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BIOC192 > Q/A Session 3 > Flashcards

Q/A Session 3 Flashcards

1
Q

Vo/Vi

A
  • Initial reaction rate

- Velocity of reaction measured at time 0 at a particular substrate concentration

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2
Q

Vmax

A
  • Maximum velocity

- Velocity of reaction when enzyme is saturated

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3
Q

Km

A
  • An inverse measure of the affinity of the enzyme for substrate
  • Defined as substrate concentration required for the reaction to proceed at 1/2 Vmax
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4
Q

What is the Michealis constant?

A
  • Km

- Measure of how well the enzyme binds to its substrate

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5
Q

What does a low Km show?

A

Tight binding

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6
Q

What does a high Km show?

A

Bad binding

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7
Q

At low substrate concentration (enzyme is unsaturated)

  • Reaction order
  • Rate
  • Velocity
A
  • First order reaction
  • Rate depends on substrate concentration
  • Velocity increases linearly with increased substrate concentration
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8
Q

At high substrate concentration (enzyme is saturated)

  • Reaction order
  • Rate
  • Velocity
  • Vmax
A
  • Zero order reaction
  • Rate is independent of substrate concentration
  • No increase in velocity with increase of substrate concentration
  • Vmax is reached
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9
Q

What is kcat?

A

Catalytic rate constant (turn over number)

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10
Q

The Lineweaver Burk Plot refers to

A

How much Substrate (moles) is converted to product (moles) per enzyme (moles) per unit time when enzyme is saturated with substrate

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11
Q

Enzymes efficiency is

A

How quickly the substrate can be converted to product (kcat) RELATIVE TO how well the enzyme binds to substrate (Km)

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12
Q

What’s the equation for enzyme efficieny?

A

kcat/km

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13
Q

What are the two types of inhibition?

A
  1. Reversible

2. Irreversible

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14
Q

What are the two types of Reversible inhibition?

A
  1. Competitive

2. Non-competitve

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15
Q

What happens in Competitive inhibition?

A

-Inhibitor competes with the substrate for the active site on E

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16
Q

(CI) Will reaction occur when inhibitor binds to active sit/

A

No. Inhibitor binding does affect S binding

17
Q

(CI) How can inhibition be overcome?

A

Increasing substrate concentation

18
Q

(CI) What happens to Vmax and Km?

A

Vmax stays the same

Km increases

19
Q

(CI) Describe the plot on LWBP

A

Km line is closer to 0, the Vmax intercept stays the same. Line comes out above Non inhibitor

20
Q

(CI) Describe the plot on MM

A

Km point decreases, reaches vmax. Line in below Non inhibitor

21
Q

What happens in PURE Non-Competitive inhibition?

A

-Inhibitors binds to other site on enzyme than the substrate (allosterically)

22
Q

(PNCI) Does inhibitor binding effect S binding

A

No it doesn’t. The enzyme cannot work when inhibitor is bound

23
Q

(PNCI) What happens to Vmax and Km?

A

Vmax decreases

Km stays the same

24
Q

(PNCI) Describe the plot on LWBP

A

Km point stays the same. The Vmax intercept increases (because it’s inverse). Line is above non-inhibitor

25
Q

(PNCI) Describe the plot on MM

A

Reaches same Km spot, Vmax is lower. Line is underneath non inhibitor

26
Q

What happens in MIXED Non-Competitive inhibition?

A

-Inhibitor binds to other side on enzyme than substrate (allosterically)

27
Q

(MNCI) Does inhibitor binding have an effect on substrate binding?

A

Yes it does.

Enzyme cannot work when inhibitor is bound

28
Q

(MNCI) What happens with Vmax and Km?

A

Vmax decreases

Km increases

29
Q

(MNCI) Describe the plot on LWBP

A

The Km intercept shifts closer towards 0
The Vmax intercept increases (inverse)
Line is above the non-inhibitor

30
Q

(MNCI) Describe the plot on MM

A

Much lower for both than the non-inhibitor

31
Q

What occurs in irreversible inhibition?

A

Inhibitors bind covalently to the enzyme, irreversibly inactivating them

32
Q

Do allosteric enzymes in enzyme kinetics follow MM kinetics?

A

No

33
Q

What shape do allosteric enzymes follow?

A

Sigmoidal rather than hyperbolic

34
Q

Activators stabilise what state?

A

R state (high affinity for the molecule it binds configuration)

35
Q

In the presence of activator what degree of cooperativity do enzymes show?

A

Low, as they are already in the high affinity configuration

36
Q

What effect does low degree of enzyme cooperativity have on the curve?
What way does the curve shift?

A

The curve is more hyperbolic and less sigmoidal.

The curve shifts LEFT

37
Q

Inhibitors stabilise what state?

A

T state (low affinity for molecules it binds configuration)

38
Q

In the presence of inhibitors what degree of cooperativity do enzymes show?

A

More cooperativity, because they are not in the high affinity configuration

39
Q

What effect does high degree of enzyme cooperativity have on the curve?
What way does the curve shift?

A

The curve is less hyperbolic and more sigmoidal.

Curve shifts RIGHT

BIOC192 (4 decks)

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