BIOL115 - Lecture 8

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  • Created by: Katherine
  • Created on: 15-05-16 21:48
Do enzymes become saturated with substrate at higher or lower concentrations?
Higher concentrations of substrate.
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Once enzymes are saturated, does addition of further substrate increase rate of reaction?
No, it doesn't
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Under these conditions, what is the way to increase reaction rate?
To add more enzyme
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What does the Michaelis Menton equation do?
It describes what rate of reaction of enzyme by the concentration of the substrate. It essentially describes the rectangular hyperbolic nature of the rate vs plot.
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For single substrate reactions, the rate vs plot is what type of curve?
A rectangular hyperbolic curve.
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What is the basis for michaelis menton equation?
The model uses a two step reaction scheme including an enzyme substrate complex as an intermediate.
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What is the eqation?
E + S -K1->
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What happens to the enzyme and the substrate?
They bind and react. You can work out the rate of change.
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What is the basis for the equation?
1.) The rate of formation of ES complex is on the concentration of E & S and the strength of interaction between E & S. And the rate of catalysis (How quickly E converts S to P.
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What is km?
It is the michaelis constant. It is equal to k-1+k2/k1
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What is Km in descriptive terms?
It is independent of enzyme concentration. It describes the equilibrium of ES formation.
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What are the units of Km?
It is expressed in units of concentration as for S (M mol/L)
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What is Vmax?
It is the maximum rate of reaction
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How do you work out Km?
Vmax/2 and on the x axis
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Is rate proportional to S at low substrate?
Yes
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At low S, what is the increase of Km?
It is linear
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At high Substrate concentration, what is the effect on the rate?
The rate is independent of S and Km+S=s Therefore : V = Vmax
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What is the significance of Km?
Km represents the substrate concentration at which the rate of reaction is half maximal. i.e. half of the enzymes are in the ES.
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What is the equation if S = KM?
If S = Km, then V= Vmax/2
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What is the alternative significance of Km?
Km represents the substrate concentration at which half the active sites are occupied.
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For many enzymes, Km approximates what?
It approximates the affinity of the enzyme for the substrate.
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What does a low value for Km mean?
It means high affinity substrate binding. i.e. strong/tight binding. The enzyme binds substrate even at low concentrations
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If Km is greater than the S within cells, enzymes will do what?
They will catalyse rate poorly.
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Km is a constant that defines what?
It defines the interaction between enzyme and substrate molecules.
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Is Km dependent or independent of the amount of enzyme and substrate molecules?
It is independent
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Is Vmax a constant?
No
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What is a constant?
It is a quantity that, under stated conditions, does not vary with changes in the environment.
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The measured value for Vmax applies to how many reaction conditions?
Just one
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Will adding more enzyme increase Km, Vmax or both?
Just Vmax, not Km.
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What can the michaelis menton equation be used for?
To see how enzymes catalyse the same reaction.
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What is Kcat?
It is the turnover number
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When is Vmax reached?
When the enzyme is completely saturated with substrate
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How is the turnover number calculated?
Kcat = Vmax/E
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What is the turnover number?
It is the number of substrate molecules turned over per enzyme, per unit time at saturating.
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When there is a high conc of substrate, what is the Kcat the same as?
The ES number approx
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What is the turnover number?
It can be thought of as a measure of the efficiency of the enzyme.
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How do you estimate Km and Vmax?
Perform enzyme assays under identical conditions at a range of substrate conditions. Plot initial rate, V0, against S.
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Km is equal to S at ...
Half Vmax
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Vmax is only ever achieved at...
Infinite S.
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As Vmax is only every achieved at infinite S, how do we know what it is?
Using a Lineweaver Burk plot
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Is a lineweaver burk plot a single or double reciprocal plot?
A double
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Card 2

Front

Once enzymes are saturated, does addition of further substrate increase rate of reaction?

Back

No, it doesn't

Card 3

Front

Under these conditions, what is the way to increase reaction rate?

Back

Preview of the front of card 3

Card 4

Front

What does the Michaelis Menton equation do?

Back

Preview of the front of card 4

Card 5

Front

For single substrate reactions, the rate vs plot is what type of curve?

Back

Preview of the front of card 5
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