Unit 2 - Enzymes Flashcards

1
Q

what are enzyme commission numbers?

A

classification of enzymes based on reaction catalysed - 4 numbers
1st - general type of reaction catalysed
2nd - sub-class/ 3rd - sub-subclass - highlights compounds/groups/ bonds/ product involved in reaction
4th - serial identifier - highlights metabolites/ co-factors involved

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2
Q

apart from EC numbers what other names do enzymes have?

A

recommended name (everyday use)/ systematic name (substrate followed by enzyme specifying type of reaction catalysed

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3
Q

what are the defined conditions under which specified activity of catalytic proteins are measured?

A

temp/ pH/ buffer/ substrate/ co-enzyme concentration

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4
Q

what is the rate of an enzymatic reaction?

A

rate of conversion of substrate to product per unit of time

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5
Q

what does 1 IU equal?

A

amount of enzyme that catalyses conversion of 1 micromole of substrate to product per minute

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6
Q

what does 1 katal equal?

A

amount of enzyme that catalyses conversion of 1 mole of substrate to product per second

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7
Q

what unit given for specific activity?

A

IU/ mg

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8
Q

what is difference between holoenzyme and apoenzyme?

A

holoenzyme has non-/covalently bound enzyme but apoenzyme does not

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9
Q

distinguish between soluble co-enzymes/ prosthetic groups/ cofactors

A

soluble: bind reversibly to protein moiety of enzyme but during reaction they are modified, dissociated and recycled by another enzyme
prosthetic groups: covalently linked to enzyme and remain associated during entire catalytic cycle
co-factors: insoluble inorganic ions required for enzymatic activity

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10
Q

what are the assumptions for the michael-menten equation?

A
  • E, S, ES in rapid equilibrium
  • conversion of ES to E + P - rate-limiting step
  • there are no other forms of the enzyme present apart from E and ES
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11
Q

what is Kcat?

A

turnover number - rate constant showing the number of substrate molecules converted to product per enzyme molecule per unit time

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12
Q

what is velocity limited by? - give an equation

A

limited by ratio of enzyme substrate complexes to total number of enzymes
equation: v= Kcat [ES]

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13
Q

what is Km

A

kinetic constant showing substrate affinity

- on graph it is point corresponding to 1/2 Vmax ([ES] = 1/2 [E]t)

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14
Q

what is the relationship of lineweaver-burk plot to michael-menten equation? what is the significance of this?

A

double reciprocal plot of the menten equation so puts the equation in form y = mx + c
-this makes it easier to obtain values for Vmax and K

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15
Q
what is represented by the following on a lineweaver plot:
x
y
x- intercept
y- intercept
slope
A
x= 1/ [S]
y = 1/ v
x-intercept: -1/ Km
y-intercept: 1/ Vmax
slope: Km/ Vmax
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16
Q

what are the limitations of the lineweaver-burk plot?

A

small experimental error at low Km so results in larger error for graphically determining Km and Vmax
- data at higher substrates are concentrated in narrow region

17
Q
what is the other transformation of michael-menten equation? what is represented by:
x
y
x- intercept
y- intercept
slope
A
eadie-hofstee plot - no data compression
x = v/ [s]
y = v
x-intercept: Vmax/Km
y-intercept: Vmax
slope: - Km
18
Q

how do competitive inhibitors affect an enzyme?

A

increase in Km but no change in V max

19
Q

how do non-competitive inhibitors affect an enzyme?

A

decrease in V-max and no change in Km

20
Q

how do uncompetitive inhibitors affect an enzyme?

A

may alter both Km and V max