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Biological chemistry > Enzyme Kinetics > Flashcards

Enzyme Kinetics Flashcards

1
Q

Describe enzymes

A

Catalysts: make reactions happen quickly
Work under mild physiological conditions
Specific for both reaction and substrate
Can be regulated

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2
Q

Describe general enzyme reaction equation

A

E + S (reversible reaction sign) ES = E + P

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3
Q

What does E stand for

A

Enzyme

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4
Q

What does S stand for

A

Substrate

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5
Q

What does P stand for

A

Product

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6
Q

What is enzyme kinetics

A

Study of enzyme reactions

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7
Q

Describe action of an enzyme (basic)

A

Enzyme substrate forms, is a reversible process

Product then dissociates and regenerates the enzyme

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8
Q

What happens with low levels of substrate

A

Only a small fraction of enzyme molecules can bind at any time

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9
Q

What happens at high substrate levels?

A

Most enzyme molecules substrate bound = saturated

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10
Q

When you measure enzyme kinetics what do you tend to be measuring?

A

Appearance of product or disappearance of substrate

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11
Q

Explain how you would measure enzyme activity of ß-galactose

A

ß-galactose is an enzyme that breaks down lactose to galactose and glucose
Give nitrophenylgalactose that breaks down to galactose and nitrophenolate which is yellow
Measure appearance of yellow colour over time

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12
Q

What is the rate of reaction?

A

Velocity of reaction

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13
Q

What does V stand for?

A

V

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14
Q

What is created when substrate concentration plotted?

A

Hyperbolic curve

-goes up then levels out over time

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15
Q

What is the Vmax

A

Maximum velocity a reaction can go

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16
Q

What is Km

A

The substrate concentration that produces the velocity of have the Vmax (not half the Vmax!!)

Tells us generally about affinity of the enzyme for the substrate

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17
Q

What is the michaelis-menten equation?

A

V = Vmax ([s]÷Km +[s])

V = velocity 
Vmax = max velocity
Km = v= sub contraction at vmax ÷ 2
S = substrate concentration
18
Q

What is k1

A

Binding rate

19
Q

What is K2

A

Dissociation rate

20
Q

What is Kcat

A

Catalytic constant (rate of production)

21
Q

How do you work out velocity?

A

V = kcat x concentration of enzyme substrate complex

22
Q

How do you mathematically describe enzyme catalysed reaction

A

Km = (k2+kcat) ÷ k1

23
Q

How do you work out Vmax

A

Vmax = Kcat [Etot]

24
Q

What is the conc ES

A

Same concentration as amount of enzyme put in

25
Q

What is Etot

A

Total enzyme concentration (how much enzyme put in)

26
Q

What is the relationship between Vmax and Etot

A

Directly proportional

E.g. 3rd less enzyme = Vmax a 3rd less

27
Q

What is a specificity constant

A

How efficiently an enzyme converts substrate to product

28
Q

Specificity constant equation

And how to tell from results if an enzymes specificity constant is good

A

Kcat/Km

Good enzyme:
Kcat = high
Km = low
Kcat/Km = high

29
Q

How to work out Kcat

A

Vmax/ Etot

30
Q

What is the lineweaver-Burke plot equation?

A

1/v = ((Km x 1)÷(Vmax x S)) + (1/Vmax)

31
Q

Which sections of line weaver - Burke plot relate to equation of straight line

A

(Equation of straight line: y = Mx + C)

1/v = y
Km/Vmax = m
1/s = x
1/vmax = c
32
Q

What does c stand for in straight line equation

A

Intercept

33
Q

How do you work out slope of line from line weaver Burke plot

A

Km/vmax

34
Q

What are the uses of enzyme inhibition?

A

Understanding how enzymes work

Producing drugs

35
Q

What are transition states

A

Help pull substrate into structure that lowers energy barrier for a reaction

36
Q

Competitive inhibition

A
  • inhibitor similar to substrate so binds to enzymes active site
  • competitive inhibition because substrate and inhibitor compete to bind
  • reversible so inhibitor will dissociate after time and then substrate gets a chance to bind

E + I (reversible reaction sign) EI

37
Q

How can you recognise competitive inhibition in enzyme kinetics

A

V max doesn’t change after inhibitor (if loads of substrate then inhibitor wont make much difference)
There’s an apparent change in Km but no actual change

38
Q

What is the equation for Kmapp (the apparent Km)

A

Km app = Km (1 + I/Ki)

39
Q

What is Ki

A

Inhibitor constant (affinity of inhibitor to enzyme)

The lower the value the best tier = more effective at lower amount

40
Q

Irreversible reaction

A
  • inhibitors that react covalently with groups within enzymes that are essential to enzymes activity
  • irreversible

E + I = EI

41
Q

How to see irreversible inhibition through enzyme kinetics

A

Vmax changes as enzymes inactivated permanently
Concentration of substrate needed to reach vmax stays the same
Km stays the same

Biological chemistry (11 decks)

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