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PHA111 > Enzyme Kinetics > Flashcards

Enzyme Kinetics Flashcards

1
Q

What is the pre-steady state?

A

Isolated enzyme mixed with substrate to build-up an enzyme-substrate complex

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2
Q

What is steady state reached in?

A

micrometres per second

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3
Q

Why do enzymes exist in the steady state most of the time?

A

Regulate metabolism due to a constant supply of substrate

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4
Q

What happens when new material is produced?

A

Current material is destroyed

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5
Q

concentration of enzyme (E) is ____ compared to substrate (S)

A

negligible (more substrate)

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6
Q

Why do we measure the rate of reaction after 1 minute?

A

Steady state has been reached

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7
Q

Vo follows saturation kinetics re ____

A

substrate

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8
Q

At low s, the reaction rate is ______

A

linear

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9
Q

At very high s, vo approaches _____

A

vmax

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10
Q

What is this known as?

A

theoretical maximum rate at which enzyme can operate

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11
Q

What is the michaelis constant and what is it a measure of?

A

Km

measure of the affinity of an enzyme for its substrate

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12
Q

What does alpha’ measure?

A

change in vmax which affects km

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13
Q

Formation of ES is _____ and _______

A

rapid and reversible

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14
Q

ES is a ________ complex

A

non-covalent, all takes place in 2nd step

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15
Q

What is kcat known as?

A

turnover number

Follows 1st order kinetics

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16
Q

Km is close to Ks, therefore _____ kinetics are ________

A

M-M

operable

17
Q

When Km>Ks what happens?

A

dissociation of ES is significant in comparison to kcat (Briggs-Haldane kinetics)

18
Q

When Km

A

Long-lived intermediates exist after substrate binding

19
Q

Why do enzymes have different kcat and km values?

A

cellular enviroment

20
Q

By assuming substrate < Km we can derive a ____ _____ in the form of a ____ order reaction

A

new equation

2nd

21
Q

What are the disadvantages of the lineweaver-burk plot?

A
  • Compression of data points with high (S) into small region
  • Favours data with low (S)
  • Eadie & Hofstee decides to multiply everything through by V0Vmax giving y=c-mx
22
Q

What are the advantages of the Eadie-Hofstee plot?

A
  • All values of (S) are weighted equally

- Considered to be more accurate determination of Km

23
Q

What are the disadvantages of the Eadie-Hofstee plot?

A
  • Time consuming

- Both axes depend on Vo introducing potential for experimental error

24
Q

What are the advantages of the Woolf-Hanes plot?

A

Quicker to obtain data than E-H

25
Q

What are the disadvantages of the Woolf-Hanes plot?

A

Km is intercept not slope, thus more prone to error than E-H

26
Q

What happens in a Lineweaver-Burk plot of a ternary complex?

A
  • Several different LB plots
  • Each plot has held S2 constant
  • Lines intersect
27
Q

LB behaviour for a ping-pong mechanism?

A
  • Same experimental set-up

- Each LB plot is parallel to one another

28
Q

Many drugs act via what inhibition?

A

Reversible inhibition

29
Q

What is the most common form of inhibition?

A

Competitive inhibition
e.g. use of ethanol to treat methanol poisoning

  • Inhibits alcohol dehydrogenase catalysed formation of formaldehyde, preventing blindness
30
Q

What is uncompetitive inhibition?

A
  • Inhibitor only binds to ES complex
  • Stabilises the complex making it harder for the substrate to react & leave
  • Never seen in isolation

e.g. Lithium ion treatment of manic depression > uncompetitive inhibition of myo-inositol monophosphatase

31
Q

What does mixed inhibition involve?

A

Binds to E or ES

32
Q

What does alpha measure?

A

measure of the extent of change in Michaelis constant (a=1 for no inhibition)

33
Q

What do non-competitive inhibitors bind to?

A

Allosteric sites rather than the active site

34
Q

What do non-competitive inhibitors act as and give example

A

Enzyme switches

e.g Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs) > HIV1

35
Q 
. In which type of graph would you plot Vo on the x-axis and Vo/[S] on the y-axis?
	A	Eadie-Hofstee
	B	Hill
	C	Lineweaver-Burk
	D	Michaelis-Menten
	E	Woolf-Hanes
A

A Eadie-Hofstee

36
Q 
On a Lineweaver-Burk plot for uncompetitive inhibition the “drug” and “no drug” lines:
	A	cross at the x-axis
	B	cross at the y-axis
	C	cross elsewhere
	D	are parallel to one another
	E	are perpendicular to one another
A

D are parallel to one another

37
Q 
On a Eadie-Hofstee plot the point at the which the line of best fit crosses the y-axis indicates:
	A	Km
	B	-Km
	C	Km/Vmax
	D	Vmax/Km
	E	Vmax
A

E Vmax

PHA111 (23 decks)

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