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Principles - Biochemistry > Enzyme Kinetics > Flashcards

Enzyme Kinetics Flashcards

1
Q

What is Vmax?

A

The maximum rate of a catalysed reaction

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2
Q

What is KM?

A

The concentration of substrate that causes the rate of a catalysed reaction to be 50% of the maximum

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3
Q

What is V?

A

The rate of a catalysed reaction

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4
Q

What does a graph of concentration of substrate against rate of reaction look like?

A

Steep gradient, decreasing in gradient until tapers off at Vmax

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5
Q

What is ES?

A

The Enzyme Substrate intermediate/complex

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6
Q

How stable is the enzyme substrate complex?

A

Inherently unstable

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7
Q

What is the enzyme substrate complex?

A

The point at which potential energy is highest and the reaction could go forwards or backwards

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8
Q

What makes the enzyme substrate complex inherently unstable?

A

The activation energy barrier

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9
Q

What is the symbol for the Michaelis constant?

A

KM

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10
Q

What is the equation for the Michaelis constant?

A

KM = (k-1 + k-2)/k1

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11
Q

What do k1, k-1 and k-2 stand for in the Michaelis constant equation?

A

k1 - forward rate constant for enzyme association with substrate
k-1 - backward rate constant for enzyme association with substrate
k-2 - forward rate constant for enzyme conversion of substrate to product

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12
Q

How is Vmax measured?

A

V0 (initial reaction velocity) is measured at a known substrate concentration.
This is repeated at increasing substrate concentrations
The results are plotted as a function of substrate concentration
As substrate concentration increases, V0 approaches Vmax

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13
Q

What has to be true for there to be a Vmax?

A

Enzyme concentration must be constant

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14
Q

Why is trying to determine Vmax and KM experimentally not straightforward?

A

The kinetics are not linear so the reaction velocity never truly reaches Vmax

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15
Q

What is the Michaelis-Menten equation?

A

V = (Vmax . [S])/(KM + [S])

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16
Q

What is the inverse of the Michaelis-Menten equation?

A

1/V = KM/Vmax . 1/[S] + 1/Vmax

17
Q

How would you do a Lineweaver-Burk plot?

A

Take the inverse of the Michaelis-Menten equation, which is equivalent to y=mx+c and plot the line accordingly

18
Q

What are the y-intercept and x-intercept on a Lineweaver-Burk plot?

A 
y-intercept = 1/Vmax aka. Vmax
x-intercept = -1/KM aka. KM
19
Q

What are the x- and y-axes on a Lineweaver-Burk plot?

A 
x-axis = 1/[S]
y-axis = 1/V0
20
Q

What is the gradient on a Lineweaver-Burk plot?

A

KM/Vmax

21
Q

What substrate concentration will an enzyme with a low KM need to reach Vmax?

A

Low

22
Q

What substrate concentration will an enzyme with a high KM need to reach Vmax?

A

High

23
Q

Can enzymes have the same Vmax but different KM?

A

Yes

24
Q

Is competitive inhibition reversible?

A

Yes

25
Q

Is non-competitive inhibition reversible?

A

It can be reversible or irreversible

26
Q

What is competitive inhibition?

A

Inhibitor binds to the active site and blocks substrate access

27
Q

What is orthosteric inhibition?

A

Where the inhibitor binds to the same site as the substrate

28
Q

What is non-competitive inhibition?

A

The inhibitor binds to a secondary bonding site and changes the enzyme’s conformation

29
Q

What is allosteric inhibition?

A

Where the inhibitor bonds tp a different site than the substrate

30
Q

What is irreversible non-competitive inhibition?

A

Inhibition cannot be reversed

Usually involves formation or breakage of covalent bonds in the enzyme complex

31
Q

How does the line in a Lineweaver-Burk plot change in competitive inhibition and what does this mean for Vmax and KM?

A

The gradient increases but the y-intercept stays the same
Vmax does not change
KM varies

32
Q

How does the line in a Lineweaver-Burk plot change in non-competitive inhibition and what does this mean for Vmax and KM?

A

The gradient increases but the x-intercept stays the same
Vmax varies
KM does not change

33
Q

What is a common mechanism of allosteric control?

A

Inhibition of rate limiting enzymes by end products

34
Q

What is feedback inhibition?

A

The final product inhibits an early enzyme and shuts downs the series

35
Q

Which enzymes do not follow Michaelis-Menten kinetics?

A

Allosteric enzymes

36
Q

In what way do the graphs (v against [S]) of allosteric enzymes differ from Michaelis-Menten kinetics?

A

They produce a sigmoidal curve (s shaped)

37
Q

Which enzymes show cooperativity?

A

Allosteric

38
Q

What can allosteric enzymes be controlled by?

A

Allosteric inhibitors and allosteric activators

Principles - Biochemistry (4 decks)

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