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Pharmacology > Enzyme Kinetics And Inhibition > Flashcards

Enzyme Kinetics And Inhibition Flashcards

1
Q

What is enzyme rate?

A

No. Of moles of product produced per unit time

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2
Q

What is first-order?

A

Dependent on the concentration

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3
Q

What is zero order?

A

No relationship

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4
Q

What is second-order?

A

Relationship between the two concentrations

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5
Q

Why to study enzymes must first order kinetics be present?

A

This is because as velocity increases the concentration increases to the point where the enzyme is saturated with the substrate (Vmax)

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6
Q

Why at Vmax is the rate of reaction unaffected by the increase of concentration?

A

All active sites are used up

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7
Q

Why does the rate of reaction increases the enzyme concentration increases?

A

it is directly proportional as there’s a great availability to catalyse the reaction

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8
Q

What is the max enzyme velocity?

A

Vmax

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9
Q

What is the Michaelis-Menten equ?

A

Vo= Vmax [s]/ Km + [s]

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10
Q

What are the assumptions for Michaelis-Menten kinetics?

A

Eqm-association + dissociation of substrate + enzyme is rapid
ES immediately comes stead state + constant
At early time point velocity = 0

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11
Q

What does Km represent?

A

Dissociation constant of ES

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12
Q

What does it mean if KM low value?

A

ES complex held tightly together

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13
Q

What is the physiological relevance of KM?

A

Utilisation of glucose in liver

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14
Q

At Vmax with high [S], what is rate determined by?

A

[E]

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15
Q

What is Kcat?

A

Catalytic constant

= max no. of S converted to P per second by each active site

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16
Q

What does Kcat measure?

A

How fast a given enzyme can catalyse a specific reaction

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17
Q

What are the units for Kcat?

A

S-1

18
Q

What does it mean if there is a larger Kcat?

A

More rapid catalytic event at enzyme’s active site

19
Q

What is the Lineweaver Burke plot?

A

1 Km 1 1
—- = —– —- + ——-
V0 Vmax [S] Vmax

20
Q

What is the Woolf-Hanes plot?

A

[S] 1 Km
—- = + ——- [S] + ——–
V0 Vmax Vmax

21
Q

What does Michaelis-Menten rely on?

A

Law of mass action

= assumes free diffusion + thermodynamically-driven random collision

22
Q

What is are the real-world limitations of heterogenous enzyme reactions?

A

Molecular mobility of E or S can be restricted = immobilisation or phase-separation of reactants

23
Q

What is are the real-world limitations of homogenous enzyme reactions?

A

Mobility of E or S may be limited

24
Q

What are multisubstrate reactions?

A

2 or 3 substrates

25
Q

In multisubstrate reactions what is the order of biochemical steps determined by?

A

Mechanism of reaction

26
Q

Describe random substrate binding

Multisubstrate reactions

A

Independent binding of substrates + products

2 independent binding sites; substrate binding independent of other substrate

27
Q

Describe ordered substrate binding

Multisubstrate reactions

A

1 substrate must bind before 2nd substrate can bind effectively

28
Q

Describe ping-pong mechanism

Multisubstrate reactions

A

Enzyme binds to substrate A then releases product
Intermediate form carriers A fragment then binds B
Product Q released + E returns to original state

29
Q

How can type of reaction be evaluated?

A 
[S1] = varied 
[S2] = constant
30
Q

What does intersecting lines at increasing [S2] indicate?

A

Ternary complex

= both donor + acceptor in active site

31
Q

What does parallel lines at increasing [S2] indicate?

A

Ping-pong mechanism

= both donor + acceptor in active site

32
Q

Describe to competitive inhibition

A

Bind to enzyme’s active site
Reversible + similar structure to S
Compete with S for active site

33
Q

How can competitive inhibition be reversed?

A

Increase [S]

34
Q

Describe non-competitive inhibition

A

Bind to allosteric set
Structure different to S
Distorts shape of E + active site, prevents S binding

35
Q

Can non-competitive inhibition be reversed by increasing [S]?

A

NO

36
Q

Describe uncompetitive inhibition

A

Bind only to ES complex
Reduces effectiveness of ES
Takes long for S or P to leave

37
Q

What happens to Km and Vmax in uncompetitive inhibition?

A

BOTH decrease

38
Q

When does uncompetitive inhibition work best?

A

[S] high

39
Q

Describe irreversible inhibition

A

Bind covalently
Inhibit permanently
Contain reactive electrophilic groups
Bind to nucleophile residues

40
Q

Describe penicillin in irreversible reaction

A

Transition-state analogues bind more tightly to enzyme than S or P
Inhibits glucopeptidyl transferase
Kills growing cells by inactivating enzymes

41
Q

What are the uncompetitive exceptions?

A

Should only occur if active site occupied by S

BUT can have affinity for unoccupied enzymes

42
Q

What are the non-competitive exceptions?

A

Inhibition affinity should be unchanged regardless whether S bound or not
BUT affinity for inhibitor usually changes when substrate bound

Pharmacology (40 decks)

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