km
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11
Q

Why are inhibitors necessary in biological systems?

A

They regulate proteins

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12
Q

What is competitive inhibitor?

A

A type of reversible inhibition. The inhibitor competes with substrate for binding, then binds to the active site but does not affect catalysis.

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13
Q

What is a mixed inhibitor?

A

Inhibitor binds enzyme or enzyme-substrate complex. Binds to the regulatory site. Inhibits catalytic function and substrate binding.

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14
Q

What is the Michaelis constant? What does it represent?

A

Km represents a dynamic, in-progress reaction where the concentration of intermediate complexes does not change

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15
Q

How do you set up Michaelis-Menten conditions?

A

The concentration of substrate must be 100x larger than Ks and the fastest initial rate of product formation/substrate disappearance is measured

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16
Q

If given a graph with Velocity on the y-axis and [S] on the x-axis, how do you find Km?

A

Just like measuring the Kd, the Km is the x-coordinate at the 1/2 Vmax

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17
Q

What does Km approximate?

A

Km is a measure of roughly how much substrate is needed for full speed. The inverse substrate binding efficiency and the cellular [S]

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18
Q

What would happen is [S] was very different from Km?

A

The enzyme would be insensitive to changes

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19
Q

In regards to the Km value, what would indicate an inhibitor?

A

If the cellular levels of substrate is larger than the Km

20
Q

In regards to the Km value, what would indicate an activator?

A

If the Km was larger than the cellular levels of substrate

21
Q

Why are small Km values important?

A

The smaller the Km, the less E and S needed to make ES. Small Km values make the most efficient enzymes.

22
Q

What is turnover?

A

The enzyme’s effect of turning substrate into product

23
Q

What is the relation between turnover and Kcat?

A

They are the same. It’s the “limiting” rate of an enzyme catalyzed reaction

24
Q

What is the Kcat equation?

A

Kcat=Vmax/[total E]

25
Q

How is Vmax affected by competitive inhibition?

A

It stays the same

26
Q

How does competitive inhibition affect Km?

A

Appears to increase

27
Q

How would competitive inhibition appear on a Lineweaver-Burk plot?

A

The slope of the line would increase making the line more vertical because the Km increases and the Vmax stays the same (remember slope is Km/Vmax)

28
Q

How is Vmax affected by uncompetitive inhibition?

A

Vmax decreases

29
Q

How does uncompetitive inhibition affect Km?

A

Km appears to decrease

30
Q

How would uncompetitive inhibition appear on a Lineweaver-Burk plot?

A

Like a normal because slope does not appear to change, the lines are parallel to the line of no inhibitor

31
Q

What is an uncompetitive inhibitor?

A

The inhibitor binds to the Enzyme-Substrate complex. It does not affect substrate binding and inhibits catalytic function.

32
Q

How is Vmax affected by mixed inhibition?

A

Vmax decreases

33
Q

How does mixed inhibition affect Km?

A

Km appears to increase

34
Q

How would mixed inhibition appear on a Lineweaver-Burk plot?

A

The slope increases, making a more vertical line

35
Q

What type of inhibitions decrease the Vmax?

A

Uncompetitive and Mixed

36
Q

What type of inhibitors decrease the Km?

A

Uncompetitive

37
Q

What type of inhibitors increase the Km?

A

Competitive and mixed

38
Q

What inhibitor keeps the same Vmax?

A

Competitive

39
Q

What inhibitor keeps the Vmax and increases the Km?

A

Competitive

40
Q

What inhibitor decreases the Vmax and decreases the Km?

A

Uncompetitive

41
Q

What inhibitor decreases the Vmax and increases the Km?

A

Mixed

42
Q

What is irreversible inhibition?

A

Something modifies the enzyme

43
Q

How do irreversible inhibitors typically function?

A

By covalently modifying the enzme or enzyme-substrate complex by highly reactive groups. Others bind so tightly that there is no measurable release under physiological conditions

44
Q

What can reveal Irreversibility?

A
  1. Fresh Enzyme and re-measuring kinetics
  2. Dilution of removal of inhibitor does not restore activity
45
Q

What are suicide Inhibitors?

A

A subset of irreversible inhibitors

Biochemistry (16 decks)

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